Electrophysiologic effects of propranolol on sinus node function in patients with sinus node dysfunction

Abstract

The electrophysiologic effects of intravenously administered propranolol (0.1 mg(kg) on 3 parameters of sinus node function were examined in 10 symptomatic patients with sinus node dysfunction. The patients ranged in age from 26 to 79 yr. Symptoms ranged from fatigue to frank syncope. Sinoatrial (SA) block and sinus pauses were observed in 1 patient; sinus pauses alone were observed in 3 patients. Five (5/10) patients had intra atrial block; 3 (3/10) patients had atrioventricular block; 4 (4/10) patients had an intraventricular condition disturbance. At the time of electrophysiologic study, 2 patients had a control spontaneous sinus cycle length that exceeded 1000 msec. Following propranolol, the mean spontaneous cycle length increased by 17.4% (924 to 1085 msec, P < 0.005) and spontaneous second degree SA block reappeared in the one patient. The maximum escape cycle ranged from 116% to 229% of the prepacing spontaneous cycle length and was considered to be prolonged in 2 of 10 patients. Propranolol had no significant effect on the maximum escape cycle/prepacing cycle length x 100 (%). The estimated sinoatrial conduction time (SACT) was determined in 7 patients and ranged in value from 120 to 238 msec. Propranolol increased the mean value of the estimated SACT from 179 to 213 msec, P < 0.025. Propranolol may cause marked bradyarrhythmias in some patients with sinus node dysfunction, and should be used with caution in these patients.