Facilitating influence of procainamide on conversion of atrial flutter by rapid atrial pacing

In a prospective, double-blind, randomized, placebocontrolled study we investigated the facilitating influence of intravenous procainamide on conversion of atrial flutter by rapid atrial pacing. Fifty consecutive patients with spontaneous sustained atrial flutter were 1:1 randomized into two homogenous groups: group A received 10 mg.kg-1 procainamide intravenously, group B placebo. After infusion there was a significant (P < 0.01) lengthening of the flutter cycle with respect to baseline in group A, exceeding the flutter cycle length of the control group (P < 0.05). The overall success rate of rapid atrial pacing in restoring sinus rhythm was significantly higher after pre-treatment with procainamide compared to placebo (100% vs 76%; P < 0.05): 20 patients of group A reverted immediately after pacing to sinus rhythm, the remaining five after a brief episode of atrial fibrillation. In the placebo group, 16 patients showed a prompt conversion to sinus rhythm and three after transient atrial fibrillation. In the remaining six patients, due to sustained pacing-induced atrial fibrillation, direct current cardioversion was necessary. After administration of procainamide a less aggressive stimulation protocol with significantly (P < 0.01) longer paced cycles to interrupt atrial flutter was achievable. In conclusion, intravenous procainamide augments the efficacy of atrial pacing to convert atrial flutter to sinus rhythm.