Carotid Sinus Hypersensitivity

Carotid sinus hypersensitivity is an exaggerated reflex response to carotid sinus stimulation, with ventricular asystole of 3 seconds or more (cardioinhibitory), a fall in systolic blood pressure of 50 mmHg or more (vasodepressor), or both (mixed). It is a laboratory finding. When it explains symptoms it is called carotid sinus syndrome.

It is found in up to a third of older people investigated for syncope or unexplained falls, and it is rare under the age of 50. It is also found in many asymptomatic older people.

Pathophysiology. Pressure on the carotid baroreceptors increases vagal and reduces sympathetic outflow. In hypersensitivity the medullary response is exaggerated, possibly from degeneration of the central circuits and sympathetic denervation of the sternocleidomastoid muscle.

Often asymptomatic. Symptomatic patients have unexplained falls or syncope, often brief and without warning, sometimes triggered by head turning, tight collars, shaving or neck extension.

Perform carotid sinus massage for 5 to 10 seconds on each side, supine and then at 60 to 70 degrees head up on a tilt table, with continuous ECG and beat-to-beat blood pressure monitoring. Do not perform the test after a stroke or transient ischaemic attack in the previous 3 months or when a carotid bruit is present unless carotid imaging shows no significant stenosis. Check lying and standing blood pressure, ECG, and echocardiography when structural disease is suspected.

Differential diagnosis.

• Cardiac arrhythmia, aortic stenosis and sick sinus syndrome.
• Orthostatic hypotension and drug induced bradycardia or hypotension.
• Vasovagal syncope and seizures.

Asymptomatic hypersensitivity needs no treatment. Stop or reduce drugs that slow the heart or lower blood pressure. For recurrent syncope or falls with cardioinhibitory hypersensitivity, implant a dual chamber pacemaker, which reduces recurrences. There is no effective treatment for the vasodepressor form; use compression stockings, fluid and avoidance of triggers.

Monitoring. Syncope and fall recurrence, and pacing checks.