Antiarrhythmic efficacy of N-acetylprocainamide in patients with premature ventricular contractions.

Oral administration of a 1.5-gm dose of N-acetylprocainamide (NAPA) to 9 patients with premature ventricular contractions (PVCs) confirmed previous indirect evidence that this metabolite of procainamide has antiarrhythmic efficacy and potency comparable to those of procainamide. Although the mechanism by which NAPA acts as an antiarrhythmic drug is not known, it was found that the 6 patients with coupled PVCs responded to NAPA therapy and that the 3 patients without coupled PVCs failed to respond. Coupling interval prolongation also occurred during NAPA therapy in 4 of the 6 responding patients. These observations suggest that NAPA may terminate coupled PVCs by slowing and then interrupting conduction of re-entrant impulses, as has been proposed for procainamide. NAPA plasma concentrations of 7.4-17.2 mug/ml were well tolerated by the patients and produced an average fall of 3 mm Hg in mean arterial pressure and a 7.6% mean increase in corrected QT interval.