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

Causal Relationship Between Electrocardiogram Parameters and Brugada Syndrome: A Bidirectional Mendelian Randomization Study

BACKGROUND

Brugada syndrome (BrS) is associated with an electrocardiogram (ECG), but the causal relationship remains unclear. This study aimed to assess the bidirectional causal relationship between ECG parameters and BrS using Mendelian randomization (MR) analysis.

METHODS

A bidirectional MR analysis using data from the OpenGWAS database. Six ECG parameters, including PR interval, PP interval, ST duration, QRS duration, T wave duration, and QT interval, were included in the forward MR analysis with BrS as the outcome. In the reverse MR analysis, BrS was the exposure and the aforementioned ECG parameters were the outcomes. The inverse-variance weighted (IVW) method was the primary analytical approach, complemented by four other methods to account for potential pleiotropy. Sensitivity analyses were performed using Cochran's Q test, MR-Egger intercept, and leave-one-out analysis to evaluate heterogeneity and pleiotropy.

RESULTS

In the forward MR, genetically predicted ST duration (OR = 1.3478, 95% CI: 1.0611-1.7118, p = 0.014) and QRS duration (OR = 0.9582, 95% CI: 0.9208-0.9972, p = 0.036) showed significant associations with BrS. The reverse MR indicated that BrS was significantly associated with PR interval, QRS duration, P wave duration, and QT interval (all p < 0.05). Sensitivity analyses confirmed the robustness of the results in both forward and reverse MR analyses. However, there were significant horizontal pleiotropy and heterogeneity in reverse MR analysis.

CONCLUSIONS

This MR study supported a causal effect of ECG parameters, including ST duration and QRS duration, on BrS development.

Late gadolinium enhancement in early repolarization syndrome

BACKGROUND

In patients with Brugada syndrome, myocardial fibrosis can be identified through epicardial biopsy or cardiac magnetic resonance (CMR) imaging with late gadolinium enhancement (LGE). However, the myocardial alterations in patients with early repolarization syndrome (ERS) remain poorly elucidated.

OBJECTIVE

The objective of this study was to investigate the presence of myocardial fibrosis in patients with ERS by LGE in CMR.

METHODS

We retrospectively evaluated 20 patients with ERS, all of whom exhibited J waves in the contiguous 2 leads. The location of J waves was classified as in the septum (V1-V2), anterior (V3-V4), lateral (I, aVL, V5-V6), inferior (II, III, aVF), or posterior (V7-V9) regions. To compare the distribution of LGE on CMR imaging with J waves, sections on short-axis view of the left ventricle (LV) were categorized as located in the septum, anterior, lateral, inferior, and posterior regions.

RESULTS

Overall, 85% of ERS patients displayed LGE, which was more prevalent in the septum and posterior regions, followed by the inferior and lateral regions. The presence or absence of J waves and LGE coincided in 61% of LV areas, whereas discordance between the distributions of J waves and LGE was observed in 38%. LGE was most frequent in the septum (75%), where its reflection in J waves may be less robust. The appearance of LGE was not associated with symptoms, electrical storm, or ventricular fibrillation occurrence during follow-up.

CONCLUSION

LGE is common in patients with ERS, and the distribution of J waves and LGE coincides in approximately 60% of LV areas.

Predictive value of cardiac magnetic resonance imaging for fatal arrhythmias in structural and nonstructural heart diseases

Background

The risk stratification for fatal arrhythmias remains inadequate. Cardiac magnetic resonance (CMR) imaging provides a detailed evaluation of arrhythmogenic substrates. This study investigated the predictive capacity of multiparametric CMR for fatal ventricular arrhythmias (VAs) in a heterogeneous disease cohort.

Methods

The study included 396 consecutive patients with structural heart disease (SHD, n = 248) and non-apparent SHD (n = 148) who underwent CMR scans between 2018 and 2022. The primary endpoint was fatal composite arrhythmias.

Results

Thirty-three patients (8.3 %) experienced fatal arrhythmias (25 with SHD, 8 with non-apparent SHD) over a median follow-up of 24 months. The independent risk factors for patients with SHD included syncope (hazard ratio [HR] = 5.347; P < 0.001), VA history (HR = 3.705; P = 0.004), right ventricular ejection fraction (RVEF) ≤ 45 % (HR = 2.587; P = 0.039), and the presence of late gadolinium enhancement (LGE) (HR = 4.767; P = 0.040). In the non-apparent SHD group, fatal arrhythmias were independently correlated with VA history (HR = 10.23; P = 0.005), RVEF ≤ 45 % (HR = 8.307; P = 0.015), and CMR myocardial abnormalities (HR = 5.203; P = 0.033). Patients at high risk of fatal arrhythmia in the SHD and non-apparent SHD groups exhibited 3-year event-free survival rates of 69.4 % and 83.5 %, respectively.

Conclusion

CMR provides effective prognostic information for patients with and without apparent SHD. The presence of LGE, CMR myocardial abnormalities, and right ventricular dysfunction are strong risk markers for fatal arrhythmias.

Electrophysiological patterns and structural substrates of Brugada syndrome: Critical appraisal and computational analyses

Brugada syndrome (BrS) is a cardiac electrophysiological disease with unknown etiology, associated with sudden cardiac death. Symptomatic patients are treated with implanted cardiac defibrillator, but no risk stratification strategy is effective in patients that are at low to medium arrhythmic risk. Cardiac computational modeling is an emerging tool that can be used to verify the hypotheses of pathogenesis and inspire new risk stratification strategies. However, to obtain reliable results computational models must be validated with consistent experimental data. We reviewed the main electrophysiological and structural variables from BrS clinical studies to assess which data could be used to validate a computational approach. Activation delay in the epicardial right ventricular outflow tract is a consistent finding, as well as increased fibrosis and subclinical alterations of right ventricular functional and morphological parameters. The comparison between other electrophysiological variables is hindered by methodological differences between studies, which we commented. We conclude by presenting a recent theory unifying electrophysiological and structural substrate in BrS and illustrate how computational modeling could help translation to risk stratification.

Brugada Syndrome: A Comprehensive Review of Fundamental and Electrophysiological New Findings

Brugada syndrome is characterized by pronounced J-ST segment elevation in the right precordial leads on surface electrocardiograms. The etiological underpinnings of these distinctive features have been the subject of extensive debate, encompassing various theories related to repolarization anomalies and conduction irregularities. Genetic investigations have unveiled SCN5A, the gene encoding NaV1.5, a critical sodium channel, as the most frequently implicated causative gene, with mutations typically manifesting as loss of function. Nonetheless, the detection rate of SCN5A mutations remains below 20%, underscoring the intricate genetic landscape of the syndrome. Histological analyses have divulged localized structural irregularities, primarily marked by fibrotic alterations, within the right ventricular outflow tract. Electrophysiological inquiries employing direct epicardial mapping techniques have uncovered localized conduction impediments concomitant with modifications in unipolar morphologies within the J-ST segment. Thus, the theory positing conduction abnormalities emerges as a compelling mechanism accounting for J-ST segment elevation. However, the precise mechanisms governing the onset of life-threatening tachyarrhythmias remain shrouded in uncertainty. Recent clinical case reports have proffered evidence supporting the notion that phase 2 reentry, arising from the marked heterogeneity in action potentials within the epicardial domain, may serve as the instigator of premature ventricular contractions, ultimately culminating in ventricular fibrillation. In light of these developments, it becomes increasingly evident that comprehending the mechanisms underlying the electrocardiographic manifestations and lethal arrhythmias in Brugada syndrome necessitates the consideration of a multifaceted perspective, transcending the binary discourse of repolarization versus depolarization anomalies.

Brugada Syndrome: More than a Monogenic Channelopathy

Brugada syndrome (BrS) is an inherited cardiac channelopathy first diagnosed in 1992 but still considered a challenging disease in terms of diagnosis, arrhythmia risk prediction, pathophysiology and management. Despite about 20% of individuals carrying pathogenic variants in the SCN5A gene, the identification of a polygenic origin for BrS and the potential role of common genetic variants provide the basis for applying polygenic risk scores for individual risk prediction. The pathophysiological mechanisms are still unclear, and the initial thinking of this syndrome as a primary electrical disease is evolving towards a partly structural disease. This review focuses on the main scientific advancements in the identification of biomarkers for diagnosis, risk stratification, pathophysiology and therapy of BrS. A comprehensive model that integrates clinical and genetic factors, comorbidities, age and gender, and perhaps environmental influences may provide the opportunity to enhance patients' quality of life and improve the therapeutic approach.

Subepicardial Cardiomyopathy: A Disease Underlying J-Wave Syndromes and Idiopathic Ventricular Fibrillation

Brugada syndrome (BrS), early repolarization syndrome (ERS), and idiopathic ventricular fibrillation (iVF) have long been considered primary electrical disorders associated with malignant ventricular arrhythmia and sudden cardiac death. However, recent studies have revealed the presence of subtle microstructural abnormalities of the extracellular matrix in some cases of BrS, ERS, and iVF, particularly within right ventricular subepicardial myocardium. Substrate-based ablation within this region has been shown to ameliorate the electrocardiographic phenotype and to reduce arrhythmia frequency in BrS. Patients with ERS and iVF may also exhibit low-voltage and fractionated electrograms in the ventricular subepicardial myocardium, which can be treated with ablation. A significant proportion of patients with BrS and ERS, as well as some iVF survivors, harbor pathogenic variants in the voltage-gated sodium channel gene, SCN5A, but the majority of genetic susceptibility of these disorders is likely to be polygenic. Here, we postulate that BrS, ERS, and iVF may form part of a spectrum of subtle subepicardial cardiomyopathy. We propose that impaired sodium current, along with genetic and environmental susceptibility, precipitates a reduction in epicardial conduction reserve, facilitating current-to-load mismatch at sites of structural discontinuity, giving rise to electrocardiographic changes and the arrhythmogenic substrate.