New insights into the pathophysiology of carotid sinus syndrome

The pathophysiology of carotid sinus syndrome remains poorly understood. Currently, two main hypotheses are provided: a lesion at the level of carotid sinus receptors or a central defect at the level of the nuclei of the autonomic nervous system. The objective of our study was to present arguments in favor of one of these two hypotheses.

Test selection was guided by the following hypothesis: a degenerative central or local lesion could be associated with dysfunctions in the structures surrounding or comprising the baroreflex centers or their pathways. To test this hypothesis, brain stem auditory-evoked potentials; somatosensory-evoked potentials; blink reflexes; sympathetic skin responses; and styloglossus, sternocleidomastoid, and superior trapezius muscle electromyography were systematically performed from the right and left sides in 17 patients with carotid sinus syndrome and in 17 sex- and age-matched control subjects. Similar responses were found in the two groups for the "central" tests. Contrasting with this result, the electromyographic analysis of the sternocleidomastoid muscle differed significantly between the groups: 13 (76%) had pathological responses in the carotid sinus syndrome group compared with only 4 (23.5%) in the control group (P < .01). Furthermore, the abnormality was found on the right and left sides in 9 patients (53%) in the study group and in none of the control group (P < .005).

This study strongly suggests that the neuromuscular structures surrounding the carotid mechanoreceptors are involved in the carotid sinus syndrome; however, the exact mechanism remains speculative.