BrS Patients Research Articles

Phenotype heterogeneity of SCN5A mutations in Brugada syndrome

Abstract Introduction Although SCN5A is the main gene associated with Brs syndrome (Brs), rare variants in this gene only affect 20 to 30 % of patients. Additionally, associated phenotype may differ even among relatives sharing the same mutation emphasizing a phenotype heterogeneity that is poorly understood for now. Objective Here we aim to investigate the association between the presence of SCN5A mutations and the expression of a BrS phenotype in large families. Methods Among Brugada patients enrolled in our prospective cohort, we included patients from families with affected proband carrier of a SCN5A mutation and at least 4 relatives carriers of the same SCN5A mutation. Patient without a spontaneous type 1 ECG and no pharmacological provocative test were excluded. Results A total of 463 individuals from 45 large families were enrolled. Among them, 258 (56%) were mutation carriers of one of the 33 identified SCN5A mutations. After pharmacological test, 219 (47%) individuals were diagnosed with BrS, including 32 not carriers of the familial mutation. Seventy-five patients (30%), carriers of the familial SCN5A mutation, remain negative for Brugada syndrome after pharmacological test. The prevalence of genotype-phenotype mismatch was 24%, including 32 BrS patients non carrier of the familial mutation (phenocopy) and 75 patients with the familial mutation but without BrS (30% of uncomplete penetrance). Conclusion Our data strongly suggest that SCN5A mutation is not either necessary nor sufficient to explain the occurrence of BrS phenotype. We now aim to identify which associated factors might interfere, focusing first on the genetic background of phenotype/genotype mismatched individuals.

Inhibition of Cardiac Kv4.3/KChIP2 Channels by Sulfonylurea Drug Gliquidone.

The Kv4.3 channel features fast N-type inactivation and also undergoes a slow C-type inactivation. The gain-of-function mutations of Kv4.3 channels cause an inherited disease called Brugada syndrome (BrS), characterized by a shortened duration of cardiac action potential repolarization and ventricular arrhythmia. The sulfonylurea drug gliquidone, an ATP-dependent K+ channel antagonist, is widely used for the treatment of type 2 diabetes. Here, we report a novel role of gliquidone in inhibiting Kv4.3 and Kv4.3/KChIP2 channels that encode the cardiac transient outward K+ currents responsible for the initial phase of action potential repolarization. Gliquidone results in concentration-dependent inhibition of both Kv4.3 and Kv4.3/KChIP2 fast or steady-state inactivation currents with an IC50 of approximately 8 μM. Gliquidone also accelerates Kv4.3 channel inactivation and shifts the steady-state activation to a more depolarizing direction. Site-directed mutagenesis and molecular docking reveal that the residues S301 in the S4 and Y312A and L321A in the S4-S5 linker are critical for gliquidone-mediated inhibition of Kv4.3 currents, as mutating those residues to alanine significantly reduces the potency for gliquidone-mediated inhibition. Furthermore, gliquidone also inhibits a gain-of-function Kv4.3 V392I mutant identified in BrS patients in voltage- and concentration-dependent manner. Taken together, our findings demonstrate that gliquidone inhibits Kv4.3 channels by acting on the residues in the S4 and the S4-S5 linker. Therefore, gliquidone may hold repurposing potential for the therapy of Brugada syndrome. SIGNIFICANCE STATEMENT: We describe a novel role of gliquidone in inhibiting cardiac Kv4.3 currents and the channel gain-of-function mutation identified from patients with Brugada syndrome, suggesting its repurposing potential for therapy for the heart disease.

Reduced right ventricular outflow tract strain at cardiac magnetic resonance correlates with low-voltage areas at unipolar electroanatomic mapping in patients with brugada syndrome

Abstract Background Brugada Syndrome (BrS) was initially described as a channelopathy without underlying structural substrate, but pathological and electroanatomic abnormalities of the right ventricular outflow tract (RVOT), are increasingly recognized, suggesting a possible role of electroanatomic mapping (EAM) in risk stratification of these patients. New echocardiographic and cardiac magnetic resonance (CMR) tools are able to identify subtle structural and functional myocardial abnormalities associated with an increased arrhythmic risk. Purpose We aimed to assess the presence of structural and functional abnormalities of RVOT by CMR-derived RV and RVOT feature tracking in BrS patients. We also sought to evaluate the relationship between RVOT functional abnormalities and the presence and extension of RVOT abnormal voltage areas at EAM. Methods we retrospectively enrolled BrS patients submitted to CMR comprehensive of RVOT sequences and bipolar and unipolar endocardial EAM. Abnormal voltage areas were defined by the presence of signal amplitude <4mV at unipolar mapping and signal amplitude <1.5mV at bipolar mapping. We included a control group of 15 healthy volunteers submitted to CMR including RVOT sequences. Results We studied 16 patients, 12/16 males, mean age 42±9 years. In all cases CMR showed normal left and right ventricular ejection fraction (LVEF 57±4%, RVEF 56±6%). RVOT peak strain values were significantly impaired in BrS patients compared to controls (-17.9±8.6% vs -26.4±9.5%, p=0.011), while RV-GLS did not differ between the two groups (-22.2±4.0% vs 24.6±2.5%, p=0.061). EAM showed the presence of pathological voltages at both unipolar and bipolar mapping in 12 patients, abnormal unipolar and normal bipolar maps in 1 case and both unipolar and bipolar normal maps in 3 patients. Median extent of abnormal voltage areas was 5.3 cm2 [IQ 1-4 = 0.6-9.3 cm2] at unipolar and 4.1 cm2 [IQ 1-4 = 0.7-7.5 cm2] at bipolar map. RVOT peak strain showed a significant correlation with abnormal voltage areas at unipolar EAM (r=0.546, r2=0.525, p=0.029). Patients with both unipolar and bipolar normal maps (n=3) had normal RVOT strain values compared to controls (-25.7±3.9 vs -26.4±9.5%, p=0.90). Conclusions In patients with BrS, RVOT peak strain is significantly reduced compared to controls and is associated with abnormal voltage areas at endocardial unipolar EAM. Noninvasive evaluation of BrS patients with CMR-derived RVOT feature tracking may help to identify patients requiring invasive evaluation with EAM. Prospective studies evaluating the prognostic role of RVOT strain and EAM in BrS patients are needed.

A non-coding SCN5A variant that reduces sodium channel function in hiPSC-derived cardiomyocytes is significantly enriched in Brugada syndrome patients from Thailand

Abstract Background/Introduction Brugada syndrome (BrS) is an inherited arrhythmia condition that can cause sudden cardiac death. Rare coding and common non-coding genetic variation in the Nav1.5 cardiac sodium channel-encoding SCN5A gene is robustly associated with BrS, but the role of rare and low frequency non-coding variants remains unexplored. BrS is several times more prevalent in Southeast Asia compared to other populations, indicating ancestry-specific genetic risk factors remain to be discovered. Purpose To identify and characterise novel genetic risk factors in BrS patients from Southeast Asia. Methods We performed genome sequencing in 231 BrS probands from Thailand and 500 population-matched controls to identify novel disease associated variants across the entire SCN5A locus. The candidate variant was engineered into human induced pluripotent stem cells (hiPSCs) by CRISPR-Cas9 and its effect was evaluated by single cell electrophysiology analysis on hiPSC-derived cardiomyocytes. Results We identified a rare (absent in gnomAD), non-coding variant in a regulatory element of the SCN5A gene (GRCh38:3-38580380-A-C) that was significantly enriched in cases (3.9%) vs controls (0.2%) (OR=20.2[2.5-160.6], p=2e-04). Transcription factor motif scanning analysis suggested the variant is likely to disrupt a Mef2 site that is conserved across species (Figure 1) – the MEF2 family of transcription factors play a critical role in cardiac transcriptional regulation. In hiPSC-derived cardiomyocytes, a significant reduction of peak Nav1.5-mediated sodium-current (INa) density (30% decrease at -20mV, p=8e-03), without changes in gating properties, was observed in cardiomyocytes carrying the variant in heterozygosity compared to isogenic controls (Figure 2). The variant also significantly reduced luciferase activity of the candidate regulatory element in HEK cells in the presence of cardiac transcription factors (Tbx5, Gata4, Mef2A, Mef2D). Conclusion A novel, non-coding variant in an SCN5A enhancer region is associated with BrS and was functionally validated using single cell electrophysiology in hiPSC-derived cardiomyocytes. This variant is found in ∼1 in every 25 BrS patients from Thailand and therefore may at least partially explain the increased prevalence of BrS in this region. Our study highlights the importance of research in understudied populations to understand the genetic aetiology of disease in diverse ancestries and to identify novel disease risk factors.

Integration of transcriptomics and mirnomics for brugada syndrome diagnosis

Abstract Background/Introduction Brugada Syndrome (BrS) presents a genetic and phenotypic heterogeneity, so integrating different omics approaches could add information on molecular mechanisms and find new diagnostic markers. Purpose This work aims to provide a transcriptomic and mirnomic profile of patients with Type 1 BrS as a preliminary step for evaluating potential biomolecular markers to assist in the diagnosis of the syndrome. Methods Subjects aged 14–75 years (inclusive) with ECG presenting a spontaneous Type 1 BrS or a suspect BrS pattern were eligible to participate in the study. All the suspect BrS subjects underwent a provocative test (i.v. ajmaline or flecainide administration). A total of 56 patients were collected by clinical centers involved in the BrAID study. According to their diagnosis, these were divided into two main groups: Brugada (28, spontaneous and positive to provocative test) and Controls (28, controls and negative to provocative test). To better characterize the population, a sub-classification was performed: Spontaneous Type 1 BrS (Group A, 14), patients with (Group B, 14) and without (Group C, 14) a Type 1 pattern after the provocative test, and Control group (Group D, 14). Patients with a history of ventricular premature contractions, normal ventricular function, and provocative negative tests were the control group. Whole blood samples (2.5 mL) were collected into PAXgene blood RNA system tubes (DIALAB ITALIA Srl, Milan, Italy) for RNA-Seq analysis. Blood samples were also collected into EDTA (1 mg/mL) for exosome isolation. Total RNA was extracted from whole blood using the PAXgene Blood RNA Kit (Qiagen). Exosomes were extracted using a dedicated and innovative assay (exoRNeasy mini/midi kit, QIAGEN). Samples were quantified and quality tested by Agilent 2100 Bioanalyzer RNA assay. Data were analyzed through web-based platforms for multi-omics integration and network visual analytics (mirNET 2.0, OmicsNet 2.0). Results The comparison of overall Brugada and Controls highlighted the presence of two genes (SLC8A2, RNA18S5) and 3 miRNAs (hsa-miR-584-5p, hsa-miR-148b-3p, hsa-miR-148a-3p) involved in BrS (Figure 1). When Group A and D were compared a statistically significant difference was observed for SLC8A2 and hsa-miR-625-3p, hsa-miR-4488, hsa-miR-328-3p. No significantly different genes were observed comparing the patients with a positive and negative provocative test, while 7 miRNAs were significantly modulated in the two subsets. Different genes and miRNAs were observed comparing spontaneous/positive patients (1 gene, 1 miRNA) and controls/negative (3 genes, 10 miRNAs). The network analysis between genes and miRNAs of the Brugada/Controls comparison showed an interaction of SESN3, ROCK1 and IGFBP5 (Figure 2). Conclusion These results indicate that a new set of molecular markers has the potential to better characterize BrS patients who present phenotypical heterogeneityFig.1Genes and miRNAs in BrS patientsFig.2Network analysis

Syncope without prodromes during fever in type 1-induced BrS patient: Looks can be deceiving.

Syncope without prodromes during fever in type 1-induced BrS patient: Looks can be deceiving.

Added value of 12-lead 24-hour ambulatory ECG monitoring in the identification of a spontaneous type 1 Brugada pattern and its prognostic role. A sub-study of the BHF RASE Brugada project

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): British Heart Foundation Background A spontaneous type 1 Brugada (spT1-BrS) pattern is a recognised marker of arrhythmic risk. However, its fluctuations may underestimate the risk in subjects with concealed T1-BrS at presentation. Aim To investigate the yield of repeat resting and high-lead 12-lead ECG and the additional role of 12-lead 24-hour Holter monitoring with leads V1 and V2 in standard and high precordial ECG positions (12-HPL Holter), and evaluate the prognostic role of spT1-BrS in a large, single-centre, cohort of BrS patients. Methods Three-hundred and eighty-one subjects with BrS enrolled in our Registry from 2008 to December 2021 and with at least 3 months follow-up data were included in this study. Seventy-seven had spT1-BrS pattern at presentation (Group 1), and 304 did not (Group 2). All received lifestyle recommendations and had regular follow-up appointments with 12-lead ECG; the majority of them were also screened with 12-HPL Holter. Medical notes and tracings were reviewed to identify a dynamic spT1-BrS and events at f-up (SCD/appropriate ICD shock). Results The mean age at presentation was 44±15 years; 52% of participants were males. All had at least 2 resting ECGs recorded; in 281 subjects at least one 12-HPL Holter was available (total 643, median 2, range 1-8). Over a median follow-up of 66 months (IQR 75), 37 subjects in Group 2 showed a spT1-BrS at least once: 10 during a repeat resting ECG, 2 during/after exercise tolerance test, 25 at 12-HPL Holter. The average time at spT1 appearance during follow-up was 23 months (range 1- 225). Those with a newly detected spT1-BrS were more frequently males and less likely to have a familial history of sudden cardiac death (Table 1). Excluding subjects with previous aCA/documented VT, 6 events occurred at f-up, all in subjects with spT1 (Figure 1). Univariate models showed that the presence of a spT1-BrS pattern was consistently associated with increased risk of events (at presentation: HR 10, 95% C.I. 1.8-54; at follow-up: HR 5.3, 95% C.I. 1.6-17). Conclusions A spontaneous T1-BrS can be detected in up to 12% of subjects with concealed BrS at presentation using 12-HPL Holter monitoring. Its presence is consistently associated with arrhythmic risk at f-up up, regardless of the time at detection. Prolonged ambulatory ECG monitoring is fundamental for risk stratification in this population.

Structural Abnormalities in Brugada Syndrome and Non-Invasive Cardiac Imaging: A Systematic Review.

The aim of this review is to identify possible structural abnormalities of BrS and their potential association with symptoms, risk stratification, and prognosis. (1) Background: BrS has always been considered a purely electrical disease and imaging techniques do not currently play a specific role in the diagnosis of this arrhythmic syndrome. Some authors have recently hypothesized the presence of structural and functional abnormalities. Therefore, several studies investigated the presence of pathological features in echocardiography and cardiac magnetic resonance imaging (MRI) in patients with BrS, but results were controversial. (2) Methods: We performed a systematic review of the literature on the spectrum of features detected by echocardiography and cardiac MRI. Articles were searched in Pubmed, Cochrane Library, and Biomed Central. Only papers published in English and in peer-reviewed journals up to November 2021 were selected. After an initial evaluation, 596 records were screened; the literature search identified 19 relevant articles. (3) Results: The imaging findings associated with BrS were as follows: right ventricular dilation, right ventricular wall motion abnormalities, delayed right ventricular contraction, speckle and feature tracking abnormalities, late gadolinium enhancement, and fat infiltration in the right ventricle. Furthermore, these features emerged more frequently in patients carrying the genetic mutation on the sodium voltage-gated channel α-subunit 5 (SCN5A) gene. (4) Conclusions: Specific imaging features detected by echocardiography and cardiac magnetic resonance are associated with BrS. However, this population appears to be heterogeneous and imaging anomalies emerged to be more frequent in patients carrying genetic mutations of SCN5A. Future studies with an evaluation of BrS patients are needed to identify the specific association linking the Brugada pattern, imaging abnormalities and their possible correlation with prognosis.

Risk stratification of sudden cardiac death in asymptomatic female Brugada syndrome patients: A literature review.

Risk stratification in Brugada syndrome remains a difficult problem. Given the male predominance of this disease and their elevated risks of arrhythmic events, affected females have received less attention. It is widely known that symptomatic patients are at increased risk of sudden cardiac death (SCD) than asymptomatic patients, while this might be true in the male population; recent studies have shown that this association might not be significant in females. Over the past few decades, numerous markers involving clinical symptoms, electrocardiographic (ECG) indices, and genetic tests have been explored, with several risk-scoring models developed so far. The objective of this study is to review the current evidence of clinical and ECG markers as well as risk scores on asymptomatic females with Brugada syndrome. Gender differences in ECG markers, the yield of genetic findings, and the applicability of risk scores are highlighted. Various clinical, electrocardiographic, and genetic risk factors are available for assessing SCD risk amongst asymptomatic female BrS patients. However, due to the significant gender discrepancy in BrS, the SCD risk amongst females is often underestimated, and there is a lack of research on female-specific risk factors and multiparametric risk scores. Therefore, multinational studies pooling female BrS patients are needed for the development of a gender-specific risk stratification approach amongst asymptomatic BrS patients.

663 OCCURRENCE OF VENTRICULAR AND SUPRAVENTRICULAR ARRHYTHMIAS IN BRUGADA SYNDROME: RESULTS OF A TERTIARY REFERRAL CENTER EXPERIENCE

Abstract Brugada Syndrome (BrS) is one of the most common channelopathies and is related to an increased risk of ventricular arrhythmias. Current guidelines recommend the implantation of a Cardiac Defibrillator (ICD) in those patients that have a diagnostic ECG pattern and a history of aborted cardiac arrest. Nevertheless, management of asymptomatic patients, who are the majority, remains controversial as their risk stratification is often based on the results of an inductive Electrophysiologic Study (EPS) the predictive accuracy of which is debated. Furthermore, BrS has also been associated to an increased risk of supraventricular tachy- and bradyarrhythmias. Aim to describe the occurrence of ventricular and supraventricular arrhythmias in BrS patients that receive an implantable cardiac monitoring device following an EPS study Methods we retrospectively identified all BrS patients followed at our tertiary referral centre that were candidate to an EPS. Patient were candidate to EPS if: (1) they had a spontaneous diagnostic Brugada pattern at ECG and (2) they had no history of previous ventricular arrhythmias or high-risk syncope. Those patients that tested positive for induction of a sustained ventricular arrhythmia at EPS received an ICD; those that tested negative received an ILR. During the follow-up visits, implantable devices were interrogated for the occurrence of ventricular and supraventricular arrhythmias. Results We identified 87 patients matching the inclusion criteria. Of these, 31 (35.7%) received an ICD for a positive EPS while the remaining 56 (64.3%) received an ILR. Over a mean follow-up period of 34 months (IQR 5-45, 249 patient-year), only one patient in the EPS positive group experienced a ventricular arrhythmia effectively treated by the ICD (0.3 events per patient-year) compared to zero patients in the EPS negative group (100% NPV, 3.2% PPV). Notably, implanted devices allowed for the detection of supraventricular arrhythmias in 12 out of the 87 patients (14%): 5 were cases of symptomatic sinus bradycardia, with an indication to permanent pacing in two of them, and 7 were cases of atrial tachycardia/fibrillation. Discussion in our registry, consistently with previous literature, ventricular arrhythmias in BrS patients are rare and a negative EPS identifies with high accuracy those that are at low risk for this event. Conversely, a positive EPS may overestimate the risk of these patients resulting, according to current practice, in frequent implantations of ICD that will never be required for defibrillation. Although the patient-year observation period of the presented cohort is sizeable, our results should be furtherly validated on multi-center cohorts with even longer follow-up periods. Nonetheless, our results support the idea that risk stratification tools other than EPS are probably needed to properly identify the minority of BrS patients that will experience a ventricular arrhythmia throughout their life. In addition, we report a considerable number of supraventricular arrhythmias recorded by the implanted cardiac monitoring devices in our population. This is consistent with the knowledge of BrS patients being at increased risk of sinoatrial node dysfunction and atrial fibrillation and may elicit a more widespread and methodical screening for these events.

Clinical role of genetic testing for overlapping between Brugada syndrome and arrhythmogenic right ventricular cardiomyopathy

Abstract Background/Introduction Brugada syndrome (BrS) and arrhythmogenic right ventricular cardiomyopathy (ARVC) are inherited arrhythmias that may predispose to sudden cardiac arrest. Although its pathogenetic mechanisms differ, overlapping features between BrS and ARVC have been demonstrated previously. However, it remains to be determined whether genetic testing for ARVC-related gene is needed in patients with BrS. Purpose This study is aimed to analyze genetic profiles of BrS patients using next generation sequencing (NGS) based multigene panel including ARVC related genes. Methods Patients who were confirmed as BrS or clinically suspected as BrS with type 2 or 3 Brugada pattern electrocardiography were studied. Genetic testing using NGS panels (Illumina Inc., San Diego, CA, USA) included 30 genetic variants associated with inherited arrhythmia and genetic cardiomyopathy. Results Among the total 119 patients from BrS registry, 63 patients were confirmed as BrS and 56 patients were clinically suspected as BrS without fulfilling diagnostic criteria. One-hundred-fourteen patients (95.8%) were male, and mean age of onset was 43.6 year-old. Genetic variants were identified in 25 of 42 patients who received genetic testing. Six out of 25 patients (24.0%) showed ARVC-related genotypes (2 PKP2, 1 DSG2, 1 TMEM43, 1 JUP, and 1 DSP) (Figure 1 and Table 1). None of the patients showed structural or electrocardiographic features that fulfill diagnostic criteria of ARVC. It is notable that ARVC-related genotypes were mostly frequently accounted for BrS patients, following SCN5A and SCN10A. Conclusion In the clinic setting, ARVC-related genetic variants were identified in significant proportion of BrS patients, supporting that genetic testing of ARVC-overlapping is needed. This study suggests that follow-up including imaging study should be considered in BrS patients with ARVC-related genotypes to monitor disease progression as ARVC. Funding Acknowledgement Type of funding sources: None.

Characterization and long-term follow-up of children with brugada syndrome: experience from a tertiary paediatric referral centre

Abstract Introduction Brugada syndrome (BrS) is an autosomal dominant channelopathy, which typically presents in young adults. It can also be diagnosed in children, but data in this age group is scarce. Purpose To describe the clinical features, management and long-term follow-up of children with BrS history followed-up in a tertiary paediatric referral centre. Methods Single centre retrospective study of consecutive patients with history of BrS, defined as having a BrS positive phenotype (BrS(+)), or a negative phenotype-positive genotype (BrS(−)). They were all followed up in a paediatric heart rhythm clinic. Clinical and demographical data were collected and analysed according to the phenotype. Results 30 patients were included, with a median age at diagnosis of 7 years (IQR 1–13) and a mean follow-up time of 7±3 years. Sixteen patients were BrS(+), predominantly male (n=13, 81%). 88% (n=14) performed a genetic test, which was positive in 57% (n=8); the most frequent mutation was SCN5A (n=5). Family history of BrS was present in 56% (n=9) and almost one third had family history of sudden cardiac death (SCD). Most of the patients had a type 1 Brugada ECG pattern (n=14) and 2 patients presented a fever and drug induced pattern, respectively. Fourteen patients were BrS(−), mostly female (n=11, 79%) with a loss-of-function mutation in the SCN5A gene (n=10). They all had family members with BrS, mainly from the paternal side, and 43% (n=6) mentioned SCD history. Although most of the patients were asymptomatic, the prevalence of rhythm or conduction disturbances was not infrequent, particularly in BrS(+) patients (n=12, 75%). Also, in this group and during follow-up, 3 patients had documented supraventricular tachyarrhythmias, and 2 patients had syncope episodes, one of which required an implantable cardioverter-defibrillator. No events were reported in the BrS(−) patients. Nine patients (n=9/30, 30%) were hospitalized, 3 due to an arrhythmic event (all in the BrS(+) group). Overall, no sudden cardiac death event was reported during follow-up. Conclusion In our study, although the majority of the patients were asymptomatic, the occurrence of arrhythmic events was not negligible, especially in the BrS(+) patients. Despite the significant family history, patients with BrS(−) had no events reported during follow-up. Nevertheless, the management of these patients is not clear cut, and a personalized therapeutic strategy with close follow-up is essential. Funding Acknowledgement Type of funding sources: None.

Functional analysis of novel SCN5A mutations related to Brugada syndrome

Abstract Brugada syndrome (BrS) is an arrhythmogenic disorder that has been linked to mutations in SCN5A, the gene encoding for the pore-forming α-subunit of the cardiac Na+ channel. Recently, novel SCN5A missense mutations (A385T and R504T) were identified in a BrS patient. Since the mutations are in the loop connecting transmembrane segments 5 and 6 in domain 1 (S5-S6 in DI) and segments 6 and 1 between domain 1 and 2 (DI-DII linker), it can lead to dysfunctional property of the Na+ channel. Here we aimed to characterize the electrophysiological properties of A385T and R504T. The wild-type (WT) and mutant SCN5A were transiently transfected in HEK293 cells, and the Na+ channel was analyzed using the whole-cell patch-clamp technique. WT, A385T, R504T, and double mutant (A385T/R504T) showed no significant differences in the current density and the voltage-dependent activation. Unexpectedly, a rightward shift of the voltage-dependent inactivation was identified in the three groups of mutation. Besides, the recovery from inactivation of double mutant was faster than that of WT. These results suggest that, contrary to the expected mechanism of BrS, the mutations cause a gain-of-function of NaV1.5. However, the current densities of R504T and double mutant transfected with β-subunit SCN1B were significantly suppressed but A385T was not different from WT. The voltage dependent activation and inactivation of all mutants were not significantly different from WT. The recovery from inactivation of all mutants were slower than that of WT. These results suggest that R504T mutation of α-subunit SCN5A interacting with β-subunit SCN1B is responsible to pathophysiological function of novel BrS. Funding Acknowledgement Type of funding sources: None.

The eligibility of patients with an inherited cardiac disease for therapy with a subcutaneous implantable cardioverter-defibrillator

Abstract Introduction The subcutaneous implantable cardioverter-defibrillator (S-ICD) is considered especially beneficial in young patients with an inherited cardiac disease, but data on these patient groups is limited. Purpose To evaluate the eligibility of patients with an inherited cardiac disease for therapy with a subcutaneous implantable cardioverter-defibrillator Methods We retrospectively analysed all patients with an inherited cardiac disease who received an S-ICD in our tertiary center between February 2009 and June 2021. ECG parameters and data on appropriate and inappropriate shocks were collected. Different diagnoses were compared using a chi-square test. Results We analysed 109 patients who were diagnosed with IVF (DPP6-based, N=41, 37.6%), HCM (N=36, 33.0%), Brugada syndrome (BrS, N=13, 11.9%), ARVC (N=9, 8.3%), PLN (N=3, 2.8%), LQTS (N=2, 1.8%) and other cardiomyopathies (N=5, 4.6%). Mean follow-up was 5.5±3.4 years. ECG parameters did not significantly change during follow-up. HCM patients were most likely to receive an appropriate shock (10/36, P=0.01), followed by ARVC (2/9, P=0.57) and Brugada patients (1/13, P=0.40). Patients with LQTS had most frequently inappropriate shocks (1/2, P=0.06), followed by BrS (4/13, P=0.008) and HCM patients (4/36, P=0.8). Conclusion Patients with an inherited cardiac disease are eligible for S-ICD therapy, but comes with a risk of inappropriate shocks, especially in patients with LQTS and BrS. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Dutch Heart Foundation (CVON 2018-10 PREDICT2)

How arrhythmic risk changes over time in patients with low risk Brugada syndrome

Abstract Background Brugada Syndrome (BrS) is an inherited disorder associated with an increased risk of sudden cardiac death (SCD) and is diagnosed by the presence of a Brugada type I ECG pattern, either spontaneous or drug-induced. A spontaneous ECG pattern is one of the two main risk factors for SCD, along with syncope. However, there is still no clear evidence on how and how often to screen patients with drug-induced BrS to detect a spontaneous ECG pattern, therefore allowing to reassess their arrhythmic risk. Purpose To determine how many subjects develop a spontaneous ECG pattern among a pool of patients with low risk BrS (drug-induced pattern without history of syncope at the time of diagnosis) observed through systematic ECG Holter monitoring. Methods We retrospectively collected data for all patients with low risk BrS treated at our center for at least 12 months between 2016 and 2021. Each patient was tested yearly with at least one 12-lead 24-hour ECG Holter monitoring with high precordial leads (V1-V2, V3-V4, V5-V6 respectively in 2nd, 3rd and 4th intercostal space parasternal left and right). In case of spontaneous pattern detection at two recordings, patients underwent electrophysiological study (EPS) and in case of inducible ventricular arrhythmias, implantable cardiac defibrillator (ICD) placement. Results We included 63 patients with low risk BrS. During a median follow-up of 48 months: 1 patient died for SCD (1.6%), 1 experienced syncope (1.6%) and 19 exhibited a spontaneous ECG pattern (30.2%). Of these 19 patients: 18 were males and 5 had a mutation of SCN5A; the average age at the time of spontaneous pattern detection was 48.1±11.5 years. The average number of ECG holters/per patient/per year was 1.1±0.6, the average number of ECG Holters until the detection of a spontaneous pattern was 3.3±1.8, whilst the average number of months in between the diagnosis and the detection of a spontaneous pattern was 43.2±41.1. After the observation of a spontaneous pattern: 6 patients were excluded from further investigation (as they had already undergone EPS or refused), 1 was directly treated with ICD and 12 underwent EPS, 4 of whom consequently underwent ICD placement. Among these 5 patients who underwent ICD placement – 7.9% of the original 63 patients – we observed 1 appropriate ICD intervention (antitachycardia pacing), 1 inappropriate ICD shock and 1 ICD related complication. Conclusions In our population of patients with low risk BrS the detection of a spontaneous ECG pattern is the most common determinant of risk reclassification. Systematic ECG Holter monitoring disclosed the presence of a spontaneous ECG pattern in a relevant number of subjects, allowing to reassess their arrhythmic risk and indication for ICD placement. Our study stresses the importance of periodic evaluation of low risk BrS patients with ECG Holter monitoring and the need for further investigation to define the optimal monitoring strategy. Funding Acknowledgement Type of funding sources: None.

217 Why it is important to recognize Brugada syndrome in athletes: a case report

Abstract Aims The Brugada syndrome (Brs) is an inherited disorder associated with risk of ventricular fibrillation and sudden cardiac death in a structurally normal heart. The purpose of this case presentation was to spread awareness about this condition, highlight the importance of timely diagnosis and effective treatment of this channelopathy especially in asymptomatic young athletes at high risk of sudden cardiac death. Methods and results In this report, we discuss the case of a 47-year-old male. He was a tennis player who performed a visit to the sports doctor to have issued a certificate for competitive fitness. He had no familiar history of sudden death or syncope. The patient’s electrocardiogram (ECG) revealed J-point elevation and ST-segment elevation in the right precordial leads V1 and V2 positioned in the second, third, or fourth intercostal space, showing classic type II ‘saddleback’ morphology in V2 and BrS was suspected. Hence, the patient underwent Holter ECG monitoring with evidence of spontaneous type 1 Brugada pattern (‘coved’ morphology), as well as frequent ventricular ectopic beats with left branch block morphology. Indeed, a diagnosis of BrS was made. Antiarrhythmic prophylaxis therapy with hydroquinidine was initiated and the patient was suspended from competitive activity with a 3-month follow-up. Conclusions The BrS is a hereditary disease characterized by a typical ECG pattern potentially predisposing active individuals with no patent structural heart disease to ventricular arrhythmias (VA) and sudden cardiac death (SCD). Nowadays, it is difficult to discern the true burden of BrS due to the unknown real prevalence of asymptomatic patients and the dynamic variability of the ECG pattern in individuals. The purpose of this case presentation was to spread awareness about this condition, highlight the importance of timely diagnosis, and effective treatment of this channelopathy especially in asymptomatic young athletes at high risk of SCD. Indeed, exercise may potentially worsen the ECG abnormalities in BrS patients, resulting in higher peak J-point amplitudes during the vasovagal reaction of the recovery period, possibly leading to an increased risk of cardiac events. Moreover, the enhanced vagal tone in athletes could be both a BrS risk factor and an exercise effect. For this reason, athletic pre-participation screening is essential for minimizing the risk for SCD in athletes participating in either competitive or leisure sporting activities.

New insights into risk stratification of Brugada syndrome from high density epicardial electroanatomic mapping

Abstract Background/Introduction Brugada syndrome (BrS) has been initially described as a channelopathy with no structural heart disease but a growing body of evidence points towards structural anomalies in the epicardium of right ventricle outflow tract (RVOT-EPI). Since its first description the electrical substrate of BrS has been thought to be a fractionation of the electrograms (EGMs) in the RVOT-EPI. Also there is recent evidence that SCN5A mutation BrS patients might be at increased risk of sudden cardiac death (SCD). No studies correlated high-density mapping substrate with clinical outcomes. Purpose The aim of the current study was to compare clinical characteristics of BRS patients with EGMs characteristics from high-density epicardial mapping with Advisor HD-Grid mapping catheter. Methods All consecutive patients with BrS who underwent hybrid RVOT-EPI substrate ablation at our University Hospital between April 2018 and March 2021 were retrospectively included in the study. Genetic analysis was performed in all patients and clinical data were collected. BrS was diagnosed following current recommendations. Inclusion criteria were: 1) use of Advisor HD-Grid mapping catheter and 3D-electroanatomical (EAM) mapping system EnSite Precision; 2) acquisition of EAM before and after ajmaline infusion at standard protocol (1 mg/kg in 5 minutes). Bipolar EGMs were considered abnormal (aEGMs) if they met at least 1 of the following: prolonged duration (>80 ms), fragmented components (at least 2 distinct peaks), and/or late potentials extending beyond the end of the QRS complex. aEGMs duration (Ed) was defined as the time from surface QRS onset in D2 to bipolar EGM offset. Results Fifteen patients were included in the study. Six patients (40%) had history of SCD or inducible ventricular arrhythmias (VAs) at electrophysiological study and 5 patients (33.3%) had a mutation of SCN5A. The mean number of points of EAMs was 1020±500. Patients with history of SCD or VAs compared with patients without history had similar Ed before ajmaline [117.5 ms (100.6–132.5) vs 110.5 ms (106.8–114.8), p=0.72] but longer Ed after ajmaline [247.5 ms (231.6–273.9) vs 188.0 ms (178.0, 211.5), p=0.034]. The best cutoff of Ed after ajmaline to predict VAs history was 233 msec (AUC of the model 0.83, sensitivity: 0.98, specificity: 0.66). Patients with SCN5A mutation compared with patients without had similar Ed before ajmaline [125.2 ms (117.9–132.6) vs 105.0 ms (103.0–119.0), p=0.24] but longer Ed after ajmaline [270.0 ms (259.0–280.5) vs 200.8 ms (181.2–224.2), p=0.037], figure 1. The best cutoff of Ed after ajmaline to predict SCN5A mutation was 256.5 ms (AUC of the model 0.84, sensitivity: 0.80, specificity: 0.98), figure 2. Conclusions High density RVOT epicardial mapping provides data of clinical meaning in risk stratification of BrS patients. These data should be interpreted in the context of a population undergone RVOT-EPI substrate ablation. Funding Acknowledgement Type of funding sources: None. aEGM duration and SCD/VA or SCN5AROC curves for EGM derived prediction

Evaluation of electrocardiographic predictors of brugada type response during flecainide challenge

Abstract Background/Introduction Brugada syndrome (BrS) is a hereditary channelopathy with an increased risk of sudden cardiac death. Most BrS patients manifest non type 1 Brugada pattern electrocardiography (ECG). Sodium channel blockade is a well-established diagnostic tool for Brugada syndrome. However, intravenous sodium channel blockade is not readily available in all parts of the world. In addition, severe ventricular arrhythmias during drug challenge have an estimated prevalence of 1%. Determining the predictors of a positive test would improve our understanding and facilitate appropriate use of these tests. Purpose We aimed to identify ECG predictors of Brugada type response during flecainide challenge and provide an independent assessment of current published ECG criteria predictive of a positive flecainide challenge. Methods We analysed the clinical and electrocardiographic data of 526 consecutive individuals referred from a national pre-participation exercise screening program who underwent flecainide challenge for an ECG suspicious of Brugada pattern. ECG recordings included both conventional and high precordial leads (1 and 2 space up ECGs in V1 and V2 – 1V1, 1V2, 2V1, 2V2). Twelve-lead ECGs were evaluated for the width of the β angle, β score, baseline J wave elevation, width of QRS, absence of isoelectric segment in lead II, ST/ QT ratio, presence of S wave in Leads II, III and V5 as well as the presence of R wave in aVR. Results Flecainide challenge was positive in 121 (23%) of the 526 cases. Baseline QRS duration was greater in the conventional lead placement [V1 (102.4±20.0 ms vs 97.6±14.0 ms, p=0.003), V2 (111.1±33.5 ms vs 100.9±13.1 ms, p=0.001)] as well as 1 space up [1V1 (108.9±21.0 ms vs 100.6±18.2 ms, p<0.001), 1V2 (117.4±26.6 ms vs 103.2±18.3, p<0.001)] and 2 space up [2V1 (113.6±23.4 ms vs 102.5±19.3 ms, p<0.001), 2V2 (121.6±26.1 ms vs 106.8±19.1 ms, p<0.001)] in cases with a subsequent positive response. A QRS duration of ≥120ms in V2 yielded a sensitivity of 16.5%, specificity of 93.8%, positive predictive value of 44.4% and negative predictive value of 79% for a positive flecainide challenge. Other predictors of positivity included that of a shorter ST duration in lead II (107.0±19.9 ms vs 118.1±24.4, p<0.001) and a shorter ST/ QT ratio (0.30±0.09 vs 0.32±0.07, p=0.006). Conclusion In this population, a wider QRS duration, shortened ST segment in lead II and ST/QT ratio were predictors of a positive response to flecainide challenge when BrS was suspected on a baseline ECG. Prior published ECG parameters such as β angle, β score, baseline J wave elevation, presence of S wave in Leads II, III and V5 as well as the presence of R wave in aVR did not perform as well in predicting for a positive response to flecainide challenge in our population. Funding Acknowledgement Type of funding sources: None. Baseline CharacteristicsECG Findings

Brugada syndrome in Hong Kong: long term outcome prediction through machine learning

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Brugada syndrome (BrS) is an ion channelopathy that predisposes affected patients to spontaneous ventricular tachycardia/fibrillation (VT/VF) and sudden cardiac death (SCD). Despite its greater prevalence in Asia and epidemiological heterogeneity in disease manifestation, the majority of the conducted cohort studies available in current literature are based in Western countries. Purpose The aim of this study is to examine the clinical and electrocardiographic predictive factors of spontaneous VT/VF for Asian BrS patients. Methods This was a territory-wide retrospective cohort study of patients diagnosed with BrS between 1997 and 2019. The primary outcome was spontaneous VT/VF detected either during hospital admission or by implantable-cardioverter defibrillator (ICD) data. Cox regression was used to identify significant clinical and electrocardiographic risk predictors. Non-linear interactions between variables (latent patterns) were extracted using non-negative matrix factorization (NMF) and used as inputs into the random survival forest (RSF) model. Results This study included 516 consecutive BrS patients (mean age of initial presentation= 50 ± 16 years, male= 92%) with a median follow-up of 86 (interquartile range: 45-118) months. The cohort was divided into subgroups based on initial disease manifestation: asymptomatic (n = 314), syncope (n = 159) or VT/VF (n = 41). Annualized event rates per person-year were 1.70%, 0.05% and 0.01% for the VT/VF, syncope and asymptomatic subgroups, respectively. Multivariate Cox regression analysis revealed initial presentation of VT/VF (HR = 24.0, 95% CI = [1.21, 479] , P= 0.037) and standard deviation of P-wave duration (HR = 1.07, 95% CI = [1.00, 1.13], P = 0.044) were significant predictors. The NMF-RSF showed the best predictive performance compared to RSF and Cox regression models (precision: 0.87 v.s. 0.83 v.s. 0.76, recall: 0.89 v.s. 0.85 v.s. 0.73, F1-score: 0.88 v.s. 0.84 v.s. 0.74). Conclusions This is one of the largest territory-wide cohort studies on BrS and the largest study in Asia published to date, with an extensive median follow-up duration of 7 years. Clinical history, electrocardiographic markers and investigation results provide important information for risk stratification. Machine learning techniques using NMF and RSF significantly improves overall risk stratification performance.

Tbx5 variants disrupt Nav1.5 function differently in patients diagnosed with Brugada or Long QT Syndrome

The transcription factor Tbx5 controls cardiogenesis and drives Scn5a expression in mice. We have identified two variants in TBX5 encoding p. D111Y and p. F206L Tbx5, respectively, in two unrelated patients with structurally normal hearts diagnosed with long QT (LQTS) and Brugada (BrS) syndrome. Here, we characterized the consequences of each variant to unravel the underlying disease mechanisms. We combined clinical analysis with in vivo and in vitro electrophysiological and molecular techniques in human-induced pluripotent stem-cell-derived cardiomyocytes (hiPSC-CMs), HL-1 cells, and cardiomyocytes from mice trans-expressing human wild-type (WT) or mutant proteins. Tbx5 increased transcription of SCN5A encoding cardiac Nav1.5 channels, while repressing CAMK2D and SPTBN4 genes encoding Ca/calmodulin kinase IIδ (CaMKIIδ) and βIV-spectrin, respectively. These effects significantly increased Na current (INa) in hiPSC-CMs and in cardiomyocytes from mice trans-expressing Tbx5. Consequently, action potential (AP) amplitudes increased and QRS interval narrowed in the mouse electrocardiogram. p. F206L Tbx5 bound to the SCN5A promoter failed to transactivate it, thus precluding the pro-transcriptional effect of WT Tbx5. Therefore, p. F206L markedly decreased INa in hiPSC-CM, HL-1 cells and mouse cardiomyocytes. The INa decrease in p. F206L trans-expressing mice translated into QRS widening and increased flecainide sensitivity. p. D111Y Tbx5 increased SCN5A expression but failed to repress CAMK2D and SPTBN4. The increased CaMKIIδ and βIV-spectrin significantly augmented the late component of INa (INaL) which, in turn, significantly prolonged AP duration in both hiPSC-CMs and mouse cardiomyocytes. Ranolazine, a selective INaL inhibitor, eliminated the QT and QTc intervals prolongation seen in p. D111Y trans-expressing mice. In addition to peak INa, Tbx5 critically regulates INaL and the duration of repolarization in human cardiomyocytes. Our original results suggest that TBX5 variants associate with and modulate the intensity of the electrical phenotype in LQTS and BrS patients.