Genetic variation in SCN10A influences cardiac conduction

Characterization of novel arrhythmogenic patterns arising secondary to heterogeneous expression and activation of Nav1.8

Background

Previous studies suggested that SCN10A/Nav1.8 may influence cardiac electrophysiology and the susceptibility to cardiac arrhythmias. Notably, the expression of SCN10A is not uniform, showing variable expression in each cardiac chamber. The present study aims to explore the functional significance of Nav1.8 expression among different cell types present in the ventricular myocardium.

Methods

The effect of the specific Nav1.8 blocker, A-803467, on action potential was recorded from epicardial, mid-myocardial (M cells) and Purkinje tissue slices isolated from the canine left ventricle using standard microelectrode techniques and on late sodium current from Purkinje cells using patch-clamp techniques.

Results

A-803467 treatment did not significantly affect maximum diastolic potential, action potential amplitude or maximum rate of rise of the action potential upstroke in epicardial cells, M cells or Purkinje fibers. Action potential duration (APD) was also unaffected by A-803467 in epicardial cells. However, administration of 1,000 nmol/L A-803467 reduced APD30, APD50, and APD90 during relatively slow pacing rates of 0.2 and 0.5 Hz in M cells. In Purkinje fibers, A-803467 (100 and 1,000 nmol/L) substantially abbreviated APD50 and APD90 at slow pacing rates (0.2 and 0.5 Hz). Moreover, 100 nmol/L A-803467 significantly inhibited the development of early afterdepolarizations induced by 10 nmol/L ATX-II (7/8 vs. 2/8, p < 0.05) as well as the amplitude of late sodium current at 0.2 Hz in Purkinje cells.

Conclusions

The functional significance of Nav1.8 varies among different types of ventricular and conduction system cardiomyocytes. The reduction in INa,L and APD, as well as suppression of early afterdepolarizations by Nav1.8 block in Purkinje fibers suggests Nav1.8 as a potential therapeutic target for bradycardia-dependent arrhythmias.

Genetic insights into cardiac conduction disorders from genome-wide association studies

BACKGROUND

Substantial data support a heritable basis for cardiac conduction disorders (CCDs), but the genetic determinants and molecular mechanisms of these arrhythmias are poorly understood, therefore, we sought to identify genetic loci associated with CCDs.

METHODS

We performed meta-analyses of genome-wide association studies to identify genetic loci for atrioventricular block (AVB), left bundle branch block (LBBB), and right bundle branch block (RBBB) from public data from the UK Biobank and FinnGen consortium. We assessed evidence supporting the potential causal effects of candidate genes by analyzing relations between associated variants and cardiac gene expression, performing transcriptome-wide analyses, and ECG-wide phenome-wide associations for each indexed SNP.

RESULTS

Analysis comprised over 700,000 individuals for each trait. We identified 10, 4 and 0 significant loci for AVB (PLEKHA3, TTN, FNDC3B, SENP2, SCN10A, RRH, PPARGC1A, PKD2L2, NKX2-5 and TBX20), LBBB (PPARGC1A, HAND1, TBX5, and ADAMTS5) and RBBB, respectively. Transcriptome-wide association analysis supported an association between reduced predicted cardiac expression of SCN10A and AVB. Phenome-wide associations identified traits with both cardiovascular and non- cardiovascular traits with indexed SNPs.

CONCLUSIONS

Our analysis highlight gene regions associated with channel function, cardiac development, sarcomere function and energy modulation as important potential effectors of CCDs susceptibility.

SCN10A gene polymorphism is associated with pain sensitivity and postoperative analgesic effects in patients undergoing gynecological laparoscopy

BACKGROUND

Postoperative pain intensity is influenced by various factors, including genetic variations. The SCN10A gene encodes the Nav1.8 sodium channel protein, which is crucial for pain signal transmission in peripheral sensory neurons.

OBJECTIVES

This study aims to investigate the relationship between genetic mutations in the SCN10A gene (rs6795970) and postoperative analgesic effects following gynecological laparoscopic surgery.

METHODS

Two hundred female patients undergoing gynecological laparoscopic surgery under general anesthesia were included. pain sensitivity was evaluated using the catastrophizing scale and pain sensitivity questionnaire (PSQ). Patients received patient-controlled intravenous analgesia with sufentanil and dexmedetomidine for 48 h post-surgery. Postoperative pain indicators, such as visual analog scale (VAS) scores, Ramsay scores, and side effects were recorded. SCN10A rs6795970 mutations were identified using MassARRAY SNP typing technology, and patients were categoried into homozygous mutant (AA), wild type (GG), and heterozygous mutation (GA) groups for analysis.

RESULTS

Patients in the AA group had higher scores on the pain Catastrophizing Scale, PSQ-total, PSQ-minor, and PSQ-moderate compared to GA and GG groups (P < 0.05). VAS scores at 4, 6, and 12 h post-operation were higher in the AA group than the GG group (P < 0.05). Ramsay scores were lower in AA patients at 2 and 4 h post-operation compared to GA and GG groups (P < 0.05). The AA group exhibited more self-control analgesic pump compressions within the first 24 h post-surgery, quicker depletion of analgesics in the pump, and lower patient satisfaction with pain relief compared to GA and GG groups (P < 0.05).

CONCLUSIONS

Female patients with homozygous SCN10A mutations may experience higher preoperative pain scores and increased sensitivity to postoperative pain following gynecological laparoscopic surgery with intravenous patient-controlled analgesia.

TRIAL REGISTRATION

www.chictr.org.cn , registration number: ChiCTR2200062425.

Impact of SCN10A Polymorphism on Abdominal Pain Perception and Visceral Hypoalgesia in Crohn's Disease and Ulcerative Colitis

INTRODUCTION

Hypoalgesic inflammatory bowel disease (IBD) may provide critical insights into human abdominal pain. This condition was previously associated with homozygosity for a polymorphism (rs6795970, A1073V; 1073 val/val ) related to Na v 1.8, a voltage-gated sodium channel preferentially expressed on nociceptors. It was unclear whether this relationship existed for both Crohn's disease (CD) and ulcerative colitis (UC). This study evaluated a larger, carefully phenotyped IBD cohort to investigate this question.

METHODS

Allelic and genotypic frequencies of rs6795970 were compared among study cohorts characterized by concomitant assessment of intestinal inflammatory status and abdominal pain experience. Visceral sensory perception was performed in healthy individuals using rectal balloon distension.

RESULTS

We analyzed 416 patients with IBD (261CD:155UC) and 142 healthy controls. In the IBD cohort, 84 individuals (43CD:41UC) were determined to have hypoalgesic disease. The allelic frequency of rs6795970 was significantly higher in patients with hypoalgesic IBD when compared with other patients with IBD and healthy controls. Patients with hypoalgesic IBD were also more likely to be homozygous for this polymorphism when compared with other patients with IBD and healthy controls. Hypoalgesic CD (30% vs 12%, P = 0.004) and hypoalgesic UC (32% vs 15%, P = 0.036) were each significantly more likely to be associated with homozygosity for the rs6795970 polymorphism. In a cohort of healthy individuals (n = 50), rs6795970 homozygotes (n = 11) also demonstrated reduced abdominal discomfort to rectal balloon distension.

DISCUSSION

These findings indicate that Na v 1.8 plays a key role in human visceral pain perception, and could serve as a novel diagnostic target in the management of hypoalgesic CD and UC, and potential therapeutic target for conditions associated with chronic abdominal pain.

Blocking NaV1.8 regulates atrial fibrillation inducibility and cardiac conduction after myocardial infarction

BACKGROUND

The role of NaV1.8 impacts in atrial fibrillation susceptibility after myocardial infarction remains only partially understood. We studied the effect of blocking NaV1.8 in the cardiac ganglionated plexi (GP) on the atrial fibrillation inducibility and cardiac conduction in the myocardial infarction model.

METHODS

Eighteen male beagles were randomly enrolled. Left anterior descending coronary artery was ligated to created myocardial infarction model. Four weeks after surgery, NaV1.8 blocker A-803,467 (n = 9) or DMSO (n = 9, control) was injected into the four cardiac major GPs. Sinus rate, ventricular rate during atrial fibrillation, PR interval, atrial effective refractory period, atrial fibrillation duration and the cumulative window of atrial vulnerability were measured before and 60 min after A-803,467 injection.

RESULTS

Administration of A-803,467 significantly increased sinus rate, shortened PR interval and increased ventricular rate during atrial fibrillation compared to control. A-803,467 also significantly shortened atrial effective refractory period, prolonged atrial fibrillation duration and increased the cumulative window of atrial vulnerability. A-803,467 suppressed the slowing of heart rate response to high-frequency electrical stimulation of the anterior right GP, which was used as the surrogate marker for GP function. Double staining of ChAT and NaV1.8 demonstrated colocalization of ChAT and NaV1.8 in canine GPs.

CONCLUSIONS

Blocking NaV1.8 in the cardiac GP may modulate atrial fibrillation inducibility and cardiac conduction after myocardial infarction, and the underlying mechanism may be associated with the regulation of the neural activity of the cardiac GP.

Advancing drug development for atrial fibrillation by prioritising findings from human genetic association studies

BACKGROUND

Drug development for atrial fibrillation (AF) has failed to yield new approved compounds. We sought to identify and prioritise potential druggable targets with support from human genetics, by integrating the available evidence with bioinformatics sources relevant for AF drug development.

METHODS

Genetic hits for AF and related traits were identified through structured search of MEDLINE. Genes derived from each paper were cross-referenced with the OpenTargets platform for drug interactions. Confirmation/validation was demonstrated through structured searches and review of evidence on MEDLINE and ClinialTrials.gov for each drug and its association with AF.

FINDINGS

613 unique drugs were identified, with 21 already included in AF Guidelines. Cardiovascular drugs from classes not currently used for AF (e.g. ranolazine and carperitide) and anti-inflammatory drugs (e.g. dexamethasone and mehylprednisolone) had evidence of potential benefit. Further targets were considered druggable but remain open for drug development.

INTERPRETATION

Our systematic approach, combining evidence from different bioinformatics platforms, identified drug repurposing opportunities and druggable targets for AF.

FUNDING

KK is supported by Barts Charity grant G-002089 and is mentored on the AFGen 2023-24 Fellowship funded by the AFGen NIH/NHLBI grant R01HL092577. RP is supported by the UCL BHF Research Accelerator AA/18/6/34223 and NIHR grant NIHR129463. AFS is supported by the BHF grants PG/18/5033837, PG/22/10989 and UCL BHF Accelerator AA/18/6/34223 as well as the UK Research and Innovation (UKRI) under the UK government's Horizon Europe funding guarantee EP/Z000211/1 and by the UKRI-NIHR grant MR/V033867/1 for the Multimorbidity Mechanism and Therapeutics Research Collaboration. AF is supported by UCL BHF Accelerator AA/18/6/34223. CF is supported by UCL BHF Accelerator AA/18/6/34223.

Sodium channels Nav1.7, Nav1.8 and pain; two distinct mechanisms for Nav1.7 null analgesia

Genetic deletion and pharmacological inhibition are distinct approaches to unravelling pain mechanisms, identifying targets and developing new analgesics. Both approaches have been applied to the voltage-gated sodium channels Nav1.7 and Nav1.8. Genetic deletion of Nav1.8 in mice leads to a loss of pain and antagonists are effective analgesics. The situation with Nav1.7 is more complex. Complete embryonic loss of Nav1.7 in humans or in mouse sensory neurons leads to anosmia as well as profound analgesia as a result of diminished neurotransmitter release. This is mediated by enhanced endogenous opioid signaling in humans and mice. In contrast, anosmia is opioid-independent. Sensory neuron excitability and autonomic function appear to be normal. Adult deletion of Nav1.7 in sensory neurons also leads to analgesia, but through diminished sensory and autonomic neuron excitability. There is no opioid component of analgesia or anosmia as shown by a lack of effect of naloxone. Pharmacological inhibition of Nav1.7 in mice and humans leads both to analgesia and dramatic side-effects on the autonomic nervous system with no therapeutic window. These data demonstrate that specific Nav1.7 channel blockers will fail as analgesic drugs. The viability of embryonic null mutants suggests that there are compensatory changes to replace the lost Nav1.7 channel. Here we show that sensory neuron sodium channels Nav1.1, Nav1.2 and β4 subunits detected by Mass Spectrometry are upregulated in Nav1.7 embryonic null neurons and, together with other proteome changes, potentially compensate for the loss of Nav1.7. Interestingly, many of the upregulated proteins are known to interact with Nav1.7.

Genomic analysis of severe COVID-19 considering or not asthma comorbidity: GWAS insights from the BQC19 cohort

BACKGROUND

The severity of COVID-19 is influenced by various factors including the presence of respiratory diseases. Studies have indicated a potential relationship between asthma and COVID-19 severity.

OBJECTIVE

This study aimed to conduct a genome-wide association study (GWAS) to identify genetic and clinical variants associated with the severity of COVID-19, both among patients with and without asthma.

METHODS

We analyzed data from 2131 samples sourced from the Biobanque québécoise de la COVID-19 (BQC19), with 1499 samples from patients who tested positive for COVID-19. Among these, 1110 exhibited mild-to-moderate symptoms, 389 had severe symptoms, and 58 had asthma. We conducted a comparative analysis of clinical data from individuals in these three groups and GWAS using a logistic regression model. Phenotypic data analysis resulted in the refined covariates integrated into logistic models for genetic studies.

RESULTS

Considering a significance threshold of 1 × 10-6, seven genetic variants were associated with severe COVID-19. These variants were located proximal to five genes: sodium voltage-gated channel alpha subunit 1 (SCN10A), desmoplakin (DSP), RP1 axonemal microtubule associated (RP1), IGF like family member 1 (IGFL1), and docking protein 5 (DOK5). The GWAS comparing individuals with severe COVID-19 with asthma to those without asthma revealed four genetic variants in transmembrane protein with EGF like and two follistatin like domains 2 (TMEFF2) and huntingtin interacting protein-1 (HIP1) genes.

CONCLUSION

This study provides significant insights into the genetic profiles of patients with severe forms of the disease, whether accompanied by asthma or not. These findings enhance our comprehension of the genetic factors that affect COVID-19 severity.

KEY MESSAGES

Seven genetic variants were associated with the severe form of COVID-19; Four genetic variants were associated with the severe form of COVID-19 in individuals with comorbid asthma; These findings help define the genetic component of the severe form of COVID-19 in relation to asthma as a comorbidity.

Translational bioinformatics approach to combat cardiovascular disease and cancers

Bioinformatics is an interconnected subject of science dealing with diverse fields including biology, chemistry, physics, statistics, mathematics, and computer science as the key fields to answer complicated physiological problems. Key intention of bioinformatics is to store, analyze, organize, and retrieve essential information about genome, proteome, transcriptome, metabolome, as well as organisms to investigate the biological system along with its dynamics, if any. The outcome of bioinformatics depends on the type, quantity, and quality of the raw data provided and the algorithm employed to analyze the same. Despite several approved medicines available, cardiovascular disorders (CVDs) and cancers comprises of the two leading causes of human deaths. Understanding the unknown facts of both these non-communicable disorders is inevitable to discover new pathways, find new drug targets, and eventually newer drugs to combat them successfully. Since, all these goals involve complex investigation and handling of various types of macro- and small- molecules of the human body, bioinformatics plays a key role in such processes. Results from such investigation has direct human application and thus we call this filed as translational bioinformatics. Current book chapter thus deals with diverse scope and applications of this translational bioinformatics to find cure, diagnosis, and understanding the mechanisms of CVDs and cancers. Developing complex yet small or long algorithms to address such problems is very common in translational bioinformatics. Structure-based drug discovery or AI-guided invention of novel antibodies that too with super-high accuracy, speed, and involvement of considerably low amount of investment are some of the astonishing features of the translational bioinformatics and its applications in the fields of CVDs and cancers.

Nanoparticle Polymers Influence on Cardiac Health: Good or Bad for Cardiac Physiology?

Cardiovascular diseases (CVD) are one of the leading causes of death and morbidity worldwide. Lifestyle modifications, medications, and addressing epidemiological factors have long been at the forefront of targeting therapeutics for CVD. Treatments can be further complicated given the intersection of gender, age, unique comorbidities, and healthcare access, among many other factors. Therefore, expanding treatment and diagnostic modalities for CVD is absolutely necessary. Nanoparticles and nanomaterials are increasingly being used as therapeutic and diagnostic modalities in various disciplines of biomedicine. Nanoparticles have multiple ways of interacting with the cardiovascular system. Some of them alter cardiac physiology by impacting ion channels, whereas others influence ions directly or indirectly, improving cellular death via decreasing oxidative stress.  While embedding nanoparticles into therapeutics can help enhance healthy cardiovascular function in other scenarios, they can also impair physiology by increasing reactive oxidative species and leading to cardiotoxicity. This review explores different types of nanoparticles, their effects, and the applicable dosages to create a better foundation for understanding the current research findings.

Role of Genetic Variation in Transcriptional Regulatory Elements in Heart Rhythm

Genetic predisposition to cardiac arrhythmias has been a field of intense investigation. Research initially focused on rare hereditary arrhythmias, but over the last two decades, the role of genetic variation (single nucleotide polymorphisms) in heart rate, rhythm, and arrhythmias has been taken into consideration as well. In particular, genome-wide association studies have identified hundreds of genomic loci associated with quantitative electrocardiographic traits, atrial fibrillation, and less common arrhythmias such as Brugada syndrome. A significant number of associated variants have been found to systematically localize in non-coding regulatory elements that control the tissue-specific and temporal transcription of genes encoding transcription factors, ion channels, and other proteins. However, the identification of causal variants and the mechanism underlying their impact on phenotype has proven difficult due to the complex tissue-specific, time-resolved, condition-dependent, and combinatorial function of regulatory elements, as well as their modest conservation across different model species. In this review, we discuss research efforts aimed at identifying and characterizing-trait-associated variant regulatory elements and the molecular mechanisms underlying their impact on heart rate or rhythm.

Whole genome sequence analysis of apparent treatment resistant hypertension status in participants from the Trans-Omics for Precision Medicine program

Introduction: Apparent treatment-resistant hypertension (aTRH) is characterized by the use of four or more antihypertensive (AHT) classes to achieve blood pressure (BP) control. In the current study, we conducted single-variant and gene-based analyses of aTRH among individuals from 12 Trans-Omics for Precision Medicine cohorts with whole-genome sequencing data. Methods: Cases were defined as individuals treated for hypertension (HTN) taking three different AHT classes, with average systolic BP ≥ 140 or diastolic BP ≥ 90 mmHg, or four or more medications regardless of BP (n = 1,705). A normotensive control group was defined as individuals with BP < 140/90 mmHg (n = 22,079), not on AHT medication. A second control group comprised individuals who were treatment responsive on one AHT medication with BP < 140/ 90 mmHg (n = 5,424). Logistic regression with kinship adjustment using the Scalable and Accurate Implementation of Generalized mixed models (SAIGE) was performed, adjusting for age, sex, and genetic ancestry. We assessed variants using SKAT-O in rare-variant analyses. Single-variant and gene-based tests were conducted in a pooled multi-ethnicity stratum, as well as self-reported ethnic/racial strata (European and African American). Results: One variant in the known HTN locus, KCNK3, was a top finding in the multi-ethnic analysis (p = 8.23E-07) for the normotensive control group [rs12476527, odds ratio (95% confidence interval) = 0.80 (0.74-0.88)]. This variant was replicated in the Vanderbilt University Medical Center's DNA repository data. Aggregate gene-based signals included the genes AGTPBP, MYL4, PDCD4, BBS9, ERG, and IER3. Discussion: Additional work validating these loci in larger, more diverse populations, is warranted to determine whether these regions influence the pathobiology of aTRH.

Noncoding RNAs and Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes in Cardiac Arrhythmic Brugada Syndrome

Hundreds of thousands of people die each year as a result of sudden cardiac death, and many are due to heart rhythm disorders. One of the major causes of these arrhythmic events is Brugada syndrome, a cardiac channelopathy that results in abnormal cardiac conduction, severe life-threatening arrhythmias, and, on many occasions, death. This disorder has been associated with mutations and dysfunction of about two dozen genes; however, the majority of the patients do not have a definite cause for the diagnosis of Brugada Syndrome. The protein-coding genes represent only a very small fraction of the mammalian genome, and the majority of the noncoding regions of the genome are actively transcribed. Studies have shown that most of the loci associated with electrophysiological traits are located in noncoding regulatory regions and are expected to affect gene expression dosage and cardiac ion channel function. Noncoding RNAs serve an expanding number of regulatory and other functional roles within the cells, including but not limited to transcriptional, post-transcriptional, and epigenetic regulation. The major noncoding RNAs found in Brugada Syndrome include microRNAs; however, others such as long noncoding RNAs are also identified. They contribute to pathogenesis by interacting with ion channels and/or are detectable as clinical biomarkers. Stem cells have received significant attention in the recent past, and can be differentiated into many different cell types including those in the heart. In addition to contractile and relaxational properties, BrS-relevant electrophysiological phenotypes are also demonstrated in cardiomyocytes differentiated from stem cells induced from adult human cells. In this review, we discuss the current understanding of noncoding regions of the genome and their RNA biology in Brugada Syndrome. We also delve into the role of stem cells, especially human induced pluripotent stem cell-derived cardiac differentiated cells, in the investigation of Brugada syndrome in preclinical and clinical studies.

Particulate matter induces arrhythmia-like cardiotoxicity in zebrafish embryos by altering the expression levels of cardiac development- and ion channel-related genes

Air pollution is a risk factor that increases cardiovascular morbidity and mortality. In this study, we investigated the cardiotoxicity of particulate matter (PM) exposure using a zebrafish embryo model. We found that PM exposure induced cardiotoxicity, such as arrhythmia, during cardiac development. PM exposure caused cardiotoxicity by altering the expression levels of cardiac development (T-box transcription factor 20, natriuretic peptide A, and GATA-binding protein 4)- and ion-channel (scn5lab, kcnq1, kcnh2a/b, and kcnh6a/b)-related genes. In conclusion, this study showed that PM induces the aberrant expression of cardiac development- and ion channel-related genes, leading to arrhythmia-like cardiotoxicity in zebrafish embryos. Our study provides a foundation for further research on the molecular and genetic mechanisms of cardiotoxicity induced by PM exposure.

Ventricular arrhythmias and cardiac arrest in atrial fibrillation patients with pacemakers and implantable cardioverter-defibrillators

BACKGROUND

Atrial fibrillation (AF) has been linked to ventricular arrhythmias (VAs) and sudden death, but few studies have specifically explored this association.

OBJECTIVE

We investigated whether AF is associated with an increased risk of ventricular tachycardia (VT), ventricular fibrillation (VF) and cardiac arrests (CA) in patients with cardiac implantable electronic devices (CIEDs).

METHODS

All patients with pacemakers and implantable cardioverter-defibrillators (ICDs) hospitalised between 2010 and 2020 were identified from the French National database. Patients with a prior history of VT/VF/CA were excluded.

RESULTS

701,195 patients were identified initially. After excluding 55,688 patients, 581,781 (90.1%) and 63,726 (9.9%) remained in the pacemaker and ICD groups respectively. 248,046 (42.6%) pacemaker patients had AF and 333,735 (57.4%) had no AF, whereas in the ICD group 20,965 (32.9%) had AF and 42,761 (67.1%) had no AF. The incidence of VT/VF/CA was higher in AF patients compared to non-AF patients both in pacemaker (1.47%/year vs. 0.94%/year) and ICD (5.30%/year vs. 4.21%/year) groups. After multivariable analysis, AF was independently associated with an increased risk of VT/VF/CA in pacemaker (HR 1.236 [95% CI 1.198-1.276]) and ICD (HR 1.167 [95% CI 1.111-1.226]) patients. This risk was still significant in the 1:1 propensity score-matched analysis of the pacemaker (n = 200,977 per subgroup) and ICD cohorts (n = 18,349 per subgroup), HR 1.230 [95% CI 1.187-1.274] and HR 1.134 [95% CI 1.071-1.200] respectively and in the competing risk analysis (pacemaker: HR 1.195 (95% CI 1.154-1.238], ICD: HR 1.094 [95% CI 1.034-1.157]).

CONCLUSION

CIED patients with AF have a higher risk of VT/VF/CA compared to CIED patients without AF.

Molecular and Functional Relevance of NaV1.8-Induced Atrial Arrhythmogenic Triggers in a Human SCN10A Knock-Out Stem Cell Model

In heart failure and atrial fibrillation, a persistent Na⁺ current (I_NaL) exerts detrimental effects on cellular electrophysiology and can induce arrhythmias. We have recently shown that Na_V1.8 contributes to arrhythmogenesis by inducing a I_NaL. Genome-wide association studies indicate that mutations in the SCN10A gene (Na_V1.8) are associated with increased risk for arrhythmias, Brugada syndrome, and sudden cardiac death. However, the mediation of these Na_V1.8-related effects, whether through cardiac ganglia or cardiomyocytes, is still a subject of controversial discussion. We used CRISPR/Cas9 technology to generate homozygous atrial SCN10A-KO-iPSC-CMs. Ruptured-patch whole-cell patch-clamp was used to measure the I_NaL and action potential duration. Ca²⁺ measurements (Fluo 4-AM) were performed to analyze proarrhythmogenic diastolic SR Ca²⁺ leak. The I_NaL was significantly reduced in atrial SCN10A KO CMs as well as after specific pharmacological inhibition of Na_V1.8. No effects on atrial APD₉₀ were detected in any groups. Both SCN10A KO and specific blockers of Na_V1.8 led to decreased Ca²⁺ spark frequency and a significant reduction of arrhythmogenic Ca²⁺ waves. Our experiments demonstrate that Na_V1.8 contributes to I_NaL formation in human atrial CMs and that Na_V1.8 inhibition modulates proarrhythmogenic triggers in human atrial CMs and therefore Na_V1.8 could be a new target for antiarrhythmic strategies.

Atrioventricular node dysfunction in pressure overload-induced heart failure—Involvement of the immune system and transcriptomic remodelling

Heart failure is associated with atrioventricular (AV) node dysfunction, and AV node dysfunction in the setting of heart failure is associated with an increased risk of mortality and heart failure hospitalisation. This study aims to understand the causes of AV node dysfunction in heart failure by studying changes in the whole nodal transcriptome. The mouse transverse aortic constriction model of pressure overload-induced heart failure was studied; functional changes were assessed using electrocardiography and echocardiography and the transcriptome of the AV node was quantified using RNAseq. Heart failure was associated with a significant increase in the PR interval, indicating a slowing of AV node conduction and AV node dysfunction, and significant changes in 3,077 transcripts (5.6% of the transcriptome). Many systems were affected: transcripts supporting AV node conduction were downregulated and there were changes in transcripts identified by GWAS as determinants of the PR interval. In addition, there was evidence of remodelling of the sarcomere, a shift from fatty acid to glucose metabolism, remodelling of the extracellular matrix, and remodelling of the transcription and translation machinery. There was evidence of the causes of this widespread remodelling of the AV node: evidence of dysregulation of multiple intracellular signalling pathways, dysregulation of 109 protein kinases and 148 transcription factors, and an immune response with a proliferation of neutrophils, monocytes, macrophages and B lymphocytes and a dysregulation of 40 cytokines. In conclusion, inflammation and a widespread transcriptional remodelling of the AV node underlies AV node dysfunction in heart failure.

Cardiac sodium channel complexes and arrhythmia: structural and functional roles of the β1 and β3 subunits

In cardiac myocytes, the voltage-gated sodium channel NaV 1.5 opens in response to membrane depolarisation and initiates the action potential. The NaV 1.5 channel is typically associated with regulatory β-subunits that modify gating and trafficking behaviour. These β-subunits contain a single extracellular immunoglobulin (Ig) domain, a single transmembrane α-helix and an intracellular region. Here we focus on the role of the β1 and β3 subunits in regulating NaV 1.5. We catalogue β1 and β3 domain specific mutations that have been associated with inherited cardiac arrhythmia, including Brugada syndrome, long QT syndrome, atrial fibrillation and sudden death. We discuss how new structural insights into these proteins raises new questions about physiological function.

Brugada Syndrome: From Molecular Mechanisms and Genetics to Risk Stratification

Brugada syndrome (BrS) is a rare hereditary arrhythmia disorder, with a distinctive ECG pattern, correlated with an increased risk of ventricular arrhythmias and sudden cardiac death (SCD) in young adults. BrS is a complex entity in terms of mechanisms, genetics, diagnosis, arrhythmia risk stratification, and management. The main electrophysiological mechanism of BrS requires further research, with prevailing theories centered on aberrant repolarization, depolarization, and current-load match. Computational modelling, pre-clinical, and clinical research show that BrS molecular anomalies result in excitation wavelength (k) modifications, which eventually increase the risk of arrhythmia. Although a mutation in the SCN5A (Sodium Voltage-Gated Channel Alpha Subunit 5) gene was first reported almost two decades ago, BrS is still currently regarded as a Mendelian condition inherited in an autosomal dominant manner with incomplete penetrance, despite the recent developments in the field of genetics and the latest hypothesis of additional inheritance pathways proposing a more complex mode of inheritance. In spite of the extensive use of the next-generation sequencing (NGS) technique with high coverage, genetics remains unexplained in a number of clinically confirmed cases. Except for the SCN5A which encodes the cardiac sodium channel NaV1.5, susceptibility genes remain mostly unidentified. The predominance of cardiac transcription factor loci suggests that transcriptional regulation is essential to the Brugada syndrome's pathogenesis. It appears that BrS is a multifactorial disease, which is influenced by several loci, each of which is affected by the environment. The primary challenge in individuals with a BrS type 1 ECG is to identify those who are at risk for sudden death, researchers propose the use of a multiparametric clinical and instrumental strategy for risk stratification. The aim of this review is to summarize the latest findings addressing the genetic architecture of BrS and to provide novel perspectives into its molecular underpinnings and novel models of risk stratification.

Atrial Fibrillation and the Risk of Ventricular Arrhythmias and Cardiac Arrest: A Nationwide Population-Based Study

BACKGROUND

Atrial fibrillation (AF) has been linked to an increased risk of ventricular arrhythmias (VAs) and sudden death. We investigated this association in hospitalised patients in France.

METHODS

All hospitalised patients from 2013 were identified from the French National database and included if they had at least 5 years of follow-up data.

RESULTS

Overall, 3,381,472 patients were identified. After excluding 35,834 with a history of VAs and cardiac arrest, 3,345,638 patients were categorised into two groups: no AF (n = 3,033,412; mean age 57.2 ± 21.4; 54.3% female) and AF (n = 312,226; 78.1 ± 10.6; 44.0% female). Over a median follow-up period of 5.4 years (interquartile range (IQR) 5.0-5.8 years), the incidence (2.23%/year vs. 0.56%/year) and risk (hazard ratio (HR) 3.657 (95% confidence interval (CI) 3.604-3.711)) of VAs and cardiac arrest were significantly higher in AF patients compared to non-AF patients. This was still significant after adjusting for confounders, with a HR of 1.167 (95% CI 1.111-1.226) and in the 1:1 propensity score-matched analysis (n = 289,332 per group), with a HR of 1.339 (95% CI 1.313-1.366). In the mediation analysis, the odds of cardiac arrest were significantly mediated by AF-associated VAs, with an OR of 1.041 (95% CI 1.040-1.042).

CONCLUSION

In hospitalised French patients, AF was associated with an increased risk of VAs and sudden death.

Whole-Genome Sequencing of 100 Genomes Identifies a Distinctive Genetic Susceptibility Profile of Qatari Patients with Hypertension

Essential hypertension (EH) is a leading risk condition for cardiovascular and renal complications. While multiple genes are associated with EH, little is known about its genetic etiology. Therefore, this study aimed to screen for variants that are associated with EH in 100 hypertensive/100 control patients comprising Qatari individuals using GWASs of whole-genome sequencing and compare these findings with genetic data obtained from more than 10,000 published peer-reviewed studies on EH. The GWAS analysis performed with 21,096 SNPs revealed 38 SNPs with a significant ≥4 log-p value association with EH. The two highest EH-associated SNPs (rs921932379 and rs113688672) revealed a significance score of ≥5 log-p value. These SNPs are located within the inter-genic region of GMPS-SETP14 and ISCA1P6-AC012451.1, respectively. Text mining yielded 3748 genes and 3078 SNPs, where 51 genes and 24 SNPs were mentioned in more than 30 and 10 different articles, respectively. Comparing our GWAS results to previously published articles revealed 194 that are unique to our patient cohort; of these, 13 genes that have 26 SNPs are the most significant with ≥4 log-p value. Of these genes, C2orf47-SPATS2L contains nine EH-associated SNPs. Most of EH-associated genes are related to ion gate channel activity and cardiac conduction. The disease–gene analysis revealed that a large number of EH-associated genes are associated with a variety of cardiovascular disorders. The clustering analysis using EH-associated SNPs across different ethnic groups showed high frequency for the minor allele in different ethnic groups, including Africans, East Asians, and South Asians. The combination of GWAS and text mining helped in identifying the unique genetic susceptibility profile of Qatari patients with EH. To our knowledge, this is the first small study that searched for genetic factors associated with EH in Qatari patients.

Genetic associations of protein-coding variants in human disease

Genome-wide association studies (GWAS) have identified thousands of genetic variants linked to the risk of human disease. However, GWAS have so far remained largely underpowered in relation to identifying associations in the rare and low-frequency allelic spectrum and have lacked the resolution to trace causal mechanisms to underlying genes1. Here we combined whole-exome sequencing in 392,814 UK Biobank participants with imputed genotypes from 260,405 FinnGen participants (653,219 total individuals) to conduct association meta-analyses for 744 disease endpoints across the protein-coding allelic frequency spectrum, bridging the gap between common and rare variant studies. We identified 975 associations, with more than one-third being previously unreported. We demonstrate population-level relevance for mutations previously ascribed to causing single-gene disorders, map GWAS associations to likely causal genes, explain disease mechanisms, and systematically relate disease associations to levels of 117 biomarkers and clinical-stage drug targets. Combining sequencing and genotyping in two population biobanks enabled us to benefit from increased power to detect and explain disease associations, validate findings through replication and propose medical actionability for rare genetic variants. Our study provides a compendium of protein-coding variant associations for future insights into disease biology and drug discovery.

Late Sodium Current of the Heart: Where Do We Stand and Where Are We Going?

Late sodium current has long been linked to dysrhythmia and contractile malfunction in the heart. Despite the increasing body of accumulating information on the subject, our understanding of its role in normal or pathologic states is not complete. Even though the role of late sodium current in shaping action potential under physiologic circumstances is debated, it’s unquestioned role in arrhythmogenesis keeps it in the focus of research. Transgenic mouse models and isoform-specific pharmacological tools have proved useful in understanding the mechanism of late sodium current in health and disease. This review will outline the mechanism and function of cardiac late sodium current with special focus on the recent advances of the area.

Ranolazine: An Old Drug with Emerging Potential; Lessons from Pre-Clinical and Clinical Investigations for Possible Repositioning

Ischemic heart disease is a significant public health problem with high mortality and morbidity. Extensive scientific investigations from basic sciences to clinics revealed multilevel alterations from metabolic imbalance, altered electrophysiology, and defective Ca²⁺/Na⁺ homeostasis leading to lethal arrhythmias. Despite the recent identification of numerous molecular targets with potential therapeutic interest, a pragmatic observation on the current pharmacological R&D output confirms the lack of new therapeutic offers to patients. By contrast, from recent trials, molecules initially developed for other fields of application have shown cardiovascular benefits, as illustrated with some anti-diabetic agents, regardless of the presence or absence of diabetes, emphasizing the clear advantage of “old” drug repositioning. Ranolazine is approved as an antianginal agent and has a favorable overall safety profile. This drug, developed initially as a metabolic modulator, was also identified as an inhibitor of the cardiac late Na⁺ current, although it also blocks other ionic currents, including the hERG/Ikr K⁺ current. The latter actions have been involved in this drug’s antiarrhythmic effects, both on supraventricular and ventricular arrhythmias (VA). However, despite initial enthusiasm and promising development in the cardiovascular field, ranolazine is only authorized as a second-line treatment in patients with chronic angina pectoris, notwithstanding its antiarrhythmic properties. A plausible reason for this is the apparent difficulty in linking the clinical benefits to the multiple molecular actions of this drug. Here, we review ranolazine’s experimental and clinical knowledge on cardiac metabolism and arrhythmias. We also highlight advances in understanding novel effects on neurons, the vascular system, skeletal muscles, blood sugar control, and cancer, which may open the way to reposition this “old” drug alone or in combination with other medications.

Early-Onset Atrial Fibrillation and the Prevalence of Rare Variants in Cardiomyopathy and Arrhythmia Genes

Importance

Early-onset atrial fibrillation (AF) can be the initial manifestation of a more serious underlying inherited cardiomyopathy or arrhythmia syndrome.

Objective

To examine the results of genetic testing for early-onset AF.

Design, Setting, and Participants

This prospective, observational cohort study enrolled participants from an academic medical center who had AF diagnosed before 66 years of age and underwent whole genome sequencing through the National Heart, Lung, and Blood Institute's Trans-Omics for Precision Medicine program. Participants were enrolled from November 23, 1999, to June 2, 2015. Data analysis was performed from October 24, 2020, to March 11, 2021.

Exposures

Rare variants identified in a panel of 145 genes that are included on cardiomyopathy and arrhythmia panels used by commercial clinical genetic testing laboratories.

Main Outcomes and Measures

Sequencing data were analyzed using an automated process followed by manual review by a panel of independent, blinded reviewers. The primary outcome was classification of rare variants using American College of Medical Genetics and Genomics criteria: benign, likely benign, variant of undetermined significance, likely pathogenic, or pathogenic. Disease-associated variants were defined as pathogenic/likely pathogenic variants in genes associated with autosomal dominant or X-linked dominant disorders.

Results

Among 1293 participants (934 [72.2%] male; median [interquartile range] age at enrollment, 56 [48-61] years; median [interquartile range] age at AF diagnosis, 50 [41-56] years), genetic testing identified 131 participants (10.1%) with a disease-associated variant, 812 (62.8%) with a variant of undetermined significance, 92 (7.1%) as heterozygous carriers for an autosomal recessive disorder, and 258 (20.0%) with no suspicious variant. The likelihood of a disease-associated variant was highest in participants with AF diagnosed before the age of 30 years (20 of 119 [16.8%; 95% CI, 10.0%-23.6%]) and lowest after the age of 60 years (8 of 112 [7.1%; 95% CI, 2.4%-11.9%]). Disease-associated variants were more often associated with inherited cardiomyopathy syndromes compared with inherited arrhythmias. The most common genes were TTN (n = 38), MYH7 (n = 18), MYH6 (n = 10), LMNA (n = 9), and KCNQ1 (n = 8).

Conclusions and Relevance

In this cohort study, genetic testing identified a disease-associated variant in 10% of patients with early-onset AF (the percentage was higher if diagnosed before the age of 30 years and lower if diagnosed after the age of 60 years). Most pathogenic/likely pathogenic variants are in genes associated with cardiomyopathy. These results support the use of genetic testing in early-onset AF.

Inhibition of G-protein signalling in cardiac dysfunction of intellectual developmental disorder with cardiac arrhythmia (IDDCA) syndrome

BACKGROUND

Pathogenic variants of GNB5 encoding the β5 subunit of the guanine nucleotide-binding protein cause IDDCA syndrome, an autosomal recessive neurodevelopmental disorder associated with cognitive disability and cardiac arrhythmia, particularly severe bradycardia.

METHODS

We used echocardiography and telemetric ECG recordings to investigate consequences of Gnb5 loss in mouse.

RESULTS

We delineated a key role of Gnb5 in heart sinus conduction and showed that Gnb5-inhibitory signalling is essential for parasympathetic control of heart rate (HR) and maintenance of the sympathovagal balance. Gnb5-/- mice were smaller and had a smaller heart than Gnb5+/+ and Gnb5+/- , but exhibited better cardiac function. Lower autonomic nervous system modulation through diminished parasympathetic control and greater sympathetic regulation resulted in a higher baseline HR in Gnb5-/- mice. In contrast, Gnb5-/- mice exhibited profound bradycardia on treatment with carbachol, while sympathetic modulation of the cardiac stimulation was not altered. Concordantly, transcriptome study pinpointed altered expression of genes involved in cardiac muscle contractility in atria and ventricles of knocked-out mice. Homozygous Gnb5 loss resulted in significantly higher frequencies of sinus arrhythmias. Moreover, we described 13 affected individuals, increasing the IDDCA cohort to 44 patients.

CONCLUSIONS

Our data demonstrate that loss of negative regulation of the inhibitory G-protein signalling causes HR perturbations in Gnb5-/- mice, an effect mainly driven by impaired parasympathetic activity. We anticipate that unravelling the mechanism of Gnb5 signalling in the autonomic control of the heart will pave the way for future drug screening.

Ventricular voltage-gated ion channels: Detection, characteristics, mechanisms, and drug safety evaluation

Cardiac voltage-gated ion channels (VGICs) play critical roles in mediating cardiac electrophysiological signals, such as action potentials, to maintain normal heart excitability and contraction. Inherited or acquired alterations in the structure, expression, or function of VGICs, as well as VGIC-related side effects of pharmaceutical drug delivery can result in abnormal cellular electrophysiological processes that induce life-threatening cardiac arrhythmias or even sudden cardiac death. Hence, to reduce possible heart-related risks, VGICs must be acknowledged as important targets in drug discovery and safety studies related to cardiac disease. In this review, we first summarize the development and application of electrophysiological techniques that are employed in cardiac VGIC studies alone or in combination with other techniques such as cryoelectron microscopy, optical imaging and optogenetics. Subsequently, we describe the characteristics, structure, mechanisms, and functions of various well-studied VGICs in ventricular myocytes and analyze their roles in and contributions to both physiological cardiac excitability and inherited cardiac diseases. Finally, we address the implications of the structure and function of ventricular VGICs for drug safety evaluation. In summary, multidisciplinary studies on VGICs help researchers discover potential targets of VGICs and novel VGICs in heart, enrich their knowledge of the properties and functions, determine the operation mechanisms of pathological VGICs, and introduce groundbreaking trends in drug therapy strategies, and drug safety evaluation.

Blockade of NaV1.8 Increases the Susceptibility to Ventricular Arrhythmias During Acute Myocardial Infarction

SCN10A/Na_V1.8 may be associated with a lower risk of ventricular fibrillation in the setting of acute myocardial infarction (AMI), but if and by which mechanism Na_V1.8 impacts on ventricular electrophysiology is still a matter of debate. The purpose of this study was to elucidate the contribution of Na_V1.8 in ganglionated plexi (GP) to ventricular arrhythmias in the AMI model. Twenty beagles were randomized to either the A-803467 group (n = 10) or the control group (n = 10). Na_V1.8 blocker (A-803467, 1 μmol/0.5 mL per GP) or DMSO (0.5 mL per GP) was injected into four major GPs. Ventricular effective refractory period, APD₉₀, ventricular fibrillation threshold, and the incidence of ventricular arrhythmias were measured 1 h after left anterior descending coronary artery occlusion. A-803467 significantly shortened ventricular effective refractory period, APD₉₀, and ventricular fibrillation threshold compared to control. In the A-803467 group, the incidence of ventricular arrhythmias was significantly higher compared to control. A-803467 suppressed the slowing of heart rate response to high-frequency electrical stimulation of the anterior right GP, suggesting that A-803467 could inhibit GP activity. SCN10A/Na_V1.8 was readily detected in GPs, but was not validated in ventricles by quantitative RT-PCR, western blot and immunohistochemistry. While SCN10A/Na_V1.8 is detectible in canine GPs but not in ventricles, blockade of Na_V1.8 in GP increases the incidence of ventricular arrhythmias in AMI hearts. Our study shows for the first time an influence of SCN10A/Na_V1.8 on the regulation of ventricular arrhythmogenesis via modulating GP activity in the AMI model.

How Cardiac Embryology Translates into Clinical Arrhythmias

The electrophysiological signatures of the myocardium in cardiac structures, such as the atrioventricular node, pulmonary veins or the right ventricular outflow tract, are established during development by the spatial and temporal expression of transcription factors that guide expression of specific ion channels. Genome-wide association studies have shown that small variations in genetic regions are key to the expression of these transcription factors and thereby modulate the electrical function of the heart. Moreover, mutations in these factors are found in arrhythmogenic pathologies such as congenital atrioventricular block, as well as in specific forms of atrial fibrillation and ventricular tachycardia. In this review, we discuss the developmental origin of distinct electrophysiological structures in the heart and their involvement in cardiac arrhythmias.

Systems biology in cardiovascular disease: a multiomics approach

Omics techniques generate large, multidimensional data that are amenable to analysis by new informatics approaches alongside conventional statistical methods. Systems theories, including network analysis and machine learning, are well placed for analysing these data but must be applied with an understanding of the relevant biological and computational theories. Through applying these techniques to omics data, systems biology addresses the problems posed by the complex organization of biological processes. In this Review, we describe the techniques and sources of omics data, outline network theory, and highlight exemplars of novel approaches that combine gene regulatory and co-expression networks, proteomics, metabolomics, lipidomics and phenomics with informatics techniques to provide new insights into cardiovascular disease. The use of systems approaches will become necessary to integrate data from more than one omic technique. Although understanding the interactions between different omics data requires increasingly complex concepts and methods, we argue that hypothesis-driven investigations and independent validation must still accompany these novel systems biology approaches to realize their full potential.

Variant Intronic Enhancer Controls SCN10A-short Expression and Heart Conduction

BACKGROUND

Genetic variants in SCN10A, encoding the neuronal voltage-gated sodium channel Na_V1.8, are strongly associated with atrial fibrillation, Brugada syndrome, cardiac conduction velocities, and heart rate. The cardiac function of SCN10A has not been resolved, however, and diverging mechanisms have been proposed. Here, we investigated the cardiac expression of SCN10A and the function of a variant-sensitive intronic enhancer previously linked to the regulation of SCN5A, encoding the major essential cardiac sodium channel Na_V1.5.

METHODS

The expression of SCN10A was investigated in mouse and human hearts. With the use of CRISPR/Cas9 genome editing, the mouse intronic enhancer was disrupted, and mutant mice were characterized by transcriptomic and electrophysiological analyses. The association of genetic variants at SCN5A-SCN10A enhancer regions and gene expression were evaluated by genome-wide association studies single-nucleotide polymorphism mapping and expression quantitative trait loci analysis.

RESULTS

We found that cardiomyocytes of the atria, sinoatrial node, and ventricular conduction system express a short transcript comprising the last 7 exons of the gene (Scn10a-short). Transcription occurs from an intronic enhancer-promoter complex, whereas full-length Scn10a transcript was undetectable in the human and mouse heart. Expression quantitative trait loci analysis revealed that the genetic variants in linkage disequilibrium with genetic variant rs6801957 in the intronic enhancer associate with SCN10A transcript levels in the heart. Genetic modification of the enhancer in the mouse genome led to reduced cardiac Scn10a-short expression in atria and ventricles, reduced cardiac sodium current in atrial cardiomyocytes, atrial conduction slowing and arrhythmia, whereas the expression of Scn5a, the presumed enhancer target gene, remained unaffected. In patch-clamp transfection experiments, expression of Scn10a-short-encoded Na_V1.8-short increased Na_V1.5-mediated sodium current. We propose that noncoding genetic variation modulates transcriptional regulation of Scn10a-short in cardiomyocytes that impacts Na_V1.5-mediated sodium current and heart rhythm.

CONCLUSIONS

Genetic variants in and around SCN10A modulate enhancer function and expression of a cardiac-specific SCN10A-short transcript. We propose that noncoding genetic variation modulates transcriptional regulation of a functional C-terminal portion of Na_V1.8 in cardiomyocytes that impacts on Na_V1.5 function, cardiac conduction velocities, and arrhythmia susceptibility.

Analysis of Brugada syndrome loci reveals that fine-mapping clustered GWAS hits enhances the annotation of disease-relevant variants

Genome-wide association studies (GWASs) are instrumental in identifying loci harboring common single-nucleotide variants (SNVs) that affect human traits and diseases. GWAS hits emerge in clusters, but the focus is often on the most significant hit in each trait- or disease-associated locus. The remaining hits represent SNVs in linkage disequilibrium (LD) and are considered redundant and thus frequently marginally reported or exploited. Here, we interrogate the value of integrating the full set of GWAS hits in a locus repeatedly associated with cardiac conduction traits and arrhythmia, SCN5A-SCN10A. Our analysis reveals 5 common 7-SNV haplotypes (Hap1-5) with 2 combinations associated with life-threatening arrhythmia-Brugada syndrome (the risk Hap1/1 and protective Hap2/3 genotypes). Hap1 and Hap2 share 3 SNVs; thus, this analysis suggests that assuming redundancy among clustered GWAS hits can lead to confounding disease-risk associations and supports the need to deconstruct GWAS data in the context of haplotype composition.

Pathogenic mutations perturb calmodulin regulation of Nav1.8 channel

The voltage-gated sodium channels play a key role in the generation and propagation of the cardiac action potential. Emerging data indicate that the Nav1.8 channel, encoded by the SCN10A gene, is a modulator of cardiac conduction and variation in the gene has been associated with arrhythmias such as atrial fibrillation (AF) and Brugada syndrome (BrS). The voltage gated sodium channels contain a calmodulin (CaM)-binding IQ domain involved in channel slow inactivation, we here investigated the role of CaM regulation of Nav1.8 channel function, and showed that CaM enhanced slow inactivation of the Nav1.8 channel and hyperpolarized steady-state inactivation curve of sodium currents. The effects of CaM on the channel gating were disrupted in the Nav1.8 channel truncated IQ domain. We studied Nav1.8 IQ domain mutations associated with AF and BrS, and found that a BrS-linked mutation (R1863Q) reduced the CaM-induced hyperpolarization shift, AF-linked mutations (R1869C and R1869G) disrupted CaM-induced enhanced inactivation, and effects of CaM on both development and recovery from slow inactivation were attenuated in all pathogenic mutations. Our findings indicate a role of CaM in the regulation of Nav1.8 channel function in cardiac arrhythmias.

Role of Non-Coding Variants in Brugada Syndrome

Brugada syndrome (BrS) is an inherited electrical heart disease associated with a high risk of sudden cardiac death (SCD). The genetic characterization of BrS has always been challenging. Although several cardiac ion channel genes have been associated with BrS, SCN5A is the only gene that presents definitive evidence for causality to be used for clinical diagnosis of BrS. However, more than 65% of diagnosed cases cannot be explained by variants in SCN5A or other genes. Therefore, in an important number of BrS cases, the underlying mechanisms are still elusive. Common variants, mostly located in non-coding regions, have emerged as potential modulators of the disease by affecting different regulatory mechanisms, including transcription factors (TFs), three-dimensional organization of the genome, or non-coding RNAs (ncRNAs). These common variants have been hypothesized to modulate the interindividual susceptibility of the disease, which could explain incomplete penetrance of BrS observed within families. Altogether, the study of both common and rare variants in parallel is becoming increasingly important to better understand the genetic basis underlying BrS. In this review, we aim to describe the challenges of studying non-coding variants associated with disease, re-examine the studies that have linked non-coding variants with BrS, and provide further evidence for the relevance of regulatory elements in understanding this cardiac disorder.

Cardiac transmembrane ion channels and action potentials: cellular physiology and arrhythmogenic behavior

Cardiac arrhythmias are among the leading causes of mortality. They often arise from alterations in the electrophysiological properties of cardiac cells and their underlying ionic mechanisms. It is therefore critical to further unravel the pathophysiology of the ionic basis of human cardiac electrophysiology in health and disease. In the first part of this review, current knowledge on the differences in ion channel expression and properties of the ionic processes that determine the morphology and properties of cardiac action potentials and calcium dynamics from cardiomyocytes in different regions of the heart are described. Then the cellular mechanisms promoting arrhythmias in congenital or acquired conditions of ion channel function (electrical remodeling) are discussed. The focus is on human-relevant findings obtained with clinical, experimental, and computational studies, given that interspecies differences make the extrapolation from animal experiments to human clinical settings difficult. Deepening the understanding of the diverse pathophysiology of human cellular electrophysiology will help in developing novel and effective antiarrhythmic strategies for specific subpopulations and disease conditions.

The Role of Voltage-Gated Sodium Channel 1.8 in the Effect of Atropine on Heart Rate: Evidence From a Retrospective Clinical Study and Mouse Model

Atropine is commonly used to counter the effects of the parasympathetic neurotransmitter acetylcholine on heart rate in clinical practice, such as in the perioperative period; however, individual differences in the response to atropine are huge. The association between SCN10A/voltage-gated sodium channel 1.8 (Na_V1.8) and cardiac conduction has been demonstrated; however, the exact role of SCN10A/Na_V1.8 in the heart rate response to atropine remains unclear. To identify the role of SCN10A variants that influence the heart rate responses to atropine, we carried out a retrospective study in 1,005 Han Chinese subjects. Our results showed that rs6795970 was associated with the heart rate response to atropine. The heart rate responses to atropine and methoctramine in Na_V1.8 knockout mice were lower, whereas the heart rate response to isoproterenol was like those in wild type mice. Furthermore, we observed that the Na_V1.8 blocker A-803467 alleviated the heart rate response to atropine in wild type mice. The retrospective study revealed a previously unknown role of Na_V1.8 in controlling the heart rate response to atropine, as shown by the animal study, a speculative mechanism that may involve the cardiac muscarinic acetylcholine receptor M2.

Dual mechanism of modulation of NaV1.8 sodium channels by ouabain

In the primary sensory neuron, ouabain activates the dual mechanism that modulates the functional activity of Na_V1.8 channels. Ouabain at endogenous concentrations (EO) triggers two different signaling cascades, in which the Na,K-ATPase/Src complex is the EO target and the signal transducer. The fast EO effect is based on modulation of the Na_V1.8 channel activation gating device. EO triggers the tangential signaling cascade along the neuron membrane from Na,K-ATPase to the Na_V1.8 channel. It evokes a decrease in effective charge transfer of the Na_V1.8 channel activation gating device. Intracellular application of PP2, an inhibitor of Src kinase, completely eliminated the effect of EO, thus indicating the absence of direct EO binding to the Na_V1.8 channel. The delayed EO effect probably controls the density of Na_V1.8 channels in the neuron membrane. EO triggers the downstream signaling cascade to the neuron genome, which should result in a delayed decrease in the Na_V1.8 channels' density. PKC and p38 MAPK are involved in this pathway. Identification of the dual mechanism of the strong EO effect on Na_V1.8 channels makes it possible to suggest that application of EO to the primary sensory neuron membrane should result in a potent antinociceptive effect at the organismal level.

A novel loss-of-function mutation of PBK associated with human kidney stone disease

Kidney stone disease (KSD) is a prevalent disorder that causes human morbidity worldwide. The etiology of KSD is heterogeneous, ranging from monogenic defect to complex interaction between genetic and environmental factors. Since mutations of genes responsible for KSD in a majority of families are still unknown, our group is identifying mutations of these genes by means of genomic and genetic analyses. In this study, we identified a novel loss-of-function mutation of PBK, encoding the PDZ binding kinase, that was found to be associated with KSD in an affected Thai family. Glycine (Gly) substituted by arginine (Arg) at position 43 (p.Gly43Arg) in PBK cosegregated with the disease in affected members of this family, but was absent in 180 normal control subjects from the same local population. Gly43 is highly evolutionarily conserved in vertebrates, and its substitution affects protein structure by alterations in H-bond forming patterns. This p.Gly43Arg substitution results in instability of the variant PBK protein as examined in HEK293T cells. The variant PBK protein (p.Gly43Arg) demonstrated decreased kinase activity to phosphorylate p38 MAPK as analyzed by immunoblotting and antibody microarray techniques. Taken together, these findings suggest a possible new mechanism of KSD associated with pathogenic PBK variation.

Epigenetic and Transcriptional Networks Underlying Atrial Fibrillation

Genome-wide association studies have uncovered over a 100 genetic loci associated with atrial fibrillation (AF), the most common arrhythmia. Many of the top AF-associated loci harbor key cardiac transcription factors, including PITX2, TBX5, PRRX1, and ZFHX3. Moreover, the vast majority of the AF-associated variants lie within noncoding regions of the genome where causal variants affect gene expression by altering the activity of transcription factors and the epigenetic state of chromatin. In this review, we discuss a transcriptional regulatory network model for AF defined by effector genes in Genome-wide association studies loci. We describe the current state of the field regarding the identification and function of AF-relevant gene regulatory networks, including variant regulatory elements, dose-sensitive transcription factor functionality, target genes, and epigenetic states. We illustrate how altered transcriptional networks may impact cardiomyocyte function and ionic currents that impact AF risk. Last, we identify the need for improved tools to identify and functionally test transcriptional components to define the links between genetic variation, epigenetic gene regulation, and atrial function.

Multi-ancestry GWAS of the electrocardiographic PR interval identifies 202 loci underlying cardiac conduction

The electrocardiographic PR interval reflects atrioventricular conduction, and is associated with conduction abnormalities, pacemaker implantation, atrial fibrillation (AF), and cardiovascular mortality. Here we report a multi-ancestry (N = 293,051) genome-wide association meta-analysis for the PR interval, discovering 202 loci of which 141 have not previously been reported. Variants at identified loci increase the percentage of heritability explained, from 33.5% to 62.6%. We observe enrichment for cardiac muscle developmental/contractile and cytoskeletal genes, highlighting key regulation processes for atrioventricular conduction. Additionally, 8 loci not previously reported harbor genes underlying inherited arrhythmic syndromes and/or cardiomyopathies suggesting a role for these genes in cardiovascular pathology in the general population. We show that polygenic predisposition to PR interval duration is an endophenotype for cardiovascular disease, including distal conduction disease, AF, and atrioventricular pre-excitation. These findings advance our understanding of the polygenic basis of cardiac conduction, and the genetic relationship between PR interval duration and cardiovascular disease.

Contribution of the neuronal sodium channel NaV1.8 to sodium- and calcium-dependent cellular proarrhythmia

OBJECTIVE

In myocardial pathology such as heart failure a late sodium current (I_NaL) augmentation is known to be involved in conditions of arrhythmogenesis. However, the underlying mechanisms of the I_NaL generation are not entirely understood. By now evidence is growing that non-cardiac sodium channel isoforms could also be involved in the I_NaL generation. The present study investigates the contribution of the neuronal sodium channel isoform Na_V1.8 to arrhythmogenesis in a clearly-defined setting of enhanced I_NaL by using anemone toxin II (ATX-II) in the absence of structural heart disease.

METHODS

Electrophysiological experiments were performed in order to measure I_NaL, action potential duration (APD), SR-Ca²⁺-leak and cellular proarrhythmic triggers in ATX-II exposed wild-type (WT) and SCN10A^-/- mice cardiomyocytes. In addition, WT cardiomyocytes were stimulated with ATX-II in the presence or absence of Na_V1.8 inhibitors. I_NCX was measured by using the whole cell patch clamp method.

RESULTS

In WT cardiomyocytes exposure to ATX-II augmented I_NaL, prolonged APD, increased SR-Ca²⁺-leak and induced proarrhythmic triggers such as early afterdepolarizations (EADs) and Ca²⁺-waves. All of them could be significantly reduced by applying Na_V1.8 blockers PF-01247324 and A-803467. Both blockers had no relevant effects on cellular electrophysiology of SCN10A^-/- cardiomyocytes. Moreover, in SCN10A^-/--cardiomyocytes, the ATX-II-dependent increase in I_NaL, SR-Ca²⁺-leak and APD prolongation was less than in WT and comparable to the results which were obtained with WT cardiomyocytes being exposed to ATX-II and Na_V1.8 inhibitors in parallel. Moreover, we found a decrease in reverse mode NCX current and reduced CaMKII-dependent RyR2-phosphorylation after application of PF-01247324 as an underlying explanation for the Na⁺-mediated Ca²⁺-dependent proarrhythmic triggers.

CONCLUSION

The current findings demonstrate that Na_V1.8 is a significant contributor for I_NaL-induced arrhythmic triggers. Therefore, Na_V1.8 inhibition under conditions of an enhanced I_NaL constitutes a promising antiarrhythmic strategy which merits further investigation.

Radiation protection in the cardiac catheterization laboratory

The trend towards more minimally invasive procedures in the past few decades has resulted in an exponential growth in fluoroscopy-guided catheter-based cardiology procedures. As these techniques are becoming more commonly used and developed, the adverse effects of radiation exposure to the patient, operator, and ancillary staff have been a subject of concern. Although occupational radiation dose limits are being monitored and seldom reached, exposure to chronic, low dose radiation has been shown to have harmful biological effects that are not readily apparent until years after. Given this, it is imperative that reducing radiation dose exposure in the cardiac catheterization laboratory remains a priority. Staff education and training, radiation dose monitoring, ensuring use of proper personal protective equipment, employment of shields, and various procedural techniques in minimizing radiation must always be diligently employed. Special care and consideration should be extended to pregnant women working in the cardiac catheterization laboratory. This review article presents a practical approach to radiation dose management and discusses best practice recommendations in the cardiac catheterization laboratory.

Brugada Syndrome: Oligogenic or Mendelian Disease?

Brugada syndrome (BrS) is diagnosed by a coved-type ST-segment elevation in the right precordial leads on the electrocardiogram (ECG), and it is associated with an increased risk of sudden cardiac death (SCD) compared to the general population. Although BrS is considered a genetic disease, its molecular mechanism remains elusive in about 70-85% of clinically-confirmed cases. Variants occurring in at least 26 different genes have been previously considered causative, although the causative effect of all but the SCN5A gene has been recently challenged, due to the lack of systematic, evidence-based evaluations, such as a variant's frequency among the general population, family segregation analyses, and functional studies. Also, variants within a particular gene can be associated with an array of different phenotypes, even within the same family, preventing a clear genotype-phenotype correlation. Moreover, an emerging concept is that a single mutation may not be enough to cause the BrS phenotype, due to the increasing number of common variants now thought to be clinically relevant. Thus, not only the complete list of genes causative of the BrS phenotype remains to be determined, but also the interplay between rare and common multiple variants. This is particularly true for some common polymorphisms whose roles have been recently re-evaluated by outstanding works, including considering for the first time ever a polygenic risk score derived from the heterozygous state for both common and rare variants. The more common a certain variant is, the less impact this variant might have on heart function. We are aware that further studies are warranted to validate a polygenic risk score, because there is no mutated gene that connects all, or even a majority, of BrS cases. For the same reason, it is currently impossible to create animal and cell line genetic models that represent all BrS cases, which would enable the expansion of studies of this syndrome. Thus, the best model at this point is the human patient population. Further studies should first aim to uncover genetic variants within individuals, as well as to collect family segregation data to identify potential genetic causes of BrS.

Inhibition of NaV1.8 prevents atrial arrhythmogenesis in human and mice

Pharmacologic approaches for the treatment of atrial arrhythmias are limited due to side effects and low efficacy. Thus, the identification of new antiarrhythmic targets is of clinical interest. Recent genome studies suggested an involvement of SCN10A sodium channels (Na_V1.8) in atrial electrophysiology. This study investigated the role and involvement of Na_V1.8 (SCN10A) in arrhythmia generation in the human atria and in mice lacking Na_V1.8. Na_V1.8 mRNA and protein were detected in human atrial myocardium at a significant higher level compared to ventricular myocardium. Expression of Na_V1.8 and Na_V1.5 did not differ between myocardium from patients with atrial fibrillation and sinus rhythm. To determine the electrophysiological role of Na_V1.8, we investigated isolated human atrial cardiomyocytes from patients with sinus rhythm stimulated with isoproterenol. Inhibition of Na_V1.8 by A-803467 or PF-01247324 showed no effects on the human atrial action potential. However, we found that Na_V1.8 significantly contributes to late Na⁺ current and consequently to an increased proarrhythmogenic diastolic sarcoplasmic reticulum Ca²⁺ leak in human atrial cardiomyocytes. Selective pharmacological inhibition of Na_V1.8 potently reduced late Na⁺ current, proarrhythmic diastolic Ca²⁺ release, delayed afterdepolarizations as well as spontaneous action potentials. These findings could be confirmed in murine atrial cardiomyocytes from wild-type mice and also compared to SCN10A^-/- mice (genetic ablation of Na_V1.8). Pharmacological Na_V1.8 inhibition showed no effects in SCN10A^-/- mice. Importantly, in vivo experiments in SCN10A^-/- mice showed that genetic ablation of Na_V1.8 protects against atrial fibrillation induction. This study demonstrates that Na_V1.8 is expressed in the murine and human atria and contributes to late Na⁺ current generation and cellular arrhythmogenesis. Blocking Na_V1.8 selectively counteracts this pathomechanism and protects against atrial arrhythmias. Thus, our translational study reveals a new selective therapeutic target for treating atrial arrhythmias.

Absence of Functional Nav1.8 Channels in Non-diseased Atrial and Ventricular Cardiomyocytes

PURPOSE

Several studies have indicated a potential role for SCN10A/NaV1.8 in modulating cardiac electrophysiology and arrhythmia susceptibility. However, by which mechanism SCN10A/NaV1.8 impacts on cardiac electrical function is still a matter of debate. To address this, we here investigated the functional relevance of NaV1.8 in atrial and ventricular cardiomyocytes (CMs), focusing on the contribution of NaV1.8 to the peak and late sodium current (INa) under normal conditions in different species.

METHODS

The effects of the NaV1.8 blocker A-803467 were investigated through patch-clamp analysis in freshly isolated rabbit left ventricular CMs, human left atrial CMs and human-induced pluripotent stem cell-derived CMs (hiPSC-CMs).

RESULTS

A-803467 treatment caused a slight shortening of the action potential duration (APD) in rabbit CMs and hiPSC-CMs, while it had no effect on APD in human atrial cells. Resting membrane potential, action potential (AP) amplitude, and AP upstroke velocity were unaffected by A-803467 application. Similarly, INa density was unchanged after exposure to A-803467 and NaV1.8-based late INa was undetectable in all cell types analysed. Finally, low to absent expression levels of SCN10A were observed in human atrial tissue, rabbit ventricular tissue and hiPSC-CMs.

CONCLUSION

We here demonstrate the absence of functional NaV1.8 channels in non-diseased atrial and ventricular CMs. Hence, the association of SCN10A variants with cardiac electrophysiology observed in, e.g. genome wide association studies, is likely the result of indirect effects on SCN5A expression and/or NaV1.8 activity in cell types other than CMs.

Differential regulation of sodium channels as a novel proarrhythmic mechanism in the human failing heart

Aims

In heart failure (HF), enhanced persistent Na+ current (INaL) exerts detrimental effects on cellular electrophysiology and can induce arrhythmias. However, the underlying regulatory mechanisms remain unclear. Our aim was to potentially investigate the regulation and electrophysiological contribution of neuronal sodium channel NaV1.8 in failing human heart and eventually to reveal a novel anti-arrhythmic therapy.

Methods and results

By western blot, we found that NaV1.8 protein expression is significantly up-regulated, while of the predominant cardiac isoform NaV1.5 is inversely reduced in human HF. Furthermore, to investigate the relation of NaV1.8 regulation with the cellular proarrhythmic events, we performed comprehensive electrophysiology recordings and explore the effect of NaV1.8 on INaL, action potential duration (APD), Ca2+ spark frequency, and arrhythmia induction in human failing cardiomyocytes. NaV1.8 inhibition with the specific blockers A-803467 and PF-01247324 decreased INaL, abbreviated APD and reduced cellular-spontaneous Ca2+-release and proarrhythmic events in human failing cardiomyocytes. Consistently, in mouse cardiomyocytes stressed with isoproterenol, pharmacologic inhibition and genetically knockout of NaV1.8 (SCN10A-/-), were associated with reduced INaL and abbreviated APD.

Conclusion

We provide first evidence of differential regulation of NaV1.8 and NaV1.5 in the failing human myocardium and their contribution to arrhythmogenesis due to generation of INaL. We propose inhibition of NaV1.8 thus constitutes a promising novel approach for selective anti-arrhythmic therapy in HF.

Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes as Models for Cardiac Channelopathies: A Primer for Non-Electrophysiologists

Life threatening ventricular arrhythmias leading to sudden cardiac death are a major cause of morbidity and mortality. In the absence of structural heart disease, these arrhythmias, especially in the younger population, are often an outcome of genetic defects in specialized membrane proteins called ion channels. In the heart, exceptionally well-orchestrated activity of a diversity of ion channels mediates the cardiac action potential. Alterations in either the function or expression of these channels can disrupt the configuration of the action potential, leading to abnormal electrical activity of the heart that can sometimes initiate an arrhythmia. Understanding the pathophysiology of inherited arrhythmias can be challenging because of the complexity of the disorder and lack of appropriate cellular and in vivo models. Recent advances in human induced pluripotent stem cell technology have provided remarkable progress in comprehending the underlying mechanisms of ion channel disorders or channelopathies by modeling these complex arrhythmia syndromes in vitro in a dish. To fully realize the potential of induced pluripotent stem cells in elucidating the mechanistic basis and complex pathophysiology of channelopathies, it is crucial to have a basic knowledge of cardiac myocyte electrophysiology. In this review, we will discuss the role of the various ion channels in cardiac electrophysiology and the molecular and cellular mechanisms of arrhythmias, highlighting the promise of human induced pluripotent stem cell-cardiomyocytes as a model for investigating inherited arrhythmia syndromes and testing antiarrhythmic strategies. Overall, this review aims to provide a basic understanding of the electrical activity of the heart and related channelopathies, especially to clinicians or research scientists in the cardiovascular field with limited electrophysiology background.

Variation in a Left Ventricle-Specific Hand1 Enhancer Impairs GATA Transcription Factor Binding and Disrupts Conduction System Development and Function

RATIONALE

The ventricular conduction system (VCS) rapidly propagates electrical impulses through the working myocardium of the ventricles to coordinate chamber contraction. GWAS (Genome-wide association studies) have associated nucleotide polymorphisms, most are located within regulatory intergenic or intronic sequences, with variation in VCS function. Two highly correlated polymorphisms (r²>0.99) associated with VCS functional variation (rs13165478 and rs13185595) occur 5' to the gene encoding the basic helix-loop-helix transcription factor HAND1 (heart- and neural crest derivatives-expressed protein 1).

OBJECTIVE

Here, we test the hypothesis that these polymorphisms influence HAND1 transcription thereby influencing VCS development and function.

METHODS AND RESULTS

We employed transgenic mouse models to identify an enhancer that is sufficient for left ventricle (LV) cis-regulatory activity. Two evolutionarily conserved GATA transcription factor cis-binding elements within this enhancer are bound by GATA4 and are necessary for cis-regulatory activity, as shown by in vitro DNA binding assays. CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9-mediated deletion of this enhancer dramatically reduces Hand1 expression solely within the LV but does not phenocopy previously published mouse models of cardiac Hand1 loss-of-function. Electrophysiological and morphological analyses reveals that mice homozygous for this deleted enhancer display a morphologically abnormal VCS and a conduction system phenotype consistent with right bundle branch block. Using 1000 Genomes Project data, we identify 3 additional single nucleotide polymorphisms (SNPs), located within the Hand1 LV enhancer, that compose a haplotype with rs13165478 and rs13185595. One of these SNPs, rs10054375, overlaps with a critical GATA cis-regulatory element within the Hand1 LV enhancer. This SNP, when tested in electrophoretic mobility shift assays, disrupts GATA4 DNA-binding. Modeling 2 of these SNPs in mice causes diminished Hand1 expression and mice present with abnormal VCS function.

CONCLUSIONS

Together, these findings reveal that SNP rs10054375, which is located within a necessary and sufficient LV-specific Hand1 enhancer, exhibits reduces GATA DNA-binding in electrophoretic mobility shift assay, and this enhancer in total, is required for VCS development and function in mice and perhaps humans.

Genome-wide studies of heart failure and endophenotypes: lessons learned and future directions

Heart failure (HF) is a complex clinical syndrome resulting from structural or functional impairments of ventricular filling or ejection of blood. HF has a poor prognosis and the burden to society remains tremendous. The unfulfilled expectation is that expanding our knowledge of the genetic architecture of HF will help to quickly advance the quality of risk assessment, diagnoses, and treatment. To date, genome-wide association studies (GWAS) of HF have led to disappointing results with only limited progress in our understanding and tempering the earlier expectations. However, the analyses of traits closely related to HF (also called 'endophenotypes') have led to promising and novel findings. For example, GWAS of NT-proBNP levels not only identified variants in the NNPA-NPPB locus but also substantiated data suggesting that natriuretic peptides in itself are associated with a lower risk of hypertension and HF. Many other genetic associates currently await experimental follow-up in which genes are prioritized based on bioinformatic analyses and various model organisms are employed to obtain functional insights. Promising genes with identified function could later be used in personalized medicine. Also, targeting specific pathogenic gene mutations is promising to protect future generations from HF, such as recently done in human embryos carrying the cardiomyopathy-associated MYBPC3 mutation. This review discusses the current status of GWAS of HF and its endophenotypes. In addition, future directions such as functional follow-up and application of GWAS results are discussed.

GWAS of QRS duration identifies new loci specific to Hispanic/Latino populations

BACKGROUND

The electrocardiographically quantified QRS duration measures ventricular depolarization and conduction. QRS prolongation has been associated with poor heart failure prognosis and cardiovascular mortality, including sudden death. While previous genome-wide association studies (GWAS) have identified 32 QRS SNPs across 26 loci among European, African, and Asian-descent populations, the genetics of QRS among Hispanics/Latinos has not been previously explored.

METHODS

We performed a GWAS of QRS duration among Hispanic/Latino ancestry populations (n = 15,124) from four studies using 1000 Genomes imputed genotype data (adjusted for age, sex, global ancestry, clinical and study-specific covariates). Study-specific results were combined using fixed-effects, inverse variance-weighted meta-analysis.

RESULTS

We identified six loci associated with QRS (P<5x10-8), including two novel loci: MYOCD, a nuclear protein expressed in the heart, and SYT1, an integral membrane protein. The top SNP in the MYOCD locus, intronic SNP rs16946539, was found in Hispanics/Latinos with a minor allele frequency (MAF) of 0.04, but is monomorphic in European and African descent populations. The most significant QRS duration association was with intronic SNP rs3922344 (P = 1.19x10-24) in SCN5A/SCN10A. Three other previously identified loci, CDKN1A, VTI1A, and HAND1, also exceeded the GWAS significance threshold among Hispanics/Latinos. A total of 27 of 32 previously identified QRS duration SNPs were shown to generalize in Hispanics/Latinos.

CONCLUSIONS

Our QRS duration GWAS, the first in Hispanic/Latino populations, identified two new loci, underscoring the utility of extending large scale genomic studies to currently under-examined populations.