Carotid Sinus Hypersensitivity

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

Carotid sinus hypersensitivity (CSH) is an exaggerated response to carotid sinus stimulation, leading to transient bradycardia, hypotension, or both, resulting in syncope or near-syncope.

Aetiology

The exact cause is unknown, but it is thought to result from increased sensitivity of the baroreceptors in the carotid sinus.

1. Possible Contributing Factors:

• Degenerative changes in the autonomic nervous system with ageing.
• Vascular conditions (e.g., atherosclerosis, hypertension).
• Neck compression (e.g., tight collars, shaving, head-turning).
• Previous head and neck surgery or radiation.
• Neurogenic causes (e.g., autonomic dysfunction).

Pathophysiology

• The carotid sinus contains baroreceptors that regulate blood pressure.
• In CSH, these baroreceptors are overly sensitive, leading to excessive vagal (parasympathetic) activation when stimulated.
• This results in one or both of the following responses:
• Cardioinhibitory response: excessive vagal stimulation causes bradycardia or asystole.
• Vasodepressor response: sympathetic inhibition causes hypotension without significant bradycardia.
• Mixed response: combination of both bradycardia and hypotension.

Risk factors

• Age over 60 years.
• Male sex (higher prevalence).
• History of unexplained falls or syncope.
• Neck manipulation or compression (e.g., tight collars, carotid massage).
• Hypertension and atherosclerosis.
• Autonomic dysfunction or neurodegenerative diseases (e.g., Parkinson’s disease).

Signs and symptoms

Symptoms occur due to transient cerebral hypoperfusion caused by bradycardia or hypotension.

Common Features:

• Syncope or near syncope: sudden loss of consciousness or lightheadedness.
• Dizziness: especially after head-turning or carotid sinus stimulation.
• Falls: often unexplained, common in older adults.
• Neck sensitivity: symptoms triggered by pressure on the carotid sinus.
• Fatigue or confusion: due to transient cerebral hypoxia.

Investigations

• Carotid sinus massage (diagnostic test):
  • Performed with continuous ECG and blood pressure monitoring.
  • Positive if asystole >3 seconds (cardioinhibitory) or systolic BP drop >50 mmHg (vasodepressor).
• ECG: rules out arrhythmias.
• 24hr Holter monitor: evaluates for intermittent bradycardia or pauses.
• Blood pressure monitoring: identifies postural hypotension as a differential.
• Carotid Doppler ultrasound: rules out significant carotid artery stenosis (carotid massage is contraindicated if severe stenosis is present).
• Autonomic function tests: assesses for underlying autonomic dysfunction.

Management

1. Conservative Measures:

• Avoidance of triggers (e.g., tight collars, head turning).
• Patient education about neck pressure sensitivity.
• Increased fluid and salt intake if hypotension is a concern.

2. Pharmacological Treatment:

• Fludrocortisone: used in vasodepressor response to increase blood pressure.
• Midodrine: alpha agonist to support blood pressure in resistant cases.

3. Pacemaker Implantation:

• Indicated in patients with severe symptomatic bradycardia (cardioinhibitory type).
• Dual chamber pacemakers are preferred to maintain heart rate stability.

4. Monitoring and Follow-Up:

• Regular assessment of symptoms and falls risk.
• Re-evaluation of medication use, particularly those that lower heart rate.