Baroreflex sensitivity measured by the phenylephrine pressor test in patients with carotid sinus and sick sinus syndromes.

Baroreflex sensitivity was measured by the heart rate response to the transient rise in blood pressure induced by phenylephrine, in 11 patients with carotid sinus syndrome, 6 patients with sick sinus syndrome and nine age and blood pressure matched controls. Patients with carotid sinus syndrome were divided into those with a hypersensitive carotid sinus reflex manifest as sinus arrest (n = 9) and those with a reflex manifest as atrioventricular block (n = 2). The mean gain of the baroreflex sensitivity was significantly increased (p less than 0.001) in patients with carotid syndrome manifest as sinus arrest (12.7 +/- 5.1 ms . mmg-1) compared to that in patients with sick sinus syndrome (3.8 +/- 2.6 ms . mmHg-1) and controls (4.2 +/- 2.1 ms . mmHg-1). Patients with carotid sinus syndrome manifest as atrioventricular block did not have increased baroreflex sensitivity measured by their sinus node response (2.1 +/- 0.5 ms . mmHg-1). There was significant correlation (p less than 0.001) between the corrected carotid sinus inhibitory response to carotid sinus massage and the measurement of baroreflex sensitivity in the carotid sinus syndrome patients. Patients with carotid sinus syndrome manifest as reflex sinus arrest have an increased gain in baroreflex sensitivity for their age, which is not seen in patients with symptomatic sinoatrial disease. This study provides further evidence of a different mechanism of bradycardiac symptoms in patients with carotid sinus and sick sinus syndromes.