A case of idiopathic ventricular fibrillation with incomplete right bundle branch block and persistent ST segment elevation

Brugada syndrome and sinus node dysfunction

Brugada syndrome (BrS) is a well-known catastrophic disease first reported in 1992 by the Brugada brothers. Ventricular fibrillation (VF) is an essential arrhythmia in BrS. An association between BrS and atrial tachyarrhythmias is not uncommon. However, sinus node dysfunction (SND) associated with BrS has not been well discussed. In this review, we focus on the association between BrS and SND. Based on previous reports describing clinical, epidemiological, and genetic evidence, SND is not a rare concomitant disorder in BrS. BrS may be a multiple conduction or arrhythmogenic disorder including not only the His-Purkinje system and right ventricle, but also the sinus node and atrium, derived from ion channel mutations.

A Tale of 2 Diseases: The History of Long-QT Syndrome and Brugada Syndrome

The Brugada syndrome (BrS) and long-QT syndrome (LQTS) present as congenital or acquired disorders with diagnostic electrocardiograms (ST-segment elevation and prolonged QT interval, respectively) and increased risk for malignant arrhythmias. Our understanding of the 2 disease forms (congenital vs. acquired) differs. A female patient on quinidine for atrial fibrillation who develops ventricular fibrillation is diagnosed with "acquired LQTS" and is discharged with no therapy other than instructions to avoid QT-prolonging medications. In contrast, an asymptomatic male patient who develops a Brugada electrocardiogram on flecainide is diagnosed with "asymptomatic BrS" and could be referred for an electrophysiological evaluation that could result in defibrillator implantation. The typical patient undergoing defibrillator implantation for BrS is asymptomatic but has a Brugada electrocardiogram provoked by a drug. The authors describe how the histories of LQTS and BrS went through the same stages, but in different sequences, leading to different conclusions.

Tricyclic antidepressants and the Brugada syndrome: an example of Brugada waves appearing after the administration of desipramine

Since its initial description in the early 1990s, the Brugada syndrome has become increasingly familiar to active researchers and practicing clinicians. The Brugada wave, a characteristic electrocardiographic abnormality of downsloping ST-segment elevation in leads V1-V3 and right bundle-branch block morphology, has now been associated with an increased risk of sudden death. Currently, very little is known about the relationship between the Brugada syndrome and tricyclic antidepressants. Accordingly, we report the case of a patient who developed prominent Brugada waves with the administration of increasing doses of desipramine. We believe the mechanism of Brugada wave augmentation or production secondary to tricyclic antidepressants is consistent with the current model of early repolarization. We also speculate that the increased risk of sudden death that may occur with tricyclic antidepressants could be related to the development of the Brugada syndrome. We advocate the judicious use of tricyclic antidepressants in cardiac and elderly patients, with careful monitoring of the electrocardiogram for the development Brugada waves.

Brief review of the recently described short QT syndrome and other cardiac channelopathies

There are many diseases related to ion-channel disorders, so-called "channelopathies." Hereditary short QT syndrome is a clinical-electrocardiographic entity with autosomal-dominant mode of transmission and it is the most recently described channelopathy. The syndrome may affect infants, children, or young adults with strong positive family background of sudden cardiac death. Short QT syndrome is characterized by short QT and heart-rate-corrected QTc intervals. It is frequently associated with tall-, peaked-, and narrow-based T waves that are reminiscent of the typical "desert tent" T waves of hyperkalemia. There is a high tendency for paroxysmal atrial fibrillation due to the heterogeneous abbreviation of action potential duration and refractoriness of atrial myocytes. The arrhythmia can also be induced by programmed electrical stimulation. The safest treatment suggested is an implantable cardioverter defibrillator, though the possibilities of inappropriate shocks have caused some concern, especially in teenagers. The ability of quinidine to prolong the QT interval has the potential to be an effective therapy for patients with short QT syndrome. This is particularly important in developing countries, where the implantable cardioverter-defibrillator therapy is not always available. Since these patients are at risk of sudden cardiac death from birth, and implantable cardioverter-defibrillator implantation has a lot of limitations in very young children, the utility of quinidine has to be evaluated further. Clinicians need to be aware of this deadly electrocardiographic (ECG) pattern as it portends a high risk of sudden cardiac death in otherwise healthy subjects with structurally normal hearts.

Link Between SCN5A Mutation and the Brugada Syndrome ECG Phenotype Simulation Study

BACKGROUND

The specific changes in the gating kinetics of the sodium current (I(Na)) responsible for its phenotype have remained to be elucidated. In the present study the effect of changes in the gating kinetics of I(Na) on early repolarization (ER) and initiation of phase 2 reentry (P2R) were evaluated in a theoretical epicardial ventricular fiber model.

METHODS AND RESULTS

Miyoshi-I(CaL) was incorporated into the modified Luo-Rudy dynamic (LRd) model. Dispersion at Ito-density was set within a theoretical fiber composed of serially arranged epicardial cells with gap junctions. The following changes in I(Na) kinetics were made: (1) a-10 mV shift in steady-state inactivation, (2) a+10 mV shift in steady-state activation curve, (3) a small inactivation time constant (DEC); P2R and ER were observed. A conduction disturbance within the fiber was simulated and only when the I(Na)-density was decreased did DEC, especially, show a marked increase in the likelihood of causing ER and P2R. Conduction disturbance significantly increased the likelihood causing ER or P2R.

CONCLUSIONS

In this one-dimension model with Ito-density dispersion, DEC-I(Na) precipitates I(Na)-blocker inducible ER. This suggests that the characteristic ST-segment elevation in the Brugada syndrome with SCN5A mutation can be interpreted in part by DEC-I(Na). Concomitant conduction disturbance may be required to cause P2R at physiological Ito density.

Manifestation of Brugada Syndrome After Pacemaker Implantation in a Patient with Sick Sinus Syndrome

A 49-year-old woman experienced syncope 10 months after DDD pacemaker implantation for sick sinus syndrome. ECG revealed abnormal ST elevation in leads V1 to V3 during a paced rhythm. Multifocal premature ventricular contractions followed by ventricular fibrillation were documented. Saddleback-type ST elevation was confirmed after a mode change to AAI. The diagnosis of Brugada syndrome was made, and the DDD pacemaker was upgraded to an implantable cardioverter defibrillator. Brugada syndrome can be easily overlooked if the classic ECG findings are not initially noted but may be observed even during pacing therapy.

A mathematical model of phase 2 reentry: role of L-type Ca current

Phase 2 reentry (P2R) is known to be one of the mechanisms of malignant ventricular arrhythmias, especially those associated with Brugada syndrome. However, little is known about the underlying mechanism for P2R. Our aim in this study was to simulate P2R in a mathematical model to enable us to understand its mechanism and identify a potential therapeutic target. A mathematical model of the L-type Ca current was composed according to whole cell current data from guinea pig ventricular myocytes recorded at 37 degrees C. Our mathematical model was incorporated into the modified Luo-Rudy phase 2 model. We set a dispersion in transient outward current (I(to)) density within the theoretical fiber, composed of 80 serially arranged epicardial cells with gap junctions and then observed the P2R. The dispersion in I(to) density within an only 0.8-cm epicardial theoretical fiber generated P2R with our Ca channel but not with the original model. When the P2R developed in the theoretical fiber, the calculated extracellular field potential showed coved-type ST segment elevation. We succeeded in generating P2R in our model for the first time. The local epicardial P2R may contribute the genesis of coved-type ST segment elevation in the Brugada syndrome.

The Brugada syndrome: clinical, genetic, cellular, and molecular abnormalities

The Brugada syndrome is an arrhythmic syndrome characterized by a right bundle branch block pattern and ST segment elevation in the right precordial leads of the electrocardiogram in conjunction with a high incidence of sudden death secondary to ventricular tachyarrhythmias. No evidence of structural heart disease is noted during diagnostic evaluation of these patients. In 25% of families, there appears to be an autosomal dominant mode of transmission with variable expression of the abnormal gene. Mutations have been identified in the gene that encodes the alpha subunit of the sodium channel (SCN5A) on chromosome 3. This genetic defect causes a reduction in the density of the sodium current and explains the worsening of the above electrocardiographic abnormalities when patients are treated with sodium channel blocking antiarrhythmic agents, which further diminish the already reduced sodium current. The prognosis is poor with up to a 10% per year mortality. Antiarrhythmic drugs including beta-blockers and amiodarone have no benefit in prolonging survival. The treatment of choice is the insertion of an implantable cardioverter-defibrillator.

Idiopathic ventricular tachycardia

Most ventricular tachycardias encountered in clinical practice occur in patients who have structural heart disease. Idiopathic ventricular tachycardia refers to those arrhythmias that occur in patients without structural heart disease, metabolic/electrolyte abnormalities, or the long QT syndrome. Three commonly recognized forms of idiopathic ventricular tachycardia include: (a) ventricular tachycardia associated with mitral valve prolapse, (b) ventricular tachycardia originating from the right ventricular outflow tract, and (c) ventricular tachycardia originating from the left ventricle. Recently, a fourth type of idiopathic ventricular tachycardia, termed the Brugada syndrome, has been identified as responsible for some cases of cardiac arrest in persons without apparent structural heart disease. Each form of ventricular tachycardia may be considered a discrete syndrome based on its electrocardiographic characteristics, mechanisms, responses to pharmacologic intervention, and prognosis (good in most cases). Ventricular tachycardias range from the common to the exotic, but all represent syndromes with which the internist and general cardiologist should be familiar.

The Brugada syndrome: clinical, electrophysiologic and genetic aspects

This review deals with the clinical, basic and genetic aspects of a recently highlighted form of idiopathic ventricular fibrillation known as the Brugada syndrome. Our primary objective in this review is to identify the full scope of the syndrome and attempt to correlate the electrocardiographic manifestations of the Brugada syndrome with cellular and ionic heterogeneity known to exist within the heart under normal and pathophysiologic conditions so as to identify the cellular basis and thus potential diagnostic and therapeutic approaches. The available data suggest that the Brugada syndrome is a primary electrical disease resulting in abnormal electrophysiologic activity in right ventricular epicardium. Recent genetic data linking the Brugada syndrome to an ion channel gene mutation (SCN5A) provides further support for the hypothesis. The electrocardiographic manifestations of the Brugada syndrome show transient normalization in many patients, but can be unmasked using sodium channel blockers such as flecainide, ajmaline or procainamide, thus identifying patients at risk. The available data suggest that loss of the action potential dome in right ventricular epicardium but not endocardium underlies the ST segment elevation seen in the Brugada syndrome and that electrical heterogeneity within right ventricular epicardium leads to the development of closely coupled premature ventricular contractions via a phase 2 reentrant mechanism that then precipitates ventricular tachycardia/ventricular fibrillation (VT/VF). Currently, implantable cardiac defibrillator implantation is the only proven effective therapy in preventing sudden death in patients with the Brugada syndrome and is indicated in symptomatic patients and should be considered in asymptomatic patients in whom VT/VF is inducible at time of electrophysiologic study.

Genetic basis and molecular mechanism for idiopathic ventricular fibrillation

Ventricular fibrillation causes more than 300,000 sudden deaths each year in the USA alone. In approximately 5-12% of these cases, there are no demonstrable cardiac or non-cardiac causes to account for the episode, which is therefore classified as idiopathic ventricular fibrillation (IVF). A distinct group of IVF patients has been found to present with a characteristic electrocardiographic pattern. Because of the small size of most pedigrees and the high incidence of sudden death, however, molecular genetic studies of IVF have not yet been done. Because IVF causes cardiac rhythm disturbance, we investigated whether malfunction of ion channels could cause the disorder by studying mutations in the cardiac sodium channel gene SCN5A. We have now identified a missense mutation, a splice-donor mutation, and a frameshift mutation in the coding region of SCN5A in three IVF families. We show that sodium channels with the missense mutation recover from inactivation more rapidly than normal and that the frameshift mutation causes the sodium channel to be non-functional. Our results indicate that mutations in cardiac ion-channel genes contribute to the risk of developing IVF.

Discrepant drug action of disopyramide on ECG abnormalities and induction of ventricular arrhythmias in a patient with Brugada syndrome

An electrophysiologic study was attempted in a patient who experienced cardiac arrest. Programmed electrical stimulation from the right ventricle, without the use of any drugs, induced ventricular fibrillation (VF) twice. Disopyramide prevented the induction of ventricular arrhythmia by rendering VF to a nonsustained polymorphic ventricular tachycardia when administered at 300 mg/day, and noninducible at 400 mg/day. However, ST-segment elevation and the rSr' pattern in leads V(1-3) characteristic of Brugada syndrome became exaggerated by disopyramide. Disopyramide exerted discrepant action on the electrocardiographic (ECG) abnormalities and induction of VF in this patient, suggesting the efficacy of antiarrhythmic drugs assessed by an electrophysiologic study may be unrelated to ECG abnormalities in cases of Brugada syndrome.

Sustained monomorphic ventricular tachycardia in a patient with Brugada syndrome

We report a patient with Brugada syndrome who developed sustained monomorphic ventricular tachycardia (SMVT). The patient was a 29-year-old man who experienced recurrent episodes of palpitation and syncope after drinking alcohol. Electrocardiogram showed right bundle branch block and ST-segment elevation in precordial leads V1-3 without Q-Tc prolongation. Organic heart disease and coronary artery disease were excluded by noninvasive and invasive tests. Ventricular fibrillation was induced by the application of a single extra-stimulus to the right ventricular outflow tract. During isoproterenol infusion, SMVT of left bundle branch block morphology (240/min) was induced by the application of a single extrastimulus to the right ventricular apex. SMVT also developed spontaneously. Pace mapping disclosed that SMVT originated at the free wall of the right ventricular outflow tract. Head-up tilt test and an alcohol provocation test both induced similar SMVT that was associated with hypotension and near syncope. SMVT was not terminated by intravenous administration of lidocaine, procainamide or adenosine triphosphate (10 mg), but was terminated by propranolol. Thus, a beta-adrenoceptor-mediated mechanism appears to play an important role in SMVT in this patient. The site of origin of SMVT might be closely related to the lesion that causes ST-segment elevation.

Autonomic and antiarrhythmic drug modulation of ST segment elevation in patients with Brugada syndrome

OBJECTIVES

We examined the modulatory effects of autonomic nervous system and antiarrhythmic drugs on the ST segment in patients with Brugada syndrome to gain an insight into the mechanism of ST segment elevation.

BACKGROUND

Right bundle branch block, ST segment elevation and ventricular tachyarrhythmias define a distinct clinical and electrocardiographic (ECG) syndrome (Brugada syndrome). However, the mechanism of ST segment elevation and the causes of this syndrome are unknown.

METHODS

The study included four patients in whom structural heart or coronary artery disease was excluded by noninvasive and invasive tests. High take-off ST segment elevation of either the coved or saddle-back type in precordial leads V1, V2 and V3 was seen in all patients. Three patients experienced recurrent episodes of syncope or aborted sudden cardiac death, and the remaining patient had palpitation. Autonomic receptor stimulation and blockade and intravenous administration of antiarrhythmic drugs were performed during sinus rhythm while the 12-lead ECG was recorded. Metaiodobenzylguanidine (MIBG) scanning and Holter monitoring were also performed.

RESULTS

Beta-adrenoceptor stimulation by intravenous isoproterenol consistently reduced (> or = 0.1 mV) ST segment elevation at or 80 ms after the J point in all four patients. Selective alpha-adrenoceptor stimulation by intravenous norepinephrine in the presence of propranolol or by intravenous methoxamine consistently augmented, whereas alpha-adrenoceptor blockade reduced, ST segment elevation in three patients. Intracoronary acetylcholine or intravenous edrophonium or neostigmine augmented ST segment elevation without inducing coronary spasm in three of four patients. Class IA antiarrhythmic drugs also consistently augmented (three patients), whereas class IB drugs had no effect on (two patients) ST segment elevation. No abnormality was found on MIBG imaging or heart rate variability in three patients, suggesting that autonomic dysfunction is not a primary disease process. Class IA drugs had no effect on ST segment in three control patients, suggesting that the ST segment elevation seen in patients with Brugada syndrome in response to the drugs is not a nonspecific response.

CONCLUSIONS

ST segment elevation in patients with Brugada syndrome was augmented by selective stimulation of alpha-adrenoceptors or muscarinic receptors or by class IA drugs but was mitigated by beta-adrenoceptor stimulation or alpha-adrenoceptor blockade. These responses might be explained by postulating the presence of an area of early repolarization or a local "depolarized" area in the ventricle causing ST segment elevation in this syndrome. Because only a small number of patients were studied, these possibilities need further evaluation.