If you guessed Type 1 Brugada syndrome, then you are correct!
Pathophysiology
Brugada syndrome is a disease resulting from a mutation in the SCN5A gene, which encodes a myocardial voltage-gated sodium channel. It is inherited via an autosomal dominant pattern with incomplete penetrance. Roughly half of reported cases are familial, with the remainder of cases resulting from sporadic mutations. The SCN5A mutation causing Brugada syndrome is one which results in a loss of function.
Repolarization hypothesis
This sodium channelopathy results in decreased phase 0 and phase 1 of the cardiac action potential, selectively affecting the epicardium against an otherwise normal endocardium. Thus causing an alteration in transmembrane ion current. When the magnitude of this altered ion current is significant enough to cause a reversal of the normal repolarization gradient, it results in a markedly elevated J-point with a coved ST-segment and an inverted T-wave (Type 1 pattern). When the altered ion current does not cross this critical threshold, there is mild J-point elevation and the T-wave remains upright, resulting in saddle-back pattern (Type 2 or 3).
Depolarization hypothesis
This model suggests that the ECG pattern seen in Type 1 Brugada syndrome results from slow depolarization with conduction delays in the right ventricle, specifically the right ventricular outflow tract (RVOT). Several studies have found a high prevalence of late action potentials in Brugada syndrome, which are also independent predictors of ventricular fibrillation/tachycardia inducibility. In addition, the arrhythmogenic area is thought to be confined to a small region of RVOT. Lastly, Holter analysis of multiple spontaneous VF episodes shows that ST-elevation with R’ in V1 (Brugada pattern) correlate with onset of VF.
**In general, the mechanism is not completely understood as there are studies which prove either hypothesis to be correct while none completely disproving the other. The actual mechanism may very well be a combination of both of the above, along with an additional component that has yet to be determined.
Epidemiology
Brugada syndrome is 8-10 times more common in men than women and much more prevalent in East and Southeast Asia. Those typically diagnosed with Brugada are otherwise healthy men aged 30-50 with mean age of sudden death at approximately 41 years of age.
ECG features
Incomplete Right Bundle Branch Block (RBBB) with characteristic ST-segment elevations in precordial leads V1-V3.
Type 1: Pronounced J-point elevation (>2mV in >1 lead in V1-V3), coved ST-segment, inverted T-wave.
Type 2: Saddle-back ST-elevation >2mV with upright or biphasic T-wave.
Type 3: Coved ST-elevation OR saddle-back ST-elevation <1mV with upright T-wave.
Patients with Brugada syndrome are prone to developing ventricular tachydysrhythmias. Many factors have been reported to unmask or exacerbate the ECG findings such as fever, alcohol or cocaine intoxication, electrolyte abnormalities (hyper/hypokalemia, hypercalcemia), sodium-channel blockers, increased vagal tone, alpha-agonists, beta-blockers, and a host of others (see below).
Diagnosis
Diagnosis of Brugada syndrome is made using both characteristic Type 1 ECG findings (either spontaneous or induced with sodium-channel blockade) in a structurally normal heart AND any of the following:
- Symptomatic patients (after non-cardiac causes have been ruled out):
- Cardiac arrest with return of spontaneous circulation (ROSC)
- Documented ventricular fibrillation or polymorphic ventricular tachycardia
- Syncope
- Seizure
- Nocturnal agonal respirations
- Asymptomatic patients:
- Family history of sudden cardiac death
- Coved ECG in family members
- Inducible VF or VT with electrophysiology study
Type 2 and Type 3 Brugada ECGs are nondiagnostic and must be followed up with EP study to assess their inducibility of a Type 1 morphology.
Management
Despite ongoing research since the early 1990s, the only proven method of preventing sudden cardiac death in Brugada Syndrome is with implantable cardioverter defibrillator (ICD) placement.
If Brugada syndrome is confirmed, genetic testing is recommended for both the patient and family members. In addition, there is a long list of drugs that can potentially unmask ECG findings in Brugada syndrome, resulting in life-threatening ventricular tachydysrhythmia. You can peruse brugadadrugs.org to review these drugs as well as pass this info on to patients. If anyone has a family history of sudden death or a Type 2/Type 3 Brugada ECG, it may be a good idea to avoid these drugs whenever possible.
Brought to you by the Rhythm Nation team of Drs. Yonatan Yohannes, Guy Carmelli, Elizabeth Abrams, and Jennifer Martindale.
References
Antzelevitch C, Brugada P, Brugada J, Brugada R. Brugada Syndrome: From Cell to Bedside. Curr Probl in Cardiol. 2005 Jan. 30(1):9-54.
Meregalli PG, Wilde AA, Tan HL. Pathophysiological Mechanisms of Brugada Syndrome: Depolarization Disorder, Repolarization Disorder, or More? Cardiovasc Res. 2005 Aug 15. 67(3):367-78.
Negase S, Kusano KF, Morita H, Nishii N, Banba K, Watanabe A, et al. Longer Repolarization in the Epicardium at the Right Ventricular Outflow Tract Causes Type 1 Electrocardiogram in Patients with Brugada Syndrome. J AM Coll Cardiol. 2008 Mar 25. 51(12):1154-61.
Martindale, Jennifer and Brown, David. “Chapter 6: Abnormal QRS Morphology”. Rapid Interpretation of ECGs in Emergency Medicine. Philadeplphia, PA: Lippincott Williams & Williams, 2012.
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