Carotid sinus hypersensitivity

Definition

Carotid sinus hypersensitivity (CSH) is an exaggerated response to carotid sinus baroreceptor stimulation. It is defined by the response to gentle carotid sinus massage (CSM) applied just below the angle of the jaw, near the carotid bifurcation for between 5 and 10 seconds¹:

• At least three-second asystole (cardio-inhibition - the most common form; 70-75% of cases).

• Lowering of blood pressure by at least 50 mm Hg (vasodepression; 5-10% of cases) without slowing of the heart.

• A combination of cardio-inhibition and vasodepression (20-25% of cases).

Syncope may occur with or without accompanying bradycardia.

Epidemiology

• Although baroreceptor function usually diminishes with age, some people experience hypersensitive carotid baroreflexes. CSH is rare before the age of 50².

• CSH is the most commonly reported cause of falls and syncope in older people. The prevalence of CSH in elderly patients presenting with falls is estimated as being about 25%.

• However, it has been claimed that the current criteria for CSH are too sensitive and this in part explains the reported high prevalence of CSH in the general older population.

• Men are affected more often than women.

• Hypersensitivity occurs more often on the right carotid sinus than the left.

Risk factors

CSH is associated with:

• Hypertension.

• Coronary artery disease.

• Other causes of syncope.

• Dementia with Lewy bodies.

• Medication - eg, digitalis, beta-blockers and methyldopa.

Presentation

• A careful history and thorough physical examination may point to an obvious diagnosis of CSH 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 CSH may occasionally occur without any stimulation³.

• Many patients remain asymptomatic.

• Signs during an attack will include hypotension, bradycardia or both.

• Auscultation for a carotid artery bruit prior to CSM is essential in the evaluation of carotid artery occlusion.

Differential diagnosis

• Postural hypotension.

• Other causes of syncope, including cough or micturition syncope, cardiac rhythm or structural abnormalities, epilepsy, myocardial ischaemia, pulmonary embolism, sick sinus syndrome, hypoglycaemia.

• Severe aortic stenosis.

• Seizures.

• Hypertrophic cardiomyopathy.

• Transient ischaemic stroke.

• Medication adverse effect.

Investigations

• The exclusion of other causes of syncope is mainly by a thorough history and examination.

• 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.

• 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 CSM.

• Exercise treadmill testing: assess cardiac function, ischaemia and exertional cardiac arrhythmias.

• An EEG may also be indicated.

Diagnostic carotid sinus massage

This should be undertaken with continuous ECG and blood pressure monitoring. CSM is potentially dangerous and may precipitate a stroke (0.24%)¹. 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.

CSM is contra-indicated in patients with³:

• Myocardial infarction.

• Transient ischaemic attack (TIA) or a cerebrovascular event in the previous three months.

• Carotid artery occlusion.

• History of ventricular tachycardia or ventricular fibrillation.

• A previous adverse reaction to CSM.

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 contra-indication and a carotid ultrasound must be performed to further evaluate any patient who is found to have a carotid bruit.

The following protocol is taken from the European Society of Cardiology's Guidelines for the Management of Syncope¹:

• CSM 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 there is:
  

  • Asystole for longer than three 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.

There is some doubt of the value of CSM; research has shown that the response to CSM in patients with and without syncope was similar²; therefore, CSH may be an unspecific condition.

Management

• 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 (eg, vasopressors or salt-retaining medications) or the use of elastic support stockings. The selective serotonin reuptake inhibitors (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.

• Cardiac pacing with a permanent cardiac pacemaker⁴:

  • Permanent pacemaker therapy may be effective if asystole (cardio-inhibitory) is a dominant feature of reflex syncope.

  • Cardiac pacing has little or no effect on the vasodepressor type of CSH.

• Surgical denervation of the carotid sinus⁵:
  

  • May be considered in cases where CSH is unilateral as a result of a mass or tumour in or near the carotid sinus.

  • Surgical denervation has been largely abandoned in favour of pacing and is only considered for severely debilitating disease not helped by other treatment methods.

Complications

• The most common and important complications are injuries related to falls and other accidents, such as motor vehicle accidents that occur during a syncopal episode.

• There is therefore a potential loss of confidence, and social isolation may occur.

Prognosis

• There is no increase in mortality rates in patients with CSH compared with the general population⁶.

• Untreated symptomatic patients have a high syncope recurrence rate.

• Patients treated with a pacemaker may experience recurrence of syncope.

• Patients with CSH showing a reduction in blood pressure after a carotid sinus stimulation have a worse prognosis than those with a pure cardio-inhibitory response or a lack of vasodepressor response.