Brugada syndrome type 1 coved ST elevation

A 34-year-old man of Southeast Asian descent presents to the emergency department following a syncopal episode during sleep. His father died suddenly at age 40 in his sleep. On examination, he is hemodynamically stable with a normal cardiovascular exam. Electrolytes, troponin, and TSH are normal. His ECG is shown in the diagram. The pattern marked **B** (coved-type ST elevation ≥2 mm in V1-V2 with negative T wave) is characteristic of Brugada syndrome type 1. Which of the following best explains the underlying electrophysiological mechanism responsible for arrhythmia generation in this patient?