Effects of procainamide and quinidine sulfate in the Wolff-Parkinson-White syndrome.

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Abstract
Patients (33) with Wolff-Parkinson-White syndrome were studied electrophysiologically before and after administration of i.v. procainamide and oral quinidine sulfate. Procainamide prolonged the shortest R-R (SRR) interval between 2 consecutive pre-excited beats during atrial fibrillation 20-70 ms in 15 of 21 patients with no change observed in 6 of 21 patients. Quinidine sulfate prolonged the SRR 20-170 ms in all 16. In 14 of 18 patients where procainamide and quinidine were comparable, quinidine prolonged the SRR 30-100 ms more than procainamide. Procainamide and quinidine both tended to prolong the effective refractory period of atrial, ventricular and accessory pathway tissue and slowed antegrade and retrograde conduction in the accessory pathway. Exceptions were noted. The assessment of pharmacological effects was frequently limited using determinations of refractory periods alone. Because of the variability observed in drug response, patients with Wolff-Parkinson-White syndrome and a history of atrial fibrillation with a rapid ventricular response should have atrial fibrillation electively induced while on therapy with procainamide or quinidine.