Risk Stratification and Treatment of Brugada Syndrome

Whole exome sequencing in Brugada and long QT syndromes revealed novel rare and potential pathogenic mutations related to the dysfunction of the cardiac sodium channel

Background

Brugada syndrome (Brs) and long QT syndrome (LQTs) are the most observed “inherited primary arrhythmia syndromes” and “channelopathies”, which lead to sudden cardiac death.

Methods

Detailed clinical information of Brs and LQTs patients was collected. Genomic DNA samples of peripheral blood were conducted for whole-exome sequencing on the Illumina HiSeq 2000 platform. Then, we performed bioinformatics analysis for 200 genes susceptible to arrhythmias and cardiomyopathies. Protein interaction and transcriptomic co-expression were analyzed using the online website and GTEx database.

Results

All sixteen cases of Brs and six cases of LQTs were enrolled in the current study. Four Brs carried known pathogenic or likely pathogenic of single-point mutations, including SCN5A p.R661W, SCN5A p.R965C, and KCNH2 p.R692Q. One Brs carried the heterozygous compound mutations of DSG2 p.F531C and SCN5A p.A1374S. Two Brs carried the novel heterozygous truncated mutations (MAF < 0.001) of NEBL (p.R882X) and NPPA (p.R107X), respectively. Except for the indirect interaction between NEBL and SCN5A, NPPA directly interacts with SCN5A. These gene expressions had a specific and significant positive correlation in myocardial tissue, with high degrees of co-expression and synergy. Two Brs carried MYH7 p.E1902Q and MYH6 p.R1820Q, which were predicted as "damaging/possibly damaging" and "damaging/damaging" by Polyphen and SIFT algorithm. Two LQTs elicited the pathogenic single splicing mutation of KCNQ1 (c.922-1G > C). Three LQTs carried a single pathogenic mutation of SCN5A p.R1880H, KCNH2 p.D161N, and KCNQ1 p.R243S, respectively. One patient of LQTs carried a frameshift mutation of KCNH2 p. A188Gfs*143.

Conclusions

The truncated mutations of NEBL (p.R882X) and NPPA (p.R107X) may induce Brugada syndrome by abnormally affecting cardiac sodium channel. SCN5A (p.R661W, p.R965C and p.A1374S) and KCNH2 (p.R692Q) may cause Brugada syndrome, while SCN5A (p.R1880H), KCNQ1 (c.922-1G > C and p.R243S) and KCNH2 (p.D161N and p.A188Gfs*143) may lead to long QT syndrome.

Brugada syndrome

Brugada syndrome (BrS) is an inherited cardiac arrhythmia syndrome that causes a heightened risk for ventricular tachyarrhythmias and sudden cardiac death. BrS is characterised by a coved ST-segment elevation in right precordial leads. The prevalence is estimated to range between 1 in 5,000 to 1 in 2,000 in different populations, with the highest being in Southeast Asia and in males. More than 18 genes associated with BrS have been discovered and recent evidence has suggested a complex polygenic mode of inheritance with multiple common and rare genetic variants acting in concert to produce the BrS phenotype. Diagnosis of BrS in patients currently relies on presentation with a type-1 Brugada pattern on ECG either spontaneously or following a drug provocation test using a sodium channel blocker. Risk assessment in patients diagnosed with BrS is controversial, especially with regard to the predictive value of programmed electrical stimulation and novel ECG parameters, such as QRS fragmentation. The first line of BrS therapy remains an implantable cardioverter defibrillator (ICD), although radiofrequency catheter ablation has been shown to be an effective option in patients with contraindications for an ICD. True BrS can be unmasked on ECG in susceptible individuals by monitoring factors such as fever, and this has been recently evident in several patients infected with the 2019 novel coronavirus (COVID-19). Aggressive antipyretic therapy and regular ECG monitoring until fever resolves are current recommendations to help reduce the arrhythmic risk in these COVID-19 patients. In this review, we summarise the current knowledge on the epidemiology, pathophysiology, genetics, clinical diagnosis, risk stratification and treatment of patients with BrS, with special emphasis on COVID-19 comorbidity.

Increased prevalence of ECG suspicious for Brugada Syndrome in recent onset schizophrenia spectrum disorders

BACKGROUND

Schizophrenia is associated with an increased risk of sudden cardiac death, traditionally attributed to prolonged QTc interval and increased prevalence of cardiovascular risk factors. However, defective ion channels implicated in both schizophrenia and Brugada Syndrome (BrS) may be associated with an increased risk of cardiac arrhythmias. Moreover, these cardiac arrhythmias can be provoked by various drugs, including psychotropic drugs.

OBJECTIVE

To assess the prevalence of the occurrence of ECG suspicious for BrS (suspect BrS-ECG) and the prevalence of BrS in patients with recent onset schizophrenia spectrum disorders (SSD).

METHODS

In this case-control study, ECGs of 388 patients with recent onset SSD admitted between 2006 and 2015 and 844 healthy controls were made. All persons who had a suspect BrS-ECG were offered an ajmaline provocation test to diagnose or exclude BrS. Data on possible confounders were ascertained. Patients with and without suspect BrS-ECG were compared regarding clinical and ECG variables.

RESULTS

Suspect BrS-ECG was found in 33 patients (8.5%) and 13 healthy controls (1.5%), with an adjusted Odds Ratio of 3.5 (p < 0.0001). This finding was not explained by potential confounders such as gender, age, ethnicity, cannabis use, cardiovascular risk factors, medication use or serum electrolytes. BrS was confirmed in three patients and one control.

CONCLUSION

A considerable subset of patients with recent onset SSD have suspect BrS-ECG, extending earlier findings in patients with chronic schizophrenia. Screening for BrS in schizophrenia could be relevant both to prevent sudden cardiac death and to identify a subgroup of patients with possible ion-channel dysfunctioning.

Value of the sodium-channel blocker challenge in Brugada syndrome

AIMS

Intravenous drug challenge is frequently performed to unmask Brugada syndrome (BrS). However, its true sensitivity has never been assessed. We used the obligate BrS transmitters in families affected by BrS to evaluate the true accuracy of drug challenge.

METHODS

All consecutive patients from 2000 to 2014 who underwent drug challenge during familial screening for BrS were included in the study. Obligate BrS transmitters were defined as the presence of a descendant and non-descendant first-degree relative affected by BrS. Two physicians blinded to the clinical and genetic status reviewed the data.

RESULTS

Among 705 drug challenges performed in 149 families, 50 were performed in obligate transmitters from 42 different families. SCN5A mutations were identified in 20 families. Two obligate transmitters were not carrier of the familial mutation. Based on obligate transmitters, sensitivity was 100% for Ajmaline vs 77% for Flecainide (P=0.002). Based on the presence of the familial SCN5A mutation in all family relatives, sensitivity and specificity of sodium channel blocker challenge were respectively 78% (95/122) and 46% (68/148). During a median follow-up of 91 (26-136) months, 2 ventricular fibrillations occurred in obligate transmitters.

CONCLUSION

We demonstrated that Ajmaline challenge presents an excellent sensitivity that may rule out the diagnosis of BrS when negative. Conversely, a negative Flecainide challenge may not prevent from Brs inheritance and risk of SCD. This may lead to suggest systematic use of Ajmaline during drug challenge.

Mutation in S6 domain of HCN4 channel in patient with suspected Brugada syndrome modifies channel function

Diseases such as the sick sinus and the Brugada syndrome are cardiac abnormalities, which can be caused by a number of genetic aberrances. Among them are mutations in HCN4, a gene, which encodes the hyperpolarization-activated, cyclic nucleotide-gated ion channel 4; this pacemaker channel is responsible for the spontaneous activity of the sinoatrial node. The present genetic screening of patients with suspected or diagnosed Brugada or sick sinus syndrome identified in 1 out of 62 samples the novel mutation V492F. It is located in a highly conserved site of hyperpolarization-activated cyclic nucleotide-gated (HCN)4 channel downstream of the filter at the start of the last transmembrane domain S6. Functional expression of mutant channels in HEK293 cells uncovered a profoundly reduced channel function but no appreciable impact on channel synthesis and trafficking compared to the wild type. The inward rectifying HCN4 current could be partially rescued by an expression of heteromeric channels comprising wt and mutant monomers. These heteromeric channels were responsive to cAMP but they required a more negative voltage for activation and they exhibited a lower current density than the wt channel. This suggests a dominant negative effect of the mutation in patients, which carry this heterozygous mutation. Such a modulation of HCN4 activity could be the cause of the diagnosed cardiac abnormality.

A Zebra Among Horses: A Case of Brugada Syndrome and Coronary Artery Disease

Brugada syndrome (BrS) is recognized as a hereditary ion channel disorder with electrocardiographic changes. First appearing in the literature about 20 years ago, contemporary thoughts are that BrS may be responsible for many sudden cardiac deaths and is associated with ventricular dysrhythmias that can lead to syncope or cardiac arrest. Many individuals with BrS may have no or limited structural heart disease, whereas others may have subtle morphological changes in histopathology. This case reviews a single patient with BrS Type 1 who was found to have a high-level of coronary artery disease. Changes noted in the original electrocardiogram were of significant importance in reaching the diagnosis.

Fever-induced type 1 Brugada pattern

Brugada syndrome, first described over 20 years ago, is characterized by a typical electrocardiographic pattern with coved-type ST-segment elevation in the right precordial leads and a high risk of sudden death in otherwise healthy young adults. The electrocardiographic pattern is sometimes intermittent, and fever is a possible trigger. The authors present the case of a 68-year-old woman who came to the emergency department with fever and syncope. A diagnosis of community-acquired pneumonia was made. The electrocardiogram performed when the patient had fever revealed a type 1 Brugada pattern, which disappeared after the fever subsided. After other causes of Brugada-like pattern were excluded, Brugada syndrome was diagnosed and a cardioverter-defibrillator was implanted. This case demonstrates that this entity can be diagnosed at more advanced ages and highlights the usefulness of electrocardiography in a febrile state.

Sudden cardiac death in the young: the bogeyman

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