Local conduction block of the atria by premature stimulus in a patient with Brugada syndrome

A 46-year-old man with type II Brugada electrocardiogram pattern changed to a type I Brugada type electrocardiogram pattern by class I antiarrhythmic drug (pilsicainide) underwent electrophysiologic study. Ventricular fibrillation was induced by double extrastimuli from the right ventricular (RV) apex. Monophasic action potentials (MAPs) were then recorded from the high right atrium. Duration of MAP at a coupling interval of 220 milliseconds was 122 milliseconds, and local activation of S2 spread to the left atrium. However, MAP at a coupling interval of 210 milliseconds was 112 milliseconds, and local activation of S2 failed to spread to the rest of atrium.