Effects of intravenous and chronic oral verapamil administration in patients with supraventricular tachyarrhythmias.

The efficacy of i.v. and oral verapamil was studied in 28 patients with supraventricular tachycardia (SVT). Verapamil (5-10 mg i.v.) terminated SVT in all six patients with atrioventricular nodal (AVN) reentrant tachycardia. In all patients verapamil prolonged antegrade but did not affect retrograde AVN conduction time. Two patients had associated sinus nodal reentrant tachycardia that persisted after the AVN tachycardia terminated. In six patients with SVT using an accessory pathway for retrograde conduction, i.v. verapamil terminated SVT in four and slowed SVT in two patients. Verapamil did not affect the electrophysiologic properties of the accessory pathway and the effect on the SVT, as with AVN reentry, was caused by changes in antegrade AVN function. Verapamil lengthened AVN antegrade conduction time in patients with accessory pathways less than it did in patients with AVN reentry. Verapamil at doses that resulted in AVN Wenckebach block had no effect on the discharge rate of the three patients with automatic atrial tachycardia. In 13 of 14 patients with atrial fibrillation or flutter, i.v. verapamil promptly decreased the ventricular rate. One patient with preexcitation had an increase in ventricular rate after verapamil. The shortest RR intervals before and after verapamil were 260 and 220 msec, respectively, and after verapamil more ventricular beats were preexcited. Oral verapamil was given to 19 of 28 patients. Ten discontinued the drug within 30 days because of side effects or ineffectiveness. Seven patients treated for a mean of 19 months have shown evidence of improvement, judged by decreased frequency and shorter duration of tachycardia when it did recur. Thus, i.v. verapamil is an effective antiarrhythmic drug for most patients with SVT, but oral verapamil is effective in only selected patients.