Key Facts

Syncope is a transient loss of consciousness (TLOC) caused by transient global cerebral hypoperfusion. It is common, affecting up to 40% of the population at some point, and ranges from benign (vasovagal) to life-threatening (cardiac arrhythmia).

Epidemiology

• Lifetime prevalence: ~40% of the general population
• Accounts for ~1-3% of ED attendances and ~1-6% of hospital admissions
• Vasovagal syncope: most common cause (~50-60% of all syncope)
• Cardiac syncope: ~10-20% of cases but carries highest mortality

Classification

1. Neurally mediated (reflex) syncope:

• Vasovagal: most common; triggered by prolonged standing, pain, emotion, heat
• Situational: cough, micturition, defecation, swallow
• Carotid sinus syncope: head turning, tight collar (elderly)

2. Orthostatic hypotension:

• Autonomic dysfunction: diabetes, Parkinson disease, MSA, drugs
• Volume depletion: dehydration, haemorrhage, diuretics
• Drug-induced: antihypertensives, alpha-blockers, vasodilators

3. Cardiac syncope:

• Arrhythmic: VT, SVT, bradycardia, heart block, long QT, Brugada, WPW
• Structural: aortic stenosis, HCM, cardiac tamponade, PE, aortic dissection

Pathophysiology

• Brain requires continuous blood flow (~50 mL/100g/min); cessation for 6-8 seconds → loss of consciousness
• Vasovagal: paradoxical vagal activation → bradycardia + vasodilation → hypotension → cerebral hypoperfusion
• Orthostatic: failure of autonomic compensation for postural blood pooling
• Cardiac: sudden reduction in cardiac output (arrhythmia, obstruction)

Vasovagal Syncope

• Prodrome: lightheadedness, nausea, warmth, pallor, sweating, visual greying
• Trigger: prolonged standing, crowded/hot environment, pain, emotional stress
• Recovery: rapid, may feel fatigued or nauseous afterwards
• Brief tonic-clonic movements may occur (convulsive syncope — NOT epilepsy)

Cardiac Syncope

• Often sudden without warning (no prodrome)
• May occur during exertion (AS, HCM) or at rest (arrhythmia)
• Palpitations preceding syncope suggest arrhythmia
• Family history of sudden cardiac death

Orthostatic Syncope

• Occurs on standing from lying/sitting
• Exacerbated by medications, dehydration, heat
• Common in elderly

Red Flags (Suggest Cardiac Syncope)

• Exertional syncope
• Syncope while supine
• Palpitations preceding episode
• Family history of sudden death <40 years
• Known structural heart disease
• Abnormal ECG (long QT, Brugada, WPW, heart block, HCM)
• No warning/prodrome
• New onset in elderly

Initial Assessment (All Patients)

• Detailed history: circumstances, prodrome, witnesses, recovery, medications, family history
• 12-lead ECG: mandatory — look for long QT, Brugada, WPW, AV block, HCM (LVH + strain), ARVC (TWI V1-V3)
• Lying and standing BP: orthostatic hypotension (≥20/10 mmHg drop)
• Blood glucose: exclude hypoglycaemia
• FBC, U&Es: anaemia, electrolyte disturbance

Further Investigations (Based on Suspicion)

• Echocardiography: if cardiac syncope suspected (structural heart disease)
• Holter monitor (24-48h): if arrhythmia suspected and frequent
• 7-day event recorder: for less frequent episodes
• Implantable loop recorder (ILR): for infrequent episodes (monitors for up to 3 years)
• Tilt table testing: recurrent unexplained syncope to diagnose vasovagal (positive = reproduction of symptoms with hypotension/bradycardia)
• Carotid sinus massage: in patients >40 years with unexplained syncope (under monitoring)
• EP study: if arrhythmic syncope strongly suspected
• CT head/MRI brain: generally NOT indicated for typical syncope (only if focal neurology or head injury)

Vasovagal Syncope

• Education and reassurance: benign condition
• Avoid triggers: prolonged standing, hot environments, dehydration
• Counter-pressure manoeuvres: leg crossing and tensing, hand gripping at onset of prodrome
• Adequate fluid and salt intake
• Tilt training: graduated standing exercises (controversial efficacy)
• Medications (rarely needed): midodrine 2.5-10mg TDS (alpha-agonist) or fludrocortisone 100-200mcg OD for refractory cases
• Pacemaker: only for cardioinhibitory vasovagal syncope (dominant bradycardia component documented on tilt testing or ILR) — NICE recommendation

Orthostatic Hypotension

• Medication review: reduce/stop causative drugs
• Physical measures: graduated compression stockings, slow positional changes, adequate hydration
• Fludrocortisone 100-300mcg OD: volume expansion
• Midodrine 2.5-10mg TDS: alpha-agonist

Cardiac Syncope

• Treat underlying cause:
  • Arrhythmic: pacemaker (bradycardia), ICD (VT/VF), catheter ablation (SVT, WPW)
  • Structural: aortic valve replacement (AS), septal myectomy (HCM), PE treatment
• ICD: for syncope due to ventricular arrhythmia or high-risk channelopathy

Referral Criteria

• Red flag features: urgent cardiology referral
• Suspected cardiac syncope: rapid access cardiology
• Recurrent unexplained syncope: specialist syncope unit/tilt testing
• Driving: advise patients regarding DVLA regulations (cardiac syncope: driving ban until treated)

• Vasovagal syncope: excellent prognosis; no increased mortality; may be recurrent but benign
• Cardiac syncope: significant mortality risk (~20-30% 1-year mortality if untreated) — depends on underlying cause
• Orthostatic syncope: associated with increased falls, fractures, and mortality in elderly
• Risk of injury: ~30% of patients with syncope experience injury; ~5% experience major injury
• Driving: DVLA regulations must be followed; cardiac syncope typically requires 6-12 months driving ban (depending on cause and treatment)
• Quality of life: significantly impaired in patients with recurrent syncope

Syncope vs Seizure

DVLA Guidance Summary