ASSESSMENT OF A NEWLY RECOGNIZED ASSOCIATION - CAROTID-SINUS HYPERSENSITIVITY AND DENERVATION OF STERNOCLEIDOMASTOID MUSCLES

Background Carotid'sinus syndrome has been reported recently to be ass ociated with chronic denervation of the sternocleidomastoid muscles. T o further understand the relationship between carotid mechanoreceptors and sternocleidomastoid denervation, the present study investigated t he relation between the results of carotid sinus massage and electromy ographic activity of the sternocleidomastoid muscles in patients witho ut syncope. Methods and Results Patients were selected prospectively i f they fulfilled strict exclusion criteria, particularly the absence o f a history of syncope, pacemaker implantation, or drugs known to modi fy the behavior of the autonomic nervous system. A right and left caro tid massage was performed for 10 seconds in 30 patients (22 men; mean age, 67.3+/-6.5 years). The results (monitoring for heart rate and blo od pressure) were classified as normal, doubtful, or hypersensitive ca rotid sinus. Sternocleidomastoid electromyography activity was recorde d from the right and left sides, and the results were classified as no rmal, moderate denervation, and severe denervation. Carotid sinus mass age was normal in 13 patients (43%), doubtful in 9 (30%), and abnormal in 8 (27%). Electromyographic activity of the sternocleidomastoids wa s normal in 13 patients (43%) and revealed moderate denervation in 7 ( 24%) and severe chronic denervation in 10 (33%). The results of caroti d sinus massage and sternocleidomastoid electromyography were highly c oncordant in each patient (kappa=.592, P<.00001) and in each side (rig ht, kappa=.381, P<.03; left,kappa=.390, P<.01). Conclusions Carotid si nus hypersensitivity and chronic denervation is a common finding in in dividuals older than 50 years of age. These two entities are significa ntly related, suggesting a pathophysiological relation of one to the o ther.