Conversion of atrial fibrillation to sinus rhythm by acute intravenous procainamide infusion.

We evaluated the efficacy of an intravenous infusion of procainamide in 26 consecutive candidates for cardioversion of atrial fibrillation. Procainamide was administered at a rate of 15 to 20 mg/min up to a maximum of 1000 mg. The treatment was considered effective only if cardioversion occurred during the procainamide infusion. Conversion to sinus rhythm occurred in 15 patients. Converters had a significantly shorter mean duration of atrial fibrillation (6 +/- 7 days, mean +/- S.D.) compared to nonconverters (79 +/- 88 days) (p less than 0.01). The mean left atrial size of converters (4.3 +/- 0.6 cm) did not differ significantly from that of nonconverters (4.7 +/- 0.9 cm). The dose of procainamide required for cardioversion ranged from 3.6 to 16.4 mg/kg. Two patients developed nonsustained ventricular tachycardia, and there was one episode of bifascicular block during the infusion. Intravenous procainamide is an effective form of therapy for conversion of atrial fibrillation of new onset.