NEW INSIGHTS INTO THE PATHOPHYSIOLOGY OF CAROTID-SINUS SYNDROME

Background The pathophysiology of carotid sinus syndrome remains poorl y 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 s tudy was to present arguments in favor of one of these two hypotheses. Methods and Results Test selection was guided by the following hypoth esis: a degenerative central or local lesion could be associated with dysfunctions in the structures surrounding or comprising the barorefle x centers or their pathways. To test this hypothesis, brain stem audit ory-evoked potentials; somatosensory-evoked potentials; blink reflexes ; sympathetic skin responses; and styloglossus, sternocleidomastoid, a nd superior trapezius muscle electromyography were systematically perf ormed from the right and left sides in 17 patients with carotid sinus syndrome and in 17 sex- and age matched control subjects. Similar resp onses were found in the two groups for the ''central'' tests. Contrast ing with this result, the electromyographic analysis of the sternoclei domastoid muscle differed significantly between the groups: 13 (76%) h ad pathological responses in the carotid sinus syndrome group compared with only 4 (23.5%) in the control group (P<.01). Furthermore, the ab normality 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). Conclusion s This study strongly suggests that the neuromuscular structures surro unding the carotid mechanoreceptors are involved in the carotid sinus syndrome; however, the exact mechanism remains speculative.