A balanced translocation disrupting SCN5A in a family with Brugada syndrome and sudden cardiac death

BACKGROUND

Brugada syndrome (BrS) is a primary arrhythmia syndrome affecting 1 in 2000 of the general population. Genetic testing identifies pathogenic variants in the sodium voltage-gated channel α-subunit 5 gene (SCN5A) in up to 25% of familial BrS. Balanced translocations, which involve the exchange of the ends of 2 different chromosomes, are found in approximately 1 in 500 people. They usually are benign and only rarely are reported to cause arrhythmogenic disorders.

OBJECTIVE

The purpose of this study was to identify the genetic mechanism underlying a family with BrS, sick sinus syndrome, cardiac hypertrophy, sudden cardiac death, and multiple miscarriages.

METHODS

We clinically evaluated family members with an electrocardiogram, 2-dimensional echocardiogram, and provocation testing with ajmaline challenge. Cytogenetic testing included karyotype and fluorescent in situ hybridization (FISH) analysis. We performed gene panel, exome, and genome sequencing analysis.

RESULTS

Sequencing of 128 cardiac genes and exome sequencing of a family with BrS, sick sinus syndrome, cardiac hypertrophy, sudden cardiac death, and multiple miscarriages did not reveal a pathogenic variant. Karyotype and FISH analysis identified a balanced translocation breaking the SCN5A gene on chromosome 3 and the multiple chromosome maintenance 10 gene (MCM10) on chromosome 10 t(3;10)(p22.2;p13). We characterized both translocation breakpoint junctions using genome sequencing and found no regions of sequence homology.

CONCLUSION

A balanced translocation breaking SCN5A is a novel mechanism underlying disease in a family with BrS, sick sinus syndrome, cardiac hypertrophy, and sudden cardiac death. Genome sequencing can identify rare chromosomal aberrations causing inherited diseases that may otherwise be missed using gene panel and exome sequencing-based approaches.

Lack of genotype-phenotype correlation in Brugada Syndrome and Sudden Arrhythmic Death Syndrome families with reported pathogenic SCN1B variants

BACKGROUND

There is limited evidence that Brugada Syndrome (BrS) is due to SCN1B variants (BrS5). This gene may be inappropriately included in routine genetic testing panels for BrS or Sudden Arrhythmic Death Syndrome (SADS).

OBJECTIVE

We sought to characterize the genotype-phenotype correlation in families who had BrS and SADS with reportedly pathogenic SCN1B variants and to review their pathogenicity.

METHODS

Families with BrS and SADS were assessed from 6 inherited arrhythmia centers worldwide, and a comprehensive literature review was performed. Clinical characteristics including relevant history, electrocardiographic parameters and drug provocation testing results were studied. SCN1B genetic testing results were reclassified using American College of Medical Genetics criteria.

RESULTS

A total of 23 SCN1B genotype-positive individuals were identified from 8 families. Four probands (17%) experienced ventricular fibrillation or sudden cardiac death at the time of presentation. All family members were free from syncope or ventricular arrhythmias. Only 2 of 23 genotype-positive individuals (9%) demonstrated a spontaneous BrS electrocardiographic pattern. Drug challenge testing for BrS in 87% (13 of 15) was negative. There was no difference in PR interval (161 ± 7 ms vs 165 ± 9 ms; P = .83), QRS duration (101 ± 6 ms vs 89 ± 5 ms; P = .35), or corrected QT interval (414 ± 35 ms vs 405 ± 8 ms; P = .7) between genotype-positive and genotype-negative family members. The overall frequency of previously implicated SCN1B variants in the Genome Aggregation Database browser is 0.004%, exceeding the estimated prevalence of BrS owing to SCN1B (0.0005%), including 15 of 23 individuals (65%) who had the p.Trp179X variant.

CONCLUSION

The lack of genotype-phenotype concordance among families, combined with the high frequency of previously reported mutations in the Genome Aggregation Database browser, suggests that SCN1B is not a monogenic cause of BrS or SADS.

Diagnosis of Arrhythmogenic Right Ventricular Cardiomyopathy: Progress and Pitfalls

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiomyopathy that predominantly affects the right ventricle. With a prevalence in the range of 1:5000 to 1:2000 persons, ARVC is one of the leading causes of sudden cardiac death in young people and in athletes. Although early detection and treatment is important, the diagnosis of ARVC remains challenging. There is no single pathognomonic diagnostic finding in ARVC; rather, current international task force criteria specify diagnostic major and minor criteria in six categories: right ventricular imaging (including echocardiography and cardiac magnetic resonance imaging (MRI)), histology, repolarisation abnormalities, depolarisation and conduction abnormalities, arrhythmias and family history (including genetic testing). Combining findings from differing diagnostic modalities can establish a "definite", "borderline" or "possible" diagnosis of ARVC. However, there are limitations inherent in the current task force criteria, including the lack of specificity for ARVC; future iterations may be improved, for example, by enhanced imaging protocols able to detect subtle changes in the structure and function of the right ventricle, incorporation of electro-anatomical data, response to adrenergic challenge, and validated criteria for interpreting genetic variants.

Reversal Agents in the Era of NOACs

The incidence and prevalence of atrial fibrillation (AF) is expected to more than double between 2010 and 2030. Accordingly, the use of non-vitamin K oral anticoagulant (NOAC) agents for thromboembolic stroke prevention is anticipated to increase. The development of effective and safe antidotes is needed to address the unmet need for rapid anticoagulation reversal. The immediate role for these novel antidotes is for reversal of NOAC activity in life threatening bleeding and urgent surgical intervention. In addition, reversal agents may play an important role in simplifying bridging protocols in the peri-procedural period for catheter ablation of AF and elective surgery. Currently, novel reversal agents are either decoy drug receptors or small molecule non-specific anticoagulant activity inhibitors. These agents are at various stages of FDA investigation and approval, with emerging prospective data for safety and efficacy. The purpose of this review is to outline the currently developed NOAC molecular antagonists, their potential clinical roles and future directions.

Feasibility and cost-effectiveness of stroke prevention through community screening for atrial fibrillation using iPhone ECG in pharmacies

Atrial fibrillation (AF) causes a third of all strokes, but often goes undetected before stroke. Identification of unknown AF in the community and subsequent anti-thrombotic treatment could reduce stroke burden. We investigated community screening for unknown AF using an iPhone electrocardiogram (iECG) in pharmacies, and determined the cost-effectiveness of this strategy. Pharmacists performed pulse palpation and iECG recordings, with cardiologist iECG over-reading. General practitioner review/12-lead ECG was facilitated for suspected new AF. An automated AF algorithm was retrospectively applied to collected iECGs. Cost-effectiveness analysis incorporated costs of iECG screening, and treatment/outcome data from a United Kingdom cohort of 5,555 patients with incidentally detected asymptomatic AF. A total of 1,000 pharmacy customers aged ≥65 years (mean 76 ± 7 years; 44% male) were screened. Newly identified AF was found in 1.5% (95% CI, 0.8–2.5%); mean age 79 ± 6 years; all had CHA2DS2-VASc score ≥2. AF prevalence was 6.7% (67/1,000). The automated iECG algorithm showed 98.5% (CI, 92–100%) sensitivity for AF detection and 91.4% (CI, 89–93%) specificity. The incremental cost-effectiveness ratio of extending iECG screening into the community, based on 55% warfarin prescription adherence, would be $AUD5,988 (€3,142; $USD4,066) per Quality Adjusted Life Year gained and $AUD30,481 (€15,993; $USD20,695) for preventing one stroke. Sensitivity analysis indicated cost-effectiveness improved with increased treatment adherence. Screening with iECG in pharmacies with an automated algorithm is both feasible and cost-effective. The high and largely preventable stroke/thromboembolism risk of those with newly identified AF highlights the likely benefits of community AF screening. Guideline recommendation of community iECG AF screening should be considered.

Previous Presentation: This study was presented in part as an oral presentation at the Cardiac Society of Australia and New Zealand Conference; 9 August 2013; Sydney, Australia, abstract published in Heart Lung Circulation 2013;22:S223.

Trial registration: Australian New Zealand clinical trials registry: ACTRN12612000406808.

Contemporary Review of Left Bundle Branch Block in the Failing Heart - Pathogenesis, Prognosis, and Therapy

Cardiac resynchronisation therapy (CRT) is a cornerstone in the contemporary management of heart failure. The most effective way of predicting response to this therapy remains electrocardiographic (ECG) criteria of electromechanical dyssynchrony. The left bundle branch block (LBBB) pattern is currently the most robust ECG criterion in predicting improvement in symptoms and reduction in mortality. However, recent studies using three-dimensional (3D) mapping and cardiac magnetic resonance imaging (CMR) have demonstrated heterogeneous left ventricular activation patterns in patients with LBBB. This has led to intense debate on the activation pattern of "true LBBB" and resulted in the proposal of stricter criteria for defining LBBB. This review will focus on the definitions and implications of LBBB in the CRT era. At a minimum, the use of stricter ECG criteria appears warranted, and adjunctive pre-implant imaging or mapping may further identify patient-specific electrophysiological patterns that determine response to CRT.

Periprocedural Management of Novel Oral Anticoagulants During Atrial Fibrillation Ablation: Controversies and Review of the Current Evidence

Oral anticoagulation (OAC) has been the cornerstone for the prevention of thromboembolic complications in patients with atrial fibrillation (AF) at significant risk of stroke. Catheter ablation is an established efficacious technique for the treatment of AF. Ameliorating the risk of stroke or transient ischaemic attack (TIA) in patients with AF undergoing ablation requires meticulous planning of pharmacotherapy. The advent of non-vitamin K oral anticoagulants (NOACs) has broadened the therapeutic scope, representing a viable alternative to traditional vitamin K antagonists (VKA) in non-valvular AF. Potential advantages of NOACs include greater pharmacokinetic predictability, at least comparable efficacy as compared to VKA and a superior haemorrhagic complication profile. However, robust evidence for the safety and efficacy of periprocedural NOAC use for AF ablation remains uncertain with a non-uniform clinical approach between and within institutions. The following review will summarise the current and emerging evidence on periprocedural management of NOACs in patients undergoing catheter ablation of AF. An overview of NOAC pharmacology will provide a foundation for the review of reversal agents in the context of catheter ablation of AF. The purpose of the review is to outline key studies and identify key areas for further critical research with the ultimate aim of developing evidence-based guidelines for optimal care.

A novel heterozygous mutation in cardiac calsequestrin causes autosomal dominant catecholaminergic polymorphic ventricular tachycardia

BACKGROUND

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a lethal inherited arrhythmia syndrome characterized by adrenergically stimulated ventricular tachycardia. Mutations in the cardiac ryanodine receptor gene (RYR2) cause an autosomal dominant form of CPVT, while mutations in the cardiac calsequestrin 2 gene (CASQ2) cause an autosomal recessive form.

OBJECTIVE

The aim of this study was to clinically and genetically evaluate a large family with severe autosomal dominant CPVT.

METHODS

Clinical evaluation of family members was performed, including detailed history, physical examination, electrocardiogram, exercise stress test, and autopsy review of decedents. We performed genome-wide linkage analysis in 12 family members and exome sequencing in 2 affected family members. In silico models of mouse and rabbit myocyte electrophysiology were used to predict potential disease mechanisms.

RESULTS

Severe CPVT with dominant inheritance in 6 members was diagnosed in a large family with 2 sudden deaths, 2 resuscitated cardiac arrests, and multiple appropriate implantable cardioverter-defibrillator shocks. A comprehensive analysis of cardiac arrhythmia genes did not reveal a pathogenic variant. Exome sequencing identified a novel heterozygous missense variant in CASQ2 (Lys180Arg) affecting a highly conserved residue, which cosegregated with disease and was absent in unaffected family members. Genome-wide linkage analysis confirmed a single linkage peak at the CASQ2 locus (logarithm of odds ratio score 3.01; θ = 0). Computer simulations predicted that haploinsufficiency was unlikely to cause the severe CPVT phenotype and suggested a dominant negative mechanism.

CONCLUSION

We show for the first time that a variant in CASQ2 causes autosomal dominant CPVT. Genetic testing in dominant CPVT should include screening for heterozygous CASQ2 variants.

Systematic Review of Defibrillation Threshold Testing at De Novo Implantation

Background—

Recent results from the largest multicenter randomized trial (Shockless IMPLant Evaluation [SIMPLE]) on defibrillation threshold (DFT) testing suggest that while shock testing seems safe, it does not reduce the risk of failed shocks or prolong survival. A contemporary systematic review of DFT versus no-DFT testing at the time of implantable cardioverter–defibrillator implantation was performed to evaluate the current evidence and to assess the impact of the SIMPLE study.

Methods and Results—

Electronic searches were performed using 6 databases from their inception to March 2014. Relevant studies investigating implant DFT were identified. Data were extracted and analyzed according to predefined clinical end points. Predefined outcomes for interrogation were all-cause mortality, composite end point of implantable cardioverter–defibrillator efficacy (arrhythmic deaths and ineffective shocks), and composite safety end point (the sum of complications recorded at 30 days). Meta-analysis was performed including 13 studies and 9740 patients. No significant differences between DFT versus no-DFT cohorts were found in terms of all-cause mortality (risk ratio, 0.90; 95% confidence interval, 0.71–1.15; P =0.41), composite efficacy outcome (risk ratio, 1.24; 95% confidence interval, 0.65–3.37; P =0.51), and 30-day postimplant complications (risk ratio, 1.18; 95% confidence interval, 0.87–1.60; P =0.29). No significant difference was found in the trends observed when the results of the SIMPLE study were excluded or included.

Conclusions—

This systematic review of contemporary data suggests a modest average effect of DFT, if any, in terms of mortality, shock efficacy, or safety. Therefore, DFT testing should no longer be compulsory during de novo implantation. However, DFT testing may still be clinically relevant in specific patient populations.