Brugada syndrome: insights of ST elevation, arrhythmogenicity, and risk stratification from experimental observations.

Brugada syndrome (BrS), caused by ion channel abnormalities, is characterized by ST segment elevation and negative T waves in the right precordial electrocardiographic (ECG) leads recorded over the right ventricular outflow tract (RVOT). BrS is sensitive to body temperature and can lead to T-wave alternans (TWA), ventricular tachycardia, and sudden death. Recent studies in an isolated canine RVOT model of BrS demonstrated that reversal of the transmural gradient of repolarization caused the ECG characteristics and that major intraepicardial and transmural dispersion of action potentials (APs) initiated phase 2 reentry, premature ventricular activations, and tachyarrhythmias. Hypothermia enhanced the heterogeneity of the AP and promoted the origination of phase 2 reentry in the epicardium of the RVOT, but the prolonged AP duration frequently blocked reentry. Hyperthermia abbreviated the AP and facilitated the maintenance of reentry and tachyarrhythmias. Bradycardia promoted alternans in the phase 2 dome of the AP within the epicardium of the RVOT, resulting in TWA. The above phenomena were localized in the epicardium of the RVOT. Blockade of the transient outward current, I(to), reduced AP heterogeneity and prevented arrhythmias in the BrS model. In addition, epicardial activation delay led to fragmented QRS, a risk marker of prognosis in BrS. Body surface mapping in patients with BrS supported these experimental findings. In conclusion, the AP heterogeneity within the epicardium of the RVOT contributes to the ECG characteristics, temperature sensitivity, TWA, and arrhythmias in BrS, and body surface mapping and fragmented QRS can be effective predictors of risk in patients with BrS.