Carotid sinus "irritability" rather than hypersensitivity: a new name for an old syndrome?

Carotid sinus hypersensitivity (CSH) is a well-described cause of syncope, resulting in bradycardia and/or hypotension in response to neck pressure. The authors hypothesized that (CSH) represents an inappropriate response of the baroreflex system to a nonphysiologic stimulus, rather than a truly hypersensitive carotid sinus (ie, excessive vagotonia and sympathoinhibition in response to arterial hypertension). To test their hypothesis, the authors used a neck chamber to deliver stepped, R-wave-triggered changes in transmural carotid sinus pressure, from +40 to -60 mm Hg, during a single held expiration. The authors studied 7 men (age 69 +/- 8y; mean age +/- SD) with carotid sinus syndrome and 10 age- and sex-matched controls. Seven repetitions of pressure changes were averaged, and the carotid sinus response described by changes in the R-R interval. There was no statistical difference in carotid-cardiac baroreflex gain (R-R interval/pressure change; mean gain +/- SD, 3.0 +/- 2.1 msec/mm Hg and 2.2 +/- 3.0 msec/mm Hg, respectively) or other markers of carotid baroreflex responses between the subjects and controls. These preliminary results suggest that (CSH) may not be a "hypersensitive" reflex, but rather an inappropriate response, or "irritability," of the baroreflex system to nonphysiologic deformation of the carotid sinus and/or surrounding tissues.