Assessment of a newly recognized association. Carotid sinus hypersensitivity and denervation of sternocleidomastoid muscles.

BACKGROUND

Carotid sinus syndrome has been reported recently to be associated with chronic denervation of the sternocleidomastoid muscles. To further understand the relationship between carotid mechanoreceptors and sternocleidomastoid denervation, the present study investigated the relation between the results of carotid sinus massage and electromyographic activity of the sternocleidomastoid muscles in patients without syncope.

METHODS AND RESULTS

Patients were selected prospectively if they fulfilled strict exclusion criteria, particularly the absence of a history of syncope, pacemaker implantation, or drugs known to modify the behavior of the autonomic nervous system. A right and left carotid 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 blood pressure) were classified as normal, doubtful, or hypersensitive carotid sinus. Sternocleidomastoid electromyography activity was recorded from the right and left sides, and the results were classified as normal, moderate denervation, and severe denervation. Carotid sinus massage was normal in 13 patients (43%), doubtful in 9 (30%), and abnormal in 8 (27%). Electromyographic activity of the sternocleidomastoids was normal in 13 patients (43%) and revealed moderate denervation in 7 (24%) and severe chronic denervation in 10 (33%). The results of carotid sinus massage and sternocleidomastoid electromyography were highly concordant in each patient (kappa = .592, P < .00001) and in each side (right, kappa = .381, P < .03; left, kappa = .390, P < .01).

CONCLUSIONS

Carotid sinus hypersensitivity and chronic denervation is a common finding in individuals older than 50 years of age. These two entities are significantly related, suggesting a pathophysiological relation of one to the other.