Effects of propranolol and of verapamil on heart rate and blood pressure in hyperthyroidism.

ABSTRACT

Cardiac manifestations of hyperthyroidism have been attributed to enhanced sympathoadrenal activity, but thyroid hormones also have a direct positive chronotropic effect on sinoatrial cells, in which there are slow calcium channels. We evaluated the effects of verapamil on heart rate, PR and QT intervals, and blood pressure in eight patients with hyperthyroidism and compared them to those effects of propranolol. Three doses of propranolol (0.05, 0.1, and 0.2 mg/kg) and verapamil (0.1, 0.2, and 0.4 mg/kg) were injected intravenously after a 72-hr withdrawal period in a double-blind, crossover fashion. Propranolol increased the RR interval from 581 +/- 51 to 734 +/- 65 msec, whereas verapamil did not have any negative chronotropic effect despite prolonging the PR interval. Systolic blood pressure decreased from 134 +/- 5 to 119 +/- 8 mm Hg after verapamil and was not affected by propranolol. Diastolic blood pressure was depressed equally by both drugs. We conclude that verapamil is not a good alternative drug to propranolol in hyperthyroidism. Our data cannot confirm the possibility of an interaction between thyroid hormones and slow calcium channels in patients with hyperthyroidism.