Syncope

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

Definition

Syncope is a transient, self limiting loss of consciousness due to temporary global cerebral hypoperfusion, followed by a spontaneous recovery.

Aetiology

1. Reflex (neurally mediated) Syncope:

  • Vasovagal syncope: triggered by emotional distress, pain, prolonged standing.
  • Situational syncope: occurs during coughing, micturition, defecation.
  • Carotid sinus hypersensitivity: triggered by head movements or tight collars.

2. Orthostatic Hypotension:

  • Caused by impaired autonomic regulation or volume depletion.
  • Common in older adults, diabetes, Parkinson’s disease.
  • Medication induced (antihypertensives, diuretics, antidepressants).

3. Cardiac Syncope:

  • Arrhythmias: bradycardia, tachycardia (e.g., ventricular tachycardia, AF with rapid ventricular response).
  • Structural heart disease: aortic stenosis, hypertrophic cardiomyopathy, myocardial infarction.
  • Pulmonary embolism: causes sudden cardiovascular collapse.

Pathophysiology

  • Temporary reduction in cerebral blood flow leads to hypoxia and loss of consciousness.
  • Blood pressure and heart rate regulation fail to maintain adequate perfusion.
  • Neurally mediated syncope involves excessive vagal activation, leading to bradycardia and vasodilation.
  • Cardiac syncope is caused by insufficient cardiac output due to arrhythmia or obstruction.

Risk factors

  • History of cardiovascular disease.
  • Older age.
  • Prolonged standing or dehydration.
  • Use of medications that lower blood pressure or heart rate.
  • Family history of sudden cardiac death.

Signs and symptoms

Pre Syncope (Prodromal Symptoms):

  • Lightheadedness.
  • Palpitations.
  • Nausea.
  • Blurred vision.
  • Weakness.

During Syncope:

  • Sudden loss of consciousness.
  • Brief duration (<1 minute).
  • Loss of postural tone (falling).
  • Spontaneous recovery without neurological deficit.

Red Flags Suggesting Cardiac Syncope:

  • Exertional syncope.
  • Family history of sudden cardiac death.
  • Syncope without warning symptoms.
  • Syncope associated with chest pain or palpitations.

Investigations

  • Clinical assessment: history, physical examination, orthostatic blood pressure measurement.
  • 12-lead ECG:
    • Detects arrhythmias (e.g., long QT syndrome, Brugada syndrome).
    • Signs of ischaemia or structural heart disease.
  • 24-hour Holter monitoring: if intermittent arrhythmia suspected.
  • Echocardiogram: if structural heart disease is suspected.
  • Tilt table test: for suspected vasovagal syncope or autonomic dysfunction.
  • Carotid sinus massage: if carotid sinus hypersensitivity suspected.
  • Blood tests:
    • FBC (anaemia), U&Es (electrolyte imbalances), troponins (if suspected cardiac cause).

Management

1. Lifestyle and Preventative Measures:

  • Identify and avoid triggers (e.g., prolonged standing, dehydration).
  • Encourage adequate fluid and salt intake.

2. Acute Management:

  • Lay patient flat with legs elevated to restore cerebral perfusion.
  • Ensure airway protection if prolonged unconsciousness occurs.

3. Pharmacological and Device Management (if needed):

Reflex Syncope:
  • Reassurance and lifestyle advice.
  • Consider fludrocortisone or midodrine for severe cases (specialist management).
Orthostatic Hypotension:
  • Review medications that may contribute.
  • Increase salt and fluid intake.
  • Fludrocortisone may be considered.
Cardiac Syncope:
  • Pacing for bradycardia (e.g., complete heart block).
  • Implantable cardioverter-defibrillator (ICD) for high-risk arrhythmias.
  • Beta blockers or antiarrhythmic drugs if indicated.
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