Background

Brugada syndrome is a disorder characterized by coved shaped saddle or ST-segment elevation in lead V1 to V3 on the ECG. It is associated with complete or incomplete right bundle branch block and reverse the wave T. In its initial description, the heart has been reported to be structurally normal, but it has recently been challenged (Frustaci, 2005). In addition, subtle structural abnormalities in the outflow tract of the right ventricle can also be observed. The ECG abnormalities may not be evident until he was unmasked by infusion of flecainide or procainamide, and is complemented by a beta-blocker.

Patients with Brugada syndrome are prone to develop ventricular tachyarrhythmia, which can lead to fainting, cardiac arrest, or sudden cardiac death (Martini, 1989; Brugada, 1992; Brugada, 2001). Brugada syndrome is genetically determined and has an autosomal dominant mode of transmission in about 50% of familial cases. About 5% of survivors of cardiac arrest have no clinically identified cardiac anomaly, almost half of these cases are thought to be due to Brugada syndrome (Alings, 1999).

Pathophysiology: cardiac dysfunction in ion channels underlying clinical manifestations of Brugada syndrome (cardiac channelopathy). In 10-30% of patients and families, mutations in the SCN5A gene, encoding cardiac voltage-gated sodium channel Nav1.5 have been reported. Another place was also reported on chromosome 3. Most SCN5A mutations lead to loss of function of the channel Nav1.5 reducing the sodium current (INa) available during phases 0 (climb) and 1 (early repolarization) of the cardiac action potential. Gain-of-function SCN5A mutations can also cause long QT syndrome type 3.

Trouble assumption of repolarization Changes in the ECG, Brugada syndrome, have been proposed to be due to an imbalance between depolarization and repolarization currents during phase 1 of the action potential, especially in cells expressing a large transient outward Ito current, such as epicardial cells right ventricular free wall. In patients with loss of function SCN5A mutations that result in fewer INa in phase 1, the mainstream may Ito prematurely repolarize the membrane and produce a loss of the dome (phase 2), the action potential ( see Image 1).

When these premature shortening of the action potential heterogeneity in the myocardium occurs, it can generate Phase 2 reentries that can cause ventricular tachycardia and ventricular fibrillation. The great tension transmural gradients generated by the short duration of action potentials in the right ventricular outflow epicardium are thought to be the basis of ECG patterns Brugada syndrome. These changes specific to cardiac electrical activity, which affect mainly the right ventricle, manifested in ST-segment elevation in precordial leads V1 through V3, with a QRS morphology similar to that of a good bundle branch block (RBBB). Such a model may also be due to an altitude aJ. This scheme is called coved type when ST elevation is the main feature, and it is called saddleback type occurs when J altitude without ST elevation (see image 2).

Dépolarisation disorder model Another hypothesis for alterations of the ECG is based on conduction delay in the path of right ventricular ejection compared to the free wall of the right ventricle. The mechanisms underlying the Brugada syndrome ECG pattern are considered by Meregalli (Meregalli, 2005).

The ECG pattern in the Brugada syndrome can be intermittent. The ECG changes may fluctuate with changes in the balance or autonomous body temperature. The anomaly may not be apparent when administering drugs that block the sodium channel (eg, flecainide, procainamide, ajmaline). The ECG abnormalities may disappear with the infusion isoprenaline or exercise, and it may increase with beta-blockers. These effects can be explained by a reduction in the current sodium in the etiology of Brugada syndrome.

Frequency:

* In the United States: because of its recent identification, the incidence of Brugada syndrome is not well established. It can cause sudden 4.10 deaths per 10000 inhabitants per year.

* International: Asia (eg, the Philippines, Thailand, Japan), Brugada syndrome, seems to be the most common cause of natural death in men aged under 50 years. It is known as Lai Tai (Thailand), Bangungut (Philippines), and Pokkuri (Japan). In northern Thailand, the death rate from Lai Tai is about 30 per 100000 population per year (Nademanee, 1997).

Mortality / morbidity:

* Polymorphic Brugada syndrome can lead to ventricular tachycardia, which may degenerate into ventricular fibrillation and cause sudden cardiac death.

* Syncope prolonged and aborted cardiac arrest can cause nightmares, seizures, other neurological deficits, or brain damage.

Race: Brugada syndrome is more common among people whose ancestors come from Asia. The reason for this finding is not yet fully understood, but may be due to an Asian-specific sequence in the region of the promoter SCN5A (Bezzina, 2005).

Sex: Brugada syndrome is 8-10 times more prevalent among males than females, although the probability of having a mutated gene does not differ by gender. The penetrance of the mutation seems to be much higher among men than among women.

Age: Brugada syndrome affects more frequent healthy men aged 30-50 years, but patients aged 0-84 years were reported. The average age of patients who die suddenly is 41 years (Antzelevitch, 2005).

Treatment

Medical Care: At present, implantation of an implantable cardiac defibrillator (ICD) is the only treatment that has been proven effective for Brugada syndrome. No proven pharmacologic approach reduces the occurrence of ventricular tachycardia or ventricular fibrillation, and no approach prevents sudden death in a prospective manner.

Indications for ICD implantation were published in the report of the Second Consensus Conference on Brugada syndrome (Antzelevitch, 2005). For patients at the 2 extremes of risk stratification, the decision to implant or not to implant an ICD is clear. Patients with Brugada syndrome with a history of cardiac arrest must be given an ICD. In contrast, close follow-up is recommended for asymptomatic patients with no family history of sudden cardiac death. For details about risk stratification and indications for implanting an ICD, readers are referred to the consensus report (Antzelevitch, 2005).

Surgical Care: Surgery (other than ICD placement) is not indicated.

Consultations: A board-certified cardiologist who specializes in cardiac arrhythmic disorders (ie, a clinical electrophysiologist) should examine patients with suspected Brugada syndrome. Consultation with a genetic counselor is also indicated for genetic screening and counseling of patients and their relatives.

Diet: No data from controlled studies support the need for a special diet for patients with Brugada syndrome.

Activity: Because regular physical activity may increase the vagal tone, sport may eventually enhance the propensity of athletes with Brugada syndrome to have ventricular fibrillation and sudden cardiac death at rest or during recovery after exercise. Therefore, Pelliccia et al recommend that patients with a definite diagnosis of Brugada syndrome should be restricted from competitive sports (Pelliccia, 2005). Regarding the asymptomatic carriers of SCN5A mutations, at the present time, whether they should also be restricted from participation in sports is uncertain.Medication

Thus far, no drug treatment for Brugada syndrome is recommended.

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