Carotid Sinus Hypersensitivity

Carotid sinus hypersensitivity is an exaggerated response to carotid sinus baroreceptor stimulation. Syncope may occur with or without accompanying bradycardia. Carotid sinus hypersensitivity is defined by the response to gentle carotid sinus massage applied just below the angle of the jaw, near the carotid bifurcation for between 5 and 10 seconds:¹

• At least 3 sec asystole (cardioinhibition - the commonest form; 70-75% of cases)
• Lowering of blood pressure by at least 50mmHg (vasodepression; 5-10% of cases) without slowing of the heart
• A combination of cardioinhibition and vasodepression (20-25% of cases)

• Although baroreceptor function usually diminishes with age, some people experience hypersensitive carotid baroreflexes. Carotid sinus hypersensitivity is rare before the age of 50.
• An important cause of falls and syncope in the elderly. The prevalence of carotid sinus hypersensitivity in elderly patients presenting with falls is estimated as being about 25%.
• Men are affected more often than women.
• Hypersensitivity occurs more often on the right carotid sinus than the left.

Risk factors

• Carotid sinus hypersensitivity is associated with:
• Hypertension
• Coronary artery disease
• Other causes of syncope
• Dementia with Lewy bodies
• Medication, e.g. digitalis, beta-blockers and methyldopa

• A careful history and thorough physical examination may point to an obvious diagnosis of carotid sinus hypersensitivity, and no further investigation may be required.
• The assessment must be part of a thorough assessment of recurrent dizziness, syncope and falls.
• Typical trigger factors are shaving, head turning, neck extension or tight collars. Even mild stimulation to the neck may cause marked bradycardia and hypotension. The features of carotid sinus hypersensitivity may occasionally occur without any stimulation.
• May present with unexplained falls, recurrent dizziness or recurrent syncope.
• Many patients remain asymptomatic.
• Signs during an attack will include hypotension, bradycardia or both.
• Auscultation for a carotid artery bruit prior to carotid sinus massage is essential in the evaluation of carotid artery occlusion.

• Postural hypotension
• Other causes of syncope, including cough or micturition syncope, cardiac rhythm or structural abnormalities, epilepsy,² myocardial ischemia, pulmonary embolism, sick sinus syndrome, hypoglycaemia, psychogenic

• The exclusion of other causes of syncope is mainly by a thorough history and examination. An ECG, 24-hour ECG monitoring and/or and EEG may be required.¹
• ECG: can be used to rule out arrhythmias and indicate structural and functional heart disease. Ambulatory ECG monitoring may be required.
• Transthoracic echocardiogram: can be used to rule out structural heart disease and problems of myocardial function.
• Carotid sinus massage with continuous ECG and blood pressure monitoring:
  • Carotid sinus massage is potentially dangerous and may precipitate a stroke. It has also been reported to precipitate ventricular fibrillation. Therefore full resuscitation facilities and expertise must be immediately available and this test is not appropriate in nearly all primary care settings.
  • Both carotids should be confirmed as pulsatile in advance. Auscultation of the carotid arteries is also essential before the test can be considered. A carotid bruit is a relative contraindication and a carotid ultrasound must be performed to further evaluate any patient who is found to have a carotid bruit.
  • Carotid sinus massage is contraindicated in patients with myocardial infarction, TIA or stroke in the previous 3 months, carotid artery occlusion, history of ventricular tachycardia or ventricular fibrillation, and if there has been a previous adverse reaction to carotid sinus massage.
  • The following protocol is taken from the European Society Guidelines for the Management of Syncope (2004).¹
  • Carotid sinus massage may be performed only in the supine position or in both supine and upright positions. The diagnosis may be missed in one third of cases if massage is not performed in the upright position (usually on a tilt table).
  • Following baseline measurements the right carotid artery is massaged for between 5 and 10 seconds at the anterior margin of the sternocleidomastoid muscle, at the level of the cricoid cartilage. The ipsilateral temporal artery may be palpated during the procedure to ensure that the carotid is not being occluded.
  • If there is no significant response in terms of blood pressure or pulse rate, after 1 or 2 seconds the procedure is repeated on the opposite side.
  • If there is an asystolic response, the massage is usually repeated after an intravenous injection of atropine. This is to ensure that a vasodepressor component has not been concealed by the asystolic response.
  • A massage is considered to be positive if:¹
    • Asystole for longer than 3 seconds.
    • Reduction in systolic blood pressure by 50 mm Hg or more, irrespective of heart rate slowing.
  • An alternative method is to attempt to reproduce symptoms during carotid massage. Massage is performed for 10 seconds in both the supine and upright positions.
• Event recording is indicated for the evaluation of patients with infrequent episodes of syncope or presyncope. Holter monitoring should be performed in patients who have no response to carotid sinus massage.
• Exercise treadmill testing: assess cardiac function, ischaemia and exertional cardiac arrhythmias.

• Lifestyle modification:
  • Avoid triggers that increase pressure on the carotid sinus. Loose clothing with open collars may be helpful.
  • Maintain adequate fluid intake.
  • Learn to be aware of warning symptoms.
• There has not been shown to be any consistent benefit of medical therapies, e.g. vasopressors or salt-retaining medications, or the use of elastic support stockings. The SSRIs sertraline and fluoxetine have been used in patients who were unresponsive to dual-chamber pacing. However, no medication has been shown to be effective.^3,4
• Cardiac pacing with a permanent cardiac pacemaker:
  • The treatment of choice to prevent syncope in patients with cardioinhibitory carotid sinus hypersensitivity.⁵
  • Cardiac pacing has little or no effect on the vasodepressor type of carotid sinus hypersensitivity.
• Surgical denervation of the carotid sinus:
  • May be considered in cases where carotid sinus hypersensitivity is unilateral as a result of a mass or tumour in or near the carotid sinus.
  • Surgical denervation has been largely abandoned in favor of pacing and is only considered for severely debilitating disease not helped by other treatment methods.

• The most common and important complications of carotid sinus hypersensitivity are injuries related to falls and other accidents, such as motor vehicle accidents, that occur during syncopal episodes.⁶
• There is therefore a potential loss of confidence and social isolation may occur.

• Untreated symptomatic patients have a syncope recurrence rate as high as 62% within 4 years.⁷
• Patients treated with a pacemaker have fewer syncope attacks but may experience a recurrence rate as high as 16% in 4 years.⁷
• There is a better overall prognosis with treatment for patients who have a cardioinhibitory response or mixed response than those with a predominantly vasodepressor response to carotid sinus stimulation.