Genetics of sudden cardiac death caused by ventricular arrhythmias

STAT4 Mediates IL-6 Trans-Signaling Arrhythmias in High Fat Diet Guinea Pig Heart

Obesity is a major risk factor for the development of life-threatening malignant ventricular tachyarrhythmias (VT) and sudden cardiac death (SCD). Risks may be highest for patients with high levels of the proinflammatory cytokine interleukin (IL)-6. We used our guinea pig model of high-fat diet (HFD)-induced arrhythmias that exhibit a heightened proinflammatory-like pathology, which is also observed in human obesity arrhythmias, as well as immunofluorescence and confocal microscopy approaches to evaluate the pathological IL-6 trans-signaling function and explore the underlying mechanisms. Using blind-stick and electrocardiogram (ECG) techniques, we tested the hypothesis that heightened IL-6 trans-signaling would exhibit increased ventricular arrhythmia/SCD incidence and underlying arrhythmia substrates. Remarkably, compared to low-fat diet (LFD)-fed controls, HFD promoted phosphorylation of the IL-6 signal transducer and activator of transcription 4 (STAT4), leading to its activation and enhanced nuclear translocation of pSTAT4/STAT4 compared to LFD controls and pSTAT3/STAT3 nuclear expression. Overactivation of IL-6 trans-signaling in guinea pigs prolonged the QT interval, which resulted in greater susceptibility to arrhythmias/SCD with isoproterenol challenge, as also observed with the downstream Janus kinase (JAK) 2 activator. These findings may have potentially profound implications for more effective arrhythmia therapy in the vulnerable obese patient population.

Catheter ablation in patients with ventricular fibrillation by purkinje de-networking

Background

Ventricular fibrillation (VF) is a leading cause of cardiovascular death worldwide. However, recurrence rates of arrhythmia are high leading to mortality and morbidity. Recently, Purkinje fibers have been identified as potential sources of VF initiation and maintenance.

Aim

The study analyzes the feasibility and effectiveness of catheter ablation in patients with recurrent VF by specific Purkinje de-networking (PDN).

Methods

Consecutive patients with recurrent VF undergoing PDN were included in this observational study. The procedural endpoint was the non-inducibility of sustained ventricular arrhythmia. A three-dimensional -anatomical mapping was conducted, and the specific cardiac conduction system and Purkinje fibers were tagged. All detectable Purkinje signals were ablated in the left ventricle (LV). Additional right ventricular (RV) PDN was performed in case of VF inducibility after LV ablation. Follow-up was performed by patient visits at our outpatient clinic including device interrogation and by telephone interviews.

Results

Eight patients were included in the study. Six patients were females (75%); the median age during the procedure was 43 [37;57] years and the median body mass index was 24 [23;33] kg/m². Four patients (50%) had known structural heart disease with two cases of ischemic cardiomyopathy and two cases of dilated cardiomyopathy. In four patients (50%), no underlying structural heart disease could be identified. The median LV ejection fraction was 42 ± 16.4%. All patients had an implantable cardioverter-defibrillator (ICD) prior to ablation with documentation of recurrent VF. The median number of ICD shocks before the ablation was 5 [3;7]. LV PDN was performed in all patients. In two patients (25%), an additional RV PDN was performed. Non-inducibility of any ventricular arrhythmia was achieved in all patients after PDN. Two patients showed complete left bundle branch block post-ablation. The median follow-up duration was 264 [58;421] days. Two patients (25%) experienced ventricular arrhythmia recurrence with recurrent ICD-shock delivery. One patient died during follow-up with an unknown cause of death. Six patients (75%) experienced no arrhythmia recurrence during follow-up.

Conclusion

Purkinje de-networking represents a novel treatment option for patients with recurrent VF without arrhythmia substrate or specific arrhythmia triggers with promising results in terms of efficiency and feasibility. Larger and more prospective studies are needed for a systematic evaluation.

The Atrium in Atrial Fibrillation - A Clinical Review on How to Manage Atrial Fibrotic Substrates

Atrial fibrillation (AF) is the most common sustained arrhythmia in the population and is associated with a significant clinical and economic burden. Rigorous assessment of the presence and degree of an atrial arrhythmic substrate is essential for determining treatment options, predicting long-term success after catheter ablation, and as a substrate critical in the pathophysiology of atrial thrombogenesis. Catheter ablation of AF has developed into an essential rhythm-control strategy. Nowadays is one of the most common cardiac ablation procedures performed worldwide, with its success inversely related to the extent of atrial structural disease. Although atrial substrate evaluation remains complex, several diagnostic resources allow for a more comprehensive assessment and quantification of the extent of left atrial structural remodeling and the presence of atrial fibrosis. In this review, we summarize the current knowledge on the pathophysiology, etiology, and electrophysiological aspects of atrial substrates promoting the development of AF. We also describe the risk factors for its development and how to diagnose its presence using imaging, electrocardiograms, and electroanatomic voltage mapping. Finally, we discuss recent data regarding fibrosis biomarkers that could help diagnose atrial fibrotic substrates.

New insights into the central sympathetic hyperactivity post-myocardial infarction: Roles of METTL3-mediated m6 A methylation

Ventricular arrhythmias (VAs) triggers by sympathetic nerve hyperactivity contribute to sudden cardiac death in myocardial infarction (MI) patients. Microglia-mediated inflammation in the paraventricular nucleus (PVN) is involved in sympathetic hyperactivity after MI. N6-methyladenosine (m⁶ A), the most prevalent mRNA and epigenetic modification, is critical for mediating cell inflammation. We aimed to explore whether METTL3-mediated m⁶ A modification is involved in microglia-mediated sympathetic hyperactivity after MI in the PVN. MI model was established by left coronary artery ligation. METTL3-mediated m⁶ A modification was markedly increased in the PVN at 3 days after MI, and METTL3 was primarily located in microglia by immunofluorescence. RNA-seq, MeRIP-seq, MeRIP-qPCR, immunohistochemistry, ELISA, heart rate variability measurements, renal sympathetic nerve activity recording and programmed electrical stimulation confirmed that the elevated toll-like receptor 4 (TLR4) expression by m⁶ A modification on TLR4 mRNA 3'-UTR region combined with activated NF-κB signalling led to the overwhelming production of pro-inflammatory cytokines IL-1β and TNF-α in the PVN, thus inducing the sympathetic hyperactivity and increasing the incidence of VAs post-MI. Targeting METTL3 attenuated the inflammatory response and sympathetic hyperactivity and reduced the incidence of VAs post-MI.

An inherited sudden cardiac arrest syndrome may be based on primary myocardial and autonomic nervous system abnormalities

BACKGROUND

A recently discovered sudden cardiac arrest (SCA) syndrome is linked to a risk haplotype that harbors the dipeptidyl-peptidase 6 (DPP6) gene as a plausible culprit.

OBJECTIVE

Because DPP6 impacts both cardiomyocyte and neuronal function, we hypothesized that ventricular fibrillation (VF) in risk haplotype carriers arises from functional changes in both the heart and autonomic nervous system.

METHODS

We studied 6 risk haplotype carriers with previous VF (symptomatic), 8 carriers without VF (asymptomatic), and 7 noncarriers (controls). We analyzed supine and standing heart rate variability, baroreflex sensitivity, pre-VF heart rate changes, and myocardial ¹²³I-meta-iodobenzylguanide (¹²³I-mIBG) scintigraphy.

RESULTS

Carriers had longer interbeat intervals than controls (1.03 ± 0.11 seconds vs 0.81 ± 0.07 seconds; P <.001), lower low-frequency (LF) and higher high-frequency (HF) activity, and lower LF/HF ratio (0.68 ± 0.50 vs 2.11 ± 1.10; P = .013) in the supine position. Upon standing up, carriers had significantly larger decrease in interbeat interval and increase in LF than controls (standing-to-supine ratio: 0.78 ± 0.07 vs 0.90 ± 0.07; P = .002; and 1.94 ± 1.03 vs 1.17 ± 0.34; P = .022, respectively), and nonsignificantly larger decrease in HF (0.62 ± 0.36 vs 0.97 ± 0.42; P = .065) and increase in LF/HF ratio (5.55 ± 6.79 vs 1.62 ± 1.24; P = .054). Sixteen of 17 VF episodes occurred at rest. Heart rate immediately before VF was 110 ± 25 bpm. Symptomatic carriers had less heterogeneous ¹²³I-mIBG distribution in the left ventricle than asymptomatic carriers (single-photon emission computed tomography score ≥3 in 7 asymptomatic and 1 symptomatic carrier; P = .008).

CONCLUSION

It can be speculated that these data are consistent with more labile autonomic tone in carriers, suggesting that the primary abnormalities may reside in both the heart and the autonomic nervous system.

Oligogenic Inheritance Underlying Incomplete Penetrance of PROKR2 Mutations in Hypogonadotropic Hypogonadism

The role of the prokineticin 2 pathway in human reproduction, olfactory bulb morphogenesis, and gonadotropin-releasing hormone secretion is well established. Recent studies have highlighted the implication of di/oligogenic inheritance in this disorder. In the present study, we aimed to identify the genetic mechanisms that could explain incomplete penetrance in hypogonadotropic hypogonadism (HH). This study involved two unrelated Tunisian patients with HH, which was triggered by identifying a homozygous p.(Pro290Ser) mutation in the PROKR2 gene in a girl (HH1) with Kallmann syndrome (KS). The functional effect of this variant has previously been well demonstrated. Unexpectedly, her unaffected father (HH1P) and brother (HH1F) also carried this genetic variation at a homozygous state. In the second family, we identified a heterozygous p.(Lys205del) mutation in PROKR2, both in a male patient with normosmic idiopathic IHH (HH12) and his asymptomatic mother. Whole-exome sequencing in the three HH1 family members allowed the identification of additional variants in the prioritized genes. We then carried out digenic combination predictions using the oligogenic resource for variant analysis (ORVAL) software. For HH1, we found the highest number of disease-causing variant pairs. Notably, a CCDC141 variant (c.2803C > T) was involved in 18 pathogenic digenic combinations. The CCDC141 variant acts in an autosomal recessive inheritance mode, based on the digenic effect prediction data. For the second patient (HH12), prediction by ORVAL allowed the identification of an interesting pathogenic digenic combination between DUSP6 and SEMA7A genes, predicted as “dual molecular diagnosis.” The SEMA7A variant p.(Glu436Lys) is novel and predicted as a VUS by Varsome. Sanger validation revealed the absence of this variant in the healthy mother. We hypothesize that disease expression in HH12 could be induced by the digenic transmission of the SEMA7A and DUSP6 variants or a monogenic inheritance involving only the SEMA7A VUS if further functional assays allow its reclassification into pathogenic. Our findings confirm that homozygous loss-of-function genetic variations are insufficient to cause KS, and that oligogenism is most likely the main transmission mode involved in Congenital Hypogonadotropic Hypogonadism.

Genome-wide association studies of cardiac electrical phenotypes

The genetic basis of cardiac electrical phenotypes has in the last 25 years been the subject of intense investigation. While in the first years, such efforts were dominated by the study of familial arrhythmia syndromes, in recent years, large consortia of investigators have successfully pursued genome-wide association studies (GWAS) for the identification of single-nucleotide polymorphisms that govern inter-individual variability in electrocardiographic parameters in the general population. We here provide a review of GWAS conducted on cardiac electrical phenotypes in the last 14 years and discuss the implications of these discoveries for our understanding of the genetic basis of disease susceptibility and variability in disease severity. Furthermore, we review functional follow-up studies that have been conducted on GWAS loci associated with cardiac electrical phenotypes and highlight the challenges and opportunities offered by such studies.

Development and Validation of a Risk Prediction Model for Ventricular Arrhythmia in Elderly Patients with Coronary Heart Disease

BACKGROUND

Sudden cardiac death is a leading cause of death from coronary heart disease (CHD). The risk of sudden cardiac death (SCD) increases with age, and sudden arrhythmic death remains a major cause of mortality in elderly individuals, especially ventricular arrhythmias (VA). We developed a risk prediction model by combining ECG and other clinical noninvasive indexes including biomarkers and echocardiology for VA in elderly patients with CHD.

METHOD

In the retrospective study, a total of 2231 consecutive elderly patients (≥60 years old) with CHD hospitalized were investigated, and finally 1983 patients were enrolled as the model group. The occurrence of VA within 12 months was mainly collected. Study parameters included clinical characteristics (age, gender, height, weight, BMI, and past medical history), ECG indexes (QTcd, Tp-e/QT, and HRV indexes), biomarker indexes (NT-proBNP, Myo, cTnT, CK-MB, CRP, K+, and Ca2+), and echocardiology indexes. In the respective study, 406 elderly patients (≥60 years old) with CHD were included as the verification group to verify the model in terms of differentiation and calibration.

RESULTS

In the multiparameter model, seven independent predictors were selected: LVEF, LAV, HLP, QTcd, sex, Tp-e/QT, and age. Increased HLP, Tp-e/QT, QTcd, age, and LAV were risk factors (RR > 1), while female and increased LVEF were protective factors (RR < 1). This model can well predict the occurrence of VA in elderly patients with CHD (for model group, AUC: 0.721, 95% CI: 0.669∼0.772; for verification group, AUC: 0.73, 95% CI: 0.648∼0.818; Hosmer-Lemeshow χ 2 = 13.541, P=0.095). After adjusting the predictors, it was found that the combination of clinical indexes and ECG indexes could predict VA more efficiently than using clinical indexes alone.

CONCLUSIONS

LVEF, LAV, QTcd, Tp-e/QT, gender, age, and HLP were independent predictors of VA risk in elderly patients with CHD. Among these factors, the echocardiology indexes LVEF and LAV had the greatest influence on the predictive efficiency of the model, followed by ECG indexes, QTcd and Tp-e/QT. After verification, the model had a good degree of differentiation and calibration, which can provide a certain reference for clinical prediction of the VA occurrence in elderly patients with CHD.

European Resuscitation Council Guidelines 2021: Epidemiology of cardiac arrest in Europe

In this section of the European Resuscitation Council Guidelines 2021, key information on the epidemiology and outcome of in and out of hospital cardiac arrest are presented. Key contributions from the European Registry of Cardiac Arrest (EuReCa) collaboration are highlighted. Recommendations are presented to enable health systems to develop registries as a platform for quality improvement and to inform health system planning and responses to cardiac arrest.

Association Between Atrial Fibrillation and Sudden Cardiac Death

Emerging evidence suggests that atrial fibrillation (AF) may be associated with an increased risk of sudden cardiac death (SCD). However, AF shares risk factors with numerous cardiac conditions, including coronary heart disease and heart failure—the 2 most common substrates for SCD—making the AF-SCD relationship particularly challenging to address. A careful consideration of confounding factors is essential, since interventions for AF will be effective in reducing SCD only if there is a causal association between these 2 conditions. In this translational review, we detail the plausible underlying pathophysiological mechanisms through which AF may promote or lead to SCD, as well as the existing epidemiological evidence supporting an association between AF and SCD. While the role of AF in predicting SCD in the general population appears limited and not established, AF might be integrated to improve risk stratification in some specific phenotypes. Optimal AF management, including that of its associated conditions, appears to be of interest to prevent AF-related SCD, especially because the AF-SCD relationship is in part driven by heart failure.

Idiopathic Ventricular Fibrillation: Diagnosis, Ablation of Triggers, Gaps in Knowledge, and Future Directions

Idiopathic ventricular fibrillation (IVF) is a diagnosis of exclusion made when no underlying cause is identified in a cardiac arrest survivor. Although the frequency of this diagnosis has declined over time due to advances in diagnostic techniques, it remains a substantial cause of sudden cardiac arrest. Further, IVF tends to recur. This article reviews the criteria for diagnosis, patient characteristics, the two primary arrhythmic phenotypes—short-coupled variant of torsades de pointes and recurrent paroxysmal IVF—and the electrophysiologic features, treatment, and ablation of premature ventricular complexes that can trigger IVF.

Using Zebrafish to Analyze the Genetic and Environmental Etiologies of Congenital Heart Defects

Congenital heart defects (CHDs) are among the most common human birth defects. However, the etiology of a large proportion of CHDs remains undefined. Studies identifying the molecular and cellular mechanisms that underlie cardiac development have been critical to elucidating the origin of CHDs. Building upon this knowledge to understand the pathogenesis of CHDs requires examining how genetic or environmental stress changes normal cardiac development. Due to strong molecular conservation to humans and unique technical advantages, studies using zebrafish have elucidated both fundamental principles of cardiac development and have been used to create cardiac disease models. In this chapter we examine the unique toolset available to zebrafish researchers and how those tools are used to interrogate the genetic and environmental contributions to CHDs.

Risk stratification for complex ventricular arrhythmia complicating ST-segment elevation myocardial infarction

OBJECTIVES

The primary aim of the study was to evaluate risk factors for ventricular fibrillation/sustained ventricular tachycardia (VF/VT) and to develop the risk score for prediction of VF/VT in patients with ST-segment elevation myocardial infarction (STEMI) treated invasively. The secondary aim was to assess the effect of VF/VT on mortality depending on timing of arrhythmia.

PATIENTS AND METHODS

We analyzed 4363 consecutive patients with STEMI treated invasively. Among them, 163 patients with pre-reperfusion arrhythmia were excluded from the study. Group ventricular arrhythmias (VA) encompassed patients with VF/VT - those with reperfusion-induced arrhythmia were included into group VA1, whereas group VA2 consisted of patients with postreperfusion arrhythmia. The control group comprised patients free of VF/VT.

RESULTS

VF or VT occurred in 313 (7.45%) patients - group VA1 encompassed 103 (32.9%) and group AV2 210 (67.1%) patients. Cardiogenic shock on admission [hazard ratio (HR) 3.5], new-onset atrial fibrillation (HR 2.1), incomplete revascularization (HR 1.7), prior myocardial infarction (HR 1.6) and symptom-to-balloon time more than 3 h (HR 1.3) were the independent predictors of VF/VT occurrence. In group VA2, the in-hospital and long-term mortality were 4- and 1.5-fold higher than in the arrhythmia-free population (20.5 vs. 4.5% and 36.2 vs. 22.6%, respectively; P<0.001). On the contrary, in group VA1, the long-term mortality was not significantly higher compared with the control group (26.2 vs. 22.6%; P=NS), whereas in-hospital mortality was almost three-fold increased (12.5 vs. 4.5%, respectively; P<0.001).

CONCLUSION

The risk score based on simple clinical parameters might be useful for risk stratification for VF/VT in patients with STEMI. The predictive value of VF/VT was strongly dependent on timing of arrhythmia.

Sudden infant death as the most severe phenotype caused by genetic modulation in a family with atrial fibrillation

AIMS

To assess the functional impact of two combined KCNH2 variants involved in atrial fibrillation, syncope and sudden infant death syndrome.

METHODS AND RESULTS

Genetic testing of a 4-month old SIDS victim identified a rare missense heterozygous in KCNH2 variant (V483I) and a missense homozygous polymorphism (K897T) which is often described as a genetic modifier. Electrophysiological characterisation of heterologous HERG channels representing two different KCNH2 genotypes within the family, showed significant differences in both voltage and time dependence of activation and inactivation with a global gain-of-function effect of mutant versus wild type channels and, also, differences between both types of recombinant channels.

CONCLUSIONS

The rare variant V483I in combination with K897T produces a gain-of-function effect that represents a pathological substrate for atrial fibrillation, syncope and sudden infant death syndrome events in this family. Ascertaining the genotype-phenotype correlation of genetic variants is imperative for the correct assessment of genetic testing and counselling.

TRANSLATIONAL PERSPECTIVE

According to the current guidelines for clinical interpretation of sequence variants, functional studies are an essential tool for the ascertainment of variant pathogenicity. They are especially relevant in the context of sudden infant death syndrome and sudden cardiac death, where individuals cannot be clinically evaluated. The patch-clamp technique is a gold-standard for analysis of the biophysical mechanisms of ion channels.

The Crossroad of Ion Channels and Calmodulin in Disease

Calmodulin (CaM) is the principal Ca²⁺ sensor in eukaryotic cells, orchestrating the activity of hundreds of proteins. Disease causing mutations at any of the three genes that encode identical CaM proteins lead to major cardiac dysfunction, revealing the importance in the regulation of excitability. In turn, some mutations at the CaM binding site of ion channels cause similar diseases. Here we provide a summary of the two sides of the partnership between CaM and ion channels, describing the diversity of consequences of mutations at the complementary CaM binding domains.

Implantable Cardioverter-Defibrillators are the Main Link in the Modern Concept of Sudden Cardiac Death Prevention. Problems and Prospects of the Development of the Method

The article covers the development of the problem of sudden cardiac death prevention with the implantable cardioverter-defibrillators from the moment of creation of these devices to our days. The current concept of primary prevention of sudden cardiac death, based on the severity of manifestation of heart failure and left ventricular dysfunction, is not effective enough. Its practical application is difficult because it requires mass application of implantable defibrillators, with low predictive accuracy of these criteria in terms of development of life-threatening arrhythmias. The development of methods for visualizing the myocardium, allowing to assess the severity of myocardial fibrosis, as well as the possibilities of medical genetics, at the present stage, allows us to clarify indications for implantation of cardioverter-defibrillators and thereby significantly improve the concept of preventing sudden cardiac death with these instruments.

Pericardial Cyst: Cause of Sudden Cardiac Death?

Cardiovascular disease is the leading cause of sudden death in the world. The etiology of sudden cardiac death involves a wide range of diseases, but seldom pericardial cysts. A pericardial cyst is an uncommon cyst usually located in the middle mediastinum and rarely in the posterior part. They are usually harmless and asymptomatic. Here, we present a case of a 63-year-old woman who presented with dyspnea and hoarseness, but died suddenly after a CT scan was attempted. The detailed forensic pathologic and histologic examination revealed a pericardial cyst located in the posterior mediastinum. Toxicology and biochemistry tests, including tryptase, found no competing cause of death.

Human pluripotent stem cell models of cardiac disease: from mechanisms to therapies

It is now a decade since human induced pluripotent stem cells (hiPSCs) were first described. The reprogramming of adult somatic cells to a pluripotent state has become a robust technology that has revolutionised our ability to study human diseases. Crucially, these cells capture all the genetic aspects of the patient from which they were derived. Combined with advances in generating the different cell types present in the human heart, this has opened up new avenues to study cardiac disease in humans and investigate novel therapeutic approaches to treat these pathologies. Here, we provide an overview of the current state of the field regarding the generation of cardiomyocytes from human pluripotent stem cells and methods to assess them functionally, an essential requirement when investigating disease and therapeutic outcomes. We critically evaluate whether treatments suggested by these in vitro models could be translated to clinical practice. Finally, we consider current shortcomings of these models and propose methods by which they could be further improved.

The role of genetics in primary ventricular fibrillation, inherited channelopathies and cardiomyopathies

Sudden cardiac death (SCD) has a strong familial component; however, our understanding of its genetic basis varies significantly according to the underlying causes. When coronary artery disease is involved, the predisposing genetic background is complex and despite some interesting findings it remains largely unknown. Quite different is the case of monogenic structural and non-structural heart diseases, in which a number of disease-causing genes have been established and are being used in clinical practice. As SCD can be the first clinical manifestation of inherited syndromes, in order to ascertain the cause of death, it is extremely important to include molecular autopsy among the standard post-mortem examinations. Indeed, molecular screening of the major disease-causing genes in the deceased person is often the only way to achieve a post-mortem diagnosis in channelopathies, which may prove crucial for the identification and management of at risk family members. Overall, these data, together with the inclusion in current guidelines of molecular screening for diagnosis and/or risk stratification of specific inherited cardiac diseases, exemplify how research on the genetic basis of SCD may be deeply translational, while the transition of genetic testing from the research to the diagnostic setting is already improving every-day clinical practice.

Barbaloin inhibits ventricular arrhythmias in rabbits by modulating voltage-gated ion channels

Barbaloin (10-β-D-glucopyranosyl-1,8-dihydroxy-3-(hydroxymethyl)-9(10H)-anthracenone) is extracted from the aloe plant and has been reported to have anti-inflammatory, antitumor, antibacterial, and other biological activities. Here, we investigated the effects of barbaloin on cardiac electrophysiology, which has not been reported thus far. Cardiac action potentials (APs) and ionic currents were recorded in isolated rabbit ventricular myocytes using whole-cell patch-clamp technique. Additionally, the antiarrhythmic effect of barbaloin was examined in Langendorff-perfused rabbit hearts. In current-clamp recording, application of barbaloin (100 and 200 μmol/L) dose-dependently reduced the action potential duration (APD) and the maximum depolarization velocity (Vmax), and attenuated APD reverse-rate dependence (RRD) in ventricular myocytes. Furthermore, barbaloin (100 and 200 μmol/L) effectively eliminated ATX II-induced early afterdepolarizations (EADs) and Ca²⁺-induced delayed afterdepolarizations (DADs) in ventricular myocytes. In voltage-clamp recording, barbaloin (10-200 μmol/L) dose-dependently inhibited L-type calcium current (I_Ca.L) and peak sodium current (I_Na.P) with IC₅₀ values of 137.06 and 559.80 μmol/L, respectively. Application of barbaloin (100, 200 μmol/L) decreased ATX II-enhanced late sodium current (I_Na.L) by 36.6%±3.3% and 71.8%±6.5%, respectively. However, barbaloin up to 800 μmol/L did not affect the inward rectifier potassium current (I_K1) or the rapidly activated delayed rectifier potassium current (I_Kr) in ventricular myocytes. In Langendorff-perfused rabbit hearts, barbaloin (200 μmol/L) significantly inhibited aconitine-induced ventricular arrhythmias. These results demonstrate that barbaloin has potential as an antiarrhythmic drug.

Serum lipid feature and potential biomarkers of lethal ventricular tachyarrhythmia (LVTA) induced by myocardial ion channel diseases: a rat model study

To determine the cause of death in myocardial ion channel diseases (MICD)-induced sudden cardiac death (SCD) cases is a difficulty in forensic identification practices. The majority of MICD-induced SCD cases would experience lethal ventricular tachyarrhythmia (LVTA) before deaths; thus, confirming the occurrence of LVTA in bodies can offer a key evidence to identify these cases. Several lipids in the myocardia were found disturbed after LVTA; yet, whether serum lipidome would be disrupted by LVTA is not clear. Therefore, we aimed to screen lipid feature and related diagnostic markers of LVTA in serum here. An aconitine-induced LVTA-SCD rat model was produced. Blood samples before LVTA and immediately after LVTA were retrieved and related serum specimens were used for ultra-performance liquid chromatography-mass spectrometry (UPLC-MS)-based lipidomics analyses. On the basis of the defined differential lipids, a lipid-related metabolic pathway network was constructed and potential biomarkers were screened. Twelve aconitine-induced LVTA rats were produced. Totally, 188 lipids in serum were disrupted during the LVTA-SCD process, which belong to 11 lipid classes. Most of the differential lipids were correlated, suggesting that they were interacted and that the changes were holistic during LVTA process. Ten lipid pathways were activated during LVTA process; the main lipid classes involved in these pathways were ceramide, sphingomyelin, phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine. Phosphatidylcholine O-40:4, sphingomyelin d46:5, and phosphatidylethanolamine 40:4 were tested as potential diagnostic markers of LVTA-SCD event in serum. The current results indicate a substantial change in serum lipidome after LVTA-SCD; lipidomics holds promise to identify MICD-induced SCDs in forensic practices.

Genetic variations involved in sudden cardiac death and their associations and interactions

Although the mechanism of sudden cardiac death (SCD) in heart failure is not completely known, genetic variations are known to play key roles in this process. Increasing numbers of mutations and variants are being discovered through genome-wide association studies. The genetic variations involved in the mechanisms of SCD have aroused widespread concern. Comprehensive understanding of the genetic variations involved in SCD may help prevent it. To this end, we briefly reviewed the genetic variations involved in SCD and their associations and interactions, and observed that cardiac ion channels are the core molecules involved in this process. Genetic variations involved in cardiac structure, cardiogenesis and development, cell division and differentiation, and DNA replication and transcription are all speculated to be loci involved in SCD. Additionally, the systems involved in neurohumoral regulation as well as substance and energy metabolism are also potentially responsible for susceptibility to SCD. They form an elaborate network and mutually interact with each other to govern the fate of SCD-susceptible individuals.

Cardiac Arrhythmias Related to Sodium Channel Dysfunction

The voltage-gated cardiac sodium channel (Na_v1.5) is a mega-complex comprised of a pore-forming α subunit and 4 ancillary β-subunits together with numerous protein partners. Genetic defects in the form of rare variants in one or more sodium channel-related genes can cause a loss- or gain-of-function of sodium channel current (I_Na) leading to the manifestation of various disease phenotypes, including Brugada syndrome, long QT syndrome, progressive cardiac conduction disease, sick sinus syndrome, multifocal ectopic Purkinje-related premature contractions, and atrial fibrillation. Some sodium channelopathies have also been shown to be responsible for sudden infant death syndrome (SIDS). Although these genetic defects often present as pure electrical diseases, recent studies point to a contribution of structural abnormalities to the electrocardiographic and arrhythmic manifestation in some cases, such as dilated cardiomyopathy. The same rare variants in SCN5A or related genes may present with different clinical phenotypes in different individuals and sometimes in members of the same family. Genetic background and epigenetic and environmental factors contribute to the expression of these overlap syndromes. Our goal in this chapter is to review and discuss what is known about the clinical phenotype and genotype of each cardiac sodium channelopathy, and to briefly discuss the underlying mechanisms.

Incomplete Penetrance and Variable Expressivity: Hallmarks in Channelopathies Associated with Sudden Cardiac Death

Sudden cardiac death is defined as an unexpected decease of cardiac origin. In individuals under 35 years old, most of these deaths are due to familial arrhythmogenic syndromes of genetic origin, also known as channelopathies. These familial cardiac syndromes commonly follow an autosomal dominant pattern of inheritance. Diagnosis, however, can be difficult, mainly due to incomplete penetrance and variable expressivity, which are hallmarks in these syndromes. The clinical manifestation of these diseases can range from asymptomatic to syncope but sudden death can sometimes be the first symptom of disease. Early identification of at-risk individuals is crucial to prevent a lethal episode. In this review, we will focus on the genetic basis of channelopathies and the effect of genetic and non-genetic modifiers on their phenotypes.

GWAS of the electrocardiographic QT interval in Hispanics/Latinos generalizes previously identified loci and identifies population-specific signals

QT interval prolongation is a heritable risk factor for ventricular arrhythmias and can predispose to sudden death. Most genome-wide association studies (GWAS) of QT were performed in European ancestral populations, leaving other groups uncharacterized. Herein we present the first QT GWAS of Hispanic/Latinos using data on 15,997 participants from four studies. Study-specific summary results of the association between 1000 Genomes Project (1000G) imputed SNPs and electrocardiographically measured QT were combined using fixed-effects meta-analysis. We identified 41 genome-wide significant SNPs that mapped to 13 previously identified QT loci. Conditional analyses distinguished six secondary signals at NOS1AP (n = 2), ATP1B1 (n = 2), SCN5A (n = 1), and KCNQ1 (n = 1). Comparison of linkage disequilibrium patterns between the 13 lead SNPs and six secondary signals with previously reported index SNPs in 1000G super populations suggested that the SCN5A and KCNE1 lead SNPs were potentially novel and population-specific. Finally, of the 42 suggestively associated loci, AJAP1 was suggestively associated with QT in a prior East Asian GWAS; in contrast BVES and CAP2 murine knockouts caused cardiac conduction defects. Our results indicate that whereas the same loci influence QT across populations, population-specific variation exists, motivating future trans-ethnic and ancestrally diverse QT GWAS.

Association of common genetic variants related to atrial fibrillation and the risk of ventricular fibrillation in the setting of first ST-elevation myocardial infarction

Background

Cohort studies have revealed an increased risk for ventricular fibrillation (VF) and sudden cardiac death (SCD) in patients with atrial fibrillation (AF). In this study, we hypothesized that single nucleotide polymorphisms (SNP) previously associated with AF may be associated with the risk of VF caused by first ST-segment elevation myocardial infarction (STEMI).

Methods

We investigated association of 24 AF-associated SNPs with VF in the prospectively assembled case–control study among first STEMI-patients of Danish ancestry.

Results

We included 257 cases (STEMI with VF) and 537 controls (STEMI without VF). The median age at index infarction was 60 years for the cases and 61 years for the controls (p = 0.100). Compared to the control group, the case group was more likely to be male (86% vs. 75%, p = 0.001), have a history of AF (7% vs. 2%, p = 0.006) or hypercholesterolemia (39% vs. 31%, p = 0.023), and a family history of sudden death (40% vs. 25%, p < 0.001). All 24 selected SNPs have previously been associated with AF. None of the 24 SNPs were associated with the risk of VF after adjustment for age and sex under additive genetic model of inheritance in the logistic regression model.

Conclusion

In this study, we found that the 24 AF-associated SNPs may not be involved in increasing the risk of VF. Larger VF cohorts and use of new next generation sequencing and epigenetic may in future identify additional AF and VF risk loci and improve our understanding of genetic pathways behind the two arrhythmias.

Targeted next-generation sequencing detects novel gene-phenotype associations and expands the mutational spectrum in cardiomyopathies

Cardiomyopathies are a heterogeneous group of primary diseases of the myocardium, including hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), and arrhythmogenic right ventricular cardiomyopathy (ARVC), with higher morbidity and mortality. These diseases are genetically diverse and associated with rare mutations in a large number of genes, many of which overlap among the phenotypes. To better investigate the genetic overlap between these three phenotypes and to identify new genotype–phenotype correlations, we designed a custom gene panel consisting of 115 genes known to be associated with cardiomyopathic phenotypes and channelopathies. A cohort of 38 unrelated patients, 16 affected by DCM, 14 by HCM and 8 by ARVC, was recruited for the study on the basis of more severe phenotypes and family history of cardiomyopathy and/or sudden death. We detected a total of 142 rare variants in 40 genes, and all patients were found to be carriers of at least one rare variant. Twenty-eight of the 142 rare variants were also predicted as potentially pathogenic variants and found in 26 patients. In 23 out of 38 patients, we found at least one novel potential gene–phenotype association. In particular, we detected three variants in OBSCN gene in ARVC patients, four variants in ANK2 gene and two variants in DLG1, TRPM4, and AKAP9 genes in DCM patients, two variants in PSEN2 gene and four variants in AKAP9 gene in HCM patients. Overall, our results confirmed that cardiomyopathic patients could carry multiple rare gene variants; in addition, our investigation of the genetic overlap among cardiomyopathies revealed new gene–phenotype associations. Furthermore, as our study confirms, data obtained using targeted next-generation sequencing could provide a remarkable contribution to the molecular diagnosis of cardiomyopathies, early identification of patients at risk for arrhythmia development, and better clinical management of cardiomyopathic patients.

Common lipid features of lethal ventricular tarchyarrhythmias (LVTAs) induced by myocardial infarction and myocardial ion channel diseases

Lethal ventricular tachyarrhythmia (LVTA) is the most prevalent electrophysiological underpinning of sudden cardiac death (SCD), a condition that occurs in response to multiple pathophysiological abnormalities. The aim of this study was to identify common lipid features of LVTA that were induced by distinct pathophysiological conditions, thereby facilitating the discovery of novel SCD therapeutic targets. Two rat LVTA-SCD models were established to mimic myocardial infarction (MI) and myocardial ion channel diseases. Myocardial and serum specimens were analyzed using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS)-based lipidomics. The lipid profiles of the myocardial and serum specimens were similar between the models. Eleven myocardial lipid classes were altered, including downregulations of: cardiolipin, ceramide, phosphatidylinositol, phosphatidylethanolamine, triacylglycerol, diacylglycerol, phosphatidylglycerol, lysophosphatidylethanolamine and phosphatidylserine, and upregulations of: lysophosphatidylcholine and phosphatidic acid. Serum concentrations of triacylglycerol, lysophosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol were also altered. Alterations of lipids in paired myocardia and sera were closely correlated. Cardiolipin 70:5, cardiolipin 74:9 and ceramide d34:2 were tested as potential biomarkers of LVTA. The results indicate that there are common LVTA lipid profiles induced by MI and myocardial ion channel diseases, potentially offering novel LVTA-SCD therapeutic targets.

An Autopsy Case of Sudden Unexpected Death of a Young Adult in a Hot Bath: Molecular Analysis Using Next-Generation DNA Sequencing

We report a case of sudden unexpected death of a young woman who was found in a bathtub of hot water. The autopsy concluded that all possible causes of sudden loss of consciousness, except cardiac origin, could be excluded. However, the heart did not show any obvious pathological changes. We used next-generation DNA sequencing (NGS) to examine 73 genes and detected 3 rare, potentially pathogenic variants with minor allele frequencies ⩽1.0%. The pathogenicity of these variants was evaluated using 8 in silico predictive algorithms, and SCN5A_p.Gly289Ser, CACNB2_p.Ser502Leu, and MYH11_p.Lys1573Glu were detected as possible pathogenic variants. Inherited heart disease is a likely cause of sudden unexpected deaths of young people in hot baths, even before the clinical manifestation of the disease. In the future, molecular analysis by NGS may help to predict young to early middle-aged people who could be at risk of sudden arrhythmogenic fatality in hot baths.

Fine mapping of QT interval regions in global populations refines previously identified QT interval loci and identifies signals unique to African and Hispanic descent populations

BACKGROUND

The electrocardiographically measured QT interval (QT) is heritable and its prolongation is an established risk factor for several cardiovascular diseases. Yet, most QT genetic studies have been performed in European ancestral populations, possibly reducing their global relevance.

OBJECTIVE

To leverage diversity and improve biological insight, we fine mapped 16 of the 35 previously identified QT loci (46%) in populations of African American (n = 12,410) and Hispanic/Latino (n = 14,837) ancestry.

METHODS

Racial/ethnic-specific multiple linear regression analyses adjusted for heart rate and clinical covariates were examined separately and in combination after inverse-variance weighted trans-ethnic meta-analysis.

RESULTS

The 16 fine-mapped QT loci included on the Illumina Metabochip represented 21 independent signals, of which 16 (76%) were significantly (P-value≤9.1×10-5) associated with QT. Through sequential conditional analysis we also identified three trans-ethnic novel SNPs at ATP1B1, SCN5A-SCN10A, and KCNQ1 and three Hispanic/Latino-specific novel SNPs at NOS1AP and SCN5A-SCN10A (two novel SNPs) with evidence of associations with QT independent of previous identified GWAS lead SNPs. Linkage disequilibrium patterns helped to narrow the region likely to contain the functional variants at several loci, including NOS1AP, USP50-TRPM7, and PRKCA, although intervals surrounding SLC35F1-PLN and CNOT1 remained broad in size (>100 kb). Finally, bioinformatics-based functional characterization suggested a regulatory function in cardiac tissues for the majority of independent signals that generalized and the novel SNPs.

CONCLUSION

Our findings suggest that a majority of identified SNPs implicate gene regulatory dysfunction in QT prolongation, that the same loci influence variation in QT across global populations, and that additional, novel, population-specific QT signals exist.

Ventricular arrhythmias in Rhodesian Ridgebacks with a family history of sudden death and results of a pedigree analysis for potential inheritance patterns

OBJECTIVE To evaluate a group of related Rhodesian Ridgebacks with a family history of sudden death for the presence of arrhythmia and to identify possible patterns of disease inheritance among these dogs. DESIGN Prospective case series and pedigree investigation. ANIMALS 25 Rhodesian Ridgebacks with shared bloodlines. PROCEDURES Pedigrees of 4 young dogs (1 female and 3 males; age, 7 to 12 months) that died suddenly were evaluated, and owners of closely related dogs were asked to participate in the study. Dogs were evaluated by 24-hour Holter monitoring, standard ECG, echocardiography, or some combination of these to assess cardiac status. Necropsy reports, if available, were reviewed. RESULTS 31 close relatives of the 4 deceased dogs were identified. Of 21 dogs available for examination, 8 (2 males and 6 females) had ventricular tachyarrhythmias (90 to 8,700 ventricular premature complexes [VPCs]/24 h). No dogs had clinical signs of cardiac disease reported. Echocardiographic or necropsy evaluation for 7 of 12 dogs deemed affected (ie, with frequent or complex VPCs or sudden death) did not identify structural lesions. Five of 6 screened parents of affected dogs had 0 to 5 VPCs/24 h (all singlets), consistent with a normal reading. Pedigree evaluation suggested an autosomal recessive pattern of inheritance, but autosomal dominant inheritance with incomplete penetrance could not be ruled out. CONCLUSIONS AND CLINICAL RELEVANCE Holter monitoring of Rhodesian Ridgebacks with a family history of an arrhythmia or sudden death is recommended for early diagnosis of disease. An autosomal recessive pattern of inheritance in the studied dogs was likely, and inbreeding should be strongly discouraged.

A Common Variant in SCN5A and the Risk of Ventricular Fibrillation Caused by First ST-Segment Elevation Myocardial Infarction

BACKGROUND

Several common genetic variants have been associated with either ventricular fibrillation (VF) or sudden cardiac death (SCD). However, replication efforts have been limited. Therefore, we aimed to analyze whether such variants may contribute to VF caused by first ST-elevation myocardial infarction (STEMI).

METHODS

We analyzed 27 single nucleotide polymorphisms (SNP) previously associated with SCD/VF in other cohorts, and examined whether these SNPs were associated with VF caused by first STEMI in the GEnetic causes of Ventricular Arrhythmias in patients with first ST-elevation Myocardial Infarction (GEVAMI) study on ethnical Danes. The GEVAMI study is a prospective case-control study involving 257 cases (STEMI with VF) and 537 controls (STEMI without VF).

RESULTS

Of the 27 candidate SNPs, one SNP (rs11720524) located in intron 1 of SCN5A which was previously associated with SCD was significantly associated with VF caused by first STEMI. The major C-allele of rs11720524 was present in 64% of the cases and the C/C genotype was significantly associated with VF with an odds ratio (OR) of 1.87 (95% CI: 1.12-3.12; P = 0.017). After controlling for clinical differences between cases and controls such as age, sex, family history of sudden death, alcohol consumption, previous atrial fibrillation, statin use, angina, culprit artery, and thrombolysis in myocardial infarction (TIMI) flow, the C/C genotype of rs11720524 was still significantly associated with VF with an OR of 1.9 (95% CI: 1.05-3.43; P = 0.032). Marginal associations with VF were also found for rs9388451 in HEY2 gene. The CC genotype showed an insignificant risk for VF with OR = 1.50 (95% CI: 0.96-2.40; P = 0.070).

CONCLUSION

One common intronic variant in SCN5A suggested an association with VF caused by first STEMI. Further studies into the functional abnormalities associated with the noncoding variant in SCN5A may lead to important insights into predisposition to VF during STEMI.

Complex Genetics of Cardiovascular Traits in Mice: F2-Mapping of QTLs and Their Underlying Genes

In this chapter, we will use the example of the identification of Tnni3k as a modulator of cardiac conduction to introduce you to the use of a murine F2-generation intercross as a powerful method for the identification of novel genes relevant for cardiovascular traits. Murine F2-progeny is a genetically diverse panel of mice with differences in phenotype manifestations, e.g. cardiovascular traits such as cardiomyopathy and ECG parameters. This chapter discusses the best strategies for using F2-mice for genetic mapping. Moreover, we provide an example of the feasibility of identification of new genes modulating cardiac function utilizing the technique of mapping quantitative trait loci (QTLs) and a systems genetics integration of available genetic, gene expression, and phenotypic data.

An insertion/deletion polymorphism within 3'UTR of RYR2 modulates sudden unexplained death risk in Chinese populations

Sudden unexplained death (SUD) constitutes a part of the overall sudden death that can not be underestimated. Over the last years, genetic testing on SUD has revealed that inherited channelopathies might play important roles in the pathophysiology of this disease. Ryanodine receptor type-2 (RYR2) is a kind of ion channel extensively distributed in the sarcoplasmic reticulum (SR) of myocardium. Studies on RYR2 have suggested that either dysfunction or abnormal expression of it could lead to arrhythmia, which may cause cardiac arrest. In this study, we conducted a case-control study to evaluate the association of a 4-base pair (4-bp) Indel polymorphism (rs10692285) in the 3'UTR of RYR2 with the risk of SUD and sudden cardiac death induced by coronary heart disease (SCD-AS) in a Chinese population. Logistic regression analysis showed that the insertion allele of rs10692285 had significantly increased the risk of SUD [OR=2.03; 95% confidence interval (CI)=1.08-3.77; P=0.0161; statistical power=0.743]. No relevance was observed between rs10692285 and SCD-AS. Further genotype-phenotype association analysis suggested that the expression level of RYR2 in human myocardium tissues with the insertion allele was higher than that with the deletion allele at both mRNA and protein levels. Dual-Luciferase activity assay system was used to detect the effect of rs10692285 on the transcription activity of RYR2. As expected, the result indicated that the transcription activity of RYR2 with the ins/ins genotype was higher than that with the del/del genotype. Finally, in-silico prediction revealed that different alleles of rs10692285 could alter the local structure of RYR2 mRNA and microRNA (miRNA) binding. In summary, our findings provided evidence that rs10692285 might contribute to SUD susceptibility through affecting the expression of RYR2, which suggest that abnormal ion channel activity is very likely to be the underlying mechanism of SUD, but not for SCD-AS. Thus, rs10692285 may become a potential marker for molecular diagnosis and genetic counseling of SUD.

Enhancing Literacy in Cardiovascular Genetics: A Scientific Statement From the American Heart Association

Advances in genomics are enhancing our understanding of the genetic basis of cardiovascular diseases, both congenital and acquired, and stroke. These advances include finding genes that cause or increase the risk for childhood and adult-onset diseases, finding genes that influence how patients respond to medications, and the development of genetics-guided therapies for diseases. However, the ability of cardiovascular and stroke clinicians to fully understand and apply this knowledge to the care of their patients has lagged. This statement addresses what the specialist caring for patients with cardiovascular diseases and stroke should know about genetics; how they can gain this knowledge; how they can keep up-to-date with advances in genetics, genomics, and pharmacogenetics; and how they can apply this knowledge to improve the care of patients and families with cardiovascular diseases and stroke.

Non-targeted metabolomics identified a common metabolic signature of lethal ventricular tachyarrhythmia (LVTA) in two rat models

Lethal ventricular tachyarrhythmia (LVTA) is the predominant underlying mechanism of sudden cardiac death (SCD). The aim of this study is to characterize the metabolic features of myocardia following LVTA, and identify potential biomarkers to diagnose LVTA. We developed two LVTA rat models induced by aconitine injection or coronary artery ligation, which represent cardiac ion channel disease-related and cardiac ischemia-related SCD, respectively. The myocardial metabolic profile was investigated by gas chromatography-mass spectrometry and proton nuclear magnetic resonance-based metabolomics. Twenty-three aconitine-injected and 14 coronary artery ligation-treated rats developed LVTA SCD. A total of 38 differential metabolites of myocardia were identified in aconitine-induced LVTA rats, of which 31 metabolites showed a similar change in coronary artery ligation-related LVTA rats. Fatty acids (stearic, palmitic, linoleic, elaidic, and myristic) and branched-chain amino acids (valine, leucine, and isoleucine) were the most down-regulated metabolites. Furthermore, elevated ADP, phosphate, lactate, glutamate, aspartate, threonine, choline and arginine were also observed. Major pathways regarding these dysregulated metabolites post LVTA are energy excessive consumption and deficit, ionic imbalance, oxidative stress, cardiac cytotoxicity and membrane injury. Valine, stearic acid and leucine collectively enable a precision of 92.9% to distinguish LVTA from its control, and are correlated with several arrhythmia indices. Our results uncovered a common metabolic feature of LVTA in myocardia in two rat models, which represent cardiac ion channel disease and cardiac ischemia, respectively. l-Valine, l-leucine and stearic acid jointly confer good potential for distinguishing LVTA, which might be potential biomarkers of LVTA-related SCD.

A mutation in the atrial-specific myosin light chain gene (MYL4) causes familial atrial fibrillation

Atrial fibrillation (AF), the most common arrhythmia, is a growing epidemic with substantial morbidity and economic burden. Mechanisms underlying vulnerability to AF remain poorly understood, which contributes to the current lack of highly effective therapies. Recognizing mechanistic subtypes of AF may guide an individualized approach to patient management. Here, we describe a family with a previously unreported syndrome characterized by early-onset AF (age <35 years), conduction disease and signs of a primary atrial myopathy. Phenotypic penetrance was complete in all mutation carriers, although complete disease expressivity appears to be age-dependent. We show that this syndrome is caused by a novel, heterozygous p.Glu11Lys mutation in the atrial-specific myosin light chain gene MYL4. In zebrafish, mutant MYL4 leads to disruption of sarcomeric structure, atrial enlargement and electrical abnormalities associated with human AF. These findings describe the cause of a rare subtype of AF due to a primary, atrial-specific sarcomeric defect.

Postmortem genetic analysis of sudden unexplained death syndrome under 50 years of age: A next-generation sequencing study

BACKGROUND

Recent studies on the genetic analysis of victims of sudden unexplained death syndrome (SUDS) have shown diagnostic potential. Previously, such analyses mainly targeted the major channelopathy-associated genes.

OBJECTIVE

The purpose of this study was to evaluate the utility of next-generation sequencing (NGS) in the postmortem diagnosis of SUDS.

METHODS

Our data are derived from 25 cases of SUDS (21 men and 4 women; age 19-50 years). A total of 70 genes were examined by NGS, and the pathogenicity of any detected rare variants with minor allele frequencies of <0.5% was evaluated using a widely used database and eight in silico algorithms.

RESULTS

Five known and 15 potentially pathogenic variants with a high in silico score were identified in 14 cases. In all, 6 channelopathy-related variants were identified in 5 cases, including 2 cases with history of arrhythmia; 11 cases had cardiomyopathy- or cardiac transcription factor-related variants. Three cases with desmosomal gene- or other cardiomyopathy-related variants showed possibly related pathologic changes. Three cases with RYR2 or TBX5 variants showed possible pathogenic fibrosis of the cardiac conduction system. Only 12 variants showed moderate or strong possible pathogenicity in SUDS cases compared with qualifying controls.

CONCLUSION

Hereditary heart diseases other than channelopathy may also be a significant cause of SUDS, even if clinical and pathologic findings do not show advanced disease. A combination of gene analysis using NGS and some predictive methods for detecting variants and careful pathologic evaluation may provide a reliable diagnosis of hereditary heart disease for potential SUDS cases.

Sudden Cardiac Arrest and Rare Genetic Variants in the Community

BACKGROUND

Sudden cardiac arrest (SCA) ranks among the most common causes of death worldwide. Because SCA is most often lethal, yet mostly occurs in individuals without previously known cardiac disease, the identification of patients at risk for SCA could save many lives. In unselected SCA victims from the community, common genetic variants (which are not disease-causing per se, but may increase susceptibility to ventricular fibrillation) are found to be associated with increased SCA risk. However, whether rare genetic variants contribute to SCA risk in the community is largely unexplored.

METHODS AND RESULTS

We here investigated the involvement of rare genetic variants in SCA risk at the population level by studying the prevalence of 6 founder genetic variants present in the Dutch population (PLN-p.Arg14del, MYBPC3-p.Trp792fsX17, MYBPC3-p.Arg943X, MYBPC3-p.Pro955fsX95, PKP2-p.Arg79X, and the Chr7q36 idiopathic ventricular fibrillation risk haplotype) in a cohort of 1440 unselected Dutch SCA victims included in the Amsterdam Resuscitation Study (ARREST). The six studied founder mutations were found to be more prevalent (1.1%) in the ARREST SCA cohort compared with an ethnically and geographically matched set of controls (0.4%, n=1379; P<0.05) or a set of Dutch individuals drawn from the Genome of the Netherlands (GoNL) study (0%, n=500; P<0.02).

CONCLUSIONS

This finding provides proof-of-concept for the notion that rare genetic variants contribute to some extent to SCA risk in the community.

Arrhythmogenic effects of mutated L-type Ca 2+-channels on an optogenetically paced muscular pump in Caenorhabditis elegans

Cardiac arrhythmias are often associated with mutations in ion channels or other proteins. To enable drug development for distinct arrhythmias, model systems are required that allow implementing patient-specific mutations. We assessed a muscular pump in Caenorhabditis elegans. The pharynx utilizes homologues of most of the ion channels, pumps and transporters defining human cardiac physiology. To yield precise rhythmicity, we optically paced the pharynx using channelrhodopsin-2. We assessed pharynx pumping by extracellular recordings (electropharyngeograms—EPGs), and by a novel video-microscopy based method we developed, which allows analyzing multiple animals simultaneously. Mutations in the L-type VGCC (voltage-gated Ca²⁺-channel) EGL-19 caused prolonged pump duration, as found for analogous mutations in the Ca_v1.2 channel, associated with long QT syndrome. egl-19 mutations affected ability to pump at high frequency and induced arrhythmicity. The pharyngeal neurons did not influence these effects. We tested whether drugs could ameliorate arrhythmia in the optogenetically paced pharynx. The dihydropyridine analog Nemadipine A prolonged pump duration in wild type, and reduced or prolonged pump duration of distinct egl-19 alleles, thus indicating allele-specific effects. In sum, our model may allow screening of drug candidates affecting specific VGCCs mutations, and permit to better understand the effects of distinct mutations on a macroscopic level.

The cardiac sodium channel gene SCN5A and its gene product NaV1.5: Role in physiology and pathophysiology

The gene SCN5A encodes the main cardiac sodium channel NaV1.5. This channel predominates the cardiac sodium current, INa, which underlies the fast upstroke of the cardiac action potential. As such, it plays a crucial role in cardiac electrophysiology. Over the last 60years a tremendous amount of knowledge regarding its function at the electrophysiological and molecular level has been acquired. Furthermore, genetic studies have shown that mutations in SCN5A are associated with multiple cardiac diseases (e.g. Brugada syndrome, Long QT syndrome, conduction disease and cardiomyopathy), while genetic variation in the general population has been associated with differences in cardiac conduction and risk of arrhythmia through genome wide association studies. In this review we aim to give an overview of the current knowledge (and the gaps therein) on SCN5A and NaV1.5.

Genetics of sudden cardiac death

Sudden cardiac death occurs in a broad spectrum of cardiac pathologies and is an important cause of mortality in the general population. Genetic studies conducted during the past 20 years have markedly illuminated the genetic basis of the inherited cardiac disorders associated with sudden cardiac death. Here, we review the genetic basis of sudden cardiac death with a focus on the current knowledge on the genetics of the primary electric disorders caused primarily by mutations in genes encoding ion channels, and the cardiomyopathies, which have been attributed to mutations in genes encoding a broader category of proteins, including those of the sarcomere, the cytoskeleton, and desmosomes. We discuss the challenges currently faced in unraveling genetic factors that predispose to sudden cardiac death in the setting of sequela of coronary artery disease and present the genome-wide association studies conducted in recent years on electrocardiographic parameters, highlighting their potential in uncovering new biological insights into cardiac electric function.

Genetics of congenital heart disease: the contribution of the noncoding regulatory genome

Congenital heart disease (CHD) is the most common type of birth defect. The advent of corrective cardiac surgery and the increase in knowledge concerning the longitudinal care of patients with CHD has led to a spectacular increase in life expectancy. Therefore, >90% of children with CHD, who survive the first year of life, will live into adulthood. The etiology of CHD is complex and is associated with both environmental and genetic causes. CHD is a genetically heterogeneous disease that is associated with long-recognized chromosomal abnormalities, as well as with mutation in numerous (developmental) genes. Nevertheless, the genetic factors underlying CHD have remained largely elusive, and it is important to realize that in the far majority of CHD patients no causal mutation or chromosomal abnormality is identified. However, new insights (alternative inheritance paradigms) and technology (next-generation sequencing) have become available that can greatly advance our understanding of the genetic factors that contribute to CHD; these will be discussed in this review. Moreover, we will focus on the discovery of regulatory regions of key (heart) developmental genes and the occurrence of variations and mutations within, in the setting of CHD.

Massive parallel sequencing applied to the molecular autopsy in sudden cardiac death in the young

Sudden cardiac death in the young is a very traumatic event that occurs often in apparently healthy individuals without an explainable cause of death after a comprehensive medico-legal investigation. Knowledge about the pathologies with a risk of sudden death is increasingly showing a greater underlying genetic heterogeneity, which provides one of the main handicaps for molecular autopsy. On the other hand the enormous technological advances in sequencing technologies, allow us to analyse as many genes as we want at a cost increasingly reduced. The sum of these two factors (increased knowledge of genetics and available technologies) allow us to make an individualized study of the causes of sudden cardiac death in young adults, through massive sequencing of all potential genes involved in the process. We define this approach as massive genomic autopsy, and with this review we will try to explain the possible scenarios and methods available for its implementation.

Arrhythmogenic cardiomyopathy in a patient with a rare loss-of-function KCNQ1 mutation

BACKGROUND

Ventricular tachycardia (VT) is a common manifestation of advanced cardiomyopathies. In a subset of patients with dilated cardiomyopathy, VT is the initial and the cardinal manifestation of the disease. The molecular genetic basis of this subset of dilated cardiomyopathy is largely unknown.

METHODS AND RESULTS

We identified 10 patients with dilated cardiomyopathy who presented with VT and sequenced 14 common causal genes for cardiomyopathies and arrhythmias. Functional studies included cellular patch clamp, confocal microscopy, and immunoblotting. We identified nonsynonymous variants in 4 patients, including a rare missense p.R397Q mutation in the KCNQ1 gene in a 60-year-old man who presented with incessant VT and had mild cardiac dysfunction. The p.R397Q mutation was absent in an ethnically matched control group, affected a conserved amino acid, and was predicted by multiple algorithms to be pathogenic. Co-expression of the mutant KCNQ1 with its partner unit KCNE1 was associated with reduced tail current density of slowly activating delayed rectifier K(+) current (IKs). The mutation reduced membrane localization of the protein.

CONCLUSIONS

Dilated cardiomyopathy with an initial presentation of VT may be a forme fruste of arrhythmogenic cardiomyopathy caused by mutations in genes encoding the ion channels. The findings implicate KCNQ1 as a possible causal gene for arrhythmogenic cardiomyopathy.

Incidence and risk factors of ventricular fibrillation before primary angioplasty in patients with first ST-elevation myocardial infarction: a nationwide study in Denmark

BACKGROUND

We aimed to investigate the incidence and risk factors for ventricular fibrillation (VF) before primary percutaneous coronary intervention (PPCI) among patients with ST-segment elevation myocardial infarction (STEMI) in a prospective nationwide setting.

METHODS AND RESULTS

In this case-control study, patients presenting within the first 12 hours of first STEMI who survived to undergo angiography and subsequent PPCI were enrolled. Over 2 years, 219 cases presenting with VF before PPCI and 441 controls without preceding VF were enrolled. Of the 219 case patients, 182 (83%) had STEMI with out-of-hospital cardiac arrest due to VF, and 37 (17%) had cardiac arrest upon arrival to the emergency room. Medical history was collected by standardized interviews and by linkage to national electronic health records. The incidence of VF before PPCI among STEMI patients was 11.6%. Multivariable logistic regression analysis identified novel associations between atrial fibrillation and alcohol consumption with VF. Patients with a history of atrial fibrillation had a 2.80-fold odds of experiencing VF before PPCI (95% CI 1.10 to 7.30). Compared with nondrinkers, patients who consumed 1 to 7 units, 8 to 14 units, or >15 units of alcohol per week had an odds ratio (OR) of 1.30 (95% CI, 0.80 to 2.20), 2.30 (95% CI, 1.20 to 4.20), or 3.30 (95% CI, 1.80 to 5.90), respectively, for VF. Previously reported associations for preinfarction angina (OR 0.46; 95% CI 0.32 to 0.67), age of <60 years (OR 1.75; 95% CI 1.20 to 2.60), anterior infarction (OR 2.10; 95% CI 1.40 to 3.00), preprocedural thrombolysis in myocardial infarction flow grade 0 (OR 1.65; 95% CI 1.14 to 2.40), and family history of sudden death (OR 1.60; 95% CI 1.10 to 2.40) were all associated with VF.

CONCLUSION

Several easily assessed risk factors were associated with VF occurring out-of-hospital or on arrival at the emergency room before PPCI in STEMI patients, thus providing potential avenues for investigation regarding improved identification and prevention of life-threatening ventricular arrhythmias.