Related Subjects:
|Transient Loss of Consciousness
|Vasovagal Syncope
|Syncope
|Aortic Stenosis
|First Seizure
|Carotid Sinus Syncope
Vasovagal syncope (simple faint) is the most common cause of transient loss of consciousness. It is usually benign but may mimic or mask more serious conditions, so careful history and examination are essential.
📖 About
- Also called neurocardiogenic syncope or reflex syncope.
- It results from a reflex causing bradycardia and vasodilation, leading to transient cerebral hypoperfusion.
- Typically seen in young, otherwise healthy individuals but can occur at any age.
- Unlike epilepsy or cardiac arrhythmia, recovery is quick and without post-ictal confusion.
🧠 Pathophysiology
- Standing → venous pooling in legs → reduced preload.
- Initial sympathetic compensation increases HR and contractility.
- An abnormal reflex (Bezold–Jarisch reflex) then triggers sudden vagal activation and sympathetic withdrawal.
- Result: bradycardia + hypotension → cerebral hypoperfusion → syncope.
⚡ Triggers
- Pain, emotional stress, sight of blood or needles.
- Prolonged standing, hot environments, crowded places.
- After large meals or alcohol.
- Situational: micturition syncope, cough syncope, carotid sinus hypersensitivity.
🩺 Clinical Features
- Prodrome: dizziness, blurred vision, buzzing in ears, sweating, nausea, pallor.
- Loss of consciousness: brief (<2 minutes), flaccid fall.
- May have brief jerks, but rapid recovery distinguishes from seizure.
- No tongue biting, incontinence, or post-ictal phase.
🔎 Investigations
- Diagnosis is clinical based on history and trigger recognition.
- ECG: mandatory to exclude arrhythmia or long QT.
- Blood tests: FBC, glucose, electrolytes (exclude anaemia, hypoglycaemia).
- Head-up tilt test: reproduces symptoms, confirms neurocardiogenic syncope.
💊 Management
- Reassurance: Benign in most cases, explain physiology to patients.
- Lifestyle advice: Adequate hydration, increased salt intake (if appropriate), avoid prolonged standing and hot crowded environments.
- Counter-manoeuvres: Leg crossing, muscle tensing when prodrome occurs.
- Pharmacological: Fludrocortisone, midodrine, or SSRIs in recurrent refractory cases.
- Pacing: Rare, but indicated in severe cardioinhibitory forms with profound bradycardia/asystole.
🚨 Differentials
- Cardiac: arrhythmias, aortic stenosis, hypertrophic cardiomyopathy, pulmonary embolism.
- Neurological: seizure, stroke, TIA.
- Metabolic: hypoglycaemia.
- Psychogenic: panic attacks, hyperventilation.
- Orthostatic hypotension: elderly, autonomic neuropathy, medications.
📌 Key Teaching Points
- Always exclude dangerous causes first (especially cardiac arrhythmia).
- Prodrome + trigger + rapid recovery = strongly suggestive of vasovagal syncope.
- Driving implications: patients must inform the DVLA if recurrent or unexplained syncope.
📚 References
