Arthur A.M. Wilde

Brugada Syndrome: Report of the Second Consensus Conference Endorsed by the Heart Rhythm Society and the European Heart Rhythm Association

Since its introduction as a clinical entity in 1992, the Brugada syndrome has progressed from being a rare disease to one that is second only to automobile accidents as a cause of death among young adults in some countries. Electrocardiographically characterized by a distinct ST-segment elevation in the right precordial leads, the syndrome is associated with a high risk for sudden cardiac death in young and otherwise healthy adults, and less frequently in infants and children. Patients with a spontaneously appearing Brugada ECG have a high risk for sudden arrhythmic death secondary to ventricular tachycardia/fibrillation. The ECG manifestations of Brugada syndrome are often dynamic or concealed and may be unmasked or modulated by sodium channel blockers, a febrile state, vagotonic agents, alpha-adrenergic agonists, beta-adrenergic blockers, tricyclic or tetracyclic antidepressants, a combination of glucose and insulin, hypo- and hyperkalemia, hypercalcemia, and alcohol and cocaine toxicity. In recent years, an exponential rise in the number of reported cases and a striking proliferation of articles defining the clinical, genetic, cellular, ionic, and molecular aspects of the disease have occurred. The report of the first consensus conference, published in 2002, focused on diagnostic criteria. The present report, which emanated from the second consensus conference held in September 2003, elaborates further on the diagnostic criteria and examines risk stratification schemes and device and pharmacological approaches to therapy on the basis of the available clinical and basic science data.

HRS/EHRA Expert Consensus Statement on the State of Genetic Testing for the Channelopathies and Cardiomyopathies: This document was developed as a partnership between the Heart Rhythm Society (HRS) and the European Heart Rhythm Association (EHRA)

Michael J. Ackerman, MD, PhD, Silvia G. Priori, MD, PhD, Stephan Willems, MD, PhD, Charles Berul, MD, FHRS, CCDS, Ramon Brugada, MD, PhD, Hugh Calkins, MD, FHRS, CCDS, A. John Camm, MD, FHRS, Patrick T. Ellinor, MD, PhD, Michael Gollob, MD, Robert Hamilton, MD, CCDS, Ray E. Hershberger, MD, Daniel P. Judge, MD, Hervè Le Marec, MD, William J. McKenna, MD, Eric Schulze-Bahr, MD, PhD, Chris Semsarian, MBBS, PhD, Jeffrey A. Towbin, MD, Hugh Watkins, MD, PhD, Arthur Wilde, MD, PhD, Christian Wolpert, MD, Douglas P. Zipes, MD, FHRS

HRS/EHRA/APHRS Expert Consensus Statement on the Diagnosis and Management of Patients with Inherited Primary Arrhythmia Syndromes: Document endorsed by HRS, EHRA, and APHRS in May 2013 and by ACCF, AHA, PACES, and AEPC in June 2013.

Developed in partnership with the Heart Rhythm Society (HRS), the European Heart Rhythm Association (EHRA), a registered branch of the European Society of Cardiology, and the Asia Pacific Heart Rhythm Society (APHRS); and in collaboration with the American College of Cardiology Foundation (ACCF), the American Heart Association (AHA), the Pediatric and Congenital Electrophysiology Society (PACES) and the Association for European Pediatric and Congenital Cardiology (AEPC).

Proposed Diagnostic Criteria for the Brugada Syndrome Consensus Report

Asyndrome characterized by ST-segment elevation in right precordial leads (V1 to V3) that is unrelated to ischemia, electrolyte disturbances, or obvious structural heart disease was reported as early as 1953,1 but was first described as a distinct clinical entity associated with a high risk of sudden cardiac death in 1992.2–4⇓⇓ The Brugada syndrome is a familial disease that displays an autosomal dominant mode of transmission, with incomplete penetrance and an incidence ranging between 5 and 66 per 10 000. In regions of Southeast Asia where it is endemic, the clinical presentation of Brugada syndrome is distinguished by a male predominance (8:1 ratio of male:female) and the appearance of arrhythmic events at an average age of 40 years (range: 1 to 77 years).2,5⇓ Although a number of candidate genes are considered plausible, thus far the syndrome has been linked only to mutations in SCN5A , the gene encoding for the α subunit of the sodium channel.6 A number of ambiguities exist concerning the diagnosis of Brugada syndrome. The electrocardiographic signature of the syndrome is dynamic and often concealed, but can be unmasked by potent sodium channel blockers such as flecainide, ajmaline, and procainamide,7 although the specificity of this effect for uncovering patients at risk for sudden death has been an issue of concern. A recent report by Remme et al8 has shown that the number of idiopathic ventricular fibrillation patients diagnosed as having Brugada syndrome is a sensitive function of the diagnostic criteria applied. What are the proper diagnostic criteria for identifying Brugada syndrome? A definitive answer to this question has been out of reach and is the reason for the establishment of a special Arrhythmia Working Group of the European Society of Cardiology that met from August 31 to …

An Entirely Subcutaneous Implantable Cardioverter–Defibrillator

BACKGROUND Implantable cardioverter-defibrillators (ICDs) prevent sudden death from cardiac causes in selected patients but require the use of transvenous lead systems. To eliminate the need for venous access, we designed and tested an entirely subcutaneous ICD system. METHODS First, we conducted two short-term clinical trials to identify a suitable device configuration and assess energy requirements. We evaluated four subcutaneous ICD configurations in 78 patients who were candidates for ICD implantation and subsequently tested the best configuration in 49 additional patients to determine the subcutaneous defibrillation threshold in comparison with that of the standard transvenous ICD. Then we evaluated the long-term use of subcutaneous ICDs in a pilot study, involving 6 patients, which was followed by a trial involving 55 patients. RESULTS The best device configuration consisted of a parasternal electrode and a left lateral thoracic pulse generator. This configuration was as effective as a transvenous ICD for terminating induced ventricular fibrillation, albeit with a significantly higher mean (+/-SD) energy requirement (36.6+/-19.8 J vs. 11.1+/-8.5 J). Among patients who received a permanent subcutaneous ICD, ventricular fibrillation was successfully detected in 100% of 137 induced episodes. Induced ventricular fibrillation was converted twice in 58 of 59 patients (98%) with the delivery of 65-J shocks in two consecutive tests. Clinically significant adverse events included two pocket infections and four lead revisions. After a mean of 10+/-1 months, the device had successfully detected and treated all 12 episodes of spontaneous, sustained ventricular tachyarrhythmia. CONCLUSIONS In small, nonrandomized studies, an entirely subcutaneous ICD consistently detected and converted ventricular fibrillation induced during electrophysiological testing. The device also successfully detected and treated all 12 episodes of spontaneous, sustained ventricular tachyarrhythmia. (ClinicalTrials.gov numbers, NCT00399217 and NCT00853645.)

Flecainide prevents catecholaminergic polymorphic ventricular tachycardia in mice and humans.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a potentially lethal inherited arrhythmia syndrome in which drug therapy is often ineffective. We discovered that flecainide prevents arrhythmias in a mouse model of CPVT by inhibiting cardiac ryanodine receptor–mediated Ca2+ release and thereby directly targeting the underlying molecular defect. Flecainide completely prevented CPVT in two human subjects who had remained highly symptomatic on conventional drug therapy, indicating that this currently available drug is a promising mechanism-based therapy for CPVT.

Sodium channel β1 subunit mutations associated with Brugada syndrome and cardiac conduction disease in humans

Brugada syndrome is a genetic disease associated with sudden cardiac death that is characterized by ventricular fibrillation and right precordial ST segment elevation on ECG. Loss-of-function mutations in SCN5A, which encodes the predominant cardiac sodium channel alpha subunit NaV1.5, can cause Brugada syndrome and cardiac conduction disease. However, SCN5A mutations are not detected in the majority of patients with these syndromes, suggesting that other genes can cause or modify presentation of these disorders. Here, we investigated SCN1B, which encodes the function-modifying sodium channel beta1 subunit, in 282 probands with Brugada syndrome and in 44 patients with conduction disease, none of whom had SCN5A mutations. We identified 3 mutations segregating with arrhythmia in 3 kindreds. Two of these mutations were located in a newly described alternately processed transcript, beta1B. Both the canonical and alternately processed transcripts were expressed in the human heart and were expressed to a greater degree in Purkinje fibers than in heart muscle, consistent with the clinical presentation of conduction disease. Sodium current was lower when NaV1.5 was coexpressed with mutant beta1 or beta1B subunits than when it was coexpressed with WT subunits. These findings implicate SCN1B as a disease gene for human arrhythmia susceptibility.

An international compendium of mutations in the SCN5A-encoded cardiac sodium channel in patients referred for Brugada syndrome genetic testing

BACKGROUND Brugada syndrome (BrS) is a common heritable channelopathy. Mutations in the SCN5A-encoded sodium channel (BrS1) culminate in the most common genotype. OBJECTIVE This study sought to perform a retrospective analysis of BrS databases from 9 centers that have each genotyped >100 unrelated cases of suspected BrS. METHODS Mutational analysis of all 27 translated exons in SCN5A was performed. Mutation frequency, type, and localization were compared among cases and 1,300 ostensibly healthy volunteers including 649 white subjects and 651 nonwhite subjects (blacks, Asians, Hispanics, and others) that were genotyped previously. RESULTS A total of 2,111 unrelated patients (78% male, mean age 39 +/- 15 years) were referred for BrS genetic testing. Rare mutations/variants were more common among BrS cases than control subjects (438/2,111, 21% vs. 11/649, 1.7% white subjects and 31/651, 4.8% nonwhite subjects, respectively, P <10(-53)). The yield of BrS1 genetic testing ranged from 11% to 28% (P = .0017). Overall, 293 distinct mutations were identified in SCN5A: 193 missense, 32 nonsense, 38 frameshift, 21 splice-site, and 9 in-frame deletions/insertions. The 4 most frequent BrS1-associated mutations were E1784K (14x), F861WfsX90 (11x), D356N (8x), and G1408R (7x). Most mutations localized to the transmembrane-spanning regions. CONCLUSION This international consortium of BrS genetic testing centers has added 200 new BrS1-associated mutations to the public domain. Overall, 21% of BrS probands have mutations in SCN5A compared to the 2% to 5% background rate of rare variants reported in healthy control subjects. Additional studies drawing on the data presented here may help further distinguish pathogenic mutations from similarly rare but otherwise innocuous ones found in cases.

Sudden Unexplained Death Heritability and Diagnostic Yield of Cardiological and Genetic Examination in Surviving Relatives

Background—Sudden death mostly follows from cardiac disorders that elicit lethal ventricular arrhythmias. In young individuals, it often remains unexplained because history and/or postmortem analysis are absent or provide no clue. Because such sudden unexplained deaths (SUDs) may have heritable causes, cardiological and genetic assessment of surviving relatives of SUD victims may reveal the underlying disease and unmask presymptomatic carriers. We aimed to establish the diagnostic yield of such assessments. Methods and Results—We investigated 43 consecutive families with ≥1 SUD victim who died at ≤40 years of age. All studied relatives underwent resting/exercise ECG and Doppler echocardiography. Molecular genetic analysis was conducted to confirm the diagnosis. We identified an inherited disease and likely cause of death in 17 of 43 families (40%). Twelve families had primary electrical disease: catecholaminergic polymorphic ventricular tachycardia (5 families), long-QT syndrome (4 families), Brugada syndrome (2 families), and long-QT/Brugada syndrome (1 family). Furthermore, we found arrhythmogenic right ventricular cardiomyopathy (3 families), hypertrophic cardiomyopathy (1 family), and familial hypercholesterolemia (1 family). Molecular genetic analysis provided confirmation in 10 families. Finding the diagnosis was more likely when more relatives were examined and in families with ≥2 SUD victims ≤40 years of age. The resting/exercise ECG had a high diagnostic yield. These efforts unmasked 151 presymptomatic disease carriers (8.9 per family). Conclusions—Examination of relatives of young SUD victims has a high diagnostic yield, with identification of the disease in 40% of families and 8.9 presymptomatic carriers per family. Simple procedures (examining many relatives) and routine tests (resting/exercise ECG) constitute excellent diagnostic strategies. Molecular genetics provide strong supportive information.

Clinical Aspects of Type-1 Long-QT Syndrome by Location, Coding Type, and Biophysical Function of Mutations Involving the KCNQ1 Gene

Background— Type-1 long-QT syndrome (LQTS) is caused by loss-of-function mutations in the KCNQ1-encoded IKs cardiac potassium channel. We evaluated the effect of location, coding type, and biophysical function of KCNQ1 mutations on the clinical phenotype of this disorder. Methods and Results— We investigated the clinical course in 600 patients with 77 different KCNQ1 mutations in 101 proband-identified families derived from the US portion of the International LQTS Registry (n=425), the Netherlands’ LQTS Registry (n=93), and the Japanese LQTS Registry (n=82). The Cox proportional hazards survivorship model was used to evaluate the independent contribution of clinical and genetic factors to the first occurrence of time-dependent cardiac events from birth through age 40 years. The clinical characteristics, distribution of mutations, and overall outcome event rates were similar in patients enrolled from the 3 geographic regions. Biophysical function of the mutations was categorized according to dominant-negative (>50%) or haploinsufficiency (≤50%) reduction in cardiac repolarizing IKs potassium channel current. Patients with transmembrane versus C-terminus mutations (hazard ratio, 2.06; P<0.001) and those with mutations having dominant-negative versus haploinsufficiency ion channel effects (hazard ratio, 2.26; P<0.001) were at increased risk for cardiac events, and these genetic risks were independent of traditional clinical risk factors. Conclusions— This genotype–phenotype study indicates that in type-1 LQTS, mutations located in the transmembrane portion of the ion channel protein and the degree of ion channel dysfunction caused by the mutations are important independent risk factors influencing the clinical course of this disorder.