Carotid Sinus Syndrome: Pathophysiology and Diagnosis

Abstract

It has been known for decades that pressure at the site where the common carotid artery bifurcates produces a slowing in heart rate and a decrease in blood pressure (BP). This physiological reflex arc, beginning in baroreceptors located in the carotid artery wall, is designed to regulate BP and therefore massage of the carotid sinus is interpreted by central nervous nuclei as an increase in BP resulting in the above-mentioned consequences intended to normalize BP. In some individuals however, carotid massage produces an excessive response with a prolonged ventricular pause and hypotension. A pause lasting >3 s and/or a fall in systolic BP of >50 mmHg is generally considered abnormal. This abnormal response defines carotid sinus hypersensitivity (CSH). While many hypotheses have been proposed, the pathophysiology of CSH remains largely unknown.

Carotid sinus syndrome (CSS) is defined when 10 s sequential right and left carotid sinus massage (CSM) is associated with spontaneous syncope and reproduction of symptoms. While CSH is a common finding in older males, CSS is more unusual and even exceptional in patients <40 years old.

The relationship between abnormal response to CSM and syncope is a crucial point that has been evaluated in different studies and their results suggest that a positive response to CSM in patients with syncope is highly predictive of the occurrence of spontaneous episodes.

The main potential complications of CSM are neurological (e.g., transient ischemic attack) but this occurrence evaluated in several thousand patients remains very rare.

Carotid sinus massage is therefore a conventional accepted method to evaluate patients (particularly older males) with syncope of unknown origin after the initial evaluation.