Podcasts about kcnq1

BUFFALO, NY- June 4, 2024 – A new research perspective was published in Oncotarget's Volume 15 on June 3, 2024, entitled, “Bruton's tyrosine kinase inhibitor-related cardiotoxicity: The quest for predictive biomarkers and improved risk stratification.” In this new perspective, researchers Jai N. Patel, Jai Singh, and Nilanjan Ghosh from Atrium Health discuss Ibrutinib — the first Bruton's tyrosine kinase (BTK) inhibitor approved for the treatment of patients with chronic lymphocytic leukemia (CLL). “While producing durable responses and prolonging survival, roughly 20–25% of patients experience dose limiting side effects, mostly consisting of cardiovascular toxicities like severe hypertension and atrial fibrillation.” While clinical predictors of BTK inhibitor-related cardiotoxicity have been proposed and may aid in risk stratification, there is no routine risk model used in clinical practice today to identify patients at highest risk. A recent study investigating genetic predictors of ibrutinib-related cardiotoxicity found that single nucleotide polymorphisms in KCNQ1 and GATA4 were significantly associated with cardiotoxic events. If replicated in larger studies, these biomarkers may improve risk stratification in combination with clinical factors. “A clinicogenomic risk model may aid in identifying patients at highest risk of developing BTK inhibitor-related cardiotoxicity in which further risk mitigation strategies may be explored.” DOI - https://doi.org/10.18632/oncotarget.28589 Correspondence to - Nilanjan Ghosh - nilanjan.ghosh@atriumhealth.org Sign up for free Altmetric alerts about this article - https://oncotarget.altmetric.com/details/email_updates?id=10.18632%2Foncotarget.28589 Subscribe for free publication alerts from Oncotarget - https://www.oncotarget.com/subscribe/ Keywords - cancer, BTK inhibitor, cardiotoxicity, biomarkers, risk, genetics About Oncotarget Oncotarget (a primarily oncology-focused, peer-reviewed, open access journal) aims to maximize research impact through insightful peer-review; eliminate borders between specialties by linking different fields of oncology, cancer research and biomedical sciences; and foster application of basic and clinical science. Oncotarget is indexed and archived by PubMed/Medline, PubMed Central, Scopus, EMBASE, META (Chan Zuckerberg Initiative) (2018-2022), and Dimensions (Digital Science). To learn more about Oncotarget, please visit https://www.oncotarget.com and connect with us: Facebook - https://www.facebook.com/Oncotarget/ X - https://twitter.com/oncotarget Instagram - https://www.instagram.com/oncotargetjrnl/ YouTube - https://www.youtube.com/@OncotargetJournal LinkedIn - https://www.linkedin.com/company/oncotarget Pinterest - https://www.pinterest.com/oncotarget/ Reddit - https://www.reddit.com/user/Oncotarget/ Spotify - https://open.spotify.com/show/0gRwT6BqYWJzxzmjPJwtVh Media Contact MEDIA@IMPACTJOURNALS.COM 18009220957

For this week's Feature Discussion, please join authors Igor Klem, Pasquale Santangeli, Mark N.A. Estes III, and Associate Editor Victoria Delgado as they discuss, in a panel forum, the articles: " The Relationship of LVEF and Myocardial Scar to Long-Term Mortality Risk and Mode of Death in Patients with Non-Ischemic Cardiomyopathy," "Prognostic Value of Non-Ischemic Ring-Like Left Ventricular Scar in Patients with Apparently Idiopathic Non-Sustained Ventricular Arrhythmias," and "Cardiac Magnetic Resonance Imaging in Nonischemic Cardiomyopathy: Prediction Without Prevention of Sudden Death." Dr. Carolyn Lam: Welcome to Circulation on the run, your weekly podcast summary and backstage pass to the journal and its editors. We're your co-hosts. I'm Dr. Carolyn Lam, Associate editor from the National Heart Center and Duke National University of Singapore. Dr. Greg Hundley: And I'm Dr. Greg Hundley, Associate editor, Director of the Pauley Heart Center in Richmond, Virginia. Well Carolyn, this week we've got another sort of double feature with a forum and our focus is going to be on myocardial scar that's observed with late gadolinium enhancement during cardiovascular magnetic resonance and the two author groups we'll be discussing the impact of that scar on the development of ventricular arrhythmias. But before we get to that, how about we grab a cup of coffee and jump into the other articles in the issue? Would you like to go first? Dr. Carolyn Lam: I certainly would. Although I have to say, can't wait for the double feature. I love those, and this is right up your alley too. All right. But first, the first paper I want to talk about provides new randomized trial information regarding the benefits of catheter ablation in atrial fibrillation in patients who also have heart failure. Now, this is a sub-study of the CABANA trial. Dr. Greg Hundley: So Carolyn, remind us a little bit about the CABANA trial first. Dr. Carolyn Lam: I thought you might ask. Well, CABANA randomized 2,204 patients with atrial fibrillation who were 65 years or older or less than 65 with one or more risk factors for stroke at, it was huge at 126 sites, and they were randomized to ablation with pulmonary vein isolation or drug therapy. Now of these, 35% of 778 patients had New York Heart Association Class II or higher at baseline, and really formed the subject of the current paper. Although this sub-study was not specifically designed to evaluate patients with heart failure with preserved ejection fraction, about 91% of the patients with a clinical diagnosis of heart failure participating in CABANA for whom such data on injection fraction were available, really had an ejection fraction of above 40% and fully 79% had an ejection fraction above 50%. So excitingly, this is really majority talking about, have HFpEF. Now, what did they find well in patients with New York heart Association Class II or III heart failure at trial entry, most of whom did not have a reduced ejection fraction. Dr. Carolyn Lam: There was substantial clinical outcome benefits with the ablation over drug therapy with a 36% relative reduction in the primary composite endpoint of death, disabling stroke, serious bleeding or cardiac arrest. Benefits were evident for both all-cause mortality and atrial fibrillation reduction. However, the effects on heart failure hospitalization were small and not significant. Authors also caution that these results should not be viewed as practice changing until they are reproduced in a confirmatory trial of ablation in the same population. And this is beautifully discussed in an editorial by Lynda Rosenfeld and Alan Enriquez from Yale University School of Medicine. Dr. Greg Hundley: Oh, wow. Thanks Carolyn. Well, my first paper comes from the world of basic science and it's from Professor Thomas Braun, from the Max Planck Institute for Heart and Lung Research. So Carolyn, vascular smooth muscle cells show a remarkable phenotypic plasticity allowing acquisition of contractile or synthetic states, but critical information is missing about the physiological signals that promote formation and maintenance of contractile vascular smooth muscle cells in vivo. So BMP-9 and BMP-10 are known to regulate endothelial quiescence after secretion from the liver and right atrium. And these investigators are studied the role of BMP-9 and 10 for controlling formation of contract, all vascular smooth muscle cells. Dr. Carolyn Lam: Greg, talking about vascular smooth muscle cells always reminds me of their role in pulmonary hypertension, am I right? Dr. Greg Hundley: Yes, Carolyn. So these investigators found that in mouse models, BMP-9 and BMP-10 act directly on vascular smooth muscle cells for induction and maintenance of their contractile state, and surprisingly the effects of BMP-9 and 10 in vascular smooth muscle cells are mediated by different combinations of BMP type 1 receptors in a vessel bed specific manner. And therefore, just as you suggest, Carolyn, these results may offer new opportunities to manipulate blood pressure in the pulmonary circulation. Dr. Carolyn Lam: Thank you, Greg. Well, my next paper provides the first proof of principle of gene therapy for complete correction of Type 1 Long QT syndrome. Dr. Greg Hundley: Ah, so tell us a little bit about Type 1 Long QT syndrome, Carolyn. Dr. Carolyn Lam: Okay. Well Type 1 long QT syndrome is caused by loss of function variants in the KCNQ1 and coded potassium channel alpha sub-unit. And that is essential for cardiac repolarization providing the slow delayed rectifier current. Now no current therapies target the molecular cause of this Type 1 long QT syndrome. Well, this study from Dr. Michael Ackerman colleagues from Mayo Clinic Rochester really established a novel dual component suppression and replacement KCNQ1 gene therapy approach for Type 1 long QT syndrome. And it's the type that contains the KCNQ1 short hairpin RNA to suppress endogenous expression and a codeine altered short hairpin RNA immune copy of this KCNQ1 for gene replacement. Dr. Carolyn Lam: So this very novel approach rescued the prolonged action potential duration in inducible pluripotent STEM cell cardiomyocytes derived from four patients with unique Type 1 Long QT syndrome, causative, KCNQ1 variants. So it's super cool. Just go have a look. Dr. Greg Hundley: Well, thanks Carolyn. Dr. Carolyn Lam: I want to also tell you about other things in the mail bag. We have ECG Challenge by Dr. Dai on “Severe Arrhythmia Caused by a Chinese Herbal Liqueur. What's the Diagnosis?” I'm not going to tell you. You have to go see. We have Dr. Karen Sliwa writing a beautiful Joint Opinion paper from the World Heart Federation and American College of Cardiology, American Heart Association, and European Society of Cardiology on "Taking a Stand Against Air Pollution, the Impact on Cardiovascular Disease." Dr. Greg Hundley: Well, thanks Carolyn. So I've got a couple other articles. First Professor Yacoub has a global rounds describing and working towards meeting the challenges of improving cardiovascular health in Egypt. Those are really interesting features to learn about cardiovascular care worldwide. Next there's an In Depth article by Professor Thum entitled, "Therapeutic and Diagnostic Translation of Extracellular Vesicles in Cardiovascular Diseases, Roadmap to the Clinic." And then finally, a Research Letter from Dr. Bottá entitled, "Risk of Coronary Artery Disease Conferred by Low Density Lipoprotein Cholesterol Depends on Apologetic Background." Well, Carolyn, what a great issue and how about now we proceed on to that double feature? Dr. Carolyn Lam: Oh, I can't wait. Thanks Greg. Dr. Greg Hundley: Well, listeners, we are here for a really exciting feature discussion today that's going to focus on imaging, in particular magnetic, resonance imaging, and some new findings in that era and how those findings may pertain to ventricular dysrhythmias. With us today, we have Dr. Igor Klem from Duke University who will be discussing a paper, Dr. Pasquale Santangeli from University of Pennsylvania, our own associate editor, Dr. Victoria Delgado from Leiden and an editorialist, Dr. Mark Estes from UPMC in Pittsburgh. Welcome to all of you. Well, Igor, we're going to start with you. Could you tell us what was the hypothesis for your study and what was your study population in study design? Dr. Igor Klem: Yes. Good morning, Greg and thanks for the invitation. We wanted to know if you have a patient who you diagnosed with non ischemic cardiomyopathy based on clinical grounds and you refer him for a cardiac MRI study with contrast, what is the additional information that you get from the MRI study? And so we wanted to compare, and that's primarily related to the findings on scar imaging with late gadolinium enhancement. And we wanted to compare that to one of the most robust clinical parameters in cardiology, which is left ventricular ejection fraction, and in particular using a cutoff of 35%, which somehow in our clinical management has sort of as established as a break point for many clinical decisions. Dr. Igor Klem: And so we created a registry among three centers of patients who undergo a cardiac MRI study, where we found an LVEF of less than 50% and we followed them for a number of outcomes. One is all caused death. And then we wanted to separate a little bit the events into those who have cardiac mortality to look at a little epidemiology because in those patients, we have two major adverse events: one as heart failure related mortality. One is arrhythmia related mortality. Dr. Greg Hundley: And how many subjects did you include? Dr. Igor Klem: We included about a thousand patients from three centers and coming to the major findings of our study, we found that both left ventricular ejection fraction, as we know, is a robust marker of all cause mortality and cardiac death. And so it was the presence of myocardial scar on cardiac MRI. But the major difference was in relation to the arrhythmic events. We founded left ventricular ejection fraction in particular, when we use the 35% cutoff actually had very little predictive power to inform us who is at risk of arrhythmic events. In contrast, there was a very strong and robust relationship or multiple statistical methods to stratify patients who are at risk for sudden cardiac death, appropriate ICD shock, as well as arrhythmic cardiac death. Dr. Greg Hundley: Very good. Well, Pasquale understand you also performed a research study utilizing cardiovascular magnetic resonance. Could you describe for us your hypothesis as well as what was your population and your study design? Dr. Pasquale Santangeli: Thank you, Greg. And of course, thanks to the editor for the interest in our paper. I need to thank also the first call authors Daniele Muser and Gaetano Nucifora for putting together a registry of 70 institutions throughout the U.S., Europe, and Japan and the our hypothesis came from a clinical need. We do know that patients with idiopathic ventricular re we ask, which includes not sustain a weakness like PVCs or non-sustained VT. Very few of them, but there is a group of them that have a higher risk of ending malignant and up comes in terms of your ethnic events over follow-up. And prior studies have shown that by doing an MRI and showings and the detecting scar related announcement, there is an increase with how we make events of a follow-up. However, if you do look at those studies late, an answer's been reported in up to 70% of these patients, which you never view is a highly practical way of re-stratifying these patients, because you have a risk factor that is present 70% of those, then it's hard to use it for clinical decision-making. Dr. Pasquale Santangeli: So in this registry, which you put it again at 686 patients with panel data idiopathic, not sustained ventricular arrhythmias, which were defined by a normal WBC gene status, a normal echocardiogram and a normal stress test. We looked at whether there is a specific pattern of late announcement. So how basically I believe lands, and it looks on the MRI, they may predict better or outcomes over follow-up. And again, we use a composite and Pauline the full cost mortality, but associated cardiac arrest due to ventricular fibrillation or a hemodynamically unstable BP, or in a subgroup of patients that underwent ICD therapy. We also looked at, I approve SED shocks. Dr. Pasquale Santangeli: The groups were divided in three different categories. The first one, which is a larger group of 85% of patients and no late announcement. The second group, the one with late announcement, which represents the remaining 50% of 15% of patients, we divided it into a ring light pattern, which was defined as that word says, as a ring like distribution of the lead announcement in the mid-market segments, which involves a three consecutive continuous segments in a short axis view. It looks like really at least half the ring or three-quarters of the ring. Dr. Pasquale Santangeli: And the other group is the one that had the leader announcement without a ring light pattern. And it's interesting that the third and the latest announcement was not that similar between the ring light and the one without ring light late announcement. What we did find though for our follow-up the patient with a ring light pattern, a significantly higher rate of the primary composite endpoint, which happened in the median follow-up about 61 months so it was quite long. And the composite outcome occurred in 50% of patients in the ring light group versus 19% in the no ring light a positive announcement group and a 0.3%. So really, really rare in patients. So then concluded that of course, late announcement does provide some information in general, particularly the type of announcement that increases the risk significantly. Probably although this has to be confirmed prospective fashion patient with a ring light pattern may benefit from other forms of interventions, including potentially defibrillator therapy in a prophylactic fashion. Dr. Greg Hundley: Very nice. So now listeners, we're going to turn to our associate editor. One of the imaging experts here at Circulation, Dr. Victoria Delgado. Victoria, you see a lot of papers come across your desk and as an imaging expert, what attracted you to these two papers? And what do you think are their significance? Dr. Victoria Delgado: Thank you, Greg. I think that these two papers are important because right now, if we follow the clinical guidelines, we decide implantation. For example, of an ICD based on the ejection fraction, and we see that in many patients based on ejection fraction, they may not benefit ever from an ICD because they don't have arrhythmias. What other patients who do not meet the criteria often injection fraction below 35%. They may have still arrhythmias. So the article by Igor highlights the relevance of the amount of burden of late government Huntsman with CMR, in patients with non ischemic cardiomyopathy, which are sometimes very challenging patients on how to decide when we implant an ICD or not. We need sometimes to base the decision on genetics. Dr. Victoria Delgado: If we have an on the other hand, the paper of Pasquale, these were patients with normal echocardiogram. So what patient, having arrhythmias where we don't see on echocardiogram, that is the first imaging technique that we usually use to evaluate these patients. We don't see anything, but CMR can give us more information in terms of structural abnormalities and particularly not only the burden of scar, but also the pattern of the scar. And we have seen in other studies that for example, not only for ICD implantation, but for ventricular tachycardia ablation. The characteristics of that scar and some areas where these are short of panel that can be targeted for that ventricular tachycardia ablation can lead to much more precise treatment if you want of these patients. Dr. Greg Hundley: Thank you, Victoria. So it sounds like listeners we're hearing late gadolinium enhancement, regardless of EF could be forecasting, future arrhythmic events. And then also the pattern of late gadolinium enhancement, where contiguous segments in a ring-like fashion may also offer additional prognostic information. Well, now we're going to turn to our editorialists and as you know, listeners at Circulation, we'll bring in an editorialist to really help put things together and uniquely here today, we have Dr. Mark Estes, who is really not an imager per se, but like many of us uses the information from imaging to make clinical decisions. Mark, how do you see this late gadolinium enhancement as perhaps a new consideration for placement of devices? Dr. N.A. Mark Estes: Greg, that's one of the key questions. There's no doubt, not only based on these two studies, which extend our prior information about LGE and patients with valid and non ischemic cardiomyopathies that scar burden is important in predicting not only total mortality, but arrhythmic events. All of the criteria that were used in the original ICD studies, which include the definite, the Skuid half Danish and made it our it trials use only ejection fraction and functional status, no imaging. These are legacy trials. Now, many of them, a decade or more older. And the treatment of advanced heart failure has progressed to the point that the total mortality is dramatically lower than it was at the time of these studies. In some instances down to 4 or 5% per year. The studies are important in that they identify a subgroup of patients with low ejection fractions, less than 35%, who might qualify for ICDs, who are unlikely to benefit. Dr. N.A. Mark Estes: They also identify a group of patients with preserved ejection fraction greater than 35%, less than 50 in whom the risk of sudden death may be substantial. And it extends prior observations about patchy, mid Meyer, cardio wall fibrosis, subendocardial, subepicardial and important ways. But the key issue here, and it was alluded to with Pasquale's comments about prospective validation, is that when one has a risk stratifier and identifies a high risk population that has to be linked to an unequivocal therapy, it improves survival. And we don't have that link quite yet. Dr. N.A. Mark Estes: Prospective randomized trials are unlikely to be done in the low ejection fraction because they would probably be considered unethical. Given the trials that have shown the benefit you can't randomize to defibrillator versus an implantable loop recorders. I think the future really lies in risk stratification for people with preserved ejection fractions greater than 35%, less than 50 using LG in that patient population. Currently, I think the best information we can give to clinicians is to stick with the AHA guidelines, which is PF less than 35% with dilated, nonischemic class II symptoms who have had optimal medical therapy for at least three months using perhaps in that patient population LGE for shared decision-making in patients about the magnitude of the risk. And I think that's as far as we can go pending future studies, and there is one which we can discuss later on the CMR study at just that preserved ejection fraction LGE randomizing to defibrillator versus ILR. Dr. Greg Hundley: Thank you, Mark. So listeners just really quickly, let's go back to each of our experts and ask them, you know, in 20 seconds, Igor, Pasquale, Victoria, and Mark, what's the next study that needs to be performed in this space? Igor, we'll start with you. Dr. Igor Klem: Well, number one, following on Mark's comment on the less than 35% population, I think that it's unlikely that they're randomized clinical trial is ethical in this population, but we may consider a wealth of registry data by now that shows that there is a subgroup of patients who have a lower risk or lower benefit from an ICD. I think in the preserved ejection fraction above 35%, maybe up to 45%, 50%. That's an interesting study that's coming up. Maybe there's more trials that can provide us that robust information that we need today in order to change the guidelines to risk stratify, not based on the LVF, but on the presence of scar or maybe subgroups of scar. Dr. Greg Hundley: Pasquale? Dr. Pasquale Santangeli: Yes. So I think of course, one of the major studies is the one already alluded by this, which is a prospective study that links as specific therapy like ICD or even additional risk factors like we've been using program's stimulation some of these patients to further risk for the five to see what they can benefit. Dr. Pasquale Santangeli: Based another one that I think is important for the study that we did is a mechanistic more study to understand why the ring light pattern was there, as opposed to other patterns. We do believe we think that some of these patients may have an initial form of lb dominant arrhythmogenic paramount. There wasn't really a detective before and ran. Now, if we actually extending our study and have a registry to try to screen also the family members or patients with ring light pattern to understand whether there is a familiar component to it, because really we do not see this type of pattern that commonly and it'd been associated with lb dominant. Magnetic kind of alpha in some others, small studies. Dr. Pasquale Santangeli: So that's the other part to dig in a little bit more into the field type for these patients to understand why one pattern versus another happens and whether that gets main to, to explain why there's a higher risk in one population versus another. Dr. Greg Hundley: Victoria. Dr. Victoria Delgado: Yeah. Following what has been said. I think that from the imaging point of view, we are always criticizing in a way that we increase the burden or the cost of healthcare. But I think that these studies or any randomized study where MRI or echo is used in order to design a therapy and show the value of using that imaging technique to optimize the health care costs is important. So I will not add much on which sort of populations, but probably patients within non ischemic cardiomyopathy with preserved ejection fraction that do not fulfill the recent scores, for example, in hypertrophic cardiomyopathy to be implanted with an ICD. But probably if we see a lot of scar on a AGE where specific patterns that can help to decide which are the patients that have benefited from an ICD implantation, for example. Dr. Greg Hundley: Thank you. And finally Mark. Dr. N.A. Mark Estes: But I think all the major points have been hit here. And unfortunately we have a bit of a dilemma. And that dilemma is that these legacy trials for ICDs, which selected based on low ejection fraction and functional class II were done at a time when contemporary heart failure treatment was not as good as it currently is pharmacologically. And it's been reflected with a lower total mortality. When the mortality in this patient population gets down to the 4 and 5% per year, it's unlikely that any intervention for prevention of sudden death is going to impact on that total mortality. Dr. N.A. Mark Estes: So I do think that the registries hold a lot of promise, giving us insights into the subgroup of patients that previously would have been selected for defibrillators who may not have as much benefit or who may benefit the most. And I think that they will play an important part in perhaps refining the risk stratification with greater sensitivity and specificity in the patient population, less than 35%. I think the CMR guide trial is going to be a critical trial and looking at ICDs in the patient population between 35 and 50%, but we need to be mindful of one thing. And that in the Danish trial, they get a sub study looking at about 240 patients using LGE. And they found that ICD in patients with LGE that was positive, did not make a difference in survival or total mortality. So again, we need to get the data. I think the best clinical practice has come out of the best clinical evidence. You'll clearly be limitations to what we can do, but I think in the future, we'll have much better data to make these judgment calls. Dr. Greg Hundley: Very good. Well listeners, we want to thank our panelists, Dr. Igor Clem, Pasquale, Santangeli, Victoria Delgado, and Dr. Mark Estes for this wonderful discussion related to magnetic resonance imaging, late gadolinium enhancement, and how it may be useful in identifying those at risk for future arrhythmic events. On behalf of both Carolyn and myself, want to wish you a great week and we will catch you next week on the run. Dr. Greg Hundley: This program is copyright of the American Heart Association, 2021.  

Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.07.29.227231v1?rss=1 Authors: Huang, H., Chamness, L. M., Vanoye, C. G., Kuenze, G., Meiler, J., George, A. L., Schlebach, J. P., Sanders, C. Abstract: Gain-of-function (GOF) mutations in the KCNQ1 voltage-gated potassium channel can induce cardiac arrhythmia. We tested whether any of the known GOF disease mutations in KCNQ1 act by increasing the amount of KCNQ1 that reaches the cell surface: super-trafficking. We found that levels of R231C KCNQ1 in the plasma membrane are 5-fold higher than wild type KCNQ1. This arises from both enhanced translocon-mediated membrane integration of the S4 voltage-sensor helix and an energetic linkage of C231 with the V129 and F166 side chains. Whole-cell electrophysiology recordings confirmed that R231C KCNQ1 in complex with KCNE1 is constitutively active, but also revealed the single channel activity of this mutant to be only 20% that of WT. The GOF phenotype associated with R231C therefore reflects the net effects of super-trafficking, reduced single channel activity, and constitutive channel activation. These investigations document membrane protein super-trafficking as a contributing mechanism to human disease. Copy rights belong to original authors. Visit the link for more info

Commentary by Dr. Valentin Fuster

Dr Carolyn Lam: Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to the Journal and its editors. I'm Dr Carolyn Lam, associate editor from the National Heart Center and Duke National University of Singapore. Dr Greg Hundley: And I'm Dr Greg Hundley, associate editor, director of the Pauley Heart Center at VCU Health in Richmond, Virginia. Well, Carolyn, our feature article this week relates to an international multi-center evidence-based reappraisal of genes reported to cause congenital long QT syndrome. But, before we get to that, how about if we grab a cup of coffee and start on our other papers? Do you have one you'd like to discuss? Dr Carolyn Lam: Yes. My favorite part of the week. So this first paper really asks the question, "What's the association between HDL functional characteristics, as opposed to HDL cholesterol levels, and acute coronary syndrome?" The paper comes from Dr Hernáez from IDIBAPS in Barcelona, Spain and colleagues who conducted a case control study nested within the PREDIMED cohort. Originally a randomized trial where participants followed a Mediterranean or low-fat diet. Cases of incident acute coronary syndrome were individually matched one is to two to controls by sex, age, intervention group, body mass index, and follow-up time. The authors measure it the following functional characteristics, which were HDL cholesterol concentration, cholesterol efflux capacity, antioxidant ability, phospholipase A2 activity and sphingosine-1-phosphate, apolipoproteins A1 and A4, serum amyloid A and complement 3 protein. Dr Greg Hundley: Wow Carolyn, a detailed analysis. What did they find? Dr Carolyn Lam: They found that low values of cholesterol efflux capacity, and levels of sphingosine-1-phosphate and apolipoprotein A1 in HDL or all associated with a higher risk of acute coronary syndrome in high cardiovascular risk individuals, irrespective of HDL cholesterol levels and other cardiovascular risk factors. Low cholesterol efflux capacity values and sphingo-1-phosphate levels were particularly associated with an increased risk of myocardial infarction, whereas HDL antioxidant or anti-inflammatory capacity was inversely related to unstable angina. Now this is significant because it's the first longitudinal study to comprehensively examine the association of several HDL function related biomarkers with incident acute coronary syndrome beyond HDL cholesterol levels in a high-risk cardiovascular risk population. Greg Hundley: Very nice. Carolyn. It sounds like function over just the levels is important. Dr Carolyn Lam: Exactly, you summarized it well. Well Greg, I've got another paper and I want to pick your brain first. Is it your impression that type 2 myocardial infarction, the type that occurs due to acute imbalance in myocardial oxygen supply versus demand in the absence of atherothrombosis, do you think that this type of MI is on the rise? It seems more and more common in my country. Dr Greg Hundley: Do we want to say it's on the rise? Certainly by measuring all these high sensitivity troponins, et cetera, we're finding, I think, more evidence of type 2 MI. So, all in all, yeah it probably is on the rise, but likely related to some of our measurement techniques. Dr Carolyn Lam: Oh, you are so smart, Greg. Because this paper that I'm about to tell you about really addresses some of these issues and it's from corresponding author Dr Gulati from Mayo Clinic in Rochester, Minnesota. And they really start by acknowledging that despite being frequently encountered in clinical practice, the population base incidents and trends of type 2 myocardial infarction is unknown and long-term outcomes are incompletely characterized. So they prospectively recruited 5,640 residents of Olmsted County, Minnesota who experienced an event associated with cardiac troponin T greater than 99th percentile of a normal reference population, which is greater than or equal to 0.01 nanograms per milliliter. And this was between 2003 and 2012, so very careful to talk about which Troponin T assay exactly to the point you discussed earlier, Greg. The events were retrospectively classified into type 1 versus type 2 MI using the universal definition. Dr Greg Hundley: So Carolyn, what did they find? Dr Carolyn Lam: They found that there was an evolution in the types of MI occurring in the community over a decade with the incidence of type 2 MI now being similar to type 1 MI. Adjusted long-term mortality following type 2 MI is markedly higher than after type 1 MI and that's driven by early and non-cardiovascular deaths. Mortality of type 2 MI is associated with a provoking factor and is more favorable when the principle provoking mechanism was an arrhythmia compared with postoperative status, hypotension, anemia or hypoxia. And these findings really underscore the healthcare burden of type 2 MI and provide benchmarks for clinical trial design. Dr Greg Hundley: Very nice, Carolyn. Well, my paper comes from type 5 long QT syndromes and an analysis. And it's from Dr Jason Roberts from Western University. Through an international, multi-center collaboration, improved understanding of the clinical phenotype and genetic features associated with rare KCNE1 variants implicated in long QT 5 was sought across 22 genetic arrhythmia clinics and four registries from nine countries that included 229 subjects with autosomal dominant long QT five. So there were 229 of those subjects. And then 19 individuals with the recessive type 2 Jervell and Lang-Nielsen syndrome. The authors compared the effects of clinical and genetic predictors on a composite primary outcome of definite arrhythmic events, including appropriate implantable cardioverter defibrillators shocks, aborted cardiac arrest, and sudden cardiac death. Dr Carolyn Lam: Wow. What did they find? Dr Greg Hundley: Well, several things, Carolyn. First, rare loss of function KCNE1 variants are weakly penetrant and do not manifest with a long QT syndrome phenotype in a majority of individuals. That's a little bit of a surprise. Second, QT prolongation and arrhythmic risk associated with type 2 Jervell and Lang-Nielsen syndrome is mild in comparison with the more malignant phenotype observed for type 1 Jervell and Lang-Nielsen syndrome. And then number three, all individuals possessing a rare loss of function KCNE1 variant should be counseled to avoid QT prolonging medications and should undergo a meticulous clinical evaluation to screen for long QTS phenotype. And then finally, Carolyn, the last finding, in the absence of a long QTS phenotype, more intensive measures, such as beta blockade and exercise restriction, may not be merited. Dr Carolyn Lam: Oh, very interesting. Well, I've got one more original paper and in this, authors describe a new cellular mechanism linking ischemia-reperfusion injury to the development of donor specific antibody, a pathologic feature of chronic antibody-mediated rejection, which mediates late graph loss. This paper is from corresponding author Dr Jane Witt from Yale University School of Medicine and colleagues who use humanized models and patient specimens to show that ischemia-reperfusion injury promoted elaboration of interleukin 18 from endothelial cells to selectively expand alloreactive interleukin 18 receptor 1 positive T peripheral helper cells in allograph tissues and this promoted donor specific antibody formation. Dr Greg Hundley: Carolyn, here's the famous question. What does that mean clinically for us? Dr Carolyn Lam: Aha, I'm prepared. Therapies targeted against endothelial cell derived factors like interleukin 18 may therefore block late complications of ischemia-reperfusion injury. Dr Greg Hundley: Very nice. Sounds like more research to come. Well, how about other articles in the issue? Dr Carolyn Lam: Well, I'd love to talk about a white paper from Dr Al-Khatib, and it's about the research needs and priorities for catheter ablation of atrial fibrillation and this is a report from the National Heart, Lung, and Blood Institute Virtual Workshop. Dr Greg Hundley: Well, I've got another arrhythmia paper, so this is from Professor Michael Ackerman at the Mayo Clinic and its minor long QT gene disease associations by coupling the genome aggregation database. It's a harmonized database of 140,000 or more exomes and genome derived in part from population-based sequencing projects, with phenotypic insights gleaned from a large long QT syndrome registry to reassess the strength of these minor long QT syndrome gene disease associations. Next, Carolyn, in an on my mind piece, Professor Gerd Heusch from University of Essen Medical School discusses, how can the many positive preclinical and clinical proof of concept studies on reduced infarct size by ischemic conditioning interventions and cardioprotective drugs be reconciled with the mostly neutral results in regard to clinical outcomes. The author discusses the important differences between animal models that have been used a lot in this ischemia reperfusion and infarct size reduction science, and then the clinical scenarios of STEMI in humans as well as the many aspects of coronary reperfusion. How is that affecting the myocytes? How is that affecting the microcirculation, et cetera, that must be addressed? And then finally Carolyn, there is a series of letters, one from Professor Oliver Weingärtner from Universitätsklinikum Jena and another from Professor Yasuyoshi Ouchi from Toranomon Hospital. They're exchanging letters debating the utility of lipid lowering with Ezetimibe in individuals over the age of 75 years. Dr Carolyn Lam: Very nice, Greg. Thanks so much. Shall we now move to our future discussion. Dr Greg Hundley: You bet. Well, welcome everyone. This is our feature discussion and today we're going to hear more about long QT syndrome. We have Dr Michael Gollob from University of Toronto and our own associate editor, Dr Sami Viskin from Tel Aviv Medical Center. Good morning. Good afternoon, gentlemen. Before we get started with a discussion of some of the study findings and results, Michael, could you tell us a little bit about why you performed the study and what were some of the hypotheses you wanted to test? Dr Michael Gollob: As you know, long QT syndrome is probably the most recognized channelopathy associated with sudden cardiac death in young individuals and adults. And at the present time, there are 17 genes available for clinical genetic testing in cases of suspected long QT syndrome. We simply ask the question, "Is there sufficient scientific evidence to support that each of these genes are single gene causes of long QT syndrome based on our contemporary knowledge of genetics and the human genome? Dr Greg Hundley: Great, Michael. So, can you tell us a little bit about your study population? How did you go about this and what was your study design? Dr Michael Gollob: We designed a methods approach that would assure that any conclusions that were made from our working group were not based on the opinions of one or two individuals. We wanted to ensure that this was a consensus conclusion with multiple experts in the field including genomic scientists, genetic counselors, inherited arrhythmia experts, and researchers in the field. We created three independent teams of genetic experts to curate the genetic evidence reported in the medical literature for each of these 17 reported causes of long QT syndrome. This was essentially an evidence-based approach using a pre-specified evidence-based matrix or scoring system depending on the level of evidence, genetic primarily, in the reported literature for each gene. Each of these curation teams worked independently of each other and they were blinded to each other's work and they were tasked with concluding whether a gene, based on the medical literature and the resource methodologies, had sufficient evidence for disease causation. Their classifications would be one of disputed evidence, limited evidence, moderate evidence, strong or definitive evidence for claims towards disease causation. Remarkably, independently, all of these teams reached the same conclusion. In the end, their summary data was reviewed by a clinical domain expert panel with individuals with expertise, particularly in long QT syndrome and other channelopathies. So in total 19 individuals reviewed all of the literature and the data presented and came to unanimous conclusions for each gene. Dr Greg Hundley: Out of the 17, were there some that were more important than others or was it uniformly all 17 were relevant? Dr Michael Gollob: Well, I think the most relevant conclusions of our study are that nine of these genes, more than half of these genes, were felt not to have sufficient evidence to support their causation as a single gene cause for typical long QT syndrome. So nine genes that are currently tested by clinical genetic testing providers do not have enough evidence to support their testing in patients with suspected long QT. And to us, that is the most relevant observation because testing genes that do not have sufficient evidence for disease causation poses a significant risk to patient harm and family harm. We concluded that only three genes had very definitive evidence for causation of long QT syndrome. Those three genes were KCNQ1, KCNH2, and SCN5A. There were another four genes that were concluded to have strong or definitive evidence for unusual presentations of long QT syndrome. And by that, I mean presentations that typically occur in the neonatal period and are associated with heart block seizures or developmental delay or in the case of one of these genes, Triadin, an autosomal recessive form of the disease. Dr Greg Hundley: So helping us perhaps what types of genes to screen for when we have someone with this condition or suspected. So Sami, can you help us put this into perspective? How does this study help us in management of this clinical situation. Dr Sami Viskin: In Circulation, we immediately recognize the importance of the manuscript, the importance of the study because unfortunately, there are too many physicians all over who will accept the results of genetic testing essentially like gospel. Now it's in the DNA, it's in the genes, so whatever you find must be true. And too often, clinical decisions on treatment including ICD implantation have been undertaken based on results of genetic testing’s; thus are wrongly interpreted. So we recognize immediately the importance of this paper. We already had a different study by Dr Gollob and his associates. Again, reassessing the role of genes in Brugada syndrome. So we were familiar with this type of analysis. We recognize the importance and we moved ahead to accept this paper, it went fairly easily, I think only one revision. At the same time, we were getting additional paper by other groups. So in the same issue, we have two more papers, one from Jason Roberts with the International Long QT Registry of long QT 5, reaching similar conclusions that this is a gene with very limited penetrants and another study by the Mayo clinic also showing that many of the genes who are not the major genes are overrepresented in the healthy population. So we put all these three papers together with a very nice editorial by Chris Semsarian in the same issue. So everything is put in the right perspective of how we should be looking at all the genes of these disease in a different way. Dr Greg Hundley: So as a clinician quickly, how can I use this information in the issue, perhaps this paper and all three, in management of patients with either suspected or long QT syndrome? Dr Michael Gollob: First off, I would emphasize that the diagnosis of long QT syndrome or any genetic base disease for that matter, should be based on clinical phenotype and not the observation of a genetic change, particularly if genes are being tested that do not have strong evidence for disease causation, as is the case for the nine genes that we've pointed out in this manuscript. So I think clinicians need to be wary of the genetic testing panels that they are requesting be screened or used in the assessment of their patients and be knowledgeable that at this point in time, we really only have three genes with very strong evidence to support disease causation of the typical form of long QT syndrome. And that for the most part, these other genes should not be tested or should only remain in the realm of research. I think that responsibility extends further than just the clinician taking care of the patient, but also clinical genetic testing providers, companies that offer these genetic testing services. I think they should assume a responsibility to ensure that they are only offering services for genes that have strong evidence for disease causation because when they report results in genes that are not valid for the disease, that only confuses the care of the patient and that creates a risk of harm to them if that information is misinterpreted by a physician. As Dr Viskin or Sami pointed out, we do see patients who are inappropriately diagnosed. We remove the diagnosis of roughly 10 to 20% of cases in our own clinic. And unfortunately, many of these patients and their families have suffered undue anxiety. Some of them have ICDs in place that should not have been there. So I think overall, the field needs to be aware of what genes are relevant and what genes still are within the realm of research. Dr Greg Hundley: Can you tell us just quickly Michael and then also Sami, what do you see as the next study in this field? Dr Michael Gollob: We're taking a step back now. The first decade of this century saw an exponential growth in reported gene disease associations. And now in the last five or six years, we've learned a lot about human genetic variation, which has provided us an opportunity to reflect back on some of these previous and reported genes as causes for long QT and other diseases. So I think many individuals in our field may say, "Well, you know, this is disappointing. We believed in these genes. We really thought these genes were causes of long QT." And to that point I would say, we need more research. If you believe in some of these genes that have now been considered to have limited or disputed evidence, research should continue if these remain plausible candidates for the disease. So I think future research has to continue. There are probably still a few other genes that have not yet been discovered. I think we've got the vast majority. I think in most cases, at least in our experience, 90 to 95% of cases are explained by the top three genes. But there are probably other genes out there and it's always fascinating to learn or discover new genes, but those sorts of studies have to be done with the correct methodologies and rigid protocols. Lastly, I think in the future us clinicians and geneticists and genetic counselors need to work closely with genetic testing providers to ensure that they are offering responsible genetic testing services. Dr Greg Hundley: Sami, do you have anything to add? Dr Sami Viskin: Just congratulate the authors. I think they did a very great service to the medical community by pointing out the limitations of the genetic testing and the way we interpret the results, and they deserve to be applauded for reminding us that we have to be careful when we read papers about genetic results or when we get genetic testing results ourselves. Dr Greg Hundley: I want to thank Michael from University of Toronto and Sami from Tel Aviv Medical Center for participating. And on behalf of both Carolyn and myself, wish you all a great week and look forward to chatting with you next week. This program is copyright, the American Heart Association 2020.  

Jane Ferguson:                Hello, welcome to Getting Personal: Omics of the Heart, Episode 22. This is a podcast from Circulation: Genomic and Precision Medicine, and the AHA Council on Genomic and Precision Medicine. I am Jane Ferguson and it's November 2018.                                            Our first article comes from Carlos Vanoye, Alfred George and colleagues from Northwestern University Feinberg School of Medicine and is entitled, High Throughput Functional Evaluation of KCNQ1 Decrypts Variance of Unknown Significance.                                            So a major growing problem in clinical genomics is that following the identification of a variant that is potentially linked to a disease phenotype, without further interrogation, it's really hard to make sense of the functional significance of that variant. Right now, the large number of variants of unknown significance lead to confusion for patients and clinicians alike. To allow for accurate diagnoses and the best treatment plans, we need a way to be able to screen variants to assess their function in a fast and cost-effective manner.                                            In this paper, the authors decided to focus in the KCNQ1 gene, a cardiac ion channel, which can affect arrhythmias. They aim to assess whether a novel high-throughput functional evaluation strategy could identify functional mutations, as well as an in vitro electrophysiological approach. Which is effective, but expensive and time-consuming. Their approach capitalized on an existing automated electrophysiological recording platform that had originally had been developed for drug discovery essays.                                            They selected 78 variants in KCNQ1 and assessed their function using the High-Throughput platform, which coupled high efficiency, cell electroporation with automated plain or patch clamp recording. They compared the results to traditional electrophysiological essays and find a high rate of concordance between the two methods. Overall, they were able to reclassify over 65% of the variants tested, with far greater efficiency than traditional methods.                                            While this method will not work for all genes and phenotypes, the authors have demonstrated an efficient method for functional interrogation of variants. Which may greatly accelerate discovery and conditions such as Long QT or other congenital arrhythmias.                                            The next paper, Nocturnal Atrial Fibrillation Caused by Mutations in KCND2 Encoding Poor Forming Alpha Subunit of the Cardiac KV 4.2 Potassium Channel, comes from Max Drabkin, Ohad Birk, and colleagues at Soroka University Medical Center in Israel. This paper also focuses on cardiac ion channels and the role of mutations in atrial fibrillation.                                            In a family with early-onset peroxisomal AF across three generations, whole XM sequencing revealed a variant in KCND2 encoding the KV 4.2 Potassium Channel, which segregated consistent with autosomal dominant heredity. This variant resulted in a replacement of a conserved [inaudible] residue with an arginine. To investigate functional consequences of this novel variant, they conducted experiments in xenopos laevis oocytes and found that there is decreased voltage depended channel and activation and impaired formation of the KV 4.2 Homotetramer and the KV 4.2, KV 4.3 Heterotetramer.                                            Overall, this study shows that a novel mutation in a conserved Protein kinase C Phosphorylation site within the KV 4.2 Potassium Channel underlies the phenotypes observed in a family of peroxisomal atrial fibrillation. The targeting Atrial KV 4.2 might be an effective therapeutic avenue.                                            Next up, Michael Levin and Scott Damrauer and colleagues from the University of Pennsylvania published an article entitled, Genomic Risks Stratification Predicts All-Cause Mortality After Cardiac Catheterization.                                            They were interested in understanding the utility of polygenic risk scores for disease prediction. They constructed a genome Y genetic risk score for CAD and applied it to individuals from the Penn Medicine Bio-bank who had undergone Coronary angiography and genotyping.                                            They included over 139,000 variants for the 1,500 ancestry subjects who were included and classified them as high or low polygenic risk. Individuals who were classified as high polygenic risk were shown to have higher risk of All-Cause mortality than low polygenic risk individuals despite no differences in traditional risk factor profiles. This was particularly evident in individuals with high genetic risk but no evidence of angiographic CAD.                                            Adding the polygenic risk score to a traditional risk assessment model was able to improve prediction of five year All-Cause mortality. Highlighting the utility of a polygenic score and underscoring traditional risk factors do not yet fully capture mortality risk.                                            The next article entitled, "Bio-marker Glycoprotein Acetyls is Associated with the Risk of A Wide Spectrum of Incident Diseases and Stratifies Mortality Risk in Angiography Patients" comes from Johannes Kettunen, Scott Ritchie, Peter Würtz and colleagues from the University of Oulu Finland.                                            GlycA is a circulating biomarker that reflects the amount of Glycated proteins in the circulation. It has been associated with cardiovascular disease, Type 2 Diabetes, and all-cause mortality. In this paper, the authors used electronic health record data from over 11,000 adults from the finish general population previously included in the "FINRISK" and "Dilgom" studies and they tested for a associations between GlycA and 468 different health outcomes over an 8-12 year follow up. They report new associations between GlycA and multiple conditions including incident alcoholic liver disease, chronic renal failure, glomerular diseases, chronic obstructive pulmonary disease, inflammatory polyarthric disease and hypertension.                                            These associations held true even after adjusting for CRP suggesting that GlycA represents an independent biological contributor to inflammation and disease. Their findings highlight potential utility for GlycA as a biomarker of many diseases and underscore the importance future functional and mechanistic studies to understand how GlycA is linked to disease risk.                                            Our last original research article entitled, "Tissue Specific Differential Expression of Novel Jeans and Long Intergenic Non-coding RNAs in Humans with Extreme Response to Endotoxic glycemia comes from Jane Ferguson, Murdock Riley, and colleagues from Vanderbilt University, Columbia University, and the University of Pennsylvania. That first author is none other than me, so I'm not unbiased reader of this particular manuscript, but I'd like to tell you a little bit about it anyway.                                            We were interested in understanding the transcriptional changes that occur in tissues during acute inflammation. As part of the genetics of evoked responses to Niacin and Endotoxemia, or gene study, we recruited healthy individuals and performed an inpatient endotoxin challenge where we administered a low dose of LPS and looked at the systemic inflammatory response. Individuals vary greatly in the degree of their inflammatory response to LPS and we identified high and low responders, men and women, of African and European ancestry, who had responses in the top or bottom 10% for cytokines and fever.                                            We conducted RNA seek and adipose tissue in 25 individuals and CD-14 positive monosites for 15 individuals in pre and two or four hours post LPS samples. We found that the differences in transcriptional response between high or low responders are mostly explained by magnitude rather than discrete sets of genes.                                            So some core genes were altered similarly, in both groups, but overall the high responders mounted a large transcription of response to LPS or low responders rather than mounting an anti-inflammatory response actually just barely responded on the transcription level. We saw clear tissue specificity between manosites and adipose tissue we identified several long non-coding RNAs that were up or down regulated in response to LPS and validated these independent samples one of these link RNAs which we have now named Monosite LPs induced link RNA regulator vile six or Mahler Isle six, with highly regulated by LPs and monosites but not in adipose tissue.                                            We [inaudible] THP-1 monosites and find a significant effect on iOS six expression suggesting that this is a novel link RNA that regulates Isle six expression in manosites potentially through a cd-86 dependent pathway. Overall our data revealed tissue specific transcriptional of changes that correlate with clinical inflammatory responses and highlight the role of specifically incarnate and inflammatory response.                                            Next up is a research letter entitled "Reduced Sodium Current in Native Cardiomyocytes of a Regatta Syndrome Patient Associated with Beta Two Central Mutation" published by Constance Schmidt, Felix Wiedmann, Ibrahim El-Battrawy, Dierk Thomas, and co-authors from University Hospital Heidelberg. They obtained cardiomyocytes from a patient with Regatta Syndrome previous whole XM sequencing had implicated a variant in the Beta Two Syntrophin or "SNTB2" gene as potentially causal in this individual. Expression analysis showed lower SNTB2 expression and atrial tissue of the affected individual compared with controls.                                            They performed electrophysiology on the Microcytes and found reduced peak sodium density and reduced late sodium current. They co-express wild type or mutant SNTB2 in heck 293 T cells and [inaudible] with the cardiac sodium channel NAV-1.5 and found a significant effect on binding which adversely affected sodium currents. This study nicely demonstrates the functional effect of this SNTB2 mutation underlying Regatta Syndrome in this patient.                                            A second research letter comes from A.T. van den Hoven and Jolien Roos- Hesselink and colleagues from Erasmus University Medical Center in the Netherlands and is entitled "Aortic Dimensions and Clinical Outcome in Patients with SMAD three mutations, they were interested in understanding how the Aortic dilation comment individuals with SMAD three mutations compared to individuals with other syndrome and causes of Aortic dilation.                                            In 28 patients with SMAD three mutations, there were significant growth in the Sinotubular Junction the ascending Aorta on the diaphragm over an average of 10 years of follow up at reads far higher population averages but lower than might be seen in other syndromes, such as [inaudible]. Intensive management and preventive surgery and many of the patients prevented any mortality in this group.                                            Rounding out this issue is a clinical letter entitled "Concealed Arrhythmogenic  Right Ventricular Cardiomyopathy in Sudden unexplained Cardiac Death events from Jodie Ingles, Chris Semsarian, and colleagues from the University of Sydney, Australia. They report on for clinical cases where individuals presented in early adulthood with unexplained cardiac arrest, which was later found to be attributable to mutations in the PKP2 gene. PKP2 or, Plakophilin 2, encodes an integral component of the Desmosome, which is important and Cell-Cell adhesion. Further PKP2 is involved in transcriptional activation of genes controlling intracellular calcium cycling. This gene has been implicated arrhythmogenic right ventricular cardiomyopathy in individuals with cardiac structural abnormalities. These four cases where unrelated individuals were all fans to have loss of function variants and PKP2 underlying sudden cardiac death or events, despite structurally normal hearts. This prompts questions on the clinical management of such cases of concealed ARVC.                                            That's all from us for November, thanks to all of you out there listening. We'll be back in December for the final episode of 2018.                                            This podcast was brought to you by Circulation Genomic and Precision Medicine and the American Heart Association Council on Genomic and Precision Medicine. This program is copyright American Heart Association 2018.                                             

Dr Carolyn Lam:                Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to the journal and its editors. I'm Dr Carolyn Lam, Associate Editor from the National Heart Center and Duke National University of Singapore.                                                 Is there a unique lipoprotein profile for incident peripheral artery disease as opposed to coronary or cerebral vascular disease? Well, you're just gonna have to wait for our feature discussion to find out. That's coming right up after these summaries.                                                 Our first original paper this week tells us that gene variance known to be associated with idiopathic and peripartum cardiomyopathy are also associated with preeclampsia. First and corresponding author Dr Gammill from University of Washington and colleagues studied 181 participants with confirmed preeclampsia from the Preeclampsia Registry in BioBank. Saliva samples were collected for DNA isolation and whole exome sequencing was performed to detect rare variants in 43 genes known to be associated with cardiomyopathy.                                                 Results were compared with data from two controlled groups, unrelated women with a gynecological disorder, sequence using the same methods and instruments, as well as published variant data from 33,000 subjects in the Exome Aggregation Consortium.                                                 The results showed that women who developed preeclampsia are more likely to carry protein altering mutations in genes associated with cardiomyopathy, particularly, the TTN gene which encodes the sarcomeric protein titin. Thus, detecting these gene variants may allow more specific diagnosis, classification, counseling and management of women at risk.                                                 Prior trials have shown that nonsteroidal anti-inflammatory drugs or NSAIDS confer cardiovascular risk. Now this has been postulated to be due to enhanced formation of methyl arginines in the kidney that would limit the action of nitric oxide throughout the vasculature. However, the next original paper in this week's journal suggests that this may not be correct. First author, Dr Ricciotti, corresponding author, Dr FitzGerald from University of Pennsylvania Perelman School of Medicine and colleagues, used multiple genetic and pharmacological approaches to disrupt the COX 2 pathway in mice and analyze plasma from patients taking NSAIDS.                                                 However, they did not observe an increase in methyl arginines. In contrast, they did observe an increase in plasma asymmetric dimethylarginine or EDMA in mice-rendered hypertensive by infusion of angiotensin II at a dose that also caused renal impairment. After a four week washout period following the infusion of angiotensin II, blood pressure, creatinine, and ADMA levels all fell back to normal levels.                                                 Celecoxib-treated mice also exhibited increased ADMA and plasma creatinine in response to infusion of angiotensin II and their levels also returned to normal thereafter. Thus, it seems likely that the previous reported elevations in ADMA reflected renal dysfunction rather than a direct consequence of COX 2 deletion or inhibition. The authors end by suggesting that the most plausible mechanism by which NSAIDS confer a cardiovascular risk, is by suppression of COX 2 derived cardioprotective prostaglandins such as Prostacyclin rather than by enhanced formation of methyl arginines.                                                 The next original paper identifies new targets with the potential to prevent vascular malformations in patients with hereditary hemorrhagic telangiectasia. Co-corresponding authors, Dr Ola and Eichmann from Yale University School of Medicine and colleagues looked at SMAD4, which is a downstream effector of transforming growth factor-beta/bone morphogenetic protein family ligands that signal via activin-like kinase receptors.                                                 The authors generated a tamoxifen inducible postnatal endo-fetal specific SMAD for a mutant mouse and showed that SMAD4 prevented flow-induced arterial venous malformations by inhibiting casein kinase II. The uncovered pathways provided novel targets for the treatment of vascular lesions in hereditary hemorrhagic telangiectasia related juvenile polyposis patients carrying SMAD4 mutations.                                                 The next original paper provides important data for the accurate diagnosis of long QT syndrome. Long QT syndrome can be a challenging diagnosis partly because the optimal method for QT assessment is not unequivocally established. QT experts advocate manual measurements with a tangent or threshold method.                                                 In today's paper, first and corresponding author, Dr Vink from Academic Medical Center University of Amsterdam and colleagues, aimed to assess similarities and differences between these two methods of QT interval analysis among 1,484 patients with a confirmed pathogenic variant in either KCNQ1, KCNH2 or SNC5A genes from 265 families. Both QT measurement methods yielded a high inter and intra reader validity and a high diagnostic accuracy.                                                 Using the same current guideline cutoff of QTC interval 480 milliseconds, both methods had similar specificity but yielded a different sensitivity. QTC interval cutoff values for the QT measured by the tangent method was lower compared to that measured by the threshold method. Plus, values were different depending on the correction for heart rate, age, and sex.                                                 The authors provided an adjusted cutoff values specified for method, correction formula, age, and sex. In addition, a freely accessible online probability calculator for long QT syndrome at www.QTcalculator.org has been made available as an aid in the interpretation of the QT interval.                                                 The next original paper demonstrates for the first time that thrombin mediated signaling may play a role in diet-induced atherogenesis. Co-first authors, Dr Raghavan and Singh, corresponding author Dr Rao from University of Tennessee Health Science Center and colleagues, used a mouse model of diet-induced atherosclerosis and molecular biological approaches and explored the role of thrombin and its G protein coupled receptor signaling in diet-induced atherosclerosis.                                                 They found that thrombin-induced CD36 expression and foam cell formation required protease activated receptor 1, G alpha 12, Pyk2, GAB 1, and protein kinase C theta dependent activating transcription factor 2 activation. Thus, inhibition of thrombin G protein coupled receptor signaling could be a promising target for the development of new drugs in reducing the risk of diet-induced atherogenesis.                                                 The next study provides insights into the long- term association of LDL cholesterol with coronary heart disease mortality in individuals at low tenure risks of atherosclerotic cardiovascular disease. First and corresponding author, Dr Abdullah, from VA North Texas Medical Center and UT Southwestern Medical Center and colleagues studied more than 36,000 subjects in the Cooper Clinic Longitudinal Study cohort who are at low tenure estimated risk of atherosclerotic cardiovascular disease. In other words, a low tenure risk of less than 7.5%. They've followed these patients for more than two decades.                                                 Results showed that LDL cholesterol and non-HDL cholesterol at or above 160 milligrams per deciliter were independently associated with a 50 to 80% increased relative risk of cardiovascular disease mortality. The associations between LDL cholesterol and cardiovascular disease mortality were more robust when follow up was extended beyond the traditional 10 year estimated risk period.                                                 The associations remain significant in those with an estimated tenure atherosclerotic cardiovascular disease risk of less than 5%. These data suggests that LDL cholesterol levels at or above 160 milligrams per deciliter in individuals deemed to be at low tenure atherosclerotic cardiovascular risk are associated with worse long term cardiovascular disease mortality. These findings, along with other observational data and data extrapolated from clinical trials, support further consideration of appropriate LDL cholesterol thresholds for lipid lowering interventions in individuals categorized as low short-term risk.                                                 The final paper this week uncovers a novel therapeutic target for the prevention and treatment of thoracic aortic aneurysms. First author, Dr Nogi, corresponding author Dr Shimokawa from Tohoku University Graduate School of Medicine and colleagues, used genetically modified mice to show a pathogenic role of the small GTP binding protein, GDP dissociation stimulator in the development of angiotensin 2 induced thoracic aortic aneurysms and dissection. Down regulation of this protein contributed to dysfunction of aortic smooth muscle cells and hence oxidative stress, and matrix metalloproteinase activities in the pathogenesis of thoracic aortic aneurysms and dissection.                                                 Local over expression of this small GTB binding protein GDP dissociation stimulator around the thoracic aorta inhibited aortic dilatation and rupture in deficient mice. And that wraps it up for this week's summaries. Now for our feature discussion.                                                 Atherosclerosis has been considered a systemic process, meaning that when we see a disease in one vascular bed, we assume that that's a risk marker for disease in other vascular territories, and that they share pathophysiology, they share risk factors. However, if we think about it, the prior studies have all been sort of focusing on coronary and cerebral vascular disease, but today's feature paper changes that a bit because it addresses a key knowledge gap in peripheral artery disease risk, and interestingly suggests that there may be a unique lipid profile that's related to peripheral artery disease.                                                 This is gonna be an exciting discussion and I have the first author, Dr Aaron Aday from Vanderbilt University Medical Center currently. We have our editorialist, Dr Parag Joshi from UT Southwestern, and our associate editor, Dr Anand Rohatgi from UT Southwestern. Welcome gentlemen and Aaron, could we start with you sharing about your study? Dr Aaron Aday:                 So, as you mentioned, a lot of the previous epidemiologic data on atherosclerosis have been primarily in coronary artery disease and stroke, and when we looked at peripheral artery disease or PAD, there seemed to be some subtle differences. So for instance, total cholesterol on HTL cholesterol seemed to be the strongest risk factors for future peripheral artery disease and in terms of LDL cholesterol, the data are somewhat mixed. Some have found a weak association, some have actually found no association. And so building on that, we wanted to see if using nuclear magnetic resonance spectroscopy, we could elucidate more details about the litho protein pathways associated with peripheral artery disease.                                                 And we did this in the women's health study which is a prospective cohort study of women free of cardiovascular disease, the baseline, they were aged 45 and older. And what we've found in terms of the standards with their profiles, we again found that there was no association between LDL cholesterol and future peripheral artery disease, whereas certain standard lipid measures like HDL cholesterol were strongly associated with PAD, and then using the Endemol spectroscopy tool, we found that actually, small LDL particles and total LDL particles were concentrations of both of those markers, were strong risk factors for future PAD and other measures like total HDL particle concentration were even more strongly associated with future PAD than coronary artery disease.                                                 So essentially the signature associated with future peripheral artery disease, had some important differences than that for a composite of coronary artery disease and stroke. Dr Carolyn Lam:                Aaron thanks for that. That's beautifully described and just so intriguing. Parag, could you tell us how should we be thinking about results like this? Dr Parag Joshi:                   It's a great paper and it really highlights a new and unique approach in that we ... Peripheral artery disease as an isolated incident event is fairly understudied I guess we could say and so, this is a really nice paper to start choosing out some of the risk factors for that. I think overall, when we think of peripheral arterial disease in general, I think historically, we've thought of it as similar pathophysiology, you know LDL particles and perhaps other particles depositing in the arterial space. But this does highlight some important differences that might exist and I think one of those seems to be that maybe this is more a signature of elevated remnant lipoproteins or triglyceride rich remnant lipoproteins, small dent LDL particles, low HDL, that sort of metabolic syndrome type patterns that we look at as a high risk factor that may be more contributory to peripheral artery disease than coronary disease, or at least more specific to peripheral artery disease.                                                 I guess one of my main questions about that from your work Aaron is, how can we be sure this isn't just a pre-clinical marker of diabetic patients which we know have this type of pattern? Dr Aaron Aday:                 Sure, it's certainly a possibility. I think what's notable in the cohort, at least a time enrollment. And there was a very little diabetes and actually there was a much greater prevalent of metabolic syndrome. So in my mind, it may be more of a metabolic syndrome specific marker rather than necessarily down the diabetes pathway, but it's certainly something that needs to be explored further. Dr Parag Joshi:                   I wonder whether women's health studies such a healthy cohort that I wonder if this is picking up some signal before the answer to diabetes or as you said, metabolic syndrome, you know which certainly suggests an insulin resistance pattern and we know the association of diabetes with peripheral artery disease is stronger and so I wonder if this may be a sort of earlier way of picking that up. Dr Aaron Aday:                 It may be. I think one thing to notice is the outcome of peripheral artery disease that we're using. So it is symptomatic disease. So, we're not picking up a lot of ulcers that are developing in the future, it's more the claudication and then people who've undergone revascularization. Certainly diabetics have both of those as well but I think that may suggest it's not fully unexplained by developing diabetes than peripheral artery disease further down the line. Dr Parag Joshi:                   Yeah that's a great point. Dr Carolyn Lam:                Yeah great questions, great thoughts. Anand, what about you? Did you have questions too? Dr Anand Rohatgi:            I think from my perspective and thinking about it for circulation and its readership, we found this really interesting for several reasons. Number one, I think is, as you all have discussed, peripheral arterial disease just is not as well characterized and you can see that here in over 25,000 people, add about a 100 a bed, so I think in younger folk, it takes a lot of people to study, to be able to really understand kind of the pathophysiology of peripheral arterial disease.                                                 The other thing that they think they really shed some light on is how this is happening in women in particular and in women, of course as we know have been understudied in all cardiovascular diseases, but in particular, diseases like this which are less common. It's really insightful to see that these lipid abnormalities in women are contributing to peripheral arterial disease more so than your typical LDL cholesterol management and interestingly enough, most of the women who had PAD events in this study, did not have other cardiovascular events.                                                 They really just had PAD events exclusively and I thought that was really intriguing, and the use of this advanced lipoprotein testing, this NMR modality has been very useful in terms of biology and research, and I think that's the case here where we really go under the hood Carolyn, as you said, and get kind of deep dive, the lipid metalobles on abnormalities. And I think Parag and Aaron hit the nail in the head that this is really capturing an insulin resistance of phenotype and what I really liked about this is, instead of studying people who are 70, 80 years old and a lot of things are sort of clustering, a lot of diseases are clustering and they're manifesting all at the same time, it's very hard to tease apart the effective age.                                                 Here, we captured women in their 50s and middle aged, just as they have kind of gone through menopause and this adverse metabolite's phenotype starts to rise in women. And then we could follow them over time and see what the natural history of that is, and the women who have this phenotype go on to have this devastating consequence, this peripheral arterial disease. One of the questions I had then, Aaron for you is, what do you think the implications are from these findings? Does it mean that in terms of diagnostics, we should be doing more advanced testings looking at LDL and HDL type particles with NMR or some other mortality? Does it change therapies with new therapies beings studies right now? What do you think the implications are from your work? Dr Aaron Aday:                 That's important right. I think you mentioned this and I see the inter marked tool in this study, is really a way to try to dig further into the biology of peripheral artery disease as a form of atherosclerosis. I think that we already know patients who are extremely high risk or PAD, those are patients with diabetes, smoking history, metabolic syndrome et cetera., and as you can see in a patient population in 28,000 middle aged women who are pretty healthy, we only had just over a 100 PAD events.                                                 So, I think even if you were to scale this up in terms of cost, I'm not sure that that would necessarily be a viable option for patients, but I think it does suggest that truly focusing on LDL in a very high-risk patient population, meaning patients with PAD, or we may not be fully addressing their risk. And so I think this is a need to highlight that important gap, think about other therapeutic options and we'll soon have ongoing trials, triglyceride low in therapy that may be particularly beneficial in this patient population and so that's how I see this being used. Dr Anand Rohatgi:            That makes a lot of sense and particular because in middle aged women like this, your standard risk score algorithms will not really capture that they're at increased risk, even if they smoke, just because they're women and they're younger and so, I think this really is a call to arms to more refined risk assessment in these women. Dr Parag Joshi:                   Aaron, do you think there's actually a difference in the biology in the peripheral arteries compared to the coronary and cerebral vascular beds, or is there data to kind of look at that or maybe histopathological data to look at that? Dr Aaron Aday:                 We know there's a lot of overlaps, so I don't wanna suggest that PAD is not a former atherosclerosis. I think one limitation is that the primary animal model for PAD is the hyperCKemia model. That doesn't fully recapitulate what's happening in a limb with PAD and so I think that has been one limitation in understanding the biology. But I think what we're starting to see in some clinical trials that have come out in the last couple of years or starting to see a somewhat different signal for therapies in patients with PAD so for instance, in 48, we actually saw that there was a greater benefit to LDL lower [inaudible 00:21:00] inhibitors than for coronary disease. We now have the compass trial results, again, more events, higher risk among these patients but for their benefit, add on River Oxodine therapy, we've seen lymph events or lymph signals in the SGLP2 inhibitor trials. So, I think we're starting to get a sense that there may be something else on top of the traditional ascariasis biology that may be a potential target on down the road. Dr Parag Joshi:                   I think it's really a fascinating biological question of how these different territories might actually differ in their pathophysiology. I think it's a really a nice time to look at this. Also I think, Anand and Aaron both mentioned ongoing trials. The omega 3 fatty acid trials I think reduce it, will be soon to be presented and hopefully published in the next month or so. It would be nice to see if they evaluate peripheral events in that group, I'm sure they will. Dr Carolyn Lam:                Indeed, these have been just such great thoughts and discussion. Nothing really much to add there. I suppose I could say something cheeky like for the first time, and I never thought I'd say it on the podcast, I feel kind of bad that there are no men included in this trial but anyway, I just learnt so much from this. I just wanna thank you gentlemen for a great discussion.                                                 Thank you, listeners, for joining us today and don't forget to tune in again next week to Circulation on the Run.

Dr. Paul Wang:           Welcome to the monthly podcast On the Beat for Circulation Arrhythmia and Electrophysiology. I'm Dr Paul Wang, editor-in-chief, with some of the key highlights for this month's issue. We'll also hear from Dr. Suraj Kapa reporting on new research from the latest journal articles in the field.                                                 In our first article, Barry Maron associates report on the long term clinical course of hypertrophic cardiomyopathy patients following ICD therapy for ventricular arrhythmias. They studied a cohort of 486 high-risk hypertrophic cardiomyopathy patients with ICDs from eight international centers. Of these 486 patients over 6.4 years, 94 patients or 19% experienced appropriate ICD interventions, terminating VT or VF. Of the 94 patients receiving appropriate ICD therapy, 87 were asymptomatic or only mildly symptomatic at the time of appropriate ICD interventions. Of these 87 patients, 74 or 85% remained in classes one or two without significant change in clinical status of the subsequent 5.9 years up to 22 years. Among the 94 patients, there was one sudden death in three patients who died from non arrhythmic hypertrophic cardiomyopathy related processes. Post ICD intervention, freedom from hypertrophic cardiomyopathy, mortality was 100% at one year, 97% at five years, and 92% at 10 years, distinctly lower than the risk of ischemic or non ischemic cardiomyopathy in ICD trials.                                                 Hypertrophic cardiomyopathy patients with ICDs interventions reported the heightened anxiety and expectation of future shocks. However, they did not affect general psychological well-being or quality of life. The authors concluded that in hypertrophic cardiomyopathy, unlike ischemic heart disease, prevention of sudden death with ICD therapies unassociated with a significant increase in cardiovascular morbidity and mortality, nor transformation into heart failure deterioration, ICD therapy does not substantially impair overall psychological and physical well-being. In our next article, Abdulla Damluji and associates examined the cost of hospitalizations for cardiac arrest using the US nationwide inpatient sample from 2003 to 2012. Using the log transformation of inflation adjusted costs the authors examined 1,387,396 patients who were hospitalized after cardiac arrest. They had a mean age of 66 years. Inpatient procedures included coronary angiography in 15%, PCI in 7%, intra-aortic balloon pump in 4.4%, therapeutic hypothermia in 1.1%, and mechanical circulatory support in 0.1% of patients.                                                 Notably the rates of therapeutic hypothermia increased from 0 in 2003 to 2.7 in 2012, p less than 0.001. Both hospital charges inflation adjusted costs linear increased over time. In a multi-variant analysis predictors of inflation adjusted costs included large hospitals size, urban teaching hospital, and length of stay. Among co-morbidities, atrial fibrillation or fluid and electrolytes imbalance were the most common associated with cost. The authors found that during the period between 2003 and 2012 post cardiac arrest, hospitalizations had a steady rise and associated healthcare costs likely related to increase length of stay, medical procedures and systems of care.                                                 In our next paper, Peter Huntjens and associates examined intrinsic interventricular dyssynchrony as a predictor of human dynamic response to cardiac resynchronization. The authors use a cardiovascular computational model CircAdapt to characterize the isolated effect of intrinsic interventricular or intraventricular activation on resynchronization therapy response that is the change in LV dP/dt max. The simulated change in LV dP to dt max had a range of 1.3 to 26.5% increased considerably with increasing inter ventricular dyssynchrony. In contrast, the isolated effect of intra ventricular dyssynchrony was limited with the change in the LV dP/dt max range and the left ventricle from 12.3 to 18.3% in the right ventricle from 14 to 15.7%.                                                 Secondly, electrocardiographic imaging derived activation characteristics of 51 CRT candidates were used to create individual models of ventricular activation in CircAdapt. The model predicted change in LV dP/dt max was close to the actual value in left bundle branch block patients with 2.7% difference between measured and simulated when only intrinsic interventricular dyssynchrony was personalized. Among non left bundle branch block patients a change in LV dP/dt max was systematically over predicted by CircAdapt with a 9.2% difference between measured and simulated. Adding intra ventricular activation to the model did not improve the accuracy of response prediction. The authors found that computer revealed intrinsic interventricular dyssynchrony is the dominant component of the electrical substrate driving the response to CRT.                                                 In the next paper Kenji Kuroki and associates examined the use of voltage limit adjustment of substrate mapping and fast Fourier transform analysis of local ventricular bipolar electrograms during sinus rhythm to predict VT isthmuses. They performed these studies and nine post infarction patients who underwent catheter ablation for total of 13 monomorphic ventricular tachycardias. Relatively higher voltage areas on electroanatomical map or defined as high voltage channels, which were further classified as full or partial if the entire or more than 30% of the high voltage channel was detectable. 12 full high voltage channels were identified in seven of nine patients. Relatively higher fast Fourier transform areas were defined as high frequency channels, which were located on seven of 12 full high voltage channels. Five VT isthmuses or 71% were included in the seven full high voltage channels positive in high frequency channel positive sites.                                                 While no VT isthmuses were found in five full high voltage channel positive but high frequency channel negative sites, high frequency channels were identical to 9 out of 16 partial high voltage channels. Eight VT isthmuses or 89% were included in nine partial high voltage channel positive in high frequency channel positive sites, whereas no VTs isthmuses were found in the seven partial high voltage channel positive and high frequency channel negative sites.                                                 All high voltage channel positive in high-frequency channel positive sites predicted VT isthmus with a sensitivity of 100% and specificity of 80%. The authors concluded that based on this small series that combined use of voltage, limited adjustment and fast Fourier transform analysis may be useful method to detect VT isthmuses.                                                 In the next study, John Whitaker and associates examined the use of lesion index, LSI index, a proprietary algorithm combining contact force, radio-frequency application duration, and RF current. Cardiac CT was used to assess atrial tissue thickness. Ablation lines two to three per animal were created in the right atrium in seven mini pigs with point lesions using 25 watts of energy. Two weeks after the ablation, serial sections of targeted atrial tissue or examine histologically to identify gaps and transmural ablation. LSI guidelines had a lower incidence of histological gaps. Four gaps in the 69 catheter moved or 5.8% compared to ablation using LSI plus two millimeter lines in which there is seven gaps in 33 catheter moves or 21.2% and using LSI plus four millimeter lines in which there are 15 gaps in 23 moves or 65.2% p less than 0.0. The change in LSI was calculated retrospectively is a distance between two adjacent lesions above the mean LSI of the two lesions. Changing LSI values of 1.5 or less were associated with no gaps in transmural ablation.                                                 The authors concluded that in this mod of chronic atrial ablation delivery of uninterrupted transmural linear lesions may be facilitated using LSI to guide catheter movement. When change in LSI between adjacent legions is 1.5 millimeters or lower, no gaps in atrial linear lesions should be expected.                                                 In our next paper, Matthew Bennett and associate examined whether their response to antitachycardia pacing in patients with ICD could further discriminate ventricular from super ventricular arrhythmias in patients receiving ATP in the RAFT trial. The RAFT trial randomized 1,798 patients with New York Heart Association class two or three heart failure, left ventricular ejection fraction less than or equal to 30%, in QRS duration 120 millisecond or greater, to an ICD plus or a minus cardiac resynchronization. Beginning with 10,916 ATP attempts for 8,150 tachycardia episodes in 924 patients, the author's excluded tachycardias where ATP terminated the episode or were the specific etiology tachycardia was uncertain. In this study, they analyzed 3,676 ATP attempts delivered to 2,046 tachycardia episodes in 541 patients. The authors found that a shorter difference between the post pacing interval is PPI minus TCL, was more likely to be associated with VT than SVT, mean of 138.1 milliseconds for VT and 277.4 milliseconds for SVT p, less than 0.001. A PPI minus TCL value of less than or equal to 300 milliseconds had a sensitivity in 97.4% and a specificity of 28.3% for VT.                                                 The authors concluded that specifically the PPI minus TCL following antitachycardia pacing may help distinguish ventricular from supraventricular arrhythmias.                                                 In the next study, Shailee Shah and Amr Barakat and associates examined the outcomes after repeat AF ablation. The authors examined 137 patients out of a total of 10,378 patients undergoing Afib ablation who had had initial long-term success defined from recurrent arrhythmias for greater than 36 months off anti-arrhythmic drugs in subsequent underwent repeat ablation for recurrent atrial fibrillation. The median arrhythmia free period that define long-term success was 52 months. In redo-ablations reconnection of at least one of the pulmonary veins was found in 111 or 81% of patients. Additional non PV ablations were performed in 127 or 92.7% of patients. After a mean follow-up of 17 months, 103 patients or 75% were arrhythmia-free, 79 off anti-arrhythmics, and 24 on arrhythmics. The authors found that repeat ablations with re-isolation to the point of veins and modifying the atrial substrate had a good success rate.                                                 In the next article Qiongling Wang and associates hypothesized that genetic inhibition of CaMKII oxidation in a mouse model of Duchenne muscular dystrophy can alleviate abnormal calcium homeostasis thus preventing ventricular arrhythmias. The authors tested whether the selective loss of oxidation of the CaMKII effects ventricular arrhythmias in the mouse model of Duchenne muscular dystrophy. Genetic inhibition of ox-CaM kinase II by knocking replacement of the regulatory domain methionines with valines, which we'll call MMVV, prevented ventricular tachycardia in the mdx mice. Confocal calcium imaging of ventricular myocytes, isolated from the mdx MMVV mice revealed normalization of intra-calcium release events compared to myocytes from the mdx mice. Abnormal action potentials as assessed by optical mapping mdx were also alleviated by genetic inhibition of ox-CaMK II. Knockout of the NADPH oxidase regulatory sub-unit P 47 Fox normalized elevated ox-CaMK II, repaired intracellular calcium hemostasis and rescued inducible ventricular arrhythmias in the mdx mice. The authors concluded that inhibition of ROS or ox-CaMK II protects against pro-arrhythmic intracellular calcium handling, preventing ventricular arrhythmias in a mouse model of Duchenne muscular dystrophy.                                                 In the next article, Kyohei Marume and Teruo Noguchi and associates examined whether the combination of QRS duration of 120 milliseconds or greater in late gadolinium enhancement is a precise prognostic indicator for the primary endpoint of all cause death and a composite of sudden cardiac death or aborted sudden cardiac death in 531 patients with dilated cardiomyopathy. They also analyzed the association between the combination of late gadolinium enhancement and increased QRS duration in these end points among patients with a class one indication for implantable defibrillator. The author's divided study patients in three groups according to late gadolinium enhancement in QRS duration. Two negative indices that is late gadolinium enhancement negative and narrow QRS, one positive index with either late gadolinium enhancement positive or wide QRS or two positive indices late gadolinium positive and wide QRS and followed them for 3.8 years. Multiple variable Cox regression analysis identified to positive indices as significant predictors of all cause death. A hazard ratio of 4.29 p equals 0.026. Among the 317 patients with a class one indication for ICD, the five year event rate of sudden cardiac death or aborted sudden cardiac death was lowest in the two negative indices groups, 1.4%. With propensity score matching cohorts the two negative indices group had a significant lower event rate of sudden cardiac death or aborted sudden cardiac death than to two other groups hazard ratio 0.2, p equals 0.046.                                                 The authors concluded that the combination of late gadolinium enhancement in wide QRS provides additional prognostic stratification compared to late gadolinium enhancement status alone.                                                 In the next study, Matthew Sulkin and associates examined whether a novel local impedance measurement on an ablation catheter identifies catheter tissue coupling and is predictive of lesion formation. The author's first studied explanted hearts, 10 swine, and then in vivo 10 swine, using an investigational electro anatomical mapping system that measures impedance from an ablation catheter with mini electrodes incorporated into the distal electrode. Rhythmia and Intellanav, Boston Scientific.                                                 Explanted tissue was placed in a warmed 37 degree celsius saline bath mounted on a scale, and the local impedance was measured 15 millimeters away from the tissue to five millimeters of catheter tissue compression at multiple catheter angles. Lesions were created for 31 and 50 watts from 5 to 45 seconds for an N of 70. During in vivo valuation of the local impedance measurements of the myocardium 90 and blood pool 30 were guided by intracardiac ultrasound while operators were blinded to the local impedance data. Lesions were created with 31 and 50 watts for 45 seconds in the ventricle with an n of 72. The local impedance of myocardium, which was 119.7 ohms, was significantly greater than in blood pool 67.6 ohms the p of less than 0.01. Models that incorporate local impedance drop to predict lesion size had better performance that models incorporate force time integral r squared of 0.75 versus r squared of 0.54 and generator impedance drop r squared of 0.2 versus r squared of 0.58. Steam pops displayed a significantly higher starting local impedance and a larger change in local impedance compared to successful RF applications, p less than 0.01.                                                 The authors concluded that local impedance recorded for miniature electrodes provides a valuable measure of catheter tissue coupling and the change in local impedance is predictive of lesion formation during RF ablation.                                                 In the next paper, Boaz Avitall and associates found that the rising impedance recorded from a ring electrode placed two millimeters from the cryoballoon signifies ice formation covering the balloon surface and indicates ice expansion. The authors studied 12 canines in a total of 57 pulmonary veins, which were targeted for isolation. Two cryoapplications were delivered per vein with a minimum of 90 and a maximum 180 second duration. Cryoapplications was terminated upon reaching a 500 ohm change from baseline. Animals recovered 38 plus or minus six days post procedure, and the veins were assessed electrically for isolation. Heart tissue was histological examined. Extra cardiac structures were examined for damage. Pulmonary vein isolation was achieved in 100% of veins if the impedance reached 500 ohms in 90 to 180 seconds. When the final impedance was between 200 and 500 ohms within 180 seconds of freeze time, pulmonary vein isolation was achieved in 86.8%. For impedance of less than 200 ohms pulmonary vein isolation was achieved in 14%. No extra cardiac damage was recorded. The authors found that impedance rise of 500 ohms at less than 90 seconds with a freeze time of 90 seconds resulted in 100% pulmonary vein isolation.                                                 In our final papers Sally-Ann Clur and associates examined left ventricular isovolumetric relaxation time as the potential diagnostic marker for fetal Long QT Syndrome. Left ventricular isovolumetric contraction time, ejection time, left ventricular isovolumetric relaxation time, cycle length, and fetal heart rate were measured using pulse doppler wave forms in fetuses. Time intervals were expressed as percentage of cycle length, and the left ventricular myocardium performance index was calculated. Single measurements were stratified and compared between Long QT Syndrome fetuses and controls. Receiver operator curves were reformed for fetal heart rate in normalized left ventricular isovolumetric relaxation time. A linear mixed effect model including multiple measurements was used to analyze fetal heart rate, the left ventricular iso volume metric relaxation time, and the left ventricular myocardial performance index. There were 33 Long QT fetuses in 469 controls. In Long QT fetuses the left ventricular isovolumetric relaxation time was prolonged in all groups, p less than 0.001, as was the left ventricular isovolumetric relaxation time.                                                 The best cutoff to diagnose Long QT syndrome was the normalized left ventricular isovolumetric relaxation time greater than equal to 11.3 at less than or equal to 20 weeks, giving a sensitivity in 92% and a specificity of 70%. Simultaneous analysis of the normalized left ventricular isovolumetric relaxation time and fetal heart rate improved the sensitivity and specificity of Long QT Syndrome, AUC of 0.96. The normalized left ventricular isovolumetric relaxation time, the left ventricular myocardial performance index, and fetal heart rate trends differed significantly between Long QT Syndrome fetuses and controls throughout gestation.                                                 The authors concluded that left ventricular volumetric relaxation time is Prolonged QT fetuses. Findings of a prolonged normalize left ventricular isovolumetric relaxation time, and sinus bradycardia can improve the prenatal detection of fetal Long QT Syndrome.                                                 That's it for this month, but keep listening. Suraj Kapa will be surveying all journals for the latest topics of interest in our field. Remember to download the podcasts On the Beat. Take it away Suraj. Suraj Kapa:                          Thank you, Paul and welcome back to On the Beat were we will be summarizing hard-hitting articles across the entire electrophysiologic literature. Today we'll be starting within the realm of atrial fibrillation where we're review an article within the realm of anticoagulation and stroke prevention. Quon et al. published in last month's issue of JACC cardiac electrophysiology on anticoagulant use and risk of ischemic stroke and bleeding in patients with secondary atrial fibrillation. It is well known that use of anticoagulation in atrial fibrillation can reduce overall thromboembolic outcomes. However, its role in secondary atrial fibrillation is unclear. Thus, the authors sought to evaluate the effects anticoagulant use on stroke and bleeding risk. Amongst those where atrial fibrillation occurred in the setting of acute coronary syndrome, pulmonary disease, or sepsis. Amongst around 2300 patients evaluated retrospectively there was no evidence of a lower incidence of ischemic stroke among those treated with anticoagulants compared to those who are not.                                                 However, anticoagulation was associated with a higher risk of bleeding in those with new onset AF associated with acute pulmonary disease. The authors suggest as a result that there is unclear overall benefit for long-term anticoagulation in patients with presumed secondary atrial fibrillation. The difficulty in assessing this is how to define secondary atrial fibrillation. However, in many studies patients who developed in the setting of acute illness still had a high risk of developing quote unquote clinically significant AF in long-term follow-up. However, this was not necessarily absolute as many patients not necessarily develop AF that could be considered clinically significant. Thus, the clinical question that arises is: how long should we treat a patient with anticoagulation when they have presumed secondary atrial fibrillation. These data seem to suggest that there may be no net overall benefits. In other words, all-comers with secondary atrial fibrillation should not necessarily be forever treated with anti-coagulation. However, this slightly requires clinical trials to evaluate further.                                                 Next we delve into the realm of cardiac mapping and ablation where we view an article by Gaita et al. entitled 'Very long-term outcome following transcatheter ablation of atrial fibrillation. Are results maintained after 10 years of follow-up?', published in Europace last month. While pulmonary vein isolation is a widely accepted approach for treatment of atrial fibrillation, most reported studies review outcomes in terms of freedom of AF over a relatively short time period, generally two to five years. However longer term follow up is inconsistently reported. Gaita et al. sought to review 10 year outcomes amongst 255 patients undergoing ablation in a single center. They noted 52% remainder arrhythmia-free amongst a mixed cohort of both paroxysmal and persistent patients while 10% progressed to permanent atrial fiBrillation. They found that absence of increases in blood pressure, BMI, and fasting glucose was protective against an arrhythmia recurrence.                                                 These findings suggest that in a relatively small cohort of patients limited to a single center that even long-term outcomes after pulmonary vein isolation are generally quite good, exceeding 50%. However, future freedom from atrial fibrillation is heavily tied to control of other risk factors. In other words, if a patient is going to have poor control of diabetes, blood pressure, or gain weight, the benefit of their pulmonary vein isolation over long-term follow-up is likely less. These data thus highlight both the potential long-term benefit of PVI, but also the importance of counseling patients regarding the need for continued management and control of future and existing risk factors.                                                 Staying within the realm of atrial fibrillation we next review an article by Weng et al. entitled 'Genetic Predisposition, Clinical Risk Factor Burden, and Lifetime Risk of Atrial Fibrillation' published in last month's issue of circulation. The probability of detecting atrial fibrillation in patients based on clinical factors and genetic risk is unknown. Weng et al. sought to clarify whether a combination of clinical and polygenic risk scores could be used to predict risk of developing atrial fibrillation over long-term followup in the Framingham Heart Study. Amongst 4,600 individuals, 580 developed incident atrial fibrillation and had an overall lifetime risk of developing atrial fibrillation of 37%. Those are the lowest risk tertile based on clinical risk factor burden and genetic predisposition had a lifetime risk of 22% versus 48% in the highest. Furthermore, a lower clinical risk factor burden was associated with delayed atrial fibrillation onset. In order to identify patients with atrial fibrillation, before negative sequelae such as stroke occur, patient and physician understanding of risk and monitoring needs is necessary. The fact is that it will be great to identify every single patient who has atrial fibrillation before they have a negative sequela of that atrial fibrillation such as ischemic stroke.                                                 However, performing continuous monitoring of all patients with potential negative sequelae of atrial fibrillation is extraordinarily difficult. The reason is it's excessively costly. We cannot monitor the entire population irrespective of whatever the risk factors are. However, if we're able to identify the highest risk cohorts early on before the atrial fibrillation onsets, this may offer opportunities for use of newer cheaper monitors. The work by Weng et al. suggests one such possible approach combines clinical and polygenic risk scores. Actionability of these data, however, remains to be seen and further validation other cohorts is necessary to clarify generalized ability.                                                 The next article we review is published in last month's issue of the Journal of American College of Cardiology by Lopes at al. entitled 'Digoxin and Mortality in Patients With Atrial Fibrillation. Lopes et al. sought to evaluate the impact of the Digoxin on mortality in patients with atrial fibrillation and the association with the Digoxin serum concentration and heart failure status. They value this association in over 17,000 patients. At baseline 32% were receiving Digoxin. Baseline Digoxin use did not associate with risk of death, but even in these patients a serum concentration of greater than 1.2 nanograms per milliliter was associated with a 56% increase in mortality risk. For each .5 nanogram per milliliter increase in oxygen concentration the hazard ratio increased by 19% for overall mortality. This was irrespective of heart failure status. Furthermore, in patients who are newly started in Digoxin over the follow-up period, the risk and death and sudden death was higher. These data suggests a significant risk associated with Digoxin use for management of atrial fibrillation irrespective of heart failure status. Furthermore, serum valleys above 1.2 require close consideration of dose de-escalation. Whether there is any optimal dose, however, from the study is unclear. These data amongst a host of prior data strongly suggest again strategic use of Digoxin  principally for the management of atrial fibrillation.                                                 Moving on within the realm of atrial fibrillation, we review an article published in last month's issue of Circulation Research by Yan et al. entitled Stress Signaling JNK2 Crosstalk with CaMKII Underlies Enhanced Atrial Arrhythmogenesis. In this more acellular based study the mechanism underlying atrial arrhythmogenesis associated with aging was evaluated. Yan et al. sought to figure out whether the stress response JNK in calcium mediated arrhythmias might contribute to atrial arrhythmogenesis in aged transgenic mouse models. They demonstrated significant increased activity of JNK2 and aging atria, those furthermore associated with rhythmic remodeling. This association was mediated through CaMKII and ryanodine receptor channel function, with activation of the former leading to increased calcium leak mediated by the ladder. This in turn related to increase atrial fibrillation likelihood. Identifying novel targets for atrial fibrillation therapy is critical. Given atrial fibrillation is a complex disease process related to a multitude of risk factors it can be assumed that the contribution of any single factor may be mediated through distinct mechanisms.                                                 Aging in particular as well regarded, but considered to be non-modifiable risk factor for atrial fibrillation. Identifying genes or pathways, the immediate aging associated fibrillation, may take the risk of aging as no longer a non-modifiable thing. The finding of the significance of JNK2 and associate downstream effects with AF risks and aging hearts may hold potential in offering unique therapeutic targets.                                                 Finally, within the realm of atrial fibrillation, we're viewing article by Chen et al. in last month's issue of the Journal of the American Heart Association entitled Association of Atrial Fibrillation With Cognitive Decline and Dementia Over 20 Years: The ARIC-NCS Study. Multiple studies have suggested a significant association between atrial fibrillation risk of dementia. However, these studies have limited time follow-up and were often done and predominantly white patients. Thus, the authors sought to use the data from ARIC, the Atherosclerosis Risk in Communities Neurocognitive Study, to assess the risk of cognitive decline associated with atrial fibrillation. Amongst over 12,000 participants, a quarter of whom are black and half of whom are white, they noted 2100 patients developed atrial fibrillation and 1,150 develop dementia over a 20 year follow up period.                                                 There was a significantly greater risk of cognitive decline amongst those who developed atrial fibrillation. In turn incident atrial fibrillation for the follow-up period was associated with a higher risk of dementia even after adjusting for other clinical and cardiovascular risk factors such as incidents that ischemic stroke. These data further strengthened prior evidence of a direct link between atrial fibrillation and risk of cognitive decline and dementia. Understanding this long-term risk raises the need to additionally identify approaches to prevent this occurrence, which in turn is dependent on understanding the underlying mechanisms. The finding that the risk of cognitive decline dementias independent of ischemic stroke events raises concern that either subclinical micro-embolic events or other factors may be playing a role in this risk and in turn raises question as to how best to prevent them. Until better understood, however, the question of whether the association is causal remains to be seen.                                                 Changing gears yet again, we now delve into the realm of ICDs, pacemakers and CRT. Published in last month, issue of Heart Rhythm Tarakji et al. published a paper entitled 'Unrecognized venous injuries after cardiac implantable electronic device transvenous lead extraction.' Overall risk of transvenous lead extraction includes that of potentially fatal venous laceration. The authors sought to evaluate the incidence of venous injury that may be unrecognized based on microscopic study of extracted leads. Amongst 861 leads obtained from 461 patients they noted 80 leads or almost 9%. Amongst 15% of patients showed segments vein on the lead body, most of which were transmural including the tissue layer. However, in terms of clinical significance, only 1% had need for emergent surgical intervention for clinically significant venous laceration. Risk factors for having the entire vein on the lead included age of lead, ICD leads, and the use of the laser sheath.                                                 These findings suggest that there may be a high incidence of subclinical venous injury after lead extraction though rarely resulting clinically apparent sequelae. As would be expected, venous injury, including transmural removal of portions of the vein traversed by the lead, was more common amongst older leads, which generally more often require laser sheets and ICD leads. The question is however, whether this carries any direct clinical implications. One they may be considered is the potential additive risk of an advancing new lead through the same venous channel, particularly in the setting of potential transmural venous injury that already exists.                                                 Next in last month's issue of Heart Rhythm we review an article by Sharma at al. entitled 'Permanent His-bundle pacing as an alternative to biventricular pacing for cardiac resynchronization therapy: A multicenter experience.' The use of resynchronization therapy for treatment of patients with heart failure and wide QRS has been shown to offer morbidity and mortality benefits. However, many patients maybe non-responders, and recent studies on His bundle pacing of suggested potential clinical benefits. His bundle pacing essentially only requires one pacing catheter attached within the region of the His bundle Sharma et al. sought to evaluate the safety and success rates of His bundle pacing for patients who have either failed standard resynchronization therapy or in whom most tried as a primary intervention. They noted His bundle pacing was successful in 90% of patients with reasonable myocardial and His bundle capture thresholds. Patients in both groups exhibits significant narrowing of QRS morphology and improvement in left ventricular ejection fraction from a mean of 30 to 43%. However, a total of seven patients had lead related complications.                                                 These database on a retrospective analysis of two types of patients, those failing standard biventricular therapy, and those on whom his bundle pacing was attempted as a primary modality suggest overall safety and efficacy in a handful of experienced centers. The promise of His bundle pacing is that a may allow for more effective resynchronization than standard approaches. The high rate of success suggests that His bundle pacing maybe both safe and reasonable to pursue. However randomized trials across more centers are needed to fully prove its benefit, particularly as a primary modality of treatments.                                                 Next we review ICDs and chronic kidney disease. In last month's issue of JAMA cardiology by Bansal at al. entitled 'Long-term Outcomes Associated With Implantable Cardioverter Defibrillator in Adults With Chronic Kidney Disease.' While the benefit of ICDs in patients with low EF is widely recognized, modifying factors that may increase risk of death are not as well defined. These include things like advanced age and chronic kidney disease. Bansal et al. sought to evaluate long-term outcomes and ICD therapy in patients with chronic kidney disease. In retrospective study of almost 5,900 ambulatory patients amongst whom 1550 had an ICD, they found no difference in all cause mortality. However, ICD placement was associated with an increased risk of subsequent hospitalization due to heart failure or any cause hospitalization.                                                 In light of recent studies such as DANISH the robust sense of ICD benefit is being questioned. One of the thoughts for the absence of similar benefit to prior studies lies in the improving care of ambulatory heart failure patients. In patients with chronic kidney disease several questions rises to the risk with ICD, including infectious risk in dialysis patients and the concomitant mortality risk with renal dysfunction. The author suggested in retrospective study, no incremental benefit of ICDs in patients with chronic kidney disease and perhaps some element of added risk is related to hospitalization. However, this study has several limitations. It is retrospective and many patients received ICDs may have been perceived to be sicker in some way. Thus care must be taken in interpretation, but consideration of randomized studies to adjudicate benefit are likely necessary.                                                 Finally, within the realm of devices, we reviewed an article by Tayal et al. entitled "Cardiac Resynchronization Therapy in Patients With Heart Failure and Narrow QRS Complexes.' publishing the Journal of American College of Cardiology last month. Several parameters have been stressed to identify benefit of resynchronization therapy in patients with wide QRS include cross correlation analysis with tissue doppler imaging. However, many patients may have evidence in mechanical dyssynchrony even in the absence of an apparent wide QRS thus Tayal et al. sought to evaluate the benefit of resynchronization therapy amongst 807 patients with heart failure and a narrow QRS mean criteria in a randomized study. Of the 807 46% had delayed mechanical activation. Those without delay mechanical activation had underwent we standardization therapy and were associated with worse overall outcomes likely due to new delayed mechanical activation potentially related to CRT pacing. These data support the absence of a role for resynchronization therapy in patients with a narrow QRS. This is expected as resynchronization therapy likely offers the most benefit in patients with mechanical dyssynchrony that results from electrical dyssynchrony.                                                 Since by its very nature resynchronization therapy relies on non physiologic cardiac pacing thus compared to normal cardiac activation the nature of resynchronization pacing is desynchronization. These data support the absence of a role for resynchronization therapy in patients with heart failure and narrow QRS complexes.                                                 Moving on to cellular electrophysiology we review an article by Kozasa et al. published in last month's issue of Journal of Physiology entitled 'HCN4 pacemaker channels attenuate the parasympathetic response and stabilize the spontaneous firing of the sinoatrial node.' Heart rate is controlled by an interplay between sympathetic and parasympathetic components. In turn HCN4 abnormalities have been implicated in congenital sick sinus syndrome. The authors sought to clarify the contribution of HCN4 to sinus node autonomic regulation. They created a novel gain-of-function mouse where the HCN4 activity could be modulating from zero to three times normal. They then evaluated ambulatory heart-rate variability and responsive heart rate to vagus nerve stimulation. They found HCN4 over-expression did not increase heart rate, but attenuated heart-rate variability. It also attenuated bradycardic response to vagus nerve stimulation. Knockdown of HCN4 in turn lead to sinus arrhythmia and enhanced parasympathetic response. These data suggest HCN4 attenuates sinus node response to vagal stimuli thus stabilizing spontaneous firing of the node. The clinical application of this remain to be seen but are maybe important in that they highlight a mechanism for a heretofore poorly understood mechanism for how exactly HCN4 abnormalities may lead to sick sinus syndrome.                                                 Within the realm of ventricular arrhythmias we highlighted a number of articles published this past month. The first article we review was published in last month's issue of JACC clinical electrophysiology, entitled characterization of the electrode atomic substrate and cardiac sarcoidosis: correlation with imaging findings of scarring inflammation published by [inaudible 00:41:40] et al. In patients with cardiac sarcoidosis one of the questions is how to define the electronic atomic substrate, particularly before we entered the electrophysiology laboratory. Both active inflammation and replacement fibrosis maybe be seen in patients. The authors evaluated in 42 patients with cardiac sarcoidosis, the association between an abnormal electrograms and cardiac imaging findings including PET and Computed Tomography, as well as Cardiac MRI. They noted that amongst these 40 patients, a total of 21,000 electrograms were obtained, and a total of 19% of these were classified as abnormal. Most of the abnormalities occurred in the basal paravalvular segments and intraventricular septum. They further noted that many of these abnormalities in terms of electrograms were located outside the low voltage areas, particularly as it relates to fractionation. In about 90% of patients they notice late gadolinium enhancements and they noted abnormal FDG uptakes suggesting active inflammation in about 48%.                                                 However, it should be noted that only 29 of the 42 patients underwent cardiac imaging. Segments with abnormal electrograms tended to have more late gadolinium enhancement evidence scar transmurality, and also they noted that the association of abnormal PET scan did not necessarily occur with abnormal electrograms. Thus, they concluded that in patients with cardiac sarcoidosis and ventricular tachycardia pre-procedural imaging with cardiac MRI could be useful in detecting electroanatomic map abnormalities that may in turn be potential targets for substrate ablation. However, they were more likely associated with more scar transmurality and lower degrees of inflammation on PET scanning. These data are important in that they highlight potential non-invasive means by which to understand where substrate might occur in patients with the cardiac sarcoidosis. It is well recognized that cardiac sarcoidosis is associated with increased risk of ventricular arrhythmias. These risks have increased ventricular arrhythmias, might be targetable with ablation. Newer therapies might even offer non invasive means by which to perform ablation in patients best. Thus if we could identify non based on mechanisms of identifying the substrate, this will be even more critical.                                                 The critical findings of this particular paper lie in noting that most of the abnormalities still is in intra ventricular sePtum in basal segments, and also that it is MRI in late gadolinium enhancement and associates more with the abnormal electrograms. Interestingly, the absence of inflammation correlating with the presence of more abnormal electrograms suggests that it is not so much the act of inflammation as being reflected in the endocardial map, but the existence of scar.                                                 Next, again within JACC clinical electrophysiology we review an article by Porta-Sánchez et al. entitled 'Multicenter Study of Ischemic Ventricular Tachycardia Ablation With Decrement Evoked Potential Mapping With Extra Stimulus.' The authors sought to conduct a multicenter study of decrement evoked potential base functional tech ventricular tachycardia substrate modification to see if such mechanistic and physiologic strategies could result in reduction in VT burden. It is noted that really only a fraction of the myocardium in what we presume to be substrate based on the presence of low voltage areas are actually involved in the initiation and perpetuation of VT. Thus if we can identify the critical areas within the presumed substrate for ablation, this would be even a better way of potentially honing in on our targets. They included 20 consecutive patients with ischemic cardiomyopathy. During substrate mapping fractionated late potentials were targeted and an extra stimulus was provided to determine which display decrements. All patients underwent DEEP focus ablation with elimination being correlated with VT non-inducibility after radio-frequency ablation. Patients were predominantly male, and they noted that the specificity of these decrement evoked potentials to detect the cardiac isthmus for VT was better than that of using late potentials alone. They noted 15 of 20 patients were free of any VT after ablation of these targets over six months of follow-up, and there was a strong reduction in VT burden compared to six months pre ablation.                                                 They concluded that detriment evoked potential based strategies towards ablation for ventricular tachycardia might identify the functional substrate and those areas most critical to ablation. They in turn regarded that by its physiologic nature it offers greater access to folks to ablation therapies.                                                 This publication is important in that it highlights another means by which we can better hone in on the most critical regions for substrate evaluation in patients with ventricular tachycardia. The fact is more extensive ablation is not necessarily better and might result in increased risk of harm if we think about the potential effects of longer ablations or more ablation lesions. Thus if we could identify ways of only targeting those areas that are most critical to the VT circuits, we could perhaps short and ablation procedural time, allow for novel ways of approaching targeted ablation with limited amounts of ablation performed, or perhaps even improve overall VT outcomes by knowing the areas that are most critical to ensure adequate ablation therapy provided. However, we need to understand that this is still a limited number of patients evaluated in a non randomized manner. Thus whether or not more extensive ablation performed might have been better is as of yet unclear                                                 Staying within the realm of ventricular tachycardia we review an article published in last month's issue of Heart Rhythm by Winterfield et al. entitled the 'Impact of ventricular tachycardia ablation on healthcare utilization.' Catheter ablation of atrial tachycardia has been well accepted to reduce recurrent shocks in patients with ICDs. However, this is a potentially costly procedure, and thus effect on overall long-term health care utilization remains to be seen. The authors sought to evaluate in a large scale real world retrospective study the effect of VT ablation on overall medical expenditures in healthcare utilization. A total 523 patients met study inclusion criteria from the market scan database. After VT ablation median annual cardiac rhythm related medical expenditures actually decreased by over $5,000. Moreover the percentage of patients with at least one cardiac rhythm related hospitalization an ER visit decreased from 53 and 41% before ablation respectively, to 28 and 26% after ablation. Similar changes we're seeing in number of all cause hospitalizations and ER visits. During the year before VT ablation interestingly there was an increasing rate of healthcare resource utilization, but a drastic slowing after ablation.                                                 These data suggests that catheter ablation may lead to reduced hospitalization in overall healthcare utilization. The importance of these findings lies in understanding why we do the things we do. We can provide a number of therapies to patients, but we seek two different effects. One is the individual effect of improving their particular health. The second thing is trying to avoid increasing healthcare expenditures on a population level and making sure resources are utilized. If we can reduce recurrent hospitalizations and overall healthcare expenditure in patients by providing a therapy in addition to provide individual benefit, this is the optimal situation. These data suggests that VT ablation might provide such a benefits, that in fact it reduces overall healthcare utilization while improving overall outcomes.                                                 Next and finally within the realm of ventricular arrhythmias, we review more on the basic side the role of Titin cardiomyopathy leads to altered mitochondrial energetics, increased fibrosis and long-term life-threatening arrhythmias, published by Verdonschot et al. in last month's issue of European Heart Journal. It is known now that truncating Titin variants might be the most prevalent genetic cause of dilated cardiomyopathy. Thus, the authors sought to study clinical parameters and long term outcomes related to Titin abnormalities in dilated cardiomyopathy. They reviewed 303 consecutive and extensively phenotype dilated cardiomyopathy patients who underwent cardiac imaging, Holter monitoring, and endomyocardial biopsy and in turn also underwent DNA sequencing of 47 cardiomyopathy associated genes. 13% of these patients had Titin abnormalities. Over long-term followup they noted that these patients had increased ventricular arrhythmias compared to other types of dilated cardiomyopathy, but interestingly, they had similar survival rates. Arrhythmias in those Titin abnormal patients were most prominent in those who were subjected to an additional environmental trigger, including viral infection, cardiac inflammation, other systemic disease or toxic exposure. They also noted the cardiac mass was relatively reduced in titan admirable patients.                                                 They felt that all components of the mitochondrial electron transport chain we're simply up-regulated in Titin abnormal patients during RNA sequencing and interstitial fibrosis was also augmented. As a result, they concluded that Titin variant associated dilated cardiomyopathy was associated with an increased risk of ventricular arrhythmias, and also with more interstitial fibrosis. For a long time we have reviewed all non ischemic cardiomyopathy as essentially equal. However, more recent data has suggested that we can actually hone in on the cause. In turn, if we hone in on the cause, we might be able to understand the effects of specific therapies for ventricular arrhythmias based on that underlying cause. Patchy fibrosis might not be as amenable, for example, to ablation as discreet substrate that we might see in infarct related VT. Understanding the relative benefit in very specific types of myopathies might hold benefit in understanding how to, one, risk stratify these patients, and two, understand what type of therapy, whether pharmacologic or ablative, might result in greatest benefit to the patients.                                                 Changing gears entirely now to the role of genetics, we review multiple articles in various genetic syndromes published this past month. First, we reviewed an article by Providência et al. published in the last month's issue of heart entitled 'Impact of QTc formulae in the prevalence of short corrected QT interval and impact on probability and diagnosis of short QT syndrome.' The authors sought to assess the overall prevalence of short corrected QT intervals and the impact on diagnosis of short QT syndrome using different methods for correcting the QT interval. In this observational study they reviewed the sudden cardiac death screening of risk factors cohorts. They then applied multiple different correction formulae to the ECGs. They noted that the prevalence of individuals with the QTc less than 330 and 320 was extremely low, namely less than .07 and .02% respectively. They were also more frequently identified using the Framingham correction. The different QTc correction formulae could lead to a shift of anywhere from 5 to 10% of individuals in the cohort overall.                                                 They further noted, that based on consensus criteria, instead of 12 individuals diagnosed with short gut syndrome using the Bazett equation, a different number of individuals would have met diagnostic criteria with other formulae, 11 using Fridericia, 9 with Hodges, and 16 using the Framingham equation. Thus, they noted that overall the prevalence of short QT syndrome exceedingly low and an apparently healthy adult population. However, reclassification as meeting criteria might be heavily dependent on which QT correction formula is used. The importance of these findings is that not all QTs are created equal.                                                 Depending on how you compute the QT interval in which formula to use may affect how you actually risk characterize a patient. Unfortunately, these data do not necessarily tell us which is the right formula, but this highlights that it might be relevant to in the future evaluate the role of different formulae and identifying which is the most necessary to classify a patient.                                                 Moving on to an article published in last month's issue of the journal of clinical investigation by Chai et al. we review an article entitled 'Physiological genomics identifies genetic modifiers of Long QT Syndrome type 2 severity.' Congenital Long QT Syndrome is a very well recognized, inherited channelopathy associated life-threatening arrhythmias. LQTS type 2 is specifically caused by mutations in casein to encoding the potassium channel hERG. However, even with the mutation not all patients exhibit the same phenotype. Namely some patients are more at risk of life threatening arrhythmias in spite of having the same mutation as others who do not exhibit the same severity phenotype. The authors sought to evaluate whether specific modifiable factors within the remaining genetic code might be modifying the existing mutation. Thus, they sought to identify contributors to variable expressivity in an LQT 2 family by using induced pluripotent stem cell derived cardiomyocytes and whole exome sequencing in a synergistic manner.                                                 They found that patients with severely effected LQT 2 displayed prolonged action potentials compare to sales from mildly effected first-degree relatives. Furthermore, stem cells derived from patients were different in terms of how much L-type calcium current they exhibited. They noted that whole exome sequencing identified variants of KCNK17 and the GTP-binding protein REM2 in those patients with more severe phenotypes in whom greater L-type calcium current was seen. This suggests that abnormalities or even polymorphisms in other genes might be modifying the risk attributed to by mutations in the primary gene. This showcases the power of combining complimentary physiological and genomic analysis to identify genetic modifiers and potential therapeutic targets of a monogenic disorder. This is extraordinarily critical as we understand on one level that when we sequence a monogenic disorder that there might exist variants of uncertain significance, namely they have not been classified as disease causing, but could be. In turn, we also recognize that mutations in a family might effect different relatives differently. However, why this is has been relatively unclear.                                                 If we can understand and identify those patients who are most at risk of dangerous abnormal rhythms, this will be useful in how much to follow them, and what type of therapy to use in them. The fact that other genes might modify the risk even in the absence of specific mutations, suggests that novel approaches to characterizing the risk might help for the risk modified patients classification in general. Clinical use, however, remains to be seen.                                                 Moving on from long QT, we evaluate 'The Diagnostic Yield of Brugada Syndrome After Sudden Death With Normal Autopsy' noted in last month's issue of the Journal of American College of Cardiology and published by Papadakis et al. It is well known, the negative autopsies are not uncommon in patients, however, families might be wondering how at risk they are. Thus, the authors sought to assess the impact of systematic ajmaline provocation testing using high right precordial leads on the diagnostic yield Brugada syndrome in a large cohort of Sudden Arrhythmic Death syndrome families. Amongst 303 families affected by Sudden Arrhythmic Death Syndrome evaluation was done to determine whether or not there was a genetic inherited channelopathy cause. An inherited cardiac disease was diagnosed in 42% of the families and 22% of relatives Brugada syndrome was the most prevalent diagnosis overall amongst 28% of families. Ajmaline testing was required, however, to unmask the Brugada Syndrome in 97% of diagnosed individuals. Furthermore, they use of high right precordial leads showed a 16% incremental diagnostic yield of ajmaline testing for diagnosing Brugada syndrome.                                                 They further noted that a spontaneous type 1 regard or pattern or a clinically significant rhythmic event developed in 17% of these concealed regardless syndrome patients. The authors concluded the systematic use of ajmaline testing with high right precordial leads increases the yield of Brugada Syndrome testing in Sudden Arrhythmic Death Syndrome families. Furthermore, they noted that assessments should be performed in expert centers or patients could also be counseled appropriately. These findings are important and one of the big questions always becomes how aggressively to test family members of patients or of deceased individuals who experienced sudden arrhythmic death. Many of these patients have negative autopsies, and genetic autopsy might not be possible due to lack of tissue or blood products that can be adequately tested.                                                 The data here suggest that amongst a group of 303 sudden arrhythmic death, families that Brugada Syndrome is by far the most frequent diagnosis. If an inherited cardiac disease was identified. In turn, it is not ECG alone or echo alone that helps identify them, but requires drug provocation testing in addition to different electrode placements. Whether or not this will consistently offer benefit in patients in general or my result in overcalling remains to be seen next within the realm of genetic predisposition.                                                 We view an area where we don't know if there's a genetic predisposition in article published by Tester et al. entitled Cardiac Genetic Predisposition in Sudden Infant Death Syndrome in last month's issue of the journal of american college of cardiology. Sudden Infant Death Syndrome is the leading cause of post-neonatal mortality and genetic heart diseases might underlie some cases of SIDS. Thus the authors sought to determine the spectrum and prevalence of genetic heart disease associated mutations as a potential monogenic basis for Sudden Infant Death Syndrome. They study the largest cohort to date of unrelated SIDS cases, including a total of 419 individuals who underwent whole exome sequencing and targeted analysis for 90 genetic heart disease susceptibility genes. Overall, 12.6% of these cases had at least one potentially informative genetic heart disease associated variants. The yield was higher in those mixed European ancestry than those of European ancestry.                                                 Infants older than four months were more likely to host a potentially informative gene. Furthermore, they noted that only 18 of the 419 SIDS cases hold a [inaudible 01:01:26] or likely pathogenic variant. So in other words, only 4% of cases really had a variant that they could say was distinctly pathogenic or likely pathogenic. Thus, overall, the minority of SIDS cases have potentially informative variant in genetic heart disease susceptibility gene, and these individuals were mostly in the 4 to 12 month age group. Also, only 4% of cases had immediately clinically actionable variance, namely a variant, which is well recognized as pathogenic and where we could actually say that a specific therapy might have had some effect. These findings can have major implications for how best to investigate SIDS cases in families. It might suggest that SIDS cases where the individual was older, nearly 4 to 12 months of age might have a greater yield in terms of identifying variance.                                                 While this might not affect the deceased in fit, it might affect, families are planning on having another child in whom a variant can be identified.                                                 Finally, within the realm of genetics, we review an article published in last month's issue of Science Advances by Huang. et al. entitled 'Mechanisms of KCNQ1 Channel Dysfunction in Long QT Syndrome Involving Voltage Sensor Domain Mutations'. Mutations that induce loss of function of human KCNQ1 underlie the Long QT Syndrome type 1. While hundreds of mutations have been identified the molecular mechanism by which they result in impaired function are not as well understood. The authors sought to investigate impact of 51 specific variants located within the voltage sensor domain and emphasized effect on cell surface expression, protein folding, and structure. For each variant efficiency of trafficking of the plasma membrane, impact of proteasome inhibition, and protein stability were evaluated. They noted that more than half of the loss of function mutations were seen to destabilized structure of the voltage sensor domain, generally accompanied by mistrafficking and degradation by the proteasome.                                                 They also noted that five of the folding defective Long QT Syndrome mutant sites were located in the S0 helix, where they tend to interact with a number of other loss of function mutation sites in other segments of the voltage sensor domain. They suggested these observations reveal a critical role for the S0 helix as a central scaffold to help organize and stabilized KCNQ1 overall. They also note the importance of these findings is that mutation-induced destabilization of membrane proteins may be a more common cause of disease functioning in humans. The importance of these findings lies in better understanding why specific mutations lead to appa

Jane Ferguson:                Hi, everyone. Welcome to Episode Four of Getting Personal: -Omics of the Heart." I'm Jane Ferguson, an assistant professor at Vanderbilt University Medical Center. This month, we have a special feature from early career member, Andrew Landstrom, who went to the Heart Rhythm Scientific Sessions in Chicago earlier this month and talked to some of the scientists who presented their research. So listen on for interviews Andrews conducted with Anneline te Riele, discussing the challenges and opportunities related to incidental findings in genetic testing, with Ernesto Fernandez, describing his research into whole exome sequencing and Long QT syndrome, and with David Tester, discussing novel variance and pathway analysis in Sudden Infant Death Syndrome. Andrew :                           My name is Andrew Landstrom and I am from the Baylor College of Medicine Department of Pediatrics' section on Cardiovascular Disease. I'm here at the 2017 Heart Rhythm Society Scientific Sessions. Anneline, will you tell us a little bit more about yourself, and what brought you to HRS? Anneline:                          Sure. So my name is Anneline Te Riele, I am a physician from The Netherlands. I finished my medical training in 2012 basically, in The Netherlands, and I started doing a PhD on ARVC in a combined project of our Netherlands patient as well as a group at Hopkins. So what brought me to HRS? I think of course the science. There's a lot of very good science. Actually, I think it's the best meeting for my purposes. Andrew :                           Absolutely. So will you just start by telling us a little bit about the spectrum of genetic testing in the clinic and about both the opportunities and the challenges that it brings? Anneline:                          Sure. So what we do in clinic, and I think this is really the challenge that we're facing currently, is we have moved from just testing on gene or one small panel of genes to bigger panels and then to whole exome or even whole genome sequencing. And I think the good part of that is that in certain cases, certain well-selected cases, you'll get a higher change of actually finding that gene that is responsible for disease.                                            On the contrary, it also leads to a lot of incidental findings. So findings that you were not expecting based on the phenotype of the patient and then you need to deal with those abnormalities that you've found and that brings on a lot of challenges as well for the family but also for us as physicians. Do we then need to screen those families, what do we do with this patient, do we treat them with medical therapies or drugs or do we give them ICDs? That kinds of question. So that I think is a virtually important part of what we're currently dealing with in clinical practice. Andrew :                           It does seem to be a very widespread problem. And here in the US of course we have the American College of Medical Genetics guidelines about reporting a variance. How do you think that that plays into the increased genetic uncertainty here in the US at least? Anneline:                          So that's a great questions. In 2013, the ACMG produced a guideline on which genes to report if you find these incidental findings. So 24 of these genes, and that's actually a big number, 24 of these genes are cardiovascular genes and that's mainly because changes in cardiovascular genes may detrimental effects down the line and really cause death or certain morbidities that are really important for the patient so we do need to deal with that.                                            And the problem with the ACMG guidelines and especially the pathogenicity guidelines is that they require two aspects. They basically require first that the variant was seen before in other cardiomyopathies or in this case other patients with disease. And that's really difficult for cardiomyopathy genes because these are large genes, they have a lot of novel or private mutations in there, so it's really hard to fulfill that requirement of having been seen before.                                            And the second thing is that the ACMG guidelines require functional studies as another proof of evidence of pathogenicity and of course, I think we would all like to do that in all of our patients, but it's just not feasible for financial purposes and all that. So that's a problem that we're facing. There are options and solutions but I think we'll talk about that later, but yeah, I think that's a problem that we're facing. Andrew :                           So on the one hand you have the ability to make a diagnostic decision based on a clear finding, but oftentimes the threshold to calling it a clearly pathologic variant is very high and oftentimes it never rises to that so it becomes more genetic uncertainty. Anneline:                          Yeah. I think that's basically right. And of course in an ideal world, we'll have certainty and say this is likely or this is definitely pathogenic, and this is likely or definitely benign, but in the real world, really, I think maybe even 80, 90% of the cases were in that gray zone in between and we need to deal with that. Andrew :                           Yeah, yeah. And you had some great resources that both scientists and clinicians alike can apply to these unknown, uncertain variants that might clarify things at least a little bit, and what are these tools? Anneline:                          So of course, from a traditional perspective, we have always looked at in silico predictive programs, we'll look at segregation data, and I think they're all very important, but they all have limitations, so for example, in silico predictive programs, they likely overcall mutations deleterious and segregation data is nothing more than evidence of pathogenicity of a locus to a disorder, not necessarily that variant, so the new things that are on the horizon, and a thing that could be the future of [inaudible 00:06:04] interpretation is collaborative project so really we should be collaborating, we should not be having our own little islands. The collaboration is the key here.                                            And collaborative efforts in the US have been for example, ClinVar and NHLBI funded effort, as well as ClinGen and ClinGen, or Clinical Genome, is perhaps the, at least it claims to be, the authoritative central resource to go back to that curates variants as being pathogenic yes or no. And I think these databases, ClinVar finally has a database entry, so the variants will be in ClinVar, but ClinGen provides an expert panel of individuals who will curate these variants as being pathogenic yes or no. I think that is a central resource that we should all be aware of. I know these are not the only ones, there are other collaborative efforts out there.                                            I mean, there are ways to connect clinicians, so for example, Match Maker Exchange is a website that you could use to enter your variant and the phenotype of the patient and you submit your own information and then you'll get matches in other databases, but not only your own match shows up. So if, say, two years later, another physician comes up and looks for the same variant, you'll get a pop up, which will actually be very nice for these clinicians to get in touch. So that's, I think, the feature ... future of variant interpretation is collaboration. That's basically my, I think my main important message here. Andrew :                           I think that's absolutely right. I think this has become sort of a big data question that requires many perspectives, and a lot of resources to be able to curate accurately. What are some of the limitations of these tools that you've seen that kind of, you have to keep in mind in terms of trying to determine whether a variant is truly pathologic or not with a patient that you have sitting in front of you? Anneline:                          So that is, I mean, of course, there's many limitations in the things that we currently do because there's so much that we don't know. But for example, to give you an example, ClinVar I think, is one central resource that we should all be aware of and if you go to ClinVar, there is actually data from two years ago, and I'm sure the numbers are high if we would look now, but if we look in ClinVar two years ago, we already saw that of the, say 120,000 variants that were in the database, 21% of these variants were called VUSes but if you look at these variants, 17% of the cases, the labs or the individual submitters of ClinVar didn't agree on the actual classification of that variant.                                            So the limitations that we all should be aware of is that there is not one single solution and you should look for evidence and really research your variants. So look at Popmap, look at what is out there, look the patient of course, look at the clinical phenotype, does it match what you think the gene should be doing or not, or is it completely unrelated? And then of course search these databases but be aware of the fact that there may be errors there.                                            Another thing I want to highlight too is that we typically go to population databases, so Exome Variant Server, ExAC, I think these are very popular databases that we use to look at the frequency of variants in a selected population. But really these databases may have sub-clinical disease patients, so I know ExAC has three NYBPC-3 mutations that are known to cause HCM, so this is something to keep in mind. There's not a gold standard truth if you open these databases, but you should have multiple pieces of information when interpreting your variant. Andrew :                           And that's a good point. I think with a lot of these cardiomyopathies and channelopathies, particularly some of the more frequent ones, when you have a database of 60,000 people, at least a couple of them are going to have disease. Anneline:                          Yeah. I think that is part of the problem. I mean HCM is pretty prevalent, I mean one in 500 individuals likely, I mean these are recent numbers, has the disease. So I think the cutoff of a minor allele frequency of five percent, which is in the ACMG guidelines, I think is way too high for this disease. So this is what the cardiovascular expert panel of ClinGen has done, so they ... This is, ClinGen, as you might know, Clinical Genome, is a one-on-one team of curators that know the framework of ClinGen and then there is disease experts that are very well accustomed with the disease and the genes associated with it. So they provide teams and these teams work together, and the cardiovascular expert group has recently published a modified, or customized, ACMG guidelines on how to deal with the intricacies of the cardiomyopathies and for example, NYH-7 which is the first genotype deposed in ClinGen or in ClinVar finally.                                            So they modify that cutoff, the minor allele frequency of five percent, which is the BA-1 ACMG guideline cutoff, they changed that to 0.1% and I think that's exactly what you were saying, that is important to keep in mind, some of the cardiomyopathies are way more prevalent so you should not consider that if you see it in a population database that you think that it's, then it's normal, it's not necessarily the case because this is a prevalent disease. Andrew :                           Yeah, and particularly when commercial genetic testing companies all can't agree that a variant is bad, and we all can't agree that a healthy variant may or may not be good, there is definitely a lot of genetic uncertainty there. Anneline:                          Exactly, exactly. Andrew :                           Now, whole-exome sequencing certainly has its role clinically, even with that genetic uncertainty that we spoke about, but it has a clear role in genetic discovery as well. Anneline:                          Sure. Andrew :                           And you were part of a very recent paper, and you led a very long list of authors, speaking more about your collaborative approach to genetics research that evaluated a novel substrate for ARVC, is that correct? Anneline:                          Yes. So this is something I'm actually pretty proud of. As you said, it's a collaborative effort, so it literally take a village to do these kind of studies and we're lucky enough to collaborate with a lot of people who are interested in the same topic. So what we did ... and I metnioned to you in the beginning, I come from the ARVC field ... So what we did is we had one ARVC patient that was discovered by whole-exome sequencing to carry an SCN5A variant and we, in and of itself, found that that was very interesting, because SCN5A, as you know, has been associated with Brugada syndrome predominantly but many other cardiomyopathies as well, so DCM, even ACM. There's been a lot of controversy about SCN5A in that matter.                                            So the computational data, the population data, it all pointed to the fact that this variant may be pathogenic, but we weren't really able to connect those dots just yet. So we then collaborated with the group in NYU with Mario Delmar, who did, first of all, functional studies on the sodium channel, but what was nice is that he was able to use his novel method of super-resolution microscopy which is a way in which we can look at the nano-scale structure of the cardiomyocytes, or really the small, small levels of molecules that you see in these cells. And what we did is we found that not only NAV1.5 which is the gene product of SCN5A but also [inaudible 00:13:53] which is an adherence structure molecule, which links the cells together was actually less present in our ARVC patient compared to the control. And this was in the IPS so cardiomyocyte molecule, which we corrected using CRISPR-Cas9 technology so I think at least in current practice, on of the best pieces of evidence that we can get.                                            So I think this shows that our SCN5A variant, I mean, in this case, probably really was pathogenic, but also in a pathophysiological standpoint, explains to us how SCN5A mutations, which are typically thought to be only affecting the sodium channel, can also lead to cardiomyopathy phenotype which has implications beyond the ARVC world, but also in DCM I think this is a nice finding of collaboration that I think ... I hope more people will look into this. Andrew :                           Absolutely I think the trouble with SCN5A is exactly like you were saying, it's been implicated in Long QT, Brugada Syndrome, SIDS, [inaudible 00:14:57], now ARVC, and even nodal disease, like sinus syndrome and things like that. So the ability to show sort of mechanistically, that while you have a change in your sodium channel gating that you also have a change in the way that the cells can connect with each other and form contractile force is, I guess, key to your study. Anneline:                          Yeah, yeah. I think this really, I mean, I'm hoping at least, it was also finally published in a journal that looks more into functional studies, so not necessarily only genetics, and I think we need to work closely not only on the genetic side, but look closely at the pathophysiological standpoint for gene discovery purposes because this will really explain to us why one gene is implicated in one disease, and also it points to possible directions to perhaps stop the disease process and treat these patients, which I think is vital in our clinical practice. Andrew :                           So are SCN5A mutations in ARVC a common finding or are they rare? Anneline:                          So they are pretty rare. I mean, we do find them every now and then and maybe they're modifiers. So what we did to follow up on that one individual, we check 281 ARVD patients who were screened just by regular screening, not by whole-exome but we did a targeted screening of SCN5A and we found five variants in these 281 patients, so that's two percent. I mean, it's still rare, but it is as rare as any other minor gene causing ARVC, but it is a rare feature, so I mean, I think it could be a player. And interestingly, the phenotype didn't change much. It wasn't really different from the ARVC patients without an SCN5A mutation which is reassuring.                                            What we also saw is that the prevalence of mutations in those with desmosomal mutations. So ARVC is, as you know, typically associated with diseases or mutations in the desmosome. It was more often seen in those without a desmosomal mutation. That was almost double as frequent as in those with a desmosomal mutation. So it does give us some direction to the fact that this may be a player out there. I mean of course it's not Plakophilin-2 which is the major player, I think, in ARVC, but I think it may cause a, at least a certain form of cardiomyopathy of arrhythmogenic cardiomyopathy that we need to be aware of. Andrew :                           And how do you think your new discovery of SCN5A being associated with ARVC, how do you think that plays into the bigger discussion we were having about expansive genetic testing and what that may mean for a patient as far as diagnostic utility but also limitations of variant interpretation? Anneline:                          That's a great question. So I think we should be cautious of saying this gene causes only this disease, and I think this is a common feature not only in ARVC but in a lot of cardiomyopathies and even in channelopathies. I think the concept of one gene causes one disease is outdated. We know that multiple genes have multiple effects and this SCN5A, of course the gene product is NAV1.5 which is the major alpha subunit of the sodium channels so it is really not the canonical function of SCN5A or NAV1.5 that causes cardiomyopathy here but it's a non-canonical function so I think we should be aware of the fact that gene products have different functions and that there can be overlap of the cardiomyopathies. So of course I think we should be screwing SCN5A in our ARVC patients and I'm hoping a lot of labs and a lot of physicians are already doing that, but it's really not the only thing that is associated with ARVC. So that's important to keep in mind. Andrew :                           What do you think the next steps are for sort of broadening the implication of your finding? Anneline:                          So what we are doing currently, and is a little bit of a sneak peek, because this data is not really out there yet, but we have, in this cohort, we found these five variants in 281 individuals, and we're currently working on one of these individuals to get another IPSO cardiomyocyte cell line and look into the functional components to that. And interestingly, this variant, that exact variant in that ARVC patient was also found in a Brugada Syndrome patient. So wouldn't it be nice to actually set them side by side and see what the differences are?                                            Of course this is a little bit of a future music, if you know what I'm saying, like this is something that we don't have just yet, but I think what we need to figure out is how epigenetic or environmental factors play into this field and to explain how one gene or one variant, even, can cause opposite functional effects in different phenotypes. Andrew :                           What do you think is needed to help clarify some of the genetic uncertainty you see clinically? Anneline:                          I think a lot of collaboration, a lot of money, quite frankly. I think we need to ... I mean, the functional data is really helping us not only for understanding that single variant, but also for gene discovery, and as I said, for treatment down the line, that is necessary, and I think the variant of uncertain significance, I mean, if we all live on our little islands and only do our little practices, then we're not going to go a lot further. So we need to work together to understand what your patient has in this variant, my patient had in that variant, and this is our phenotype, so we need to connect those dots to be able to make certain conclusions. Andrew :                           Well, I'm all for collaboration, as well as additional money, that's good. Anneline:                          Good. Andrew :                           Well, thank you so much for spending time with us. Anneline:                          Sure. Andrew :                           And again, congratulations on a wonderful presentation. Anneline:                          Thank you very much. Andrew :                           I'm joined by Dr. Ernesto Fernandez from the Baylor College of Medicine to talk about his research project. Ernesto, I'm wondering if we can just start by introducing yourself and what your project is. Ernesto:                            I am a second-year pediatric resident, I'm applying to a cardiology fellowship right now and I'm interested in, obviously, all aspects of pediatric cardiology. We're trying to figure out whether testing for Long QT genes or Long QT syndrome is actually warranted in otherwise healthy individuals. We're trying to see what the yield is on these testings, specifically whole-exome sequencing. Andrew :                           And I think this project really hits on an important point, whereby, because we've been able to interrogate the genome more comprehensively with clinical testing, that we've run into more incidentally identified variants. And these variants can pop up in genes, like the genes responsible for Long QT syndrome. Talk a little bit more about these variants, what the implication is of finding these variants incidentally, and what your project hoped to target as far as the diagnostic value of these variants. Ernesto:                            Yeah. So I guess the answer to your first question is that we are coming up with these marvelous new techniques of analyzing the genome and now we're using whole-exome sequence testing to look up is someone has any exome that's abnormal and this has caused a huge problem whereby we're now finding all these variants that we don't really know what they mean. We call them variants of undetermined significance.                                            Our study is basically premised by the fact that if you have no underlying suspicion for any arrhythmic disease, there's really no need or no indication to be referred for whole-exome sequencing testing, given that the most likely result is a variant that we don't really know what it means. And it's probably going to be benign. Andrew :                           So on the one hand, you have a well-established gene panel that's being used for diagnostic purposes with you index of suspicion being high for Long QT syndrome versus something like a whole-exome gene screen where somebody may not be thinking about Long QT syndrome as a diagnosis and have low pre-test suspicion but then comes back with a variant found in these genes sort of incidentally. Is that sort of the dichotomy you're drawing? Ernesto:                            Yeah. I think the best way of explaining it is through Bay's Theorem whereby if you have someone with a high index of suspicion when you start off to have sudden cardiac death, a family history of an arrhythmic disease, and you get a test for it, such as a gene panel for Long QT syndrome, and they come up with a positive test result, then you're going to say, "Oh. I should probably evaluate this further," whereas if you have someone who has some dysmorphism, they have delay, they might have seizures, but there's no family history of sudden cardiac death, no personal history of syncope, then there's really no need to send off this big gun, the whole-exome sequence, because you're likely to either get a normal variant or you're likely to get a variant that we don't know what to make of. Andrew :                           So I think, Ernesto, that nicely summarizes the clinical question that you had in mind. What was your hypothesis going into the study, and how did you seek to approach that hypothesis, sort of experimentally? Ernesto:                            So we came up with the hypothesis that if you have an incidentally identified variant within the whole-exome sequencing tests without any other clinical suspicion, it's likely to represent a benign finding. We went about by analyzing the data from the Baylor Miraca labs on the whole-exome sequencing data that they achieved, and we looked specifically at individuals who had gotten these tests and found to have a variant of undetermined significance, or had a pathologic variant for either one or all 17 of the genes for Long QT syndrome. We compared them to individuals who had known Long QT syndrome that had undergone genotype testing, and we [inaudible 00:25:21] these individuals from the literature. And we wanted to compare the whole-exome sequencing cohort to individuals who were otherwise healthy and had obtained a whole-exome sequence. So these are patients or individuals from the well-established ExAC database that are believed to be ostensibly healthy individuals. Andrew :                           So if I understand you correctly, you're comparing this unknown cohort, that being the rare variants found in whole-exome sequencing, against a positive control cohort of pathologic cases versus a negative control cohort of healthy individuals derived from the ExAC database to look for whether those west variants are more similar to the cases or the controls. With regards to the west cohort, what was the prevalence of individuals with these incidentally identified variants, how many did you find? Ernesto:                            So we actually found just about 49% of individuals had some variant in Long QT syndrome gene, and noted that about 12% of them had a mutation in the major causes of Long QT syndrome, and just over a third, or 36% had a mutation in the more rare causes of long QT syndrome. Andrew :                           That's a pretty surprising finding. So you're saying that one in two individuals who get whole-exome sequencing sent for whatever reason, have a variant in a Long QT-associated gene? Ernesto:                            That's what the data suggests. Andrew :                           And where did you go from here? Ernesto:                            So from there, we went onto compare the variant frequency between the case's cohort, those individuals with known Long QT syndrome, those individuals in our west cohort from the Baylor Miraca labs, and those individuals from the ExAC database who are otherwise healthy. So we noted that in our west cohort, there was about 13% of individuals who had a positive variant in the Long QT syndrome one through three genes, the major causes of Long QT syndrome. When we compare that to the ostensibly healthy individuals from the ExAC database, it was 12% in that study that had some variant in Long QT syndrome genes that are major causes of Long QT syndrome itself.                                            This was statistically similar, it was indistinguishable. And then when we compared it to the pathologic cases, it was actually about 50% of those cases who had a positive variant in a Long QT syndrome gene one through three. Andrew :                           So there was a relatively low frequency of individuals who had variants in one of the big three Long QT genes in both controls and the west cohort, and was obviously much higher among individuals with a diagnosis of Long QT syndrome. Ernesto:                            Yep. That's exactly what we found. Andrew :                           And where did you go from here? Ernesto:                            And then from there, we had a good idea that there was probably a big difference between cases and west, but we wanted to make sure, gene by gene, that there was no difference between our west cases and the ExAC database, the control cases. So we mapped each variant frequency by gene for the major causes of Long QT syndrome. There was no statistically significant difference between the west and the controls. Andrew :                           So the gene frequencies between the controls and the west were indistinguishable and very much different, both of them, it would seem, to the pathologic cases. Ernesto:                            Correct. Andrew :                           And you then looked at the position of these variants, the actual amino acid residues, correct? Ernesto:                            Yeah. So we looked at, for KCNQ1, KCNH2, and SCM5A, the three major causes of Long QT syndrome, one, two, three respectively, and we mapped out the amino acid positions where there was actually a mutation for each individuals. So the cases, controls, and pathologic cohorts. We determined the percent overlap between the west cohort and the controls and the percent overlap between the west cohort and the cases and noticed that for all three, there is a huge preference for west and control versus west and cases. Andrew :                           So if you're a west variant you're more likely to reside in the residue also occupied by a healthy individual variant as opposed to a pathologic variant? Ernesto:                            Yeah. Exactly. Andrew :                           And so what did you do next? You retrospectively looked at some of the charts of the patients who were seen at Texas Children's Hospital, correct? Ernesto:                            Mm-hmm (affirmative). So then we had 223 total individuals that had an incidentally identified variant within one of the major three genes, the Long QT syndrome genes. We looked at the reasons for their referrals and noticed that the vast majority of individuals were referred for some developmental delay, for some dysmorphism, for a non-cardiac cause, and then it was only about 23% of these individuals that actually had a reason for referral that was cardiac in nature. And less than on percent of individuals were referred for a solely cardiovascular reason. And we concluded that it's unlikely that these individuals were referred for a cardiac reason, as the data suggests, and that as a result, the index of suspicion for an arrhythmia is likely lower in these individuals. Andrew :                           And what did you find when you looked at the charts of those individuals? Ernesto:                            We had EKG data for a good number of them, and we excluded individuals who obviously had no EKG data, and we excluded individuals who had some congenital abnormality and then anyone with any other arrhythmia that would make the QTC interpretation more difficult, such as interventricular conduction defects.                                            We ended up with 62 individuals and 61 of them had a normal QTC, so there was no evidence of QT prolongation at all. There was one individual who was left who had borderline elevated QTC of 460, which was our cutoff for borderline elevation and this individual had actually been seen by pediatric cardiology at Texas Children's Hospital and found to have ... a history of syncope and it was found to be non-cardiogenic in nature. Andrew :                           So matching the variant data which suggested that you had likely found background variation in the west, you found no evidence of Long QT syndrome in these individuals who had variants in Long QT genes. Ernesto:                            That's correct. So, the overall percent was very similar between the healthy individuals and the west individuals. The variant frequencies were almost indistinguishable, and then the variant co-mapping for all, for both the west and the controls, was preferential to the western cases. So that kind of matched what we found in our study, that there was no clinical suspicion or clinical diagnosis of Long QT syndrome in these individuals who had been found incidentally. Andrew :                           Well that sounds to me to be a pretty big finding. Ernesto:                            Yeah. I think it's pretty important to get this information out there. Andrew :                           So what do you think the take home message for your study is? Ernesto:                            I think the take home message is if you don't have a suspicion of Long QT syndrome or of an arrhythmia, there's low likelihood that such a big gun test as the whole-exome sequence is likely going to change your mind. Andrew :                           So Ernesto, what would you advise a cardiologist who maybe gets a patient in clinic with a chief complaint of a VUS in a Long QT associated gene picked up on west, what would you advise based on your study findings? Ernesto:                            They're going to have to determine their own pre-test suspicion. They're going to have to get a good history and physical, probably get a baseline EKG to determine what the QTC intervals are, and if there's really no other clinical suspicion for Long QT syndrome, they're likely to be able to provide reassurance at that point in time. Andrew :                           Ernesto, what do you think the next steps are for this project, and what do you think still needs to be done in the field to reinforce your conclusions? Ernesto:                            I think my study is one of the early studies of this field, so getting more studies like this and other channelopathies, getting not just looking at Long QT one through three but looking at all of them, and in patients who've been evaluated at Texas Children's or any other institution would be helpful. And then moving forward to give more credence to the idea that if you have history that's reassuring and physical exam that's reassuring, then you probably don't need to have further testing. Andrew :                           What do you recommend if your index of suspicion is high for Long QT syndrome, so maybe a QTC in the low 480s, maybe a family history of syncope or seizures, do you think whole-exome sequencing is the way to go? Ernesto:                            Right now, that's probably not the best test, given all these incidental findings that we don't really know what to do with. There's other tests that are more high-tailored for those specific diseases, like Long QT syndrome panel among others, that are probably more likely to give you a positive post-test probability. Andrew :                           So testing for the disease you're suspicious for as opposed to testing indiscriminately? Ernesto:                            Yeah. Andrew :                           So Ernesto, thank you so much for taking the time our of your day to speak with us. Ernesto:                            Thank you, Andrew. Andrew :                           I'm here with David Tester, senior research technologist working with Mike Ackerman at Mayo Clinic, and he just gave a wonderful talk on whole-exome sequencing and next-generation sequencing as an unbiased look to determine underlying causes of Sudden Infant Death Syndrome, or SIDS. So David, I'm wondering if you can introduce yourself and talk a little bit about your project. Dave:                                 Sure. I'm Dave Tester and I'm at the Mayo Clinic, again with Mike Ackerman. Dr. Ackerman and I have been together for about 18 years now, with a real focus on genetics of sudden cardiac death disorders. So this latest study was looking at whole-exome sequencing in a population of SIDS cases in collaboration with Dr. Elijah Behr at St. George's University in London.                                            And really the approach, what we were aiming for is really kind of two-fold. First we were looking to determine what is the yield of ultra-rare variance within genes that have been implicated in cardiovascular disorders? These would be the cardiac channelopathies and some of the cardiomyopathies such as ACM or ARVC, for example.                                            And the second thing that we were wanting to look at was can we use this to search for sort of novel candidate genes for Sudden Infant Death Syndrome susceptibility? And so we took that aim and really the main result was to show that about 14% of our SIDS cases had what we term potentially informative variants. And those are going to be variants that were within sort of the major channelopathy genes that are implicated in Long QT syndrome or CPVT as well as loss of function variants within the 90 ICC genes that we had examined.                                            Using the ACMG guidelines for determining the pathogenicity of variants, about 4.3% of our SIDS cases hosted an ACMG guideline predicated likely pathogenic to pathogenic variant. And most of those variants represent either a frame shift or splice site error variance really in minor cardiomyopathy genes and channelopathy genes. So there's still a lot of work that needs to be done in terms of looking at specifically missense variance within channel genes and that sort of thing, and really kind of functionally characterizing those to determine whether or not they truly are pathogenic or if they should remain variants of uncertain significance. Andrew :                           And so you took a very complex disease like SIDS with probably a number of differens ideologies and found a pretty good percentage have suspicious variants, that 14% or so, and then 4% had variants that were so suspicious they would meet American College of Medical Genetics guidelines for being a possible or likely pathologic variant. Where do you think this study lies in sort of the continuum of identifying the genetic ideology of SIDS, and what do you think these findings sort of add to that overall picture? Dave:                                 Well I think these findings in general really just kind of show the complexity of SIDS. Whether or not SIDS is really truly genetic or not, or perhaps it just, if it's not monogenic, perhaps it's polygenic, and so those are some things that we should be considering and looking at. Now some of those questions might be able to be answer through our whole-exome sequencing data set that we have, and I think those are really going to be kind of the next phases.                                            We can also take and do some pathway analyses of the exome sequencing data, for example, and see our variance kind of lining up on certain pathways that may contribute to certain pathologies that could contribute to SIDS. Andrew :                           And in your study, you had a few genes where the number of variants that were found in SIDS cases were higher than in your controls. Can you speak some more about what those genes may tell you in the context of pathway analysis for SIDS? Dave:                                 Yes. So there was ... There were not genes that came out with sort of a genome-wide significance level. But there were at least 400 genes that had a p-value of 0.05 over representation in SIDS versus our ethnic match controls and 17 of those genes have a p-value of 0.005 and we're really kind of focused on some of those that have a little bit higher p-value for us to assess. A few of those genes may represent biologically plausible candidate genes for SIDS and we were kind of actually going through and considering which ones we'd like to follow up on in terms of function. Some of these genes do play a role in, say, cardiorespiratory system and function of the heart as well as in the brain. Andrew :                           So then given all these findings, and the fact that you may have some candidate genes and candidate pathways that might be interesting to look at further, what are the next steps that you think would help this project move forward, and what do you think the field of Sudden Infant Death Syndrome and Sudden Unexplained Death Syndrome needs to kind of move forward? Dave:                                 Well I think from a genetic standpoint, the study that we just complete was really on a large set of unrelated infants that had died suddenly. We did not have access to parental DNA and so moving forward in terms of the genetics, I think incorporating sort of a trio analysis I think would get at the question of sort of [inaudible 00:42:01] variance for example. The other things, in terms of genetic standpoint is perhaps looking at different genetic mechanisms. Whether these are copy number variance that may be missed by exome sequencing, perhaps some of the SIDS could be due to epigenetic abnormalities or even small chromosomal abnormalities that perhaps may not be detected on certain arrays on there being used. So I think going forward, kind of taking those approaches to look for sort of unique genetic variation. Andrew :                           Well Dave, thank you so much for taking the time to speak with me and congratulations on a great project. Dave:                                 All right, great, thank you. Jane Ferguson:  Thanks to Andrew for highlighting the interesting precision medicine research presented at HRS and thanks to you all for listening. We'll be back with more next month.

Geoffrey Abbot discusses how a potassium channel and a small molecule transporter cooperate to regulate the composition of cerebrospinal fluid and seizure susceptibility.

Ventrikuläre Tachyarrhythmien sind die Hauptursachen für den plötzlichen Herztod, der eine bedeutende Todesursache in der westlichen Welt darstellt. Dabei sind, neben strukturellen Veränderungen im Myokard wie Narben, Hypertrophie oder Ventrikeldilatation, elektrophysiologische Veränderungen der Repolarisationsphase ursächlich. Für die Repolarisation essentielle Kanäle sind die delayed rectifier Kaliumkanäle IKr und IKs; Mutationen in diesen Kanälen sind ursächlich für das angeborene Long QT-Syndrom, das mit lebensbedrohlichen Herzrhythmusstörungen assoziiert ist. Pharmakologische Wirkungen und Nebenwirkungen auf die repolarisierenden Kaliumkanäle können ebenfalls Herzrhythmusstörungen auslösen; man spricht dabei vom erworbenen oder Medikamenten-induzierten Long QT-Syndrom. Auch bei Herzinsuffizienz zum Beispiel aufgrund einer dilatativen Kardiomyopathie wird oft eine QT-Zeit Verlängerung und Rhythmusstörungen beobachtet. Dabei ist die Herunterregulation von Kaliumkanälen wie Ito ein oft beobachtetes Phänomen; in tierexperimentellen Untersuchungen wird teilweise auch eine Reduktion von IKr und IKs beschrieben. Für viele Ionenkanäle sind Unterschiede in der transmuralen Verteilung bekannt, so dass die Messung der delayed rectifier Kaliumkanäle in vorliegender Untersuchung getrennt nach subepikardialen, mittleren und subendokardialen Arealen des linksventrikulären Myokards durchgeführt wurde. Ein weiterer Aspekt der Arbeit ist der Vergleich der Repolarisation in verschiedenen Spezies, was bei der Interpretation von tierexperimentell gewonnenen Ergebnissen von großer Bedeutung ist. Dazu wurden IKr und IKs in verschiedenen Tiermodellen (Meerschweinchen, Schwein und Hund) unter Berücksichtigung der transmuralen Verteilung gemessen und mit den aus humanem Myokard gewonnenen Ergebnissen verglichen. Die porenbildenden alpha-Untereinheiten von IKr und IKs, KCNH2 und KCNQ1, wurden im heterologen Zellsystem exprimiert und deren Sensitivität auf IKr bzw. IKs spezifische Kanalblocker überprüft. Methodisch wurde für oben genannte Fragestellungen die patch clamp Technik in Ganzzellkonfiguration verwendet; zur Aufzeichnung von Aktionspotentialen und zum Nachweis von IKs in humanem Myokard wurde die perforated patch Methode verwendet, um eine Veränderung des intrazellulären Milieus mit Dialyse von Botenstoffen zu vermeiden. Auf molekularbiologischer Ebene wurde die mRNA-Menge der IKr und IKs alpha-Untereinheiten KCNH2 und KCNQ1, sowie deren (potentielle) beta-Untereinheiten KCNE1 und KCNE2 mit Hilfe der quantitativen real-time PCR bestimmt. Dabei konnten folgende Ergebnisse erzielt werden: IKr ließ sich im Menschen in allen Zellen in relevanter Größe nachweisen; der Strom ließ sich sowohl durch den spezifischen IKr-Blocker Dofetilide, aber auch durch Pharmaka aus nicht-kardiologischen Anwendungsgebieten wie das Neuroleptikum Haloperidol inhibieren. Dabei wies der Kanal eine Abhängigkeit von der extrazellulären Kaliumkonzentration auf, die sich umgekehrt zum elektrochemischen Gradienten verhielt: höhere extrazelluläre Kaliumkonzentrationen bewirkten eine Steigerung von IKr. IKs (definiert als HMR 1556 sensitiver Strom) ließ sich in humanem Myokard nur unter speziell optimierten Bedingungen (perforated patch Technik, adrenerge Stimulation mit Isoproterenol) nachweisen. Er hatte dann eine sehr kleine Stromdichte, die eine weitere elektrophysiologische und pharmakologische Charakterisierung nicht erlaubte. In Meerschwein, Schwein und Hund war IKr und IKs nachweisbar; dabei hatte das Meerschweinchen die höchsten Stromdichten von delayed rectifier Kaliumkanälen, das Schwein kleinere, aber robuste IKr und IKs-Ströme. Beim Hund fanden sich deutlich geringere Stromdichten für IKr und IKs; IKs war nicht in allen Zellen nachweisbar. IKr wies in allen Spezies epikardial eine kleinere Stromdichte auf als in mittleren und endokardialen Arealen. Dieser transmurale Gradient mit geringerer Stromdichte in epikardialen Arealen war nur in nicht-insuffizienten humanen Herzen nachweisbar; bei Herzinsuffizienz kam es zur Angleichung der Stromdichten in allen drei untersuchten Schichten. KCNH2 und KCNQ1 generierten im heterologen Zellsystem IKr bzw. IKs ähnliche Ströme, die jeweils typische Sensitivität für IKr bzw. IKs Blocker aufwiesen. Für KCNH2 und KCNQ1 mRNA waren keine transmuralen Gradienten und keine Regulation bei Herzinsuffizienz nachweisbar; KCNE1 und KCNE2 zeigten bei Herzinsuffizienz höhere Expressionslevel. Somit ließ sich das Vorhandensein und die Bedeutung von IKr und IKs in humanem Myokard belegen, wobei IKs nur in sehr geringer – in Ruhe gerade noch nachweisbarer – Stromdichte vorkommt. Dennoch lässt sich seine Bedeutung am Vorhandensein von Mutationen in KCNQ1, die lebensbedrohliche Rhythmusstörungen verursachen können, ablesen. Auch für KCNH2, das für die alpha-Untereinheit von IKr kodiert, sowie für die (potentiellen) beta-Untereinheiten KCNE1 und KCNE2 sind Mutationen beschrieben, die ursächlich für das angeborene Long QT-Syndrom sind. Damit scheinen IKr und IKs für die Repolarisation des humanen Aktionspotentials essentiell zu sein, wobei IKr aufgrund der relativ großen Stromdichte die wesentliche Rolle bei der Repolarisation des Aktionspotenials in humanem Myokard zukommt. IKs hat große Bedeutung als „Repolarisationsreserve“ zur Stabilisierung der Repolarisation unter Bedingungen erhöhter Katecholaminspiegel, bei tachykarden Herzfrequenzen und bei verzögerter Repolarisation wie durch Hypokaliämie, IKr-Blocker oder IKr-Mutationen und Polymorphismen. Mutationen in Proteinuntereinheiten von IKs können zur Störung dieser Repolarisationsreserve führen und somit Rhythmusstörungen auslösen, die charakteristischerweise in Situationen erhöhter sympathischer Aktivierung auftreten. Die Ausstattung der unterschiedlichen Spezies mit repolarisierenden Kaliumströmen wies erhebliche Unterscheide auf, was bei der Interpretation tierexperimentell gewonnener Daten zu berücksichtigen ist. Insbesondere korreliert eine Abnahme der Ruheherzfrequenz der Spezies mit einer deutlichen Reduktion der repolarisierenden Ströme entsprechend dem Konzept der speziesabhängigen Variabilität der repolarisierenden bei Konstanz der depolarisierenden Ströme (INa und ICa). Transmurale Unterschiede in der Expression von Ionenkanälen scheinen notwendig für den Ablauf der Erregungsbildung und Erregungsrückbildung zu sein. Die epikardial geringeren Stromdichten für IKr waren in allen untersuchten Spezies nachweisbar. Die Beobachtung einer geringeren Stromdichte der repolarisierenden Kaliumströme epikardial bedeutet, dass andere Ionenkanäle als IKr und IKs für die dort kürzere Aktionspotentialdauer verantwortlich sein müsssen. Eine Reduktion der Stromdichte bei Herzinsuffizienz, wie sie beispielsweise für Ito beschrieben ist, konnte für IKr nicht nachgewiesen werden. Jedoch fand sich eine Nivellierung des physiologischerweise Vorhandenen transmuralen Gradienten, was grundsätzlich zu einer Störung des physiologischen Erregungsablaufes mit Begünstigung von Rhythmusstörungen in insuffizienten Herzen beitragen könnte. Aus dem dualen Repolarisationsmechanismus im menschlichen Ventikelmyokard werden klinische Konstellationen mit Rhythmusstörungen verständlich, insbesondere in Hinblick auf die Variabilität der Empfindlichkeit gegenüber Medikamenten mit blockierender Wirkung auf IKr. Dabei stellt IKs in unterschiedlichem Maße eine Kompensation im Sinne einer Repolarisationsreserve bereit.