Syncope
Summary
Syncope is transient loss of consciousness (TLOC) due to cerebral hypoperfusion, characterised by rapid onset, short duration, and spontaneous complete recovery. It is classified as reflex (vasovagal most common), orthostatic, or cardiac. Cardiac syncope carries significant mortality risk and must be excluded. History is the most important diagnostic tool. ECG is mandatory. Risk stratification guides need for admission and investigation. Treatment is directed at the underlying cause.
Key Facts
- Definition: Transient loss of consciousness due to cerebral hypoperfusion
- Prevalence: 40% lifetime incidence; common ED presentation
- Classification: Reflex (vasovagal), orthostatic, cardiac
- Pathognomonic: Trigger + prodrome + brief unconsciousness + rapid recovery = vasovagal
- Gold Standard Investigation: History + ECG (mandatory)
- First-line Treatment: Depends on cause; education for vasovagal
- Prognosis: Reflex = benign; Cardiac = serious (1-year mortality up to 30%)
Clinical Pearls
History Pearl: Detailed history and witness account are THE most important diagnostic tools.
ECG Pearl: ECG is mandatory in ALL syncope. Look for: long QT, Brugada, WPW, HCM, AV block.
Red Flag Pearl: Syncope during exertion, with chest pain, with FHx sudden death, or abnormal ECG = high risk.
Driving Pearl: Syncope has DVLA implications. Single unexplained syncope = 6 months off driving.
| Type | Mechanism | Examples |
|---|---|---|
| Reflex (neurally mediated) | Vagal/sympathetic imbalance | Vasovagal, situational, carotid sinus |
| Orthostatic | BP drop on standing | Dehydration, drugs, autonomic failure |
| Cardiac | Arrhythmia or structural | VT/VF, bradycardia, AS, HCM, PE |
Vasovagal (Most Common)
Cardiac Syncope (High Risk)
Orthostatic
Mandatory
- 12-lead ECG (in ALL patients)
- Lying and standing BP (orthostatic hypotension: drop greater than 20/10 mmHg)
Additional (based on suspicion)
| Test | Indication |
|---|---|
| Echo | Suspected structural heart disease |
| Holter/loop recorder | Suspected arrhythmia |
| Tilt table test | Recurrent unexplained (suspected reflex) |
| Implantable loop recorder | Recurrent unexplained after workup |
| Carotid sinus massage | Suspected carotid sinus hypersensitivity |
Risk Stratification
High Risk Features:
- ECG abnormality
- Structural heart disease
- Syncope during exertion
- Syncope supine
- Palpitations at time
- Family history sudden death
- Severe anaemia
Reflex Syncope
- Reassurance and education
- Avoid triggers
- Recognise prodrome and abort (lie down, leg crossing)
- Adequate hydration and salt
- Rarely: fludrocortisone, midodrine
Orthostatic
- Review medications
- Compression stockings
- Rise slowly
- Increase fluid/salt
- Fludrocortisone/midodrine
Cardiac
- Treat underlying cause
- Pacemaker if bradyarrhythmia
- ICD if high-risk arrhythmia
- Surgery for structural (AS, HCM)
- Single unexplained syncope: 6 months off driving
- Recurrent syncope: until controlled
- Group 2 (HGV): more stringent rules
- Cardiac syncope: until pacemaker/ICD in place
-
Brignole M et al. 2018 ESC Guidelines for the diagnosis and management of syncope. Eur Heart J. 2018;39(21):1883-1948. PMID: 29562304
-
NICE Guideline CG109. Transient loss of consciousness. 2014.
Viva Points
"Syncope is TLOC due to cerebral hypoperfusion. Classified as reflex (vasovagal - most common), orthostatic, or cardiac (most dangerous). ECG mandatory in ALL. Red flags: exertional, no prodrome, FHx sudden death, abnormal ECG. Cardiac syncope has high mortality - needs investigation. DVLA implications."
Last Reviewed: 2026-01-01 | MedVellum Editorial Team