Value of the sodium-channel blocker challenge in Brugada syndrome

Systematic analysis of SCN5A variants associated with inherited cardiac diseases

BACKGROUND

SCN5A variants are associated with a spectrum of cardiac electrical disorders with clear phenotypes. However, they may also be associated with complex phenotypic traits like overlap syndromes or pleiotropy, which have not been systematically described. In addition, the involvement of SCN5A in dilated cardiomyopathies (DCMs) remains controversial.

OBJECTIVE

We aimed to evaluate the different phenotypes associated with pathogenic (P)/likely pathogenic (LP) SCN5A variants and to determine the prevalence of pleiotropy in a large multicentric cohort of P/LP SCN5A variant carriers.

METHODS

The DNA of 13,510 consecutive probands (9960 with cardiomyopathies) was sequenced with a custom panel of genes. Individuals carrying a heterozygous single P/LP SCN5A variant were selected and phenotyped.

RESULTS

The study included 170 P/LP variants found in 495 patients. Of them, 119 (70%) were exclusively associated with a single well-established phenotype: 91 with Brugada syndrome, 15 with type 3 long QT syndrome, 6 with progressive cardiac conduction disease, 4 with multifocal ectopic Purkinje-related premature contractions, and 3 with sick sinus syndrome. Thirty-two variants (19%) were associated with overlap syndromes or pleiotropy. The 19 remaining variants (11%) were associated with atypical or unclear phenotypes. Of those, 8 were carried by 8 patients presenting with DCM with a debatable causative genotype/phenotype link.

CONCLUSION

Most P/LP SCN5A variants were found in patients with primary electrical disorders, mainly Brugada syndrome. Nearly 20% were associated with overlap syndromes or pleiotropy, underscoring the need for comprehensive phenotypic evaluation. The concept of SCN5A variants causing DCM is extremely rare (8/9960) if not questionable.

Clinical Management of Brugada Syndrome: Commentary From the Experts

Although there is consensus on the management of patients with Brugada Syndrome with high risk for sudden cardiac arrest, asymptomatic or intermediate-risk patients present clinical management challenges. This document explores the management opinions of experts throughout the world for patients with Brugada Syndrome who do not fit guideline recommendations. Four real-world clinical scenarios were presented with commentary from small expert groups for each case. All authors voted on case-specific questions to evaluate the level of consensus among the entire group in nuanced diagnostic and management decisions relevant to each case. Points of agreement, points of controversy, and gaps in knowledge are highlighted.

Management of Inherited Arrhythmia Syndromes: a HiRO Consensus Handbook on Process of Care

Inherited arrhythmia syndromes are rare genetic conditions that predispose seemingly healthy individuals to sudden cardiac arrest and death. The Hearts in Rhythm Organization is a multidisciplinary Canadian network of clinicians, researchers, patients, and families that aims to improve care for patients and families with inherited cardiac conditions, focused on those that confer predisposition to arrhythmia and sudden cardiac arrest and/or death. The field is rapidly evolving as research discoveries increase. A streamlined, practical guide for providers to diagnose and follow pediatric and adult patients with inherited cardiac conditions represents a useful tool to improve health system utilization, clinical management, and research related to these conditions. This review provides consensus care pathways for 7 conditions, including the 4 most common inherited cardiac conditions that confer predisposition to arrhythmia, with scenarios to guide investigation, diagnosis, risk stratification, and management. These conditions include Brugada syndrome, long QT syndrome, arrhythmogenic right ventricular cardiomyopathy and related arrhythmogenic cardiomyopathies, and catecholaminergic polymorphic ventricular tachycardia. In addition, an approach to investigating and managing sudden cardiac arrest, sudden unexpected death, and first-degree family members of affected individuals is provided. Referral to specialized cardiogenetic clinics should be considered in most cases. The intention of this review is to offer a framework for the process of care that is useful for both experts and nonexperts, and related allied disciplines such as hospital management, diagnostic services, coroners, and pathologists, in order to provide high-quality, multidisciplinary, standardized care.

T-Peak to T-End Interval for Prediction of Positive Response to Ajmaline Challenge Test in Suspected Brugada Syndrome Patients

BACKGROUND

Brugada syndrome (BrS) is diagnosed in patients with ST-segment elevation with coved-type morphology in the right precordial leads, occurring spontaneously or after provocative drugs. Due to electrocardiographic (ECG) inconsistency, provocative drugs, such as sodium-channel blockers, are useful for unmasking BrS. Ajmaline is superior to flecainide and procainamide to provoke BrS. Prolonged T-peak to T-end (TpTe) is associated with an increased risk of ventricular arrhythmia and sudden cardiac death in Brugada syndrome patients.

OBJECTIVE

This study aimed to investigate the predictive value of T-peak to T-end interval and corrected T-peak to T-end interval for predicting the positive response of the ajmaline challenge test in suspected Brugada syndrome patients.

METHODS

Patients who underwent the ajmaline test in our center were enrolled. Clinical characteristics and electrocardiographic parameters were analyzed, including TpTe, corrected TpTe, QT, corrected QT(QTc) interval, and S-wave duration, compared with the result of the ajmaline challenge test.

RESULTS

The study found that TpTe and corrected TpTe interval in suspected BrS patients were not significantly associated with a positive response to the ajmaline challenge test.

CONCLUSIONS

The T-peak to T-end interval and corrected T-peak to T-end interval could not predict the positive response of the ajmaline challenge test in suspected Brugada syndrome patients.

Brugada Syndrome

Brugada syndrome (BrS) is an "inherited" condition characterized by predisposition to syncope and cardiac arrest, predominantly during sleep. The prevalence is ∼1:2,000, and is more commonly diagnosed in young to middle-aged males, although patient sex does not appear to impact prognosis. Despite the perception of BrS being an inherited arrhythmia syndrome, most cases are not associated with a single causative gene variant. Electrocardiogram (ECG) findings support variable extent of depolarization and repolarization changes, with coved ST-segment elevation ≥2 mm and a negative T-wave in the right precordial leads. These ECG changes are often intermittent, and may be provoked by fever or sodium channel blocker challenge. Growing evidence from cardiac imaging, epicardial ablation, and pathology studies suggests the presence of an epicardial arrhythmic substrate within the right ventricular outflow tract. Risk stratification aims to identify those who are at increased risk of sudden cardiac death, with well-established factors being the presence of spontaneous ECG changes and a history of cardiac arrest or cardiogenic syncope. Current management involves conservative measures in asymptomatic patients, including fever management and drug avoidance. Symptomatic patients typically undergo implantable cardioverter defibrillator insertion, with quinidine and epicardial ablation used for patients with recurrent arrhythmia. This review summarizes our current understanding of BrS and provides clinicians with a practical approach to diagnosis and management.

Predicting cardiac electrical response to sodium-channel blockade and Brugada syndrome using polygenic risk scores

Aims

Sodium-channel blockers (SCBs) are associated with arrhythmia, but variability of cardiac electrical response remains unexplained. We sought to identify predictors of ajmaline-induced PR and QRS changes and Type I Brugada syndrome (BrS) electrocardiogram (ECG).

Methods and results

In 1368 patients that underwent ajmaline infusion for suspected BrS, we performed measurements of 26 721 ECGs, dose–response mixed modelling and genotyping. We calculated polygenic risk scores (PRS) for PR interval (PRS_PR), QRS duration (PRS_QRS), and Brugada syndrome (PRS_BrS) derived from published genome-wide association studies and used regression analysis to identify predictors of ajmaline dose related PR change (slope) and QRS slope. We derived and validated using bootstrapping a predictive model for ajmaline-induced Type I BrS ECG. Higher PRS_PR, baseline PR, and female sex are associated with more pronounced PR slope, while PRS_QRS and age are positively associated with QRS slope (P < 0.01 for all). PRS_BrS, baseline QRS duration, presence of Type II or III BrS ECG at baseline, and family history of BrS are independently associated with the occurrence of a Type I BrS ECG, with good predictive accuracy (optimism-corrected C-statistic 0.74).

Conclusion

We show for the first time that genetic factors underlie the variability of cardiac electrical response to SCB. PRS_BrS, family history, and a baseline ECG can predict the development of a diagnostic drug-induced Type I BrS ECG with clinically relevant accuracy. These findings could lead to the use of PRS in the diagnosis of BrS and, if confirmed in population studies, to identify patients at risk for toxicity when given SCB.

Number of electrocardiogram leads in the diagnosis of spontaneous Brugada syndrome

BACKGROUND

The recently recommended single lead-based criterion for the diagnosis of Brugada syndrome may lead to overdiagnosis of this disorder and overestimation of the risk of sudden cardiac death.

AIM

To investigate the value of a single-lead diagnosis in patients with Brugada syndrome and a spontaneous type 1 electrocardiogram.

METHODS

Consecutive patients with Brugada syndrome were included in a multicentre prospective registry; only those with a spontaneous type 1 electrocardiogram were enrolled. Clinical and electrocardiogram data were reviewed by two physicians blinded to the patients' clinical and genetic status.

RESULTS

Among 1613 patients, 505 (31%) were enrolled (79% male; mean age 46±15 years). A spontaneous type 1 electrocardiogram pattern was found in one lead in 250 patients (group 1), in two leads in 227 patients (group 2) and in three leads in 27 patients (group 3). Groups were similar except for individuals in group 3, who presented more frequently a fragmented QRS complex, an early repolarization pattern and a prolonged T_peak-T_end interval. After a mean follow-up of 6.4±4.7 years, ventricular arrhythmia, sudden cardiac death or implantable cardiac defibrillator shock occurred in 46 (9%) patients, without differences between groups.

CONCLUSION

The prognosis of Brugada syndrome with a spontaneous type 1 electrocardiogram pattern does not appear to be affected by the number of leads required for the diagnosis.

Epsilon wave: A review of historical aspects

The epsilon wave of the electrocardiogram (ECG) together with fragmented QRS (fQRS), the terminal conduction delay, incomplete right bundle branch block (IRBBB) and complete/advanced RBBB (CRBBB) of peripheral origin are part of a spectrum of ventricular depolarization abnormalities of arrhythmogenic cardiomyopathy(AC). Although the epsilon wave is considered a major diagnostic criterion for AC since 2010 (AC Task Force Criteria), its diagnostic value is limited because it is a sign of the later stage of the disease. It would be more appropriate to say that the epsilon wave is a “hallmark” of AC, but is of low diagnostic sensitivity. Although the epsilon wave has high specificity for AC, it can be present in other pathological conditions. In this update we will cover the nomenclature, association with disease states and electrocardiographic aspects of the epsilon wave.

German Cardiac Society Working Group on Cellular Electrophysiology state-of-the-art paper: impact of molecular mechanisms on clinical arrhythmia management

Cardiac arrhythmias remain a common challenge and are associated with significant morbidity and mortality. Effective and safe rhythm control strategies are a primary, yet unmet need in everyday clinical practice. Despite significant pharmacological and technological advances, including catheter ablation and device-based therapies, the development of more effective alternatives is of significant interest to increase quality of life and to reduce symptom burden, hospitalizations and mortality. The mechanistic understanding of pathophysiological pathways underlying cardiac arrhythmias has advanced profoundly, opening up novel avenues for mechanism-based therapeutic approaches. Current management of arrhythmias, however, is primarily guided by clinical and demographic characteristics of patient groups as opposed to individual, patient-specific mechanisms and pheno-/genotyping. With this state-of-the-art paper, the Working Group on Cellular Electrophysiology of the German Cardiac Society aims to close the gap between advanced molecular understanding and clinical decision-making in cardiac electrophysiology. The significance of cellular electrophysiological findings for clinical arrhythmia management constitutes the main focus of this document. Clinically relevant knowledge of pathophysiological pathways of arrhythmias and cellular mechanisms of antiarrhythmic interventions are summarized. Furthermore, the specific molecular background for the initiation and perpetuation of atrial and ventricular arrhythmias and mechanism-based strategies for therapeutic interventions are highlighted. Current "hot topics" in atrial fibrillation are critically appraised. Finally, the establishment and support of cellular and translational electrophysiology programs in clinical rhythmology departments is called for to improve basic-science-guided patient management.

A novel mutation of dipeptidyl aminopeptidase-like protein-6 in a family with suspicious idiopathic ventricular fibrillation

BACKGROUND

Sudden cardiac death (SCD) occurs in a broad spectrum of cardiac pathologies and is an important cause of mortality in the general population. Idiopathic ventricular fibrillation (IVF) is a rare but important factor resulting in SCD. It is diagnosed in a resuscitated cardiac arrest victim underlying unknown cause, with documented ventricular fibrillation. Previous studies have demonstrated that mutations in dipeptidyl aminopeptidase-like protein-6 (DPP6) and cardiac sodium channel Nav1.5 (SCN5A) are the most important genetic factors involve in IVF.

AIM

By using whole sequencing to identify the genetic lesion of a family with suspicious idiopathic ventricular fibrillation.

DESIGN

Prospective genetic study.

METHODS

In this study, we employed whole-exome sequencing in combination with arrhythmia-related gene filtering to identify the genetic lesion for a family suffering from suspicious IVF, syncope and SCD. We then generated the plasmids of DPP6-pcDNA3.1+ (WT and c.1578G>C/p.Q526H). Kv4.3-pcDNA3.1+ was co-transfected together with/without DPP6-pcDNA3.1+ (WT and/or c.1578G>C/p.Q526H) into HEK293 cells to perform the patch clamp experiments.

RESULTS

A novel missense mutation (c.1578G>C/p.Q526H) of DPP6 was identified and co-segregated with affected patients in this family. Patch clamp experiments suggested that this novel mutation might result in a gain of function and disturb the efflux of potassium ion.

CONCLUSION

Our study not only reported the second missense mutation of DPP6 in heart disease and expanded the spectrum of DPP6 mutations, but also contribute to the genetic diagnosis and counseling of families with suspicious IVF, syncope and SCD.