GPAtlas🧭 When to suspect
A transient loss of consciousness (TLoC), or ‘blackout’, is a state of real or apparent loss of consciousness with rapid onset, short duration, and spontaneous, complete recovery.
• TLoC is extremely common, affecting up to half the UK population at some point.
• An uncomplicated faint (vasovagal syncope) is by far the commonest cause.
• The challenge is that the same brief event can be the first presentation of a life-threatening cardiac condition.
The first task is to confirm it really was TLoC, and not a mimic:
• A fall without loss of consciousness.
• An epileptic seizure.
• A psychogenic event.
• A metabolic cause such as hypoglycaemia.
If this is uncertain, assume TLoC until proven otherwise.
A good collateral history from a witness – or a smartphone video – is often worth more than any test.
The second task drives everything else: record a 12-lead ECG in everyone, and decide whether the pattern points to a benign reflex/orthostatic cause or to the dangerous cardiac group that must not be missed.
| Pattern | Typical features | Why it matters |
|---|---|---|
| Reflex (vasovagal/situational) | • Provoked by prolonged standing, pain, emotion, heat, or by micturition, coughing or swallowing • A warning prodrome (light-headed, hot, nauseated, vision greying) • Brief, with rapid full recovery |
Commonest cause and usually benign. |
| Orthostatic (postural) | • On standing or sitting up • Older adults, volume depletion (D&V, bleeding) or culprit drugs • Systolic BP falls ≥ 20 mmHg or diastolic ≥ 10 mmHg |
Benign in itself, but flags dehydration, bleeding or medication to review. |
| Cardiac (arrhythmic/structural) | • During exertion or while lying flat • Little or no prodrome • Palpitations beforehand • Known heart disease, or family history of sudden death aged < 40 |
• The dangerous group – highest risk of sudden death • Must be actively excluded |
|
🧠 Clinical pearl • Pin down the relationship to exercise. • Syncope during exertion suggests a sinister cardiac cause (aortic stenosis, hypertrophic cardiomyopathy, exercise-induced arrhythmia) and warrants urgent assessment. • Syncope shortly after stopping exercise is usually benign vasovagal. • One word in the history – during versus just after – changes the urgency completely. |
Source: NICE CG109 · ESC 2018
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