Absence of Pathognomonic or Inflammatory Patterns in Cardiac Biopsies From Patients With Brugada Syndrome

Zebrafish as a Model System for Brugada Syndrome

Brugada syndrome (BrS) is an inheritable cardiac arrhythmogenic disease, associated with an increased risk of sudden cardiac death. It is most common in males around the age of 40 and the prevalence is higher in Asia than in Europe and the United States. The pathophysiology underlying BrS is not completely understood, but several hypotheses have been proposed. So far, the best effective treatment is the implantation of an implantable cardioverter-defibrillator (ICD), but device-related complications are not uncommon. Therefore, there is an urgent need to improve diagnosis and risk stratification and to find new treatment options. To this end, research should further elucidate the genetic basis and pathophysiological mechanisms of BrS. Several experimental models are being used to gain insight into these aspects. The zebrafish (Danio rerio) is a widely used animal model for the study of cardiac arrhythmias, as its cardiac electrophysiology shows interesting similarities to humans. However, zebrafish have only been used in a limited number of studies on BrS, and the potential role of zebrafish in studying the mechanisms of BrS has not been reviewed. Therefore, the present review aims to evaluate zebrafish as an animal model for BrS. We conclude that zebrafish can be considered as a valuable experimental model for BrS research, not only for gene editing technologies, but also for screening potential BrS drugs.

More than 30 years of Brugada syndrome: a critical appraisal of achievements and open issues

Over the last three decades, what is referred to as Brugada syndrome (BrS) has developed from a clinical observation of initially a few cases of sudden cardiac death (SCD) in the absence of structural heart disease with ECG signs of "atypical right bundle brunch block" to a predominantly electrocardiographic, and to a lesser extent genetic, diagnosis. Today, BrS is diagnosed in patients without overt structural heart disease and a spontaneous Brugada type 1 ECG pattern regardless of symptoms. The diagnosis of BrS is less clear in those with an only transient or drug-induced type 1 Brugada pattern, but should be considered in the presence of an arrhythmic syncope, family history of BrS, or family history of sudden death. In addition to survived cardiac arrest, syncope is probably the single most decisive risk marker for future arrhythmias. For asymptomatic BrS, risk stratification remains challenging. General recommendations to lower the risk in BrS include avoidance of drugs/agents known to induce and/or increase right precordial ST-segment elevation, including treatment of fever with antipyretic drugs. Several ECG markers that have been associated with an increased risk of SCD have been incorporated into a recently published risk score for BrS. The aim of this article is to provide an overview of the status of risk stratification and to illustrate open issues und gaps in evidence in BrS.

The new European Society of Cardiology guideline for the management of cardiomyopathies: key messages for cardiac electrophysiologists

Electrocardiographic findings and arrhythmias are common in cardiomyopathies. Both may be an early indication of a specific diagnosis or may occur due to myocardial fibrosis and/or reduced contractility. Brady- and tachyarrhythmias significantly contribute to increased morbidity and mortality in patients with cardiomyopathies. Antiarrhythmic therapy including risk stratification is often challenging and plays a major role for these patients. Thus, an "electrophysiological" perspective on guidelines on cardiomyopathies may be warranted. As the European Society of Cardiology (ESC) has recently published a new guideline for the management of cardiomyopathies, this overview aims to present key messages of these guidelines. Innovations include a new phenotype-based classification system with emphasis on a multimodal imaging approach for diagnosis and risk stratification. The guideline includes detailed chapters on dilated and hypertrophic cardiomyopathy and their phenocopies, arrhythmogenic right ventricular cardiomyopathy, and restrictive cardiomyopathy as well as syndromic and metabolic cardiomyopathies. Patient pathways guide clinicians from the initial presentation to diagnosis. The role of cardiovascular magnetic resonance imaging and genetic testing during diagnostic work-up is stressed. Concepts of rhythm and rate control for atrial fibrillation have led to new recommendations, and the role of defibrillator therapy in primary prevention is discussed in detail. Whilst providing general guidelines for management, the primary objective of the guideline is to ascertain the disease etiology and disease-specific, individualized management.

Postmortem genetic testing in sudden unexplained death: A public health laboratory experience

Sudden unexplained death in the young poses a diagnostically challenging situation for practicing autopsy pathologists, especially in the absence of anatomic and toxicological findings. Postmortem genetic testing may identify pathogenic variants in the deceased of such cases, including those associated with arrhythmogenic channelopathies and cardiomyopathies. The Wisconsin State Laboratory of Hygiene (WSLH) is a state-run public health laboratory which performs postmortem genetic testing at no cost to Wisconsin medical examiners and coroners. The current study examines sequencing data from 18 deceased patients (ages 2 months to 49 years, 5 females) submitted to WSLH, from 2016 to 2021. Panel-based analysis was performed on 10 cases, and whole exome sequencing was performed on the most recent 8 cases. Genetic variants were identified in 14 of 18 decedents (77.8%), including 7 with pathogenic or likely pathogenic variants (38.9%). Whole exome sequencing was more likely to yield a positive result, more variants per decedent, and a larger number of variants of uncertain significance. While panel-based testing may offer definitive pathogenic variants in some cases, less frequent variants may be excluded. Whole exome testing may identify rare variants missed by panels, but increased yield of variants of uncertain significance may be difficult to interpret. Postmortem genetic testing in young decedents of sudden unexplained death can provide invaluable information to autopsy pathologists to establish accurate cause and manner of death and to decedent's relatives to allow appropriate management. A public health laboratory model may be a financially advisable alternative to commercial laboratories for medical examiner's/coroner's offices.

Arrhythmogenic right ventricular cardiomyopathy mimicking Brugada - a case report

We report a rare case of arrhythmogenic right ventricular cardiomyopathy (ARVC). Middle-aged Kuwaiti gentleman presented to a polyclinic with complaints of dizziness and palpitation. Electrocardiogram (ECG) at the polyclinic showed polymorphic ventricular tachycardia, and hence he was referred to our center. ECG at the emergency room showed a Brugada pattern with epsilon waves. Echo showed right ventricular dysfunction with pulmonary arterial hypertension. Magnetic resonance imaging showed evidence of ARVC. He was referred to the electrophysiology team and implanted an implantable cardioverter-defibrillator electively.

Longitudinal assessment of structural phenotype in Brugada syndrome using cardiac magnetic resonance imaging

Background

Despite historically being considered a channelopathy, subtle structural changes have been reported in Brugada syndrome (BrS) on histopathology and cardiac magnetic resonance (CMR) imaging. It is not known if these structural changes progress over time.

Objective

The study sought to assess if structural changes in BrS evolve over time with serial CMR assessment and to investigate the utility of parametric mapping techniques to identify diffuse fibrosis in BrS.

Methods

Patients with a diagnosis of BrS based on international guidelines and normal CMR at least 3 years prior to the study period were invited to undergo repeat CMR. CMR images were analyzed de novo and compared at baseline and follow-up.

Results

Eighteen patients with BrS (72% men; mean age at follow-up 47.4 ± 8.9 years) underwent serial CMR with an average of 5.0 ± 1.7 years between scans. No patients had late gadolinium enhancement (LGE) on baseline CMR, but 4 (22%) developed LGE on follow-up, typically localized to the right ventricular (RV) side of the basal septum. RV end-systolic volume increased over time (P = .04) and was associated with a trend toward reduction in RV ejection fraction (P = .07). Four patients showed a reduction in RV ejection fraction >10%. There was no evidence of diffuse myocardial fibrosis observed on parametric mapping.

Conclusions

Structural changes may evolve over time with development of focal fibrosis, evidenced by LGE on CMR in a significant proportion of patients with BrS. These findings have implications for our understanding of the pathological substrate in BrS and the longitudinal evaluation of patients with BrS.

Concealed Substrates in Brugada Syndrome: Isolated Channelopathy or Associated Cardiomyopathy?

Brugada syndrome (BrS) is an inherited autosomal dominant genetic disorder responsible for sudden cardiac death from malignant ventricular arrhythmia. The term "channelopathy" is nowadays used to classify BrS as a purely electrical disease, mainly occurring secondarily to loss-of-function mutations in the α subunit of the cardiac sodium channel protein Nav1.5. In this setting, arrhythmic manifestations of the disease have been reported in the absence of any apparent structural heart disease or cardiomyopathy. Over the last few years, however, a consistent amount of evidence has grown in support of myocardial structural and functional abnormalities in patients with BrS. In detail, abnormal ventricular dimensions, either systolic or diastolic dysfunctions, regional wall motion abnormalities, myocardial fibrosis, and active inflammatory foci have been frequently described, pointing to alternative mechanisms of arrhythmogenesis which challenge the definition of channelopathy. The present review aims to depict the status of the art of concealed arrhythmogenic substrates in BrS, often resulting from an advanced and multimodal diagnostic workup, to foster future preclinical and clinical research in support of the cardiomyopathic nature of the disease.

Structural Heart Alterations in Brugada Syndrome: Is it Really a Channelopathy? A Systematic Review

Brugada syndrome (BrS) is classified as an inherited cardiac channelopathy attributed to dysfunctional ion channels and/or associated proteins in cardiomyocytes rather than to structural heart alterations. However, hearts of some BrS patients exhibit slight histologic abnormalities, suggesting that BrS could be a phenotypic variant of arrhythmogenic cardiomyopathy. We performed a systematic review of the literature following Preferred Reporting Items for Systematic Reviews and Meta-Analyses Statement (PRISMA) criteria. Our comprehensive analysis of structural findings did not reveal enough definitive evidence for reclassification of BrS as a cardiomyopathy. The collection and comprehensive analysis of new cases with a definitive BrS diagnosis are needed to clarify whether some of these structural features may have key roles in the pathophysiological pathways associated with malignant arrhythmogenic episodes.

The Genetics of Brugada Syndrome

Brugada syndrome is a heritable channelopathy characterized by a peculiar electrocardiogram (ECG) pattern and increased risk of cardiac arrhythmias and sudden death. The arrhythmias originate because of an imbalance between the repolarizing and depolarizing currents that modulate the cardiac action potential. Even if an overt structural cardiomyopathy is not typical of Brugada syndrome, fibrosis and structural changes in the right ventricle contribute to a conduction slowing, which ultimately facilitates ventricular arrhythmias. Currently, Mendelian autosomal dominant transmission is detected in less than 25% of all clinical confirmed cases. Although 23 genes have been associated with the condition, only SCN5A, encoding the cardiac sodium channel, is considered clinically actionable and disease causing. The limited monogenic inheritance has pointed toward new perspectives on the possible complex genetic architecture of the disease, involving polygenic inheritance and a polygenic risk score that can influence penetrance and risk stratification. Expected final online publication date for the Annual Review of Genomics and Human Genetics, Volume 23 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Electrocardiographic Findings, Arrhythmias, and Left Ventricular Involvement in Familial ST-Depression Syndrome

BACKGROUND

Familial ST-depression syndrome is an inherited disease characterized by persistent, nonischemic ST-deviations, and risk of arrhythmias and heart failure. We aimed at further characterizing the ECG, arrhythmias, and structural characteristics associated with this novel syndrome.

METHODS

Retrospective analysis of data from consecutive families with familial ST-depression Syndrome in Denmark. ECG features, prevalence and type of arrhythmias, occurrence of systolic dysfunction, and medium-term outcome were analyzed.

RESULTS

Forty affected individuals (43% men; mean age at diagnosis 49.1 years) from 14 apparently unrelated families with ≥2 affected members were included. Autosomal dominant inheritance was observed in all families. The ECG phenotype seemed to develop in prepuberty and the ST-deviations were persistent and most pronounced in leads V4/V5/II, respectively. Serial ECG analyses showed stable to slow progression of the ECG phenotype. Exercise accentuated the ST-deviations with a maximum difference between rest/stress (mean) of -117 μV in lead V5. During a mean follow-up of 9.3±7.1 years 5 (13%) patients developed sustained ventricular arrhythmias or (aborted) sudden cardiac death, 10 (25%) developed atrial fibrillation, 2 (5%) other supraventricular arrhythmias, and 10 (25%) were diagnosed with left ventricular ejection fraction ≤50%. The ventricular arrhythmias were polymorphic with relatively short-coupled premature ventricular contractions at onset (300-360 ms); no QT prolongation was observed. Seven patients had at least one catheter ablation; 5 for supraventricular arrhythmias and 2 for ventricular arrhythmias. Males experienced more arrhythmic end points than females (P<0.01).

CONCLUSIONS

The familial ST-depression ECG phenotype is stable to slowly progressive after medium-term follow-up. Clinically, both supra- and ventricular arrhythmias are common; as are some degree of left ventricular systolic dysfunction. Familial ST-depression represent a novel inherited cause of polymorphic ventricular tachycardia.

Biventricular Myocardial Fibrosis and Sudden Death in Patients With Brugada Syndrome

BACKGROUND

Electrophysiological, imaging, and pathological studies have reported the presence of subtle structural abnormalities in hearts from patients with Brugada syndrome (BrS). However, data concerning disease involvement outside of the right ventricular outflow tract are limited.

OBJECTIVES

This study sought to characterize the presence and distribution of ventricular myocardial fibrosis in a cohort of decedents experiencing sudden cardiac death caused by BrS.

METHODS

The authors evaluated 28 whole hearts from consecutive sudden cardiac death cases attributed to BrS and 29 hearts from a comparator group comprised of noncardiac deaths (control subjects). Cardiac tissue from 6 regions across the right and left ventricle were stained with Picrosirius red for collagen and tissue composition was determined using image analysis software. Postmortem genetic testing was performed in cases with DNA retained for analysis.

RESULTS

Of 28 BrS decedents (75% men; median age of death 25 years), death occurred in sleep or at rest in 24 of 28 (86%). The highest proportion of collagen was observed in the epicardial right ventricular outflow tract of the BrS group (23.7%; 95% CI: 20.8%-26.9%). Ventricular myocardium from BrS decedents demonstrated a higher proportion of collagen compared with control subjects (ratio 1.45; 95% CI: 1.22-1.71; P < 0.001), with no significant interactions with respect to sampling location or tissue layer. There was insufficient evidence to support differences in collagen proportion in SCN5A-positive cases (n = 5) when compared with control subjects (ratio 1.23; 95% CI: 0.75-1.43; P = 0.27).

CONCLUSIONS

Brugada syndrome is associated with increased collagen content throughout right and left ventricular myocardium, irrespective of sampling location or myocardial layer.

Risk stratification of patients with Brugada syndrome: the impact of myocardial strain analysis using cardiac magnetic resonance feature tracking

OBJECTIVE

This study evaluated the prognostic significance of cardiac magnetic resonance myocardial feature tracking (CMR-FT) in patients with Brugada syndrome (BrS) to detect subclinical alterations and predict major adverse events (MAE).

METHODS

CMR was performed in 106 patients with BrS and 25 healthy controls. Biventricular global strain analysis was assessed using CMR-FT. Patients were followed over a median of 11.6 [8.8 ± 13.8] years.

RESULTS

The study cohort was subdivided according to the presence of a spontaneous type 1 ECG (sECG) into sBrS (BrS with sECG, n = 34 (32.1%)) and diBrS (BrS with drug-induced type 1 ECG, n = 72 (67.9%)). CMR-FT revealed morphological differences between sBrS and diBrS patients with regard to right ventricular (RV) strain (circumferential (%) (sBrS -7.9 ± 2.9 vs diBrS - 9.5 ± 3.1, p = 0.02) and radial (%) (sBrS 12.0 ± 4.3 vs diBrS 15.4 ± 5.4, p = 0.004)). During follow-up, MAE occurred in 11 patients (10.4%). Multivariable analysis was performed to identify independent predictors for the occurrence of events during follow-up. The strongest predictive value was found for RV circumferential strain (OR 3.2 (95% CI 1.4 - 6.9), p = 0.02) and RVOT/BSA (OR 3.1 (95% CI 1.0 - 7.0), p = 0.03).

CONCLUSIONS

Myocardial strain analysis detected early subclinical alterations, prior to apparent changes in myocardial function, in patients with BrS. While usual functional parameters were within the normal range, CMR-FT revealed pathological results in patients with an sECG. Moreover, RV circumferential strain and RVOT size provided additional prognostic information on the occurrence of MAE during follow-up, which reflects electrical vulnerability.

Brugada syndrome and reduced right ventricular outflow tract conduction reserve: a final common pathway?

Brugada syndrome (BrS) was first described as a primary electrical disorder predisposing to the risk of sudden cardiac death and characterized by right precordial lead ST elevation. Early description of right ventricular structural abnormalities and of right ventricular outflow tract (RVOT) conduction delay in BrS patients set the stage for the current controversy over the pathophysiology underlying the syndrome: channelopathy or cardiomyopathy; repolarization or depolarization. This review examines the current understanding of the BrS substrate, its genetic and non-genetic basis, theories of pathophysiology, and the clinical implications thereof. We propose that the final common pathway for BrS could be viewed as a disease of 'reduced RVOT conduction reserve'.

Brugada syndrome and arrhythmogenic cardiomyopathy: overlapping disorders of the connexome?

Arrhythmogenic cardiomyopathy (ACM) and Brugada syndrome (BrS) are inherited diseases characterized by an increased risk for arrhythmias and sudden cardiac death. Possible overlap between the two was suggested soon after the description of BrS. Since then, various studies focusing on different aspects have been published pointing to similar findings in the two diseases. More recent findings on the structure of the cardiac cell-cell junctions may unite the pathophysiology of both diseases and give further evidence to the theory that they may in part be variants of the same disease spectrum. In this review, we aim to summarize the studies indicating the pathophysiological, genetic, structural, and electrophysiological overlap between ACM and BrS.

Mechanisms of Arrhythmias in the Brugada Syndrome

Arrhythmias in Brugada syndrome patients originate in the right ventricular outflow tract (RVOT). Over the past few decades, the characterization of the unique anatomy and electrophysiology of the RVOT has revealed the arrhythmogenic nature of this region. However, the mechanisms that drive arrhythmias in Brugada syndrome patients remain debated as well as the exact site of their occurrence in the RVOT. Identifying the site of origin and mechanism of Brugada syndrome would greatly benefit the development of mechanism-driven treatment strategies.

Ventricular Dysrhythmias During Long-Term Follow-Up in Patients With Inherited Cardiac Arrhythmia

Reports on development of frequent ventricular premature complexes (fVPC), (non)sustained ventricular tachycardias ([n]sVT), or ventricular fibrillation (VF) and their interrelationship in patients with different inherited cardiac arrhythmia (ICA) have sofar not been reported. The aim of this study is therefore to examine incidences and recurrences rates of sVT and VF ("malignant ventricular tachyarrhythmias, VTA") in addition to the incidence of fVPC and nsVT ("ventricular dysrhythmias, VDR") in patients with various ICA during long-term follow up. Patients (N = 167, 88 male, age 45 ± 15 years) with ICA including definite/borderline arrhythmogenic right ventricular cardiomyopathy (ARVC, N = 47), Brugada syndrome (BrS, N = 71), catecholaminergic polymorphic ventricular tachycardia (CPVT, N = 7), long QT syndrome (LQTS, N = 41) or short QT syndrome (SQTS, N = 1) who had frequent 24-hour Holter monitoring during a follow-up period of 4.6 ± 4.4 years. During the initial screening visit, 15 patients had a history of malignant VTA. fVPC and nsVT was observed in respectively 19% (OHCA/VF/sVT: N = 9) and 13% (OHCA/VF/sVT: N = 4) of all patients. Compared with the ARVC group, patients with BrS and LQTS had less frequent fVPC and nsVT (fVPC: odds ratio [OR] 0.20, 95% confidence interval [CI] 0.08 to 0.49, p <0.000 and OR 0.09, 95% CI 0.02 to 0.33, p <0.000; nsVT:OR 0.17, 95% CI 0.06 to 0.50, p = 0.001 and OR 0.09, 95% CI 0.02 to 0.46, p = 0.003). The recurrence rate of malignant VTA was 33%. In conclusion, variety of VDR and malignant VTA were found during long-term follow-up in patients with ICA. During nearly a 5 years follow-up period, the recurrence rate of malignant VTA was considerable. fVPC, nsVT, and malignant VTA were most often found in patients with an ARVC.

2019 HRS expert consensus statement on evaluation, risk stratification, and management of arrhythmogenic cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is an arrhythmogenic disorder of the myocardium not secondary to ischemic, hypertensive, or valvular heart disease. ACM incorporates a broad spectrum of genetic, systemic, infectious, and inflammatory disorders. This designation includes, but is not limited to, arrhythmogenic right/left ventricular cardiomyopathy, cardiac amyloidosis, sarcoidosis, Chagas disease, and left ventricular noncompaction. The ACM phenotype overlaps with other cardiomyopathies, particularly dilated cardiomyopathy with arrhythmia presentation that may be associated with ventricular dilatation and/or impaired systolic function. This expert consensus statement provides the clinician with guidance on evaluation and management of ACM and includes clinically relevant information on genetics and disease mechanisms. PICO questions were utilized to evaluate contemporary evidence and provide clinical guidance related to exercise in arrhythmogenic right ventricular cardiomyopathy. Recommendations were developed and approved by an expert writing group, after a systematic literature search with evidence tables, and discussion of their own clinical experience, to present the current knowledge in the field. Each recommendation is presented using the Class of Recommendation and Level of Evidence system formulated by the American College of Cardiology and the American Heart Association and is accompanied by references and explanatory text to provide essential context. The ongoing recognition of the genetic basis of ACM provides the opportunity to examine the diverse triggers and potential common pathway for the development of disease and arrhythmia.

Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia (ARVC/D) - What We Have Learned after 40 Years of the Diagnosis of This Clinical Entity

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) was initially recognized as a clinical entity by Fontaine and Marcus, who evaluated a group of patients with ventricular tachyarrhythmia from a structurally impaired right ventricle (RV). Since then, there have been significant advances in the understanding of the pathophysiology, manifestation and clinical progression, and prognosis of the pathology. The identification of genetic mutations impairing cardiac desmosomes led to the inclusion of this entity in the classification of cardiomyopathies. Classically, ARVC/D is an inherited disease characterized by ventricular arrhythmias, right and / or left ventricular dysfunction; and fibro-fatty substitution of cardiomyocytes; its identification can often be challenging, due to heterogeneous clinical presentation, highly variable intra- and inter-family expressiveness, and incomplete penetrance.

In the absence of a gold standard that allows the diagnosis of ARVC/D, several diagnostic categories were combined and recently reviewed for a higher diagnostic sensitivity, without compromising the specificity. The finding that electrical abnormalities, particularly ventricular arrhythmias, usually precede structural abnormalities is extremely important for risk stratification in positive genetic members. Among the complementary exams, cardiac magnetic resonance imaging (CMR) allows the early diagnosis of left ventricular impairment, even before morpho-functional abnormalities. Risk stratification remains a major clinical challenge, and antiarrhythmic drugs, catheter ablation and implantable cardioverter defibrillator are the currently available therapeutic tools. The disqualification of the sport prevents cases of sudden death because the effort can trigger not only the electrical instability, but also the onset and progression of the disease.

Diagnostic and therapeutic strategies for arrhythmogenic right ventricular dysplasia/cardiomyopathy patient

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is a rare inherited heart muscle disease characterized by ventricular tachyarrhythmia, predominant right ventricular dysfunction, and sudden cardiac death. Its pathophysiology involves close interaction between genetic mutations and exposure to physical activity. Mutations in genes encoding desmosomal protein are the most common genetic basis. Genetic testing plays important roles in diagnosis and screening of family members. Syncope, palpitation, and lightheadedness are the most common symptoms. The 2010 Task Force Criteria is the standard for diagnosis today. Implantation of a defibrillator in high-risk patients is the only therapy that provides adequate protection against sudden death. Selection of patients who are best candidates for defibrillator implantation is challenging. Exercise restriction is critical in affected individuals and at-risk family members. Antiarrhythmic drugs and ventricular tachycardia ablation are valuable but palliative components of the management. This review focuses on the current diagnostic and therapeutic strategies in ARVD/C and outlines the future area of development in this field.

Brugada syndrome in children - Stepping into unchartered territory

Brugada syndrome (BrS) is an autosomal dominant inherited channelopathy. It is associated with a typical pattern of ST-segment elevation in the precordial leads V1-V3 and potentially lethal ventricular arrhythmias in otherwise healthy patients. It is frequently seen in young Asian males, in whom it has previously been described as sudden unexplained nocturnal death syndrome. Although it typically presents in young adults, it is also known to present in children and infants, especially in the presence of fever. Our understanding of the genetic pathogenesis and management of BrS has grown substantially considering that it has only been 24 years since its first description as a unique clinical entity. However, there remains much to be learned, especially in the pediatric population. This review aims to discuss the epidemiology, genetics, and pathogenesis of BrS. We will also discuss established standards and new innovations in the diagnosis, prognostication, risk stratification, and management of BrS. Literature search was run on the National Center for Biotechnology Information's website, using the Medical Subject Headings (MeSH) database with the search term "Brugada Syndrome" (MeSH), and was run on the PubMed database using the age filter (birth-18 years), yielding 334 results. The abstracts of all these articles were studied, and the articles were categorized and organized. Articles of relevance were read in full. As and where applicable, relevant references and citations from the primary articles were further explored and read in full.

Early Repolarization Syndrome; Mechanistic Theories and Clinical Correlates

The early repolarization (ER) pattern on the 12-lead electrocardiogram is characterized by J point elevation in the inferior and/or lateral leads. The ER pattern is associated with an increased risk of ventricular arrhythmias and sudden cardiac death (SCD). Based on studies in animal models and genetic studies, it has been proposed that J point elevation in ER is a manifestation of augmented dispersion of repolarization which creates a substrate for ventricular arrhythmia. A competing theory regarding early repolarization syndrome (ERS) proposes that the syndrome arises as a consequence of abnormal depolarization. In recent years, multiple clinical studies have described the characteristics of ER patients with VF in more detail. The majority of these studies have provided evidence to support basic science observations. However, not all clinical observations correlate with basic science findings. This review will provide an overview of basic science and genetic research in ER and correlate basic science evidence with the clinical phenotype.

Fibrosis, Connexin-43, and Conduction Abnormalities in the Brugada Syndrome

BACKGROUND

The right ventricular outflow tract (RVOT) is acknowledged to be responsible for arrhythmogenesis in Brugada syndrome (BrS), but the pathophysiology remains controversial.

OBJECTIVES

This study assessed the substrate underlying BrS at post-mortem and in vivo, and the role for open thoracotomy ablation.

METHODS

Six whole hearts from male post-mortem cases of unexplained sudden death (mean age 23.2 years) with negative specialist cardiac autopsy and familial BrS were used and matched to 6 homograft control hearts by sex and age (within 3 years) by random risk set sampling. Cardiac autopsy sections from cases and control hearts were stained with picrosirius red for collagen. The RVOT was evaluated in detail, including immunofluorescent stain for connexin-43 (Cx43). Collagen and Cx43 were quantified digitally and compared. An in vivo study was undertaken on 6 consecutive BrS patients (mean age 39.8 years, all men) during epicardial RVOT ablation for arrhythmia via thoracotomy. Abnormal late and fractionated potentials indicative of slowed conduction were identified, and biopsies were taken before ablation.

RESULTS

Collagen was increased in BrS autopsy cases compared with control hearts (odds ratio [OR]: 1.42; p = 0.026). Fibrosis was greatest in the RVOT (OR: 1.98; p = 0.003) and the epicardium (OR: 2.00; p = 0.001). The Cx43 signal was reduced in BrS RVOT (OR: 0.59; p = 0.001). Autopsy and in vivo RVOT samples identified epicardial and interstitial fibrosis. This was collocated with abnormal potentials in vivo that, when ablated, abolished the type 1 Brugada electrocardiogram without ventricular arrhythmia over 24.6 ± 9.7 months.

CONCLUSIONS

BrS is associated with epicardial surface and interstitial fibrosis and reduced gap junction expression in the RVOT. This collocates to abnormal potentials, and their ablation abolishes the BrS phenotype and life-threatening arrhythmias. BrS is also associated with increased collagen throughout the heart. Abnormal myocardial structure and conduction are therefore responsible for BrS.

An overlap of Brugada syndrome and arrhythmogenic right ventricular cardiomyopathy/dysplasia

Overlapping characteristics of Brugada syndrome (BrS) and arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) have been reported in recent studies, but little is known about the overlapping disease state of BrS and ARVC/D. A 36-year-old man, hospitalized at our institution for syncope, presented with this overlapping disease state. The electrocardiogram showed spontaneous coved-type ST-segment elevation, and ventricular fibrillation was induced by right ventricular outflow tract stimulation in an electrophysiological study. BrS was subsequently diagnosed; additionally, the presence of epsilon-like waves and right ventricular structural abnormalities met with the 2010 revised task force criteria for ARVC/D. After careful investigation for both BrS and ARVC/D, an implantable cardioverter defibrillator was inserted in the patient. This case revealed 2 important clinical findings: (1) BrS and ARVC/D clinical features can coexist in a single patient, and EPS might be useful for determining the phenotype of overlapping disease (e.g., BrS-like or ARVC/D-like). (2) An overlapping disease state of BrS and ARVC/D can change phenotypically during its clinical course. Therefore, careful examination and attentive follow-up are required for patients with BrS or ARVC/D.

Brugada syndrome: a heterogeneous disease with a common ECG phenotype?

Our understanding of Brugada syndrome (BrS) has evolved since the syndrome was first described in 1992. BrS is considered to be a primary inherited channelopathy often involving the inward sodium current and the diagnosis has traditionally required the exclusion of overt structural heart disease. In view of recently published observations about BrS, we propose that the term BrS may actually encompass a heterogeneous group of disorders with a variety of genetic and clinical phenotypes. This disease has classically been described as a primary electrical disorder involving the sodium channel leading to the characteristic electrocardiogram (ECG) changes of BrS. We challenge the current understanding and propose that patients with structurally normal hearts, family history of sudden cardiac death, with associated genetic abnormalities only account for a subset of patients with the "Brugada pattern" ECG. There may also be some patients with a diagnosis of BrS who may also have features which overlap with arrhythmogenic right ventricular cardiomyopathy. In these patients there may be an underlying structural abnormality. In this context, it is possible that catheter ablation may abolish the "Brugada pattern" ECG changes as well as abolishing the risk of life threatening arrhythmias in these patients. Given the recent developments in the field, we propose a novel comprehensive multimodality model for risk stratification and assessment of patients with BrS. Identification of variations of diseases may facilitate more specific risk stratification models and management paradigms in patients with Brugada ECG pattern.

Brugada syndrome: an update

More than 20 years have passed since the description of Brugada syndrome as a clinical entity. The original case series depicted patients who all had coved ST-segment elevation in the right precordial leads, associated with a high risk of sudden death and no apparent structural heart disease. As subsequent registry data were published, it became apparent that the spectrum of risk is wide, with the majority of patients classified as low risk. Two consensus documents have been published that will continue to be updated. Despite intense research efforts, many controversies still exist over its pathophysiology and the risk stratification for sudden death. Management continues to be challenging with a lack of drug therapy and high complication rates from implantable cardioverter defibrillators. In this review, we highlight the current state-of-the-art therapies and their controversies.

Acute ST segment elevation secondary to acute gastric distention

An adolescent male trauma patient developed new asymptomatic ST segment elevations that mimicked a myocardial infarction on infero-lateral telemetry leads on hospital day #8, following burn excision and skin grafting. This was confirmed on 12 lead electrocardiogram. Laboratory test results indicated normal potassium. Troponins ×3 were negative. X-rays indicated marked gaseous gastric distention. A nasogastric tube was placed with evacuation of 400 mL of fluid and resolution of gastric distention. After gastric decompression, the ST segment elevations resolved. This case illustrates the need to consider acute gastric distention in the differential of acute ST segment elevation. <Learning objective: Electrocardiographic ST segment elevation generally indicates myocardial infarction. However, in the asymptomatic patient with normal troponins, alternative explanations, such as gastric distention should be considered.>.

A heterozygous deletion mutation in the cardiac sodium channel gene SCN5A with loss- and gain-of-function characteristics manifests as isolated conduction disease, without signs of Brugada or long QT syndrome

BACKGROUND

The SCN5A gene encodes for the α-subunit of the cardiac sodium channel NaV1.5, which is responsible for the rapid upstroke of the cardiac action potential. Mutations in this gene may lead to multiple life-threatening disorders of cardiac rhythm or are linked to structural cardiac defects. Here, we characterized a large family with a mutation in SCN5A presenting with an atrioventricular conduction disease and absence of Brugada syndrome.

METHOD AND RESULTS

In a large family with a high incidence of sudden cardiac deaths, a heterozygous SCN5A mutation (p.1493delK) with an autosomal dominant inheritance has been identified. Mutation carriers were devoid of any cardiac structural changes. Typical ECG findings were an increased P-wave duration, an AV-block I° and a prolonged QRS duration with an intraventricular conduction delay and no signs for Brugada syndrome. HEK293 cells transfected with 1493delK showed strongly (5-fold) reduced Na(+) currents with altered inactivation kinetics compared to wild-type channels. Immunocytochemical staining demonstrated strongly decreased expression of SCN5A 1493delK in the sarcolemma consistent with an intracellular trafficking defect and thereby a loss-of-function. In addition, SCN5A 1493delK channels that reached cell membrane showed gain-of-function aspects (slowing of the fast inactivation, reduction in the relative fraction of channels that fast inactivate, hastening of the recovery from inactivation).

CONCLUSION

In a large family, congregation of a heterozygous SCN5A gene mutation (p.1493delK) predisposes for conduction slowing without evidence for Brugada syndrome due to a predominantly trafficking defect that reduces Na(+) current and depolarization force.

Brugada ECG pattern: a physiopathological prospective study based on clinical, electrophysiological, angiographic, and genetic findings

Introduction: Brugada syndrome (BrS) is considered a primary electrical disease. However, morphological abnormalities have been reported and localized arrhythmogenic right ventricular (RV) dysplasia/cardiomyopathy (ARVD/C) may mimic its phenotype, raising the question of an overlap between these two conditions and making difficult the therapeutic management of patients with borderline forms. The main objective of this study was to assess prospectively the prevalence of BrS and ARVD/C on the basis of international criteria, in patients with BrS-ECG and normal echocardiography, looking for a potential overlap between the two pathologies. The secondary objectives were to describe and quantify angiographic structural alterations, hemodynamics, electrophysiology, and genetics in the setting of BrS-ECG. Materials and Methods: Hundred and fourteen consecutive patients matched in age underwent prospectively cardiac catheterization and quantitative biventricular contrast angiography to rule out a structural heart disease. Fifty-one patients with a BrS-ECG (BrS group, 7 F, 44 M, 43 ± 11 y) had a spontaneous or ajmaline-induced BrS coved type ECG. For angiographic comparison, 49 patients with localized ARVD/C but without ST segment elevation in the right precordial leads (14 F, 35 M, 39 ± 13 y) were also studied. They fulfilled international ESC/WHF 2000 criteria and presented angiographic localized forms, mainly confined to hypokinetic anteroapical zone (characterized by trabecular dysarray and hypertrophy), and/or diaphragmatic wall, thus resulting in RV normal volumes and preserved systolic function. These two populations were also compared with 14 control patients (7 F, 7 M, 38 ± 16 y). Among BrS group, we identified three main angiographic phenotypes: BrS group I = patients with normal RV (n = 15, 29%); BrS group II = patients with segmental RV wall motion abnormalities but no structural arguments for ARVD/C (n = 26, 51%); BrS group III = patients with localized abnormalities suggestive of focal ARVD/C (n = 10, 20%). Results: Among BrS group, 34/51 patients (67%) fulfilled BrS HRS/EHRA 2005 criteria. Nineteen (37%) were symptomatic for aborted sudden death, agonal nocturnal respiration or syncope. Ventricular stimulation was positive in 14 patients (28%). Angiography showed RV abnormalities in 36/51 patients (71%) of BrS group (BrS groups II and III). Late potentials were present in 73% (100% sensitivity and NPV for an angiographic ARVD/C, but poor specificity and PPV, both 37%). In BrS group III, 8/10 patients (16% of BrS patients) finally fulfilled international ESC/WHF 2000 ARVD/C criteria and 5/10 (10% of BrS patients) fulfilled BrS diagnostic criteria. An overlap was observed in 4 patients (8% of BrS patients) who fulfilled both ARVD/C and BrS criteria. Among the 45 genotyped patients, only one presented a SCN5A mutation, whereas a TRPM4 mutation was found in another patient. Both belonged to BrS group II. MOG1 gene analysis was negative for all patients, as were PKP2, DSP, DSG2, and DSC2 analyzes performed in BrS group III. Conclusions: Seventy-one percent of patients with a BrS-ECG had abnormal RV wall motion and 16 had structural alterations corresponding to localized (anteroapical and/or diaphragmatic) ARVD/C. Moreover, 8% of BrS-ECG patients fulfilled both BrS and ARVD/C criteria. Our results support the hypothesis of an overlap between BrS and localized forms of ARVD/C. Conversely, genetic screening was poorly contributive for both diseases in the present series.

SCN5A mutations in Brugada syndrome are associated with increased cardiac dimensions and reduced contractility

Background

The cardiac sodium channel (Na_v1.5) controls cardiac excitability. Accordingly, SCN5A mutations that result in loss-of-function of Na_v1.5 are associated with various inherited arrhythmia syndromes that revolve around reduced cardiac excitability, most notably Brugada syndrome (BrS). Experimental studies have indicated that Na_v1.5 interacts with the cytoskeleton and may also be involved in maintaining structural integrity of the heart. We aimed to determine whether clinical evidence may be obtained that Na_v1.5 is involved in maintaining cardiac structural integrity.

Methods

Using cardiac magnetic resonance (CMR) imaging, we compared right ventricular (RV) and left ventricular (LV) dimensions and ejection fractions between 40 BrS patients with SCN5A mutations (SCN5a-mut-positive) and 98 BrS patients without SCN5A mutations (SCN5a-mut-negative). We also studied 18 age/sex-matched healthy volunteers.

Results

SCN5a-mut-positive patients had significantly larger end-diastolic and end-systolic RV and LV volumes, and lower LV ejection fractions, than SCN5a-mut-negative patients or volunteers.

Conclusions

Loss-of-function SCN5A mutations are associated with dilatation and impairment in contractile function of both ventricles that can be detected by CMR analysis.

Diagnostic dilemmas: overlapping features of brugada syndrome and arrhythmogenic right ventricular cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) and Brugada syndrome are distinct clinical entities which diagnostic criteria exclude their coexistence in individual patients. ARVC is a myocardial disorder characterized by fibro-fatty replacement of the myocardium and ventricular arrhythmias. In contrast, the Brugada syndrome has long been considered a functional cardiac disorder: no gross structural abnormalities can be identified in the majority of patients and its electrocardiographic hallmark of coved-type ST-segment elevation in right precordial leads is dynamic. Nonetheless, a remarkable overlap in clinical features has been demonstrated between these conditions. This review focuses on this overlap and discusses its potential causes and consequences.

C-reactive protein levels in the brugada syndrome

Background. Inflammation in the Brugada syndrome (BrS) and its clinical implication have been little studied. Aims. To assess the level of inflammation in BrS patients. Methods. All studied BrS patients underwent blood samples drawn for C-reactive protein (CRP) levels at admission, prior to any invasive intervention. Patients with a previous ICD placement were controlled to exclude those with a recent (<14 days) shock. We divided subjects into symptomatic (syncope or aborted sudden death) and asymptomatic groups. In a multivariable analysis, we adjusted for significant variables (age, CRP ≥ 2 mg/L). Results. Fifty-four subjects were studied (mean age 45 ± 13 years, 49 (91%) male). Twenty (37%) were symptomatic. Baseline characteristics were similar in both groups. Mean CRP level was 1,4 ± 0,9 mg/L in asymptomatic and 2,4 ± 1,4 mg/L in symptomatic groups (P = .003). In the multivariate model, CRP concentrations ≥ 2 mg/L remained an independent marker for being symptomatic (P = .018; 95% CI: 1.3 to 19.3). Conclusion. Inflammation seems to be more active in symptomatic BrS. C-reactive protein concentrations ≥ 2 mg/L might be associated with the previous symptoms in BrS. The value of inflammation as a risk factor of arrhythmic events in BrS needs to be studied.

Epsilon-like waves and ventricular conduction abnormalities in subjects with type 1 ECG pattern of Brugada syndrome

BACKGROUND

Previous studies have demonstrated an overlap between the arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) and Brugada syndrome (BS). Conduction delay in the right ventricle has been demonstrated in both entities.

OBJECTIVE

This study investigated specific ARVC/D electrocardiographic (ECG) markers in subjects with spontaneous or drug-induced type 1 ECG pattern of BS.

METHODS

The study population consisted of 47 apparently healthy individuals (38 men, mean age 44.1 ± 13.3 years) with spontaneous (n = 17) or drug-induced (n = 30) type 1 ECG phenotype of BS. The clinical records of these individuals were retrospectively analyzed.

RESULTS

Fifteen subjects (31.9%) were symptomatic, with a history of syncope. A family history of BS or sudden cardiac death was reported in 10 (21.3%) and 8 (17.0%) cases, respectively. Epsilon-like waves in leads V1-V3 were observed in 6 subjects (12.7%). Epsilon-like waves were seen in spontaneous type 1 ECGs in 2 cases and after sodium channel blocking test in 4 cases. In baseline ECGs, localized prolongation (>110 ms) of the QRS complex in leads V1-V3, QRS duration ratio in (V1+V2+V3)/(V4+V5+V6) ≥ 1.2, and prolonged S wave upstroke (>55 ms) in leads V1-V3 were seen in 48.8%, 29.8%, and 40.4% of subjects, respectively. Epsilon-like waves and delayed S wave upstroke were more commonly observed in subjects with family history of BS (P = .014 and P = .038, respectively).

CONCLUSION

Specific ECG markers that reflect ventricular conduction delay in ARVC/D are commonly observed in subjects with spontaneous or drug-induced type 1 ECG pattern of BS as well. These depolarization abnormalities may be related to subtle underlying structural abnormalities.

Isoproterenol-induced FKBP12.6/12 downregulation is modulated by ETA and ETB receptors and reversed by argirhein, a derivative of rhein

AIM

To investigate which endothelin receptors mediated isoproterenol (ISO)-induced downregulation of FKBP12.6/12 in cardiomyocytes and study whether argirhein, a novel compound containing rhein and L-arginine that has anti-inflammatory activity, could reverse the downregulation of FKBP12.6/12 induced by ISO.

METHODS

Neonatal rat cardiomyocytes were incubated with ISO to downregulate FKBP12.6/12. Then the cells were treated with a selective ET(A) blocker (PD156707) and a ET(B) blocker (IRL1038), a dual ET(A)/ET(B) antagonist (CPU0213), and argirhein, respectively. FKBP12.6/12 expression was assayed by RT-PCR, Western blot, and immunocytochemistry.

RESULTS

The expression of FKBP12.6 mRNA was reduced by 37.7% (P<0.01) and 28.9% (P<0.05) relative to the control by ISO 1 and 0.1 μmol/L, respectively, but no response to ISO 0.01 μmol/L was observed in vitro. FKBP12.6/12 protein expression was reduced by 47.2% (P<0.01) and 37.8% (P<0.05) by ISO 1 and 0.1 μmol/L, respectively. This decrease was reversed significantly by PD156707, or IRL1038, and CPU0213. CPU0213 was more potent than either PD156707 or IRL-1038. Argirhein 10 μmol/L blunted the downregulation of FKBP12.6/12 by ISO, as demonstrated by the rising mRNA and protein levels and by the fluorescent density of the ISO-incubated cardiomyocytes.

CONCLUSION

In cardiomyocytes, the ISO induced downregulation of FKBP12.6/12 is modulated by both ET(A) and ET(B). A new compound, argirein, reversed the down-regulation of FKBP12.6/12 expression in myocardial cells stimulated with ISO.

ST segment elevation by current-to-load mismatch: an experimental and computational study

BACKGROUND

Recently, we demonstrated that ajmaline caused ST segment elevation in the heart of an SCN5A mutation carrier by excitation failure in structurally discontinuous myocardium. In patients with Brugada syndrome, ST segment elevation is modulated by cardiac sodium (I(Na)), transient outward (I(to)), and L-type calcium currents (I(CaL)).

OBJECTIVE

To establish experimentally whether excitation failure by current-to-load mismatch causes ST segment elevation and is modulated by I(to) and I(CaL).

METHODS

In porcine epicardial shavings, isthmuses of 0.9, 1.1, or 1.3 mm in width were created parallel to the fiber orientation. Local activation was recorded electrically or optically (di-4-ANEPPS) simultaneously with a pseudo-electrocardiogram (ECG) before and after ajmaline application. Intra- and extracellular potentials and ECGs were simulated in a computer model of the heart and thorax before and after introduction of right ventricular structural discontinuities and during varying levels of I(Na), I(to), and I(CaL).

RESULTS

In epicardial shavings, conduction blocked after ajmaline in a frequency-dependent manner in all preparations with isthmuses ≤ 1.1 mm width. Total conduction block occurred in three of four preparations with isthmuses of 0.9 mm versus one of seven with isthmuses ≥ 1.1 mm (P<.05). Excitation failure resulted in ST segment elevation on the pseudo-ECG. In computer simulations, subepicardial structural discontinuities caused local activation delay and made the success of conduction sensitive to I(Na), I(to), and I(CaL). Reduction of I(to) and increase of I(CaL) resulted in a higher excitatory current, overcame subepicardial excitation failure, and reduced the ST segment elevation.

CONCLUSIONS

Excitation failure by current-to-load mismatch causes ST segment elevation and, like ST segment elevation in Brugada patients, is modulated by I(to) and I(CaL).

The pathophysiological mechanism underlying Brugada syndrome: depolarization versus repolarization

This Point/Counterpoint presents a scholarly debate of the mechanisms underlying the electrocardiographic and arrhythmic manifestations of Brugada syndrome (BrS), exploring in detail the available evidence in support of the repolarization vs. depolarization hypothesis.

Right ventricular histological substrate and conduction delay in patients with Brugada syndrome

The reported pathogenesis of Brugada syndrome is phase 2 reentry resulting from shortening of the epicardial action potential duration at the right ventricular outflow tract (RVOT). However, several studies have revealed a high incidence of ventricular late potentials and high rate of ventricular fibrillation (VF) induced by programmed ventricular stimulation (PVS). The aim of the present study was to evaluate the role of slow conduction at the RVOT for the initiation of VF by PVS and any underlying pathological conditions in Brugada syndrome. Endocardial mapping of the RVOT and endomyocardial biopsy of the right ventricle were performed in 25 patients with Brugada syndrome with inducible VF. Late potentials were positive in 11 of the 25 (44%) patients. Low-amplitude fragmented and delayed electrograms were recorded at the RVOT in 13 of 18 (72.2%) patients. Histologic examination of the biopsy samples revealed fatty tissue infiltration, interstitial fibrosis, lymphocyte infiltration, and/or myocyte disorganization in 13 patients. Slow conduction at the RVOT may contribute to the induction of VF by PVS in Brugada syndrome. Various pathomorphologic changes may contribute to slow conduction at the RVOT.

Mechanism of right precordial ST-segment elevation in structural heart disease: excitation failure by current-to-load mismatch

BACKGROUND

The Brugada sign has been associated with mutations in SCN5A and with right ventricular structural abnormalities. Their role in the Brugada sign and the associated ventricular arrhythmias is unknown.

OBJECTIVE

The purpose of this study was to delineate the role of structural abnormalities and sodium channel dysfunction in the Brugada sign.

METHODS

Activation and repolarization characteristics of the explanted heart of a patient with a loss-of-function mutation in SCN5A (G752R) and dilated cardiomyopathy were determined after induction of right-sided ST-segment elevation by ajmaline. In addition, right ventricular structural discontinuities and sodium channel dysfunction were simulated in a computer model encompassing the heart and thorax.

RESULTS

In the explanted heart, disappearance of local activation in unipolar electrograms at the basal right ventricular epicardium was followed by monophasic ST-segment elevation. The local origin of this phenomenon was confirmed by coaxial electrograms. Neither early repolarization nor late activation correlated with ST-segment elevation. At sites of local ST-segment elevation, the subepicardium was interspersed with adipose tissue and contained more fibrous tissue than either the left ventricle or control hearts. In computer simulations entailing right ventricular structural discontinuities, reduction of sodium channel conductance or size of the gaps between introduced barriers resulted in subepicardial excitation failure or delayed activation by current-to-load mismatch and in the Brugada sign on the ECG.

CONCLUSION

Right ventricular excitation failure and activation delay by current-to-load mismatch in the subepicardium can cause the Brugada sign. Therefore, current-to-load mismatch may underlie the ventricular arrhythmias in patients with the Brugada sign.