Acute and chronic effects of verapamil in patients with paroxysmal supraventricular tachycardia.

Efficacy of acute intravenous verapamil, 10 mg, and chronic oral verapamil, 320 mg, daily were studied electrophysiologically in 15 patients with paroxysmal supraventricular tachycardia (PSVT). Plasma verapamil concentrations were measured concurrently. Both intravenous and oral verapamil significantly increased the AV node conduction time, the cycle length producing a Wenckebach period, and the refractory period of the AV node. These changes were reflected in changes in plasma verapamil concentration. The echo zone and the supraventricular tachycardia (SVT) zone markedly narrowed after administration of both intravenous and chronic oral verapamil. Verapamil's efficacy was found to be related to the type of SVT. For instance, verapamil was more effective in SVT due to AV nodal re-entry than in SVT due to concealed accessory pathway. Fourteen patients were followed from 3 to 31 months and all except one were well controlled. In conclusion, verapamil was effective in prophylaxis of paroxysmal SVT.