Effect of disopyramide on initiation of atrial fibrillation and relation to effective refractory period

Electrophysiologic studies were performed before and after intravenous administration of disopyramide (2 mg/kg) to 40 patients with either documented or suspected atrial fibrillation (AF). In control studies, sustained AF (greater than 1 minute), nonsustained AF (1 to 60 seconds) and no AF were found in 14, 18 and 8 patients, respectively. After disopyramide, the ability to initiate AF was totally lost in 18 patients (group A), while 22 patients (group B) showed sustained AF (11 patients) or nonsustained AF (11 patients). The effective refractory period of the atrium was 232 +/- 41 ms in the control study and 266 +/- 49 ms after disopyramide. Atrial functional refractory periods before and after disopyramide were 282 +/- 43 and 317 +/- 48 ms, respectively. The differences and ratios of the refractory periods after and before disopyramide were higher in group A than in group B (p less than 0.001). The prolongation of atrial refractoriness after disopyramide was important to suppress the initiation of AF in group A. In some group B patients, on the other hand, the initiation of AF was promoted after disopyramide. Disopyramide may alter the atrial electrophysiologic substrate required for AF initiation.