The electrocardiographic and electrophysiologic effects, clinical efficacy and safety of intravenous and oral
nadolol therapy were examined in 34 patients with recurrent supraventricular
tachyarrhythmias (SVT) undergoing electrophysiologic evaluation. Programmed electrical stimulation was performed in the control (drug-free) state, after infusion of intravenous
nadolol (mean dose 0.09 +/- 0.03 mg/kg) and after chronic oral
nadolol therapy in patients who responded to intravenous
nadolol (mean dose 83 +/- 12 mg for 5 days). Intravenous
nadolol administration prolonged mean sinus cycle length (p = 0.009), mean PR interval (p = 0.001) and mean AH interval (p = 0.001), with no significant electrophysiologic effects in the atrium, ventricle or accessory bypass tracts. Oral
nadolol had similar electrocardiographic and electrophysiologic effects, but of lesser magnitude. Intravenous
nadolol resulted in complete suppression of induced SVT in 78% of patients with sinus and
atrioventricular nodal reentrant tachycardia and 11% of patients with atrioventricular (AV) reentrant
tachycardia (p less than 0.001). Partial responses were frequent in intraatrial or AV reentrant
tachycardia (37%). Oral
nadolol suppressed induction of SVT in patients who responded to intravenous
nadolol. Adverse reactions to intravenous and oral
nadolol were infrequent--6% and 8%, respectively--and usually did not require
drug withdrawal. Intravenous
nadolol is highly effective in sinus and
AV nodal reentrant tachycardia, and a successful electrophysiologic response to it predicts efficacy of long-term oral
nadolol therapy. It has limited efficacy alone in AV reentrant
tachycardia and should be considered in combination with other antiarrhythmic
therapy in this type of SVT.