Vasovagal syncope

Overview

Three phases - prodrome, brief LOC (<1 min), rapid full recovery. Diagnosis is clinical.

•Prodrome (seconds to minutes before): warmth/flushing, nausea, pallor, diaphoresis, lightheadedness, greying/darkening vision, whooshing sound in ears

•LOC: brief (<1 min), limp and pale; ~10% have brief myoclonic jerks ('convulsive syncope') - can mimic seizure

•Recovery: rapid and complete; no post-ictal confusion, no focal deficit, orientation returns almost immediately

🎯

The key discriminator from tonic-clonic seizure is the post-ictal state. After a faint, recovery is immediate. Prolonged confusion after LOC = seizure until proved otherwise.

Investigations

•First-line (classic presentation in young healthy person): 12-lead ECG - exclude arrhythmia, long QT, Brugada, conduction disease; normal ECG + typical history = no further investigation required

•Lying and standing BP - postural hypotension = symptomatic fall in systolic >20 mmHg, diastolic fall >10 mmHg, or systolic falling to <90 mmHg

•Blood glucose - exclude hypoglycaemia

🥈 Second-line

•echocardiogram - if structural heart disease suspected (murmur, exertional syncope, abnormal ECG)

•24-hour/7-day ambulatory ECG - if episodic arrhythmia suspected

🚨

Exertional syncope + systolic murmur radiating to the carotids = aortic stenosis until proved otherwise. First investigation = echocardiogram. Exercise tolerance test is contraindicated in suspected aortic stenosis.

Differential diagnosis

Vasovagal syncope vs cardiogenic syncope vs seizure

Feature	Vasovagal syncope	Cardiogenic syncope	Tonic-clonic seizure
Prodrome	Yes - warmth, nausea, visual darkening	No - sudden collapse	Sometimes aura
Trigger	Standing, heat, pain, venepuncture, crowds	Often exertional	Variable
Duration of LOC	<1 minute	Seconds	Minutes
Movements	Limp; occasional brief myoclonic jerks	Limp	Tonic-clonic activity
Recovery	Rapid, full, no confusion	Rapid	Prolonged confusion 5-30+ min (post-ictal)
Tongue biting / incontinence	No	No	Yes

📌

Atonic seizure: sudden loss of muscle tone, fall, brief LOC (<15 s), motionless, then confusion - can mimic vasovagal but no prodrome and post-ictal confusion distinguishes it.

Management

🥇 First-line

•reassurance and education - explain benign nature; single classic episode with normal ECG requires no admission and no further investigation

•Trigger identification and avoidance - prolonged standing, hot environments, dehydration, alcohol, crowds

•Adequate hydration and increased dietary salt - expands intravascular volume, reduces venous pooling

•Physical counterpressure manoeuvres - leg crossing, squatting, hand-gripping when prodrome begins; raises venous return and aborts episode

🥈 Second-line

•referral to cardiology/syncope clinic for recurrent or disabling episodes; drug therapy (fludrocortisone, midodrine, beta-blockers) occasionally used under specialist guidance - evidence generally weak