Comparison of long-term follow-up of electrocardiographic features in Brugada syndrome between the SCN5A-positive probands and the SCN5A-negative probands

Longitudinal Electrocardiographic Assessment in the Brugada Syndrome

Background

The type 1 electrocardiographic (ECG) pattern diagnostic of Brugada syndrome (BrS) can be dynamic. Limited studies have rigorously evaluated the temporal stability of the Brugada ECG pattern.

Objective

We sought to evaluate fluctuations of the Brugada pattern in serial resting ECGs from BrS patients managed within a large health care system.

Methods

In our cohort of BrS patients with at least 2 standard, resting ECGs recorded on separate clinical encounters, we evaluated serial changes in the Brugada pattern and categorized patients into 1 of 3 groups: dynamic was defined as the presence of both type 1 and non–type 1 patterns in available ECGs; the provoked-only group was defined as having a non–type 1 Brugada pattern across resting ECGs; and the persistent group was defined as having a type 1 pattern on all ECGs. We also evaluated the clinical risk in this cohort according to the Shanghai risk score.

Results

In 72 patients with BrS (mean age 46 ± 15 years, 69% male), 828 standard, resting ECGs were recorded over a median duration of 30.2 (interquartile range 6.3–68.1) months. The dynamic group comprised 50 (69% of the cohort) patients, the provoked-only group consisted of 17 patients (24% of the cohort), and the persistent group included 5 patients. No significant differences were detected in the total number of ECGs evaluated during the follow-up period between any of the groups. Only sinus node dysfunction and a prior cardiac arrest were associated with the persistent type 1 group. The majority of patients had a low annualized risk of lethal arrhythmic events.

Conclusion

Most BrS patients have a dynamic Brugada pattern noted on longitudinal, resting ECGs. Expert consensus statements should provide clarity on the frequency of obtaining resting ECGs in patients suspected of having BrS during follow-up.

Dynamic Changes in Electrocardiogram Parameters After Epicardial Substrate Catheter Ablation of Brugada Syndrome

BACKGROUND

Catheter ablation (CA) is effective for recurrent episodes of ventricular fibrillation (VF) in Brugada syndrome (BrS). VF development in BrS is associated with several electrocardiogram (ECG) abnormalities. This study investigated changes in ECG parameters in high-risk BrS patients who underwent epicardial CA.

METHODS AND RESULTS

In all, 27 BrS patients were implanted with an implantable cardioverter-defibrillator (ICD). Patients were divided into 2 groups: (1) an ablation group (n=11) that underwent epicardial CA because of VF recurrence; and (2) a primary prevention (PP) group (n=16) with ICD implantation only. ECG parameters were evaluated before and 12 months after CA and compared with ECG parameters in the PP group. The T wave peak-to-end interval was significantly longer and the number of abnormal spikes in leads V1-V3 at the second, third, and fourth intercostal spaces was greater in the ablation than PP group. After ablation, ST levels and the sum of abnormal spikes in leads V1-V3 were significantly decreased. The mean (±SD) number of ICD shocks decreased markedly during a mean follow-up period of 42.0 months (from 3.8±3.7 to 0.2±0.4/year). Four patients had an ICD shock following the ablation procedure. Greater reductions in ST-segment elevation and abnormal spikes were observed in the group without than with VF recurrence.

CONCLUSIONS

Improvements in surface ECG parameters appear to be associated with successful ablation in high-risk BrS patients.

Wide QRS complex and the risk of major arrhythmic events in Brugada syndrome patients: A systematic review and meta-analysis

BACKGROUND

Brugada syndrome (BrS) is an inherited arrhythmic disease associated with an increased risk of major arrhythmic events (MAE). Previous studies reported that a wide QRS complex may be useful as a predictor of MAE in BrS patients. We aimed to assess the correlation of wide QRS complex with MAE by a systematic review and meta-analysis.

METHODS

We comprehensively searched the databases of MEDLINE and EMBASE from inception to June 2019. Included studies were cohort and case control studies that reported QRS duration and the relationship between wide QRS complex (>120 milliseconds) and MAE (sudden cardiac death, sudden cardiac arrest, ventricular fibrillation, sustained ventricular tachycardia, or appropriate shock). Data from each study were combined using the random-effects model.

RESULTS

Twenty-two studies from 2007 to 2018 were included in this meta-analysis involving 4,814 BrS patients. The mean age was 46.1 ± 12.8 years. The patients were predominately men (77.6%). Wide QRS duration was an independent predictor of MAE (pooled risk ratio 1.55, 95% confidence interval: 1.04-2.30, P = .30, I 2 = 38.4%). QRS duration was wider in BrS who had history of MAE (weight mean difference = 8.12 milliseconds, 95% confidence interval: 5.75-10.51 milliseconds).

CONCLUSIONS

Our study demonstrated that QRS duration is wider in BrS who had history of MAE, and a wide QRS complex is associated with 1.55 times higher risk of MAE in BrS populations. Wide QRS complex can be considered for risk stratification in prediction of MAE in patients with BrS, especially when considering implantable cardioverter-defibrillator placement in asymptomatic patients.

Pilsicainide Administration Unmasks a Phenotype of Brugada Syndrome in a Patient with Overlap Syndrome due to the E1784K SCN5A Mutation

Mutations in the cardiac sodium channel SCN5A can cause phenotypic overlap syndrome of long QT syndrome and Brugada syndrome. However, Brugada-type ST elevations in patients with overlap syndrome are often concealed, which creates a diagnostic challenge. A 38-year-old man was admitted due to ventricular fibrillation (VF). The 12-lead electrocardiogram showed a prolonged QT interval and saddleback-type ST elevation. Pilsicainide administration induced coved-type ST elevation and VF triggered by a single premature ventricular contraction. A genetic analysis showed an SCN5A c.5350G>A p.E1784K mutation. The present case suggests the importance of a drug administration test being performed in the clinical management of overlap syndrome.

Brugada syndrome with SCN5A mutations exhibits more pronounced electrophysiological defects and more severe prognosis: A meta-analysis

Whether the presence of SCN5A mutation is a predictor of BrS risk remains controversial, and patient selection bias may have weakened previous findings. Therefore, we performed this study to clarify the clinical characteristics and outcomes of BrS probands with SCN5A mutations. We systematically retrieved eligible studies published through October 2018. A total of 17 studies enrolling 1780 BrS patients were included. Overall, our results found that compared with BrS patients without SCN5A mutations, patients with SCN5A mutations exhibited a younger age at the onset of symptoms and higher rate of the spontaneous type-1 electrocardiogram pattern, more pronounced conduction or repolarization abnormalities, and increased atrial vulnerability. In addition, the presence of SCN5A mutations was associated with an elevated risk of major arrhythmic events in both Asian (odds ratio [OR] = 1.82, 95% confidence interval [CI] 1.07-3.11; P = .03) and Caucasian (OR = 2.24, 95% CI 1.02-4.90; P = .04) populations. In conclusions, patients with SCN5A mutations exhibit more pronounced electrophysiological defects and more severe prognosis. Clinicians should be cautious when utilizing genetic testing for risk stratification or treatment guidance before determining whether the causal relationship regarding SCN5A mutation status is an independent predictor of risk.

Atrial fibrillation and risk of major arrhythmic events in Brugada syndrome: A meta-analysis

BACKGROUND

Brugada syndrome (BrS) is a common cause of sudden cardiac death (SCD). There is recent evidence that atrial fibrillation (AF) is associated with increased risk of SCD in general population. However, whether AF increases a risk of major arrhythmic events (MAE) in patients with BrS is still unclear. We performed a systematic review and meta-analysis to explore the effect of AF on MAE in BrS population.

METHODS

We searched the databases of MEDLINE and EMBASE from inception to March 2019. Included studies were published cohort studies reporting rates of MAE (ventricular fibrillation, sustained ventricular tachycardia, SCD, or sudden cardiac arrest) in BrS patients, with and without previous documented AF. Data from each study were combined using the random-effects model.

RESULTS

Six studies from 1,703 patients were included. There was a significant association between AF and an increased risk of MAE in patients with BrS (pooled OR = 2.37, 95% CI = 1.36-4.13, p-value = .002, I²  = 40.3%).

CONCLUSIONS

Our meta-analysis demonstrated that AF is associated with an increased risk of MAE in patients with BrS.

Clinical and Electrocardiographic Differences in Brugada Syndrome With Spontaneous or Drug-Induced Type 1 Electrocardiogram

BACKGROUND

Spontaneous type 1 electrocardiogram (ECG) in the right precordial lead is a dominant predictor of ventricular fibrillation (VF) in Brugada syndrome (BrS). In some BrS patients with VF, however, spontaneous type 1 ECG is undetectable, even in repeated ECG and immediately after VF. This study investigated differences between BrS patients with spontaneous or drug-induced type 1 ECG.

METHODS AND RESULTS

We evaluated 15 BrS patients with drug-induced (D-BrS) and 29 with spontaneous type 1 ECG (SP-BrS). All patients had had a previous VF episode. In each D-BrS patient, ECG was recorded more than 15 times (mean, 46±34) during 7.2±5.1 years of follow-up. Age and family history were comparable between groups. Inferolateral early repolarization (ER) was observed in 13 D-BrS (87%) at least once but in only 3 SP-BrS (10%, P<0.01). Immediately after VF, inferolateral ER was accentuated in 9 of 10 D-BrS, while type 1 ECG was accentuated in 12 of 16 SP-BrS. Fragmented QRS in the right precordial lead and aVR sign were absent in D-BrS but present in 20 (69%, P<0.01) and 11 (38%, P<0.01) SP-BrS, respectively. There was no prognostic difference between groups.

CONCLUSIONS

Although having similar clinical profiles, there are obvious ECG differences between VF-positive BrS patients with spontaneous or drug-induced type 1 ECG. The inferolateral lead rather than the right precordial lead on ECG may be particularly crucial in some BrS patients.

SCN5A gene mutations and the risk of ventricular fibrillation and syncope in Brugada syndrome patients: A meta-analysis

Mutations in the gene encoding the main cardiac sodium channel (SCN5A) are the commonest genetic cause of Brugada syndrome (BrS). However, the effect of SCN5A mutations on the outcomes of ventricular fibrillation (VF) and syncope remains uncertain. To clarify this relationship, a meta-analysis was performed. A comprehensive search was conducted to identify all eligible studies from PubMed, MEDLINE, EBSCO, ProQuest, Science Direct, Clinical Key, and Cochrane database for cohort studies of BrS populations that had been systematically tested for SCN5A mutations. We did meta-analysis to see the relationship between SCN5A mutations and the occurrence of VF and/or syncope using RevMan 5.3. Five clinical studies met our criteria and included a total of 665 BrS patients. These studies included 45 patients with VF and 178 patients with syncope. We found that in BrS patients with SCN5A mutations the rate of VF event was 30.7% while in patients without mutations was 28.5% (Risk Ratio [RR] = 1.11, [95% CI: 0.61, 2.00], P = 0.73, I 2 = 0%). The occurrence of syncope events was 35.9% in patients with SCN5A mutations and 34.5% in patients without mutations (RR = 1.12, [95% CI: 0.87, 1.45], P = 0.37, I 2 = 39%). Furthermore, the occurrence of combined VF and syncope events were similar between the 2 groups (RR = 1.12, [95% CI: 0.89, 1.42], P = 0.34, I 2 = 11%). BrS patients with SCN5A mutations exhibit a similar risk of future occurence of VF and/or syncope as compared to those without SCN5A mutations.

SCN5A mutation status increases the risk of major arrhythmic events in Asian populations with Brugada syndrome: systematic review and meta-analysis

BACKGROUND

Brugada syndrome (BrS) is an inherited arrhythmic disease linked to SCN5A mutations. It is controversial whether SCN5A mutation carriers possess a greater risk of major arrhythmic events (MAE). We examined the association of SCN5A mutations and MAE in BrS patients.

METHODS

We comprehensively searched the databases of MEDLINE and EMBASE from inception to September 2017. Included studies were published cohort and case-control studies that compared MAE in BrS patients with and without SCN5A mutations. Data from each study were combined using the random-effects model. Generic inverse variance method of DerSimonian and Laird was employed to calculate the risk ratios (RR) and 95% confidence intervals (CI).

RESULTS

Seven studies from March 2002 to October 2017 were included (1,049 BrS subjects). SCN5A mutations were associated with MAE in Asian populations (RR = 2.03, 95% CI: 1.37-3.00, p = 0.0004, I²  = 0.0%), patients who were symptomatic (RR = 2.66, 95% CI: 1.62-4.36, p = 0.0001, I²  = 23.0%), and individuals with spontaneous type-1 Brugada pattern (RR = 1.84, 95% CI: 1.05-3.23, p = 0.03, I²  = 0.0%).

CONCLUSIONS

SCN5A mutations in BrS increase the risk of MAE in Asian populations, symptomatic BrS patients, and individuals with spontaneous type-1 Brugada pattern. Our study suggests that SCN5A mutation status should be an important tool for risk assessment in BrS patients.

Genotype-Phenotype Correlation of SCN5A Mutation for the Clinical and Electrocardiographic Characteristics of Probands With Brugada Syndrome

Background:

The genotype-phenotype correlation of SCN5A mutations as a predictor of cardiac events in Brugada syndrome remains controversial. We aimed to establish a registry limited to probands, with a long follow-up period, so that the genotype-phenotype correlation of SCN5A mutations in Brugada syndrome can be examined without patient selection bias.

Methods:

This multicenter registry enrolled 415 probands (n=403; men, 97%; age, 46±14 years) diagnosed with Brugada syndrome whose SCN5A gene was analyzed for mutations.

Results:

During a mean follow-up period of 72 months, the overall cardiac event rate was 2.5%/y. In comparison with probands without mutations ( SCN5A (–), n=355), probands with SCN5A mutations ( SCN5A (+), n=60) experienced their first cardiac event at a younger age (34 versus 42 years, P =0.013), had a higher positive rate of late potentials (89% versus 73%, P =0.016), exhibited longer P-wave, PQ, and QRS durations, and had a higher rate of cardiac events ( P =0.017 by log-rank). Multivariate analysis indicated that only SCN5A mutation and history of aborted cardiac arrest were significant predictors of cardiac events ( SCN5A (+) versus SCN5A (–): hazard ratio, 2.0 and P =0.045; history of aborted cardiac arrest versus no such history: hazard ratio, 6.5 and P <0.001).

Conclusions:

Brugada syndrome patients with SCN5A mutations exhibit more conduction abnormalities on ECG and have higher risk for cardiac events.

Sirtuin 1 regulates cardiac electrical activity by deacetylating the cardiac sodium channel

The voltage-gated cardiac Na+ channel (Nav1.5), encoded by the SCN5A gene, conducts the inward depolarizing cardiac Na+ current (INa) and is vital for normal cardiac electrical activity. Inherited loss-of-function mutations in SCN5A lead to defects in the generation and conduction of the cardiac electrical impulse and are associated with various arrhythmia phenotypes. Here we show that sirtuin 1 deacetylase (Sirt1) deacetylates Nav1.5 at lysine 1479 (K1479) and stimulates INa via lysine-deacetylation-mediated trafficking of Nav1.5 to the plasma membrane. Cardiac Sirt1 deficiency in mice induces hyperacetylation of K1479 in Nav1.5, decreases expression of Nav1.5 on the cardiomyocyte membrane, reduces INa and leads to cardiac conduction abnormalities and premature death owing to arrhythmia. The arrhythmic phenotype of cardiac-Sirt1-deficient mice recapitulated human cardiac arrhythmias resulting from loss of function of Nav1.5. Increased Sirt1 activity or expression results in decreased lysine acetylation of Nav1.5, which promotes the trafficking of Nav1.5 to the plasma membrane and stimulation of INa. As compared to wild-type Nav1.5, Nav1.5 with K1479 mutated to a nonacetylatable residue increases peak INa and is not regulated by Sirt1, whereas Nav1.5 with K1479 mutated to mimic acetylation decreases INa. Nav1.5 is hyperacetylated on K1479 in the hearts of patients with cardiomyopathy and clinical conduction disease. Thus, Sirt1, by deacetylating Nav1.5, plays an essential part in the regulation of INa and cardiac electrical activity.

Genetics of Brugada syndrome

In 1992, the Brugada syndrome (BrS) was recognized as a disease responsible for sudden cardiac death, characterized by a right bundle-branch block with ST segment elevation in the leads V1 and V2. This syndrome is highly associated with sudden cardiac death, especially in young males. BrS is currently diagnosed in patients with ST-segment elevation showing type 1 morphology ≥ 2 mm in ≥1 leads among the right precordial leads V1 or V2 positioned in the 2nd, 3rd, or 4th intercostal space, and occurring either spontaneously or after a provocative drug test by the intravenous administration of Class I antiarrhythmic drugs. With accumulated findings, the BrS inheritance model is believed to be an autosomal dominant inheritable model with incomplete penetrance, although most patients with BrS were sporadic cases. SCN5A, which was identified as the first BrS-associated gene in 1998, has emerged as the most common gene associated with BrS, and more than 10 BrS-associated genes have been identified thereafter. Mutation-specific genetic testing is recommended for the family members and appropriate relatives following the identification of BrS-causative mutations in an index patient. In addition, comprehensive or BrS1 (SCN5A) targeted genetic testing could be useful for patients in whom a cardiologist has established a clinical index of suspicion for BrS based on the patient׳s clinical history, family history, and the expressed electrocardiographic (resting 12-lead ECGs and/or provocative drug challenge testing) phenotype.

Over the past 20 years, extensive research in this field has allowed better understanding of the pathophysiology, genetic background, and management of BrS even though controversies still exist. In this review article, a background of genetics, the genetic background of BrS, the genotype and phenotype relationship, the role of genetic screening in clinical practice, and the interpretation of the identified genetic variants have been addressed based on this understanding.

Electrocardiographic methods for diagnosis and risk stratification in the Brugada syndrome

The Brugada syndrome (BrS) is a malignant, genetically-determined, arrhythmic syndrome manifesting as syncope or sudden cardiac death (SCD) in individuals with structurally normal hearts. The diagnosis of the BrS is mainly based on the presence of a spontaneous or Na + channel blocker induced characteristic, electrocardiographic (ECG) pattern (type 1 or coved Brugada ECG pattern) typically seen in leads V1 and V2 recorded from the 4th to 2nd intercostal (i.c.) spaces. This pattern needs to be distinguished from similar ECG changes due to other causes (Brugada ECG phenocopies). This review focuses mainly on the ECG-based methods for diagnosis and arrhythmia risk assessment in the BrS. Presently, the main unresolved clinical problem is the identification of those patients at high risk of SCD who need implantable cardioverter-defibrillator (ICD), which is the only therapy with proven efficacy. Current guidelines recommend ICD implantation only in patients with spontaneous type 1 ECG pattern, and either history of aborted cardiac arrest or documented sustained VT (class I), or syncope of arrhythmic origin (class IIa) because they are at high risk of recurrent arrhythmic events (up to 10% or more annually for those with aborted cardiac arrest). The majority of BrS patients are asymptomatic when diagnosed and considered to have low risk (around 0.5% annually) and therefore not indicated for ICD. The majority of SCD victims in the BrS, however, had no symptoms prior to the fatal event and therefore were not protected with an ICD. While some ECG markers such as QRS fragmentation, infero-lateral early repolarisation, and abnormal late potentials on signal-averaged ECG are known to be linked to increased arrhythmic risk, they are not sufficiently sensitive or specific. Potential novel ECG-based strategies for risk stratification are discussed based on computerised methods for depolarisation and repolarisation analysis, a composite approach targeting several major components of ventricular arrhythmogenesis, and the collection of large digital ECG databases in genotyped BrS patients and their relatives.

Sudden cardiac death in the young: the bogeyman

Sudden cardiac death in the young is a relatively uncommon but marked event usually related to congenital diseases or anomalies. Despite the prevalence of each condition being variable, most common causes include primary myocardial diseases and arrhythmic disorder, frequently with inheritance pattern. Sudden cardiac death is usually preceded by symptoms, thus making personal and family history fundamental for its prevention. Nevertheless, in more than 50% of cases, sudden cardiac death is the first manifestation of the disease. In this review, we describe the different causes of sudden cardiac death, their incidence, and currently used preventive strategies.

The Brugada Syndrome - Diagnosis, Clinical Implications and Risk Stratification

The Brugada syndrome (BrS) is a hereditary arrhythmic syndrome manifesting as syncope or sudden cardiac death (SCD) in individuals without overt structural heart disease. Currently, its diagnosis is mainly based on the presence of a spontaneous or Na+-channel blocker induced so-called "type 1" Brugada electrocardiographic (ECG) pattern typically seen in leads V1 and V2 recorded from the 4th to 2nd intercostal spaces. Presently the main unresolved clinical problem in the BrS is the identification of patients at high risk of SCD who need implantable cardioverter-defibrillator (ICD). Current guidelines recommend ICD implantation only in patients with spontaneous type 1 ECG pattern and either history of aborted cardiac arrest or documented sustained ventricular tachycardia (class I) or syncope of arrhythmic origin (class IIa) because they are at high risk of recurrent arrhythmias. However, the majority of BrS patients are asymptomatic when diagnosed and have generally low risk (0.5 % annually or lower) and therefore are not indicated for ICD. Most of SCD victims in the BrS have had no symptoms prior to the fatal event and therefore were not protected with an ICD. Currently there are no reliable methods to identify these potential victims of SCD. Although some ECG markers such as QRS fragmentation and infero-lateral early repolarisation have been demonstrated to signify increased arrhythmic risk their value still needs to be confirmed in large prospective studies. Novel risk assessment strategies need to be developed based on computerised quantitative ECG analysis of large digital ECG databases in patients with BrS and their relatives, and combined assessment of the most important factors of ventricular arrhythmogenesis.

The clinical significance of pregnancy in Brugada syndrome

INTRODUCTION AND OBJECTIVES

Little is known about the risks and outcomes of pregnancy in women with Brugada syndrome. We therefore evaluated pregnancy outcomes and the influence of pregnancy in patients with Brugada syndrome.

METHODS

A retrospective analysis was performed in all pregnant women with Brugada syndrome. We included 104 women with a total of 219 deliveries.

RESULTS

There were 15 spontaneous abortions. One infant died suddenly during the night 3 months after birth. Six pregnant women reported they had experienced at least 1 syncope during the pregnancy. Of the 3 women who received an implantable cardioverter-defibrillator before the pregnancy, none received arrhythmia episodes. There were no events during the pregnancy in 4 patients with a previously aborted sudden cardiac death. Of 24 patients with syncope when not pregnant, 18 were asymptomatic and 6 experienced a recurrent syncope during the pregnancy. During the follow-up (mean follow-up 298.9 days; 95% confidence interval, 289.6-308.2), 2 women received appropriate shocks.

CONCLUSIONS

In this retrospective, single-center study, serious events were not more frequent during pregnancy and the peripartum period in women with Brugada syndrome. The occurrence of syncope during pregnancy was not associated with a worst outcome in the peri- and postpartum periods or during follow-up. The reported rate of miscarriage and sudden infant death will require further studies to confirm or rule out its association with Brugada syndrome.

Update of diagnosis and management of inherited cardiac arrhythmias

Over the past 2 decades, a number of inherited cardiac arrhythmias, including congenital long QT syndrome (LQTS) and Brugada syndrome (BrS), have been shown to have a link to mutations in genes encoding for ion channels or other membrane components. The recent HRS/EHRA/APHRS expert consensus statement on the diagnosis and management of patients with inherited arrhythmia syndromes has updated the clinical diagnosis of congenital LQTS and BrS. Genetic studies have identified 13 forms of congenital LQTS in 50-80% of clinically affected patients. Genotype-phenotype correlations have been investigated in the 3 major genotypes, LQT1, LQT2 and LQT3 syndromes, resulting in genotype-specific management and therapy. More detailed analyses of each genotype have suggested mutation location-, type-, or function-specific differences in clinical phenotype among the LQT1, LQT2, and possibly LQT3 genotypes. In BrS, only one-third of affected patients can be genotyped, mainly in the sodium channel gene, SCN5A; therefore, clinical studies of genotype-phenotype relationships have been limited. More recently, a genome-wide association study using a gene array explored the role of common genetic variants (polymorphisms) as the susceptible or modifier gene in both congenital LQTS and BrS.

Sinus node disease in subjects with type 1 ECG pattern of Brugada syndrome

BACKGROUND

The spectrum of phenotypes related to mutations of the SCN5A gene include Brugada syndrome (BS), long QT syndrome, progressive cardiac conduction defect, and sinus node disease (SND). The present study investigated the incidence of SND in subjects with type 1 electrocardiogram (ECG) pattern of BS.

METHODS AND RESULTS

The study population consisted of 68 individuals (55 males, mean age 44.8±12.8 years) with spontaneous (n=27) or drug-induced (n=41) type 1 ECG pattern of BS. Twenty-eight subjects were symptomatic with a history of syncope (41.2%). SND was observed in 6 symptomatic subjects (8.8%), and was mainly attributed to sino-atrial block with sinus pauses. Two patients were initially diagnosed with SND, and received a pacemaker. Patients with SND displayed an increased P-wave duration in leads II and V2, PR interval in leads II and V2, QRS duration in leads II and V2, and increased QTc interval in lead V2 (p<0.05). AH and HV intervals as well as corrected sinus node recovery time (cSNRT) were significantly prolonged in subjects with SND (p<0.05). During a mean follow-up period of 5.0±3.6 years, five subjects with a history of syncope suffered appropriate implantable cardioverter defibrillator (ICD) discharges due to ventricular arrhythmias (7.4%). None of those diagnosed with SND suffered syncope or ICD therapies.

CONCLUSION

SND is not an uncommon finding in subjects with type 1 ECG pattern of BS. The occurrence of SND in relatively young patients may deserve meticulous investigation including sodium channel blocking test.

Determinants of incomplete penetrance and variable expressivity in heritable cardiac arrhythmia syndromes

Mutations in genes encoding ion channel pore-forming α-subunits and accessory β-subunits as well as intracellular calcium-handling proteins that collectively maintain the electromechanical function of the human heart serve as the underlying pathogenic substrate for a spectrum of sudden cardiac death (SCD)-predisposing heritable cardiac arrhythmia syndromes, including long QT syndrome (LQTS), short QT syndrome (SQTS), Brugada syndrome (BrS), and catecholaminergic polymorphic ventricular tachycardia (CPVT). Similar to many Mendelian disorders, the cardiac "channelopathies" exhibit incomplete penetrance, variable expressivity, and phenotypic overlap, whereby genotype-positive individuals within the same genetic lineage assume vastly different clinical courses as objectively assessed by phenotypic features such electrocardiographic abnormalities and number/type of cardiac events. In this Review, we summarize the current understanding of the global architecture of complex electrocardiographic traits such as the QT interval, focusing on the role of common genetic variants in the modulation of ECG parameters in health and the environmental and genetic determinants of incomplete penetrance and variable expressivity in the heritable cardiac arrhythmia syndromes most likely to be encountered in clinical practice.

Repolarization syndromes

Repolarization syndromes, including early repolarization, Brugada, and short and long QT, have been implicated increasingly as causes of sudden cardiac death (SCD) despite no obvious mechanical cardiac abnormalities. So-called idiopathic ventricular fibrillation is now often reassigned to one of the aforementioned entities. Underlying causes are diverse; genetic mutation has been proven in many but not all cases. Although high-risk individuals generally can be identified, most of the potential victim pool is still unknown and cannot be discovered at this time. Awareness of these entities' existence, knowledge of family history, and 12-lead electrocardiography are the initial steps toward preventing SCD in this population. Underlying mechanisms for ventricular tachycardia/fibrillation in such individuals include phase 2 reentry, early after depolarization, and vortex reentry. For the time-being, although most forms of long QT syndrome can be treated with β-blockers, an implantable cardioverter-defibrillator remains the only definitive therapy for the prevention of arrhythmic death among high-risk populations.

A new approach for the comparison of conduction abnormality between arrhythmogenic right ventricular cardiomyopathy/dysplasia and Brugada syndrome

BACKGROUND

Right ventricular outflow tract ventricular tachycardia (RVOT-VT), arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/ARVD), and Brugada syndrome (BrS) were characterized by arrhythmias originating in the right ventricle, and the pathophysiologic mechanism underlying these arrhythmias has not been fully understood.

METHODS

This study consisted of 40 subjects, including 20 patients with RVOT-VT, 10 patients with BrS, and 10 ARVD patients. The parameters on the signal-averaged electrocardiography (ECG) and the frequency components recorded from the wavelet-transformed ECG were compared between the three groups. Late potentials were positive in none of the patients with RVOT-VT, seven of the patients with BrS, and all of ARVD patients.

RESULTS

In Brugada and ARVD patients, the power of high-frequency components (80-150 Hz) was developed to a greater extent than in RVOT-VT patients. In the power analysis of the high-frequency components between BrS and ARVD, the frequency showing the greatest power was significantly higher in ARVD patients than that in BrS patients (145.4 ± 27.9 Hz vs 81.7 ± 19.9 Hz, P < 0.01).

CONCLUSIONS

High-frequency components were developed in ARVD and BrS, but not in RVOT-VT. The frequency levels showing high power by wavelet analysis obviously differ between ARVD and BrS. Wavelet analysis may provide new insight into unsolved mechanisms in arrhythmogenic right heart disease.

Effect of sodium-channel blockade on early repolarization in inferior/lateral leads in patients with idiopathic ventricular fibrillation and Brugada syndrome

BACKGROUND

A high incidence of early repolarization (ER) pattern in the inferolateral leads has been reported in patients with idiopathic ventricular fibrillation (IVF). Brugada syndrome (BS) is characterized by J-point or ST-segment elevation in the right precordial leads and ventricular fibrillation, and some patients with BS also have ER in the inferolateral leads.

OBJECTIVE

To compare the clinical characteristics and effects of sodium-channel blockade on ER between IVF patients with ER (early repolarization syndrome [ERS]) and BS patients with or without ER.

METHODS

Fourteen patients with ERS and 21 patients with BS were included in this study. ER was defined as an elevation of at least 0.1 mV from baseline in the QRS-T junction in the inferorolateral leads. Provocative tests with sodium-channel blockers were conducted in all patients with ERS to distinguish ERS from BS.

RESULTS

In the ERS group, all patients were male and most patients experienced ventricular fibrillation during sleep or low activity (79%). ER was attenuated by sodium-channel blockers in most patients with ERS (13/14, 93%) and BS (5/5, 100%), whereas ST-segment elevation was augmented in the right precordial leads in the BS group. The rates of positive late potentials were significantly higher in the BS group (60%) than in the ERS group (7%) (P <.01).

CONCLUSIONS

Some similarities were observed between ERS and BS, including gender, arrhythmia triggers, and response of ER to sodium-channel blockers. Unlike the ST segment in the right precordial leads in BS, ER was attenuated in patients with both ERS and BS, suggesting a differential mechanism between ER in the inferolateral leads and ST elevation in the right precordial leads.

Electrical storm in Brugada syndrome during pregnancy

Clinical and molecular characterization of the Brugada syndrome has progressed rapidly since its initial description. The role of hormonal changes during pregnancy and postpartum period on the pathogenesis of Brugada syndrome has not been studied. Herein, we describe a case of revelation of Brugada syndrome during pregnancy in a young woman who presented with electrical storm as the first manifestation. Low-dose isoproterenol infusion followed by oral quinidine inhibited the recurrence of ventricular tachyarrhythmia and normalized the electrocardiographic pattern. We emphasize the importance of hormonal changes during pregnancy as a precipitating factor for arrhythmic events in Brugada syndrome.

Genetic Testing for Cardiac Arrhythmias: Ready for Prime Time?

Despite the heterogeneity of substrates and clinical expressivity, genetic testing has a direct impact on clinical practice: it allows a specific diagnosis, including silent carriers (ie, asymptomatic diagnosis) and, in select diseases, the identification of a mutation has major impact for risk stratification and treatment of patients. This article addresses the role of genetic testing for each of the most epidemiologically relevant inherited arrhythmogenic diseases, specifically long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, hypertrophic cardiomyopathy, and arrhythmogenic right ventricular cardiomyopathy.

SCN5A mutation is associated with early and frequent recurrence of ventricular fibrillation in patients with Brugada syndrome

BACKGROUND

Mutations in SCN5A are reportedly linked to Brugada syndrome (BS), but recent observations suggest that they are not necessarily associated with ventricular fibrillation (VF) in BS patients. Therefore, the clinical importance of SCN5A mutations in BS patients was examined in the present study.

METHODS AND RESULTS

 The 108 BS patients were examined for SCN5A mutations and various parameters were compared between patients with and without mutations. An implantable cardioverter defibrillator (ICD) was implanted in 49 patients and a predictor of appropriate ICD shock was investigated. The existence of a SCN5A mutation was not associated with initial VF episodes (21.7% vs 20.0%, P=0.373). In the secondary prevention group, appropriate shock-free survival rate was significantly lower in patients with spontaneous type 1 ECG than in those without (41.1% vs 85.7% at 2 years, P=0.014). The appropriate shock-free survival rate was also significantly lower in patients with SCN5A mutations than in those without (28.6% vs 83.3% at 1 year, P=0.040). Appropriate shock was more frequent in patients with SCN5A mutations than in those without (6.6±6.2 vs 1.7±3.0, P=0.007).

CONCLUSIONS

SCN5A mutations are associated with early and frequent VF recurrence, but not with initial VF episodes. This is the first report on the genotype-phenotype interaction and clinical significance of this mutation.

When is genetic testing useful in patients suspected to have inherited cardiac arrhythmias?

PURPOSE OF REVIEW

In this article, we will review the appropriate use of genetic testing in those patients suspected to have inherited arrhythmogenic diseases, with specific focus on the indications for testing and the expected probability of positive genotyping.

RECENT FINDINGS

Important advances have been made in the identification of new genes, associated mutations, and polymorphisms that modulate susceptibility of acquired arrhythmias. We will examine the most recent advances relevant to the rational application of genetic analysis, guided by genotype-phenotype correlations derived from disease and patient-specific evaluation, as well as discussing novel technologies and recently published cost-effectiveness data.

SUMMARY

Genetic analysis can be performed to identify the molecular substrate in those patients suspected to be affected by an inherited arrhythmogenic disease; however, the clinical usefulness of this information is often not straightforward. We hope to emphasize the concept that there is a significant difference in the impact of genetic testing within the various arrhythmogenic disorders, and the benefit of accessing genetic testing is not the same in all patients. The resultant integration between the expected yield of genetic screening and cost may allow the formation of criteria to prioritize access for those who could derive the most clinical benefit.

Dual variation in SCN5A and CACNB2b underlies the development of cardiac conduction disease without Brugada syndrome

BACKGROUND

Inherited loss of function mutations in SCN5A have been linked to overlapping syndromes including cardiac conduction disease and Brugada syndrome (BrS). The mechanisms responsible for the development of one without the other are poorly understood.

METHODS

Direct sequencing was performed in a family with cardiac conduction disease. Wild-type (WT) and mutant channels were expressed in TSA201 cells for electrophysiological study. Green fluorescent protein (GFP)-fused WT or mutant genes were used to assess channel trafficking.

RESULTS

A novel SCN5A mutation, P1008S, was identified in all family members displaying first-degree atrioventricular block, but not in unaffected family members nor in 430 reference alleles. Peak P1008S current was 11.77% of WT (P < 0.001). Confocal microscopy showed that WT channels tagged with GFP were localized on the cell surface, whereas GFP-tagged P1008S channels remained trapped in intracellular organelles. Trafficking could be rescued by incubation at room temperature, but not by incubation with mexiletine (300 muM) at 37 degrees C. We also identified a novel polymorphism (D601E) in CACNB2b that slowed inactivation of L-type calcium current (I(Ca,L)), significantly increased total charge. Using the Luo-Rudy action potential (AP) model, we show that the reduction in sodium current (I(Na)) can cause loss of the right ventricular epicardial AP dome in the absence but not in the presence of the slowed inactivation of I(Ca,L). Slowed conduction was present in both cases.

CONCLUSIONS

Our results suggest genetic variations leading to a loss-of-function in I(Na) coupled with a gain of function in I(Ca,L) may underlie the development of cardiac conduction disease without BrS.

Tpeak-Tend interval and Tpeak-Tend/QT ratio as markers of ventricular tachycardia inducibility in subjects with Brugada ECG phenotype

AIMS

The present study investigated whether several ECG markers of ventricular repolarization are associated with ventricular tachycardia/fibrillation (VT/VF) inducibility in subjects with type 1 ECG pattern of Brugada syndrome (BS).

METHODS AND RESULTS

The clinical data of 23 individuals (19 males, age 42.69 +/- 14.63) with spontaneous (n = 10) or drug-induced (n = 13) type 1 ECG pattern of BS who underwent programmed ventricular stimulation were analysed. Sustained VT/VF was induced in 17 subjects (74%) and was significantly associated with the presence of spontaneous type 1 ECG of BS (P = 0.012). Among the studied ECG repolarization markers, subjects with inducible VT/VF displayed an increased T(peak)-T(end) interval in leads V(2) (88.82 +/- 15.70 vs. 78.33 +/- 4.08 ms, P = 0.02) and V(6) (76.33 +/- 10.08 vs. 66.66 +/- 5.16 ms, P = 0.04) and a greater T(peak)-T(end)/QT ratio in lead V(6) (0.214 +/- 0.028 vs. 0.180 +/- 0.014, P = 0.009) compared with those without arrhythmias. Ventricular tachycardia/fibrillation inducibility was not associated with arrhythmic events during a mean follow-up period of 4.61 +/- 2.14 years (P = 0.739).

CONCLUSION

The T(peak)-T(end) interval and T(peak)-T(end)/QT ratio were associated with VT/VF inducibility in BS. The utility of T(peak)-T(end)/QT ratio as a new marker of arrhythmogenesis in BS requires further studies, including a large number of patients.

Brugada syndrome: insights of ST elevation, arrhythmogenicity, and risk stratification from experimental observations

Brugada syndrome (BrS), caused by ion channel abnormalities, is characterized by ST segment elevation and negative T waves in the right precordial electrocardiographic (ECG) leads recorded over the right ventricular outflow tract (RVOT). BrS is sensitive to body temperature and can lead to T-wave alternans (TWA), ventricular tachycardia, and sudden death. Recent studies in an isolated canine RVOT model of BrS demonstrated that reversal of the transmural gradient of repolarization caused the ECG characteristics and that major intraepicardial and transmural dispersion of action potentials (APs) initiated phase 2 reentry, premature ventricular activations, and tachyarrhythmias. Hypothermia enhanced the heterogeneity of the AP and promoted the origination of phase 2 reentry in the epicardium of the RVOT, but the prolonged AP duration frequently blocked reentry. Hyperthermia abbreviated the AP and facilitated the maintenance of reentry and tachyarrhythmias. Bradycardia promoted alternans in the phase 2 dome of the AP within the epicardium of the RVOT, resulting in TWA. The above phenomena were localized in the epicardium of the RVOT. Blockade of the transient outward current, I(to), reduced AP heterogeneity and prevented arrhythmias in the BrS model. In addition, epicardial activation delay led to fragmented QRS, a risk marker of prognosis in BrS. Body surface mapping in patients with BrS supported these experimental findings. In conclusion, the AP heterogeneity within the epicardium of the RVOT contributes to the ECG characteristics, temperature sensitivity, TWA, and arrhythmias in BrS, and body surface mapping and fragmented QRS can be effective predictors of risk in patients with BrS.

Gender differences in clinical manifestations of Brugada syndrome

OBJECTIVES

We sought to assess differences in phenotype and prognosis between men and women in a large population of patients with Brugada syndrome.

BACKGROUND

A male predominance has been reported in the Brugada syndrome. No specific data are available, however, concerning gender differences in the clinical manifestations and their role in prognosis.

METHODS

Patients with Brugada syndrome were prospectively included in the study. Data on baseline characteristics, electrocardiogram parameters before and after pharmacological test, and events in follow-up were recorded for all patients.

RESULTS

Among 384 patients, 272 (70.8%) were men and 112 (29.2%) women. At inclusion, men had experienced syncope more frequently (18%) or aborted sudden cardiac death (6%) than women (14% and 1%, respectively, p = 0.04). Men also had greater rates of spontaneous type-1 electrocardiogram, greater ST-segment elevation, and greater inducibility of ventricular fibrillation (p < 0.001 for all). Conversely, conduction parameters and corrected QT intervals significantly increased more in women in response to sodium blockers (p = 0.03 and p = 0.001, respectively). During a mean follow-up of 58 +/- 48 months, sudden cardiac death or documented ventricular fibrillation occurred in 31 men (11.6%) and 3 women (2.8%; p = 0.003). The presence of previous symptoms was the most important predictor for cardiac events in men, whereas a longer PR interval was identified among those women with a greater risk in this series.

CONCLUSIONS

Men with Brugada syndrome present with a greater risk clinical profile than women and have a worse prognosis. Although classical risk factors identify male patients with worse outcome, conduction disturbances could be a marker of risk in the female population.

Malignant perinatal variant of long-QT syndrome caused by a profoundly dysfunctional cardiac sodium channel

BACKGROUND

Inherited cardiac arrhythmia susceptibility contributes to sudden death during infancy and may contribute to perinatal and neonatal mortality, but the molecular basis of this risk and the relationship to genetic disorders presenting later in life is unclear. We studied the functional and pharmacological properties of a novel de novo cardiac sodium channel gene (SCN5A) mutation associated with an extremely severe perinatal presentation of long-QT syndrome in unrelated probands of different ethnicity.

METHODS AND RESULTS

Two subjects exhibiting severe fetal and perinatal ventricular arrhythmias were screened for SCN5A mutations, and the functional properties of a novel missense mutation (G1631D) were determined by whole-cell patch clamp recording. In vitro electrophysiological studies revealed a profound defect in sodium channel function characterized by approximately 10-fold slowing of inactivation, increased persistent current, slowing of recovery from inactivation, and depolarized voltage dependence of activation and inactivation. Single-channel recordings demonstrated increased frequency of late openings, prolonged mean open time, and increased latency to first opening for the mutant. Subjects carrying this mutation responded clinically to the combination of mexiletine with propranolol and survived. Pharmacologically, the mutant exhibited 2-fold greater tonic and use-dependent mexiletine block than wild-type channels. The mutant also exhibited enhanced tonic (2.4-fold) and use-dependent block ( approximately 5-fold) by propranolol, and we observed additive effects of the 2 drugs on the mutant.

CONCLUSIONS

Our study demonstrates the molecular basis for a malignant perinatal presentation of long-QT syndrome, illustrates novel functional and pharmacological properties of SCN5A-G1631D, which caused the disorder, and reveals therapeutic benefits of propranolol block of mutant sodium channels in this setting.

SCN5A channelopathies--an update on mutations and mechanisms

Voltage-gated Na+ channels mediate the rapid upstroke of the action potential in excitable tissues. Na(v)1.5, encoded by the SCN5A gene, is the predominant isoform in the heart. Mutations in SCN5A are associated with distinct cardiac excitation disorders often resulting in life-threatening arrhythmias. This review outlines the currently known SCN5A mutations linked to three distinct cardiac rhythm disorders: long QT syndrome subtype 3 (LQT3), Brugada syndrome (BS), and cardiac conduction disease (CCD). Electrophysiological properties of the mutant channels are summarized and discussed in terms of Na+ channel structure-function relationships and regarding molecular mechanisms underlying the respective cardiac dysfunction. Possible reasons for less convincing genotype-phenotype correlations are suggested.

Clinical impact of genetic studies in lethal inherited cardiac arrhythmias

Over the past decade, molecular genetic studies have established a link between a number of inherited cardiac arrhythmias, including congenital long QT syndrome (LQTS) and Brugada syndrome (BrS), and mutations in genes encoding for ion channels or other membrane components. Twelve forms of LQTS have been identified in 50-70% of clinically affected patients. Genotype-phenotype correlations have been rigorously investigated in LQT1, LQT2 and LQT3 syndromes, which constitute more than 90% of genotyped LQTS patients, enabling stratification of risk and effective treatment of genotyped patients. Genotype-specific triggers for both the cardiac events and the clinical course have been reported, and genotype-specific therapy has been already introduced. More recently, mutation site-specific differences in the clinical phenotype have been reported in LQT1 and LQT2 patients, indicating the possibility of mutation site-specific management or treatment. In contrast, only one-third of BrS patients can be genotyped, and data on genotype-phenotype relationships in clinical studies are limited. A Haplotype B consisting of 6 individual DNA polymorphisms within the proximal promoter region of the SCN5A gene was recently identified only in Asians (frequency 22%). Individuals with Haplotype B show significantly longer duration of both PQ and QRS than those without Haplotype B, indicating that Haplotype B likely contributes to the higher incidence of BrS in Asian populations.

Prognosis of subjects with Brugada-type electrocardiogram in a population of middle-aged Japanese diagnosed during a health examination

There is controversy about the clinical significance of an incidental finding of a Brugada-type electrocardiogram (ECG) pattern. To assess the prognosis of subjects with a diagnosis of a Brugada-type ECG pattern during a health examination, 13,904 subjects (mean age 58 +/- 10 years) who had the annual health examination including an ECG offered to adult citizens of Moriguchi City, Osaka, Japan, in 1997 were studied. A Brugada-type ECG pattern was found in 98 subjects, and 37 subjects had type 1. During a mean follow-up of 7.8 +/- 1.6 years, there were 4 deaths (4.1%) and 1 cardiovascular death (1.0%) in subjects with a Brugada-type ECG pattern, whereas there were 612 deaths (4.4%) and 142 cardiovascular deaths (1.0%) in those without. One cardiovascular death in a subject with a Brugada-type ECG pattern was sudden death. Unadjusted proportional hazards regression analyses showed that Brugada-type ECG pattern was not associated with either all-cause (hazard ratio [HR] 0.90, 95% confidence interval [CI] 0.34 to 2.41) or cardiovascular mortality (HR 0.97, 95% CI 0.14 to 6.93). After adjustment for cardiovascular risk factors, Brugada-type ECG pattern had no association with either all-cause (HR 0.77, 95% CI 0.29 to 2.07) or cardiovascular mortality (HR 1.01, 95% CI 0.14 to 7.31). In conclusion, Brugada-type ECG patterns diagnosed during a health examination in a middle-aged population had a low risk of sudden death and were not associated with increased risk of either cardiovascular or all-cause mortality.

Brugada syndrome

Since its first description in 1992 as a new clinical entity, the Brugada syndrome has aroused great interest among physicians and basic scientists. Two consensus conferences held in 2002 and 2005 helped refine the current accepted definite diagnostic criteria for the syndrome, briefly, the characteristic ECG pattern (right bundle branch block and persistent ST segment elevation in right precordial leads) together with the susceptibility for ventricular fibrillation and sudden death. In the last years, clinical and basic research have provided very valuable knowledge on the genetic basis, the cellular mechanisms responsible for the typical ECG features and the electrical susceptibility, the clinical particularities and modulators, the diagnostic value of drug challenge, the risk stratification of sudden death (possibly the most controversial issue) and, finally, the possible therapeutic approaches for the disease. Each one of these points is discussed in this review, which intends to provide updated information supplied by recent clinical and basic studies.