The Brugada syndrome revisited

The Brugada syndrome is a rare but well-defined cause of sudden cardiac death. The key underlying abnormality is a decrease in net depolarising current due to a genetic defect, though recent evidence also implicates structural abnormalities in some patients. Diagnosis requires a Brugada-type ECG as well as typical clinical features: such clinical considerations are currently key in guiding risk stratification and hence management. Whilst pharmacological therapies are under investigation, the only intervention with a robust evidence base remains insertion of an implantable cardioverter defibrillator. Further research will be required to allow more effective risk stratification and hence more rational therapy.

Pulmonary vein isolation in patients with Brugada syndrome and atrial fibrillation: a 2-year follow-up

AIMS

Pharmacological treatment of atrial fibrillation (AF) in the setting of Brugada syndrome (BS) might be challenging as many antiarrhythmic drugs (AADs) with sodium channel blocking properties might expose the patients to the development of ventricular arrhythmias. Moreover, patients with BS and implantable cardioverter-defibrillator (ICD) might experience inappropriate shocks because of AF with rapid ventricular response. The role of pulmonary vein isolation (PVI) in patients with BS and recurrent episodes of AF has not been established yet. In this study, we analysed the outcome of PVI using radiofrequency energy or cryoballoon (CB) ablation at 2 years follow-up.

METHODS AND RESULTS

Consecutive patients with BS having undergone PVI for drug-resistant paroxysmal AF were eligible for this study. Nine patients (three males; mean age: 52 ± 26 years) were included. Six patients (67%) had an ICD implanted of whom three had inappropriate shocks because of rapid AF. At a mean 22.1 ± 6.4 months follow-up, six patients (67%) were free of AF without AADs. None of the three patients who had experienced inappropriate ICD interventions for AF had further ICD shocks after ablation.

CONCLUSION

In our study PVI can be an effective and safe procedure to treat patients with BS and recurrent episodes of paroxysmal AF.

Genetic biomarkers in Brugada syndrome

Brugada syndrome is an inherited arrhythmia syndrome predisposing to sudden cardiac death. Six years after its initial description as a clinical entity, the first mutations in SCN5A encoding the cardiac sodium channel Nav1.5 were reported. Over 300 mutations in SCN5A have since been described in addition to mutations in genes encoding Nav1.5 auxiliary units, potassium and calcium channels. This review summarizes the current knowledge on the genetics of Brugada syndrome, focusing on SCN5A, and discusses its use as a biomarker for diagnosis, prognosis and treatment.

Current electrocardiographic criteria for diagnosis of Brugada pattern: a consensus report

Brugada syndrome is an inherited heart disease without structural abnormalities that is thought to arise as a result of accelerated inactivation of Na channels and predominance of transient outward K current (I(to)) to generate a voltage gradient in the right ventricular layers. This gradient triggers ventricular tachycardia/ventricular fibrillation possibly through a phase 2 reentrant mechanism. The Brugada electrocardiographic (ECG) pattern, which can be dynamic and is sometimes concealed, being only recorded in upper precordial leads, is the hallmark of Brugada syndrome. Because of limitations of previous consensus documents describing the Brugada ECG pattern, especially in relation to the differences between types 2 and 3, a new consensus report to establish a set of new ECG criteria with higher accuracy has been considered necessary. In the new ECG criteria, only 2 ECG patterns are considered: pattern 1 identical to classic type 1 of other consensus (coved pattern) and pattern 2 that joins patterns 2 and 3 of previous consensus (saddle-back pattern). This consensus document describes the most important characteristics of 2 patterns and also the key points of differential diagnosis with different conditions that lead to Brugada-like pattern in the right precordial leads, especially right bundle-branch block, athletes, pectus excavatum, and arrhythmogenic right ventricular dysplasia/cardiomyopathy. Also discussed is the concept of Brugada phenocopies that are ECG patterns characteristic of Brugada pattern that may appear and disappear in relation with multiple causes but are not related with Brugada syndrome.

Arrhythmogenesis in Brugada syndrome: impact and constrains of current concepts

Brugada syndrome (BrS), an inherited arrhythmogenic disease first described in 1992, is characterized by ST segment elevations on the electrocardiogram in the right precordium and by a high occurrence of arrhythmias including the life-threatening ventricular tachycardia/fibrillation. Knowledge of the underlying mechanisms of formation of arrhythmogenic substrate in BrS is essential, namely for the risk stratification of BrS patients and their therapy which is still restrained almost exclusively to the implantation of cardioverter/defibrillator. In spite of many crucial findings in this field published within recent years, the final consistent view has not been established so far. Hence, BrS described 20 years ago remains an actual topic of both clinical and experimental studies. This review presents an overview of the current knowledge related to the pathogenesis of BrS arrhythmogenic substrate, namely of the genetic basis of BrS, functional consequences of mutations related to BrS, and arrhythmogenic mechanisms in BrS.

Brugada pattern masquerading as ST-segment elevation myocardial infarction in flecainide toxicity

Flecainide (a class 1c antiarrhythmic) produces a dose-dependent decrease in intracardiac conduction. Its well known common electrocardiographic effects are prolongation of PR and QT intervals and the QRS complex duration. We report a case of flecainide toxicity in an elderly female who presented with a type 1 Brugada pattern who essentially had a previously normal ECG pattern on therapeutic dose of flecainide therapy. The case describes a rare electrocardiographic abnormality induced by flecainide toxicity which otherwise could be easily misinterpreted as a ST-segment elevation myocardial infarction (STEMI) without lack of expertise and high clinical suspicion.

Involvement of neuroleptic drugs in selenium deficiency and sudden death of cardiac origin: study and human post-mortem examination

The involvement of psychotropic drugs in sudden deaths has been highlighted. The objective of this work was to establish a link between selenium levels in heart tissue, psychotropic treatment and sudden death. Selenium levels were measured by electrothermal atomic absorption spectroscopy post-mortem in heart, brain and liver. Histological examination evidenced dilated cardiomyopathy in 45% of cases, left ventricular hypertrophy in 36%, and ischemic coronaropathy in 18%. A significant reduction of myocardial selenium levels compared to controls was seen in patients treated with neuroleptic drugs or meprobamate. No changes in brain or liver selenium levels were seen. These results suggest that selenium deficiency can facilitate sudden death in patients on psychotropic drugs. The reduced activity of glutathione peroxidase due to selenium deficiency can result in augmented oxidative stress in myocardial cells and myocardiopathy leading to sudden death.

Sudden death of cardiac origin and psychotropic drugs

Mortality rate is high in psychiatric patients versus general population. An important cause of this increased mortality is sudden cardiac death (SCD) as a major side-effect of psychotropic drugs. These SCDs generally result from arrhythmias occurring when the posology is high and may attain a toxic threshold but also at dosages within therapeutic range, in the presence of risk factors. There are three kinds of risk factors: physiological (e.g., low cardiac rate of sportsmen), physiopathological (e.g., hepatic insufficiency, hypothyroidism) and "therapeutic" (due to interactions between psychotropic drugs and other medicines). Association of pharmacological agents may increase the likelihood of SCDs either by (i) a pharmacokinetic mechanism (e.g., increased torsadogenic potential of a psychotropic drug when its destruction and/or elimination are compromised) or (ii) a pharmacodynamical mechanism (e.g., mutual potentiation of proarrhythmic properties of two drugs). In addition, some psychotropic drugs may induce sudden death in cases of pre-existing congenital cardiopathies such as (i) congenital long QT syndrome, predisposing to torsade de pointes that eventually cause syncope and sudden death. (ii) A Brugada syndrome, that may directly cause ventricular fibrillation due to reduced sodium current through Nav1.5 channels. Moreover, psychotropic drugs may be a direct cause of cardiac lesions also leading to SCD. This is the case, for example, of phenothiazines responsible for ischemic coronaropathies and of clozapine that is involved in the occurrence of myocarditis. The aims of this work are to delineate: (i) the risk of SCD related to the use of psychotropic drugs; (ii) mechanisms involved in the occurrence of such SCD; (iii) preventive actions of psychotropic drugs side effects, on the basis of the knowledge of patient-specific risk factors, documented from clinical history, ionic balance, and ECG investigation by the psychiatrist.

Prevalence of the type 1 Brugada electrocardiogram in Caucasian patients with suspected coronary spasm

AIMS

Sporadic cases have reported the coexistence of coronary spasm and Brugada syndrome. However, the prevalence of the Brugada phenotype in coronary spasm is unknown, particularly in non-Japanese populations. In this study, we sought to examine the prevalence of the type 1 Brugada electrocardiogram (ECG) in a large European patient population undergoing intracoronary provocation testing for suspected coronary spasm.

METHODS AND RESULTS

We retrospectively evaluated ECG data for the presence of type 1, 2, and 3 Brugada ECGs from 955 consecutive German patients without obstructive coronary artery disease undergoing intracoronary acetylcholine (ACH) provocation (ACH-test). Eight hundred and twenty-seven patients (age 63 ± 12 years; 42% male) with complete ECG data were eligible for further analysis. The ACH-test revealed coronary spasm in 325 patients (39.3%). A Brugada ECG of any type was found in six patients (0.7%) at baseline and eight patients (0.9%) at any time. There was no difference in the prevalence of coronary spasm in patients with (37.5%) and without (39.3%) Brugada-type ECGs. The type 1 Brugada ECG was not seen at baseline, but two type 1 Brugada ECGs were observed during ACH-administration into the right coronary artery (RCA; 0.2%), one with simultaneous RCA spasm and one without. Ajmaline provocation testing reproduced the type-1 Brugada ECG in the patient without coronary spasm but she had no other features of the Brugada syndrome.

CONCLUSIONS

This study reports a low prevalence of the type 1 Brugada ECG in the largest known European collection of intracoronary ACH provocation. In these patients, we found no evidence for the coexistence of Brugada syndrome and coronary spasm. This is in contrast to available Japanese data.

Assessing use-dependent inhibition of the cardiac Na(+/-) current (I(Na)) in the PatchXpress automated patch clamp

INTRODUCTION

The cardiac Na+ current (I(Na)) underlies the rapid depolarization of the cardiac myocyte, and block of the current slows cardiac conduction and increases the risk of ventricular arrhythmia. A feature of Na+ channel block termed use-dependence is important to the assessment of blocking potency. We developed a robust automated patch clamp assay to rapidly and routinely assess the use-dependent block of I(Na) by drug candidates. The assay clarifies whether drug candidates block more potently at increased heart rates and provides a quantitative score of use-dependence.

METHODS

A use-dependent cardiac I(Na) assay was implemented on the PatchXpress 7000A, an automated whole-cell patch clamp device, using a HEK cell line stably expressing the human cardiac Na+ channel, Na(V)1.5. Stable recordings lasting up to 30 minutes were achieved by selection of holding potential (-100 mV) as well as an appropriate osmotic gradient to prevent time-dependent loss of cell capacitance and current. The final protocol allows evaluation of I(Na) inhibition at three pulsing rates at three test concentrations for each recorded cell.

RESULTS

IC(50) values obtained for three standard I(Na) blockers lidocaine, mexiletine, and flecainide, at pulsing frequencies of 0.2 Hz, 1 Hz, and 3 Hz, were compared to IC(50) values obtained with conventional pipette patch clamp of the Na(V)1.5 cell line and of guinea pig cardiac myocytes using matched voltage protocols and pulsing rates. Absolute potencies were well correlated only under conditions of matched holding potential and fell within an approximately three-fold window. While absolute potencies could vary widely with holding potential, the fold increases in potency with increases in pulsing rates were less prone to variation of the holding potential.

DISCUSSION

Use-dependence of cardiac Na+ channel block can be rapidly assessed in the PatchXpress platform and quantified at early stages of drug development to guide lead optimization.

Recovery following propofol-associated brugada electrocardiogram

Brugada syndrome is a genetic disorder associated with an increased risk of sudden cardiac death that has typical electrocardiographic (ECG) patterns. Recently, there have been reports of Brugada ECG patterns seen in critically ill patients who received propofol,(1) and this pattern was associated with a very high imminent mortality. We report a case in which a critically ill patient developed a Brugada ECG pattern following high-dose propofol infusion. Once the ECG pattern was recognized, the propofol was discontinued and the ECG pattern resolved, and the patient was discharged home with no arrhythmic sequelae.