What is the usual underlying culprit rhythm in patients with Brugada syndrome experiencing transient syncopal episodes?

Culprit Rhythm in Brugada Syndrome Syncope

The usual underlying culprit rhythm in patients with Brugada syndrome experiencing transient syncopal episodes is polymorphic ventricular tachycardia (VT) or ventricular fibrillation (VF), with VF being the most common life-threatening arrhythmia. 1, 2

Primary Arrhythmic Mechanisms

Ventricular fibrillation is the hallmark arrhythmia responsible for sudden cardiac death in Brugada syndrome, occurring predominantly during rest or sleep. 1 The mechanism involves:

• Rapid polymorphic VT degenerating into VF as the primary cause of syncope and sudden cardiac death 1, 2
• Electrical heterogeneity within right ventricular epicardium creating the substrate for phase 2 reentry that precipitates VT/VF 3
• Loss of action potential dome in right ventricular epicardium (but not endocardium) underlying both the ST elevation and arrhythmia susceptibility 3

Clinical Context and Triggers

The arrhythmic events in Brugada syndrome have distinct characteristics:

• Events occur most frequently at rest or during sleep when vagal tone is increased 1
• Fever is a critical acute trigger that can precipitate VF and must be treated aggressively with antipyretics 1, 4, 5
• Patients typically do not have ventricular extrasystoles or nonsustained VT runs on Holter monitoring, distinguishing this from other cardiomyopathies 1

Monomorphic VT: A Rare Exception

While polymorphic VT/VF dominates, recent data reveals that monomorphic VT can occur in a small subset of Brugada patients with distinct characteristics:

• Monomorphic VT patients are older at first event (47.7 vs 40.7 years) and have later recurrences after ICD implantation 6
• Rapid heart rates >100 bpm precede MVT more frequently (48.1% vs 8.5% for VF), with lower incidence of ectopy 6
• Broader abnormal epicardial substrate is associated with MVT presentation (11.3 vs 6.8 cm²) 6

Diagnostic Considerations During Electrophysiology Study

The European Heart Journal guidelines note important limitations:

• Induction of polymorphic VT or VF during programmed ventricular stimulation may be considered diagnostic in Brugada patients with syncope 1
• However, the prognostic value of EPS remains controversial, with low positive predictive value (23%) but high negative predictive value (93%) over 3-year follow-up 1
• In a meta-analysis of 1036 Brugada patients, 54% had inducible VT/VF, but no difference in outcome was observed at 34 months regardless of inducibility 1

Risk Stratification Based on Rhythm

The annual arrhythmic event rates clearly demonstrate the prognostic significance:

• 13.5% per year in cardiac arrest survivors 1, 5
• 3.2% per year in patients with syncope 1, 5
• 1% per year in asymptomatic patients 1, 5

Patients with syncope and spontaneous type 1 ECG pattern have a 6-fold higher risk of cardiac arrest compared to those without syncope, making the presumption of ventricular arrhythmia as the culprit mechanism clinically appropriate. 1, 2

Clinical Pitfalls to Avoid

• Do not assume syncope is vasovagal or benign in diagnosed or suspected Brugada syndrome—it should be presumed arrhythmic until proven otherwise 4
• The ECG pattern can be intermittent, so a single normal ECG does not exclude the diagnosis or ongoing arrhythmic risk 1, 2
• Electrophysiology study cannot reliably exclude future arrhythmic events, as negative EPS does not identify a truly low-risk group 1