To assess antiarrhythmic efficacy of oral
nadolol, 15 patients with recurrent
supraventricular tachycardia were studied. Eight patients had atrioventricular (
AV) nodal reentrant tachycardia and seven had AV
reciprocating tachycardia involving an accessory AV pathway. Electrophysiologic studies were performed before and after
intravenous infusion of
propranolol (0.20 mg/kg), and were repeated 5 to 8 days after oral
nadolol therapy at a daily dose of 80 to 160 mg. Both intravenous
propranolol and oral
nadolol induced significant prolongation of the sinus cycle length from 741 +/- 73 ms to 834 +/- 97 and 1,029 +/- 95 ms, respectively (p less than 0.001 and p less than 0.0001, respectively). Both intravenous
propranolol and oral
nadolol depressed AV nodal but not accessory AV pathway conduction, and shifted the dual AV nodal pathway conduction curves (A1A2, A2H2; A1A2, H1H2) upward and to the right by prolonging the conduction time and increasing the refractory period. Ten patients (seven with AV nodal reentry and three with AV reciprocation) who responded to intravenous
propranolol also responded to oral
nadolol with loss of the inducibility of sustained
tachycardia; the remaining five patients (one with AV nodal reentry and four with AV reciprocation) who did not respond to intravenous
propranolol also failed to respond to oral
nadolol with persistence of the inducibility of sustained
tachycardia. Thus, in conclusion, intravenous
propranolol testing predicts the therapeutic efficacy of oral
nadolol therapy and oral
nadolol in once-daily doses may be used for long-term prophylaxis of recurrent
supraventricular tachycardia.