Changes in heart rate by verapamil during carotid sinus stimulation in patients with hyperparathyroidism, pre- and postoperatively

It has been investigated whether calcium- and verapamil-dependent sensitivities of carotis baroreceptors also exist in man. To answer this question, we pre- and postoperatively measured changes in heart rate during carotid sinus stimulation before and after intravenous administration of 5 mg verapamil in 23 patients with primary hyperparathyroidism. Findings during hypercalcemia were as expected: a more pronounced reduction of heart rate at comparatively low calcium levels. During normocalcemia, we found an opposite effect: a more pronounced reduction at relatively high calcium levels, which was statistically significant. This fact could be explained according to our interpretation. In previous reports, local effects on baroreceptors were examined, whereas we measured the combined effect of several calcium actions. As expected, verapamil attenuated the decrease in heart rate which, however, was not statistically significant.