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. It is extremely common – affecting up to half the UK population at some point – and 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, or 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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