Adverse effects of sympatholytic agents in patients with hypertension and sinus node dysfunction

Abstract

Over a period of 15 months, symptomatic sinus bradycardia developed in eight hypertensive patients treated with various sympatholytic agents: α-methyldopa (0.5 to 1.5 g/day) in three patients; propranolol (80 to 120 mg/day) in two; clonidine (0.4 mg/day) in two; and guanethidine (25 mg/day) in one. On admission, in addition to sinus bradycardia (38 ± 5 beats/min) (mean ± standard deviation), neurologic symptoms or hypotension, or both, were present in all. After cessation of drug therapy, heart rate increased to a mean rate of 60 ± 7 beats/min and symptoms disappeared. During a mean follow-up time of 15 ± 3 months, six patients were managed successfully by appropriate manipulation of their medical regimen, and two required permanent ventricular pacing. Electrophysiologic studies were performed in four patients, three of whom were challenged with intravenously administered propranolol (0.1 mg/kg body weight). Abnormal responses to rapid atrial pacing occurred in all four patients. Increases in mean spontaneous cycle length of 28, 33 and 2.5 per cent and maximal sinus node recovery time of 412, 48 and 44 per cent occurred after propranolol administration. Severe bradyarrhythmias may be precipitated by sympatholytic agents, particularly in patients suspected of having sinus node disease. These bradyarrhythmias can usually be managed successfully by modification of their pharmacologic regimen.