Effects of Procainamide

Electrophysiological effects of 750 mg i.v. procainamide were studied in 14 patients with dual pathway atrioventricular (A-V) nodal re-entrant paroxysmal tachycardia (PSVT). All patients utilized an A-V nodal slow pathway for antegrade and an A-V nodal fast pathway for retrograde conduction during PSVT. In all 14 patients, procainamide depressed retrograde fast pathway conduction, manifest by increase in mean ± SEM ventricular paced cycle length (CL) producing V-A block from 5 295 ± 25 to 385 ± 17 msec (P < 0.001). Antegrade fast and slow pathway properties were unchanged with procainamide. Eleven of the 14 patients had induction of sustained PSVT before procainamide. Eight of these lost ability to induce or sustain PSVT after procainamide, reflecting depression of retrograde fast pathway