Intermittent alternance of Brugada ECG patterns: Insights from a unique electrophysiological phenomenon
A 38‐year‐old patient affected by Brugada syndrome (BrS), with previous ventricular fibrillation episodes, was admitted for epicardial ablation of the right ventricle outflow tract (RVOT) arrhythmogenic substrate (AS). Baseline 12‐lead electrocardiogram (ECG) with standard and high right precordial leads showed a spontaneous type 1 Brugada pattern (Fig. 1). During general anesthesia, before epicardial mapping, continuous ECG monitoring revealed a BrS ECG variability, determining a repetitive shifting among the patterns (Fig. 2). This alternance continued with an apparently unpredictable behavior in the following beats. BrS belongs to the family of J wave syndromes and the ECG manifestations, which have been reported to be dynamic and transient, are supposed to be due to a transmural voltage gradient caused by the existence of an action potential notch in epicardium but not endocardium, secondary to a transmural distribution of transient outward current (Ito) in the presence of a defective function of the sodium channel (INa). Although three ECG patterns have been described, only the coved type 1 has to be considered for definitive diagnosis. Two main hypotheses have been postulated to explain the mechanisms underlying BrS electrocardiographic and arrhythmic consequences. According to the depolarization hypothesis, slow conduction in the RVOT plays a primary role, while the repolarization hypothesis suggests that an outward shift in the balance of currents in RVOT epicardium leads to transmural or transregional repolarization dispersion, resulting in the development of phase 2 reentry. The most compelling evidence supporting the depolarization hypothesis derives from the proof that epicardial ablation prevents ventricular arrhythmias and normalizes the ECG. Nevertheless, the ECG manifestations may show different behavior in reaction to a change in heart rate. In fact, J waves are usually accentuated with bradycardia or long pauses, although the opposite has also been described. The typical response of patients with BrS to rate acceleration is the reduction of ST‐segment elevation, consistent with the reduced availability of Ito at the faster rate due to slow recovery of the current from inactivation. Therefore, these theories are not mutually exclusive and may be synergistic. In fact, the degree of J wave amplitude/ST elevation has been shown to correlate with AS dimension, since type 1 pattern bares a wider substrate than type 2 or even type 3. This is a rare documentation of an intermittent shifting of the Brugada pattern in the same rhythm strip. Anesthesia and further unknown mechanisms may be involved.