Responses to carotid sinus stimulation before and after propranolol.

The response to carotid sinus stimulation was studied in nine elderly men (mean age 67) with no history of cardiac disease, dizziness, or syncope. The response to manual carotid sinus pressure (during one of two studies) was positive (an RR interval of greater than 3s) in three men. But seven men showed positive responses after intravenous propranolol (0.1 mg/kg). Similarly, the RR interval was lengthened by greater than 10 ms/mm Hg in two men during neck suction. Neck suction produced a positive result in four men after intravenous propranolol. The detection of hypersensitivity of the carotid sinus in a high proportion of apparently healthy men, especially during beta blockade, suggests that an abnormal response to carotid sinus massage may not be a reliable indicator for pacemaker treatment.