Approach to syncope

At a glance

• Syncope is transient loss of consciousness (TLOC) from global cerebral hypoperfusion: rapid onset, short, with spontaneous complete recovery.
• First separate syncope from its mimics, then find the patients at risk of a cardiac cause.
• History, examination, lying and standing BP, and a 12-lead ECG give a diagnosis in most cases.

Causes

Class	Examples
Reflex (neurally mediated), the commonest	Vasovagal (pain, fear, prolonged standing), situational (cough, micturition, defecation, after eating), carotid sinus hypersensitivity
Orthostatic hypotension	Drugs (antihypertensives, diuretics, nitrates, alpha-blockers), volume depletion, autonomic failure (Parkinson's, diabetes, amyloid)
Cardiac	Arrhythmia (bradycardia, conduction disease, VT, inherited channelopathies), structural (aortic stenosis, HCM, PE, tamponade, myxoma)

Mimics (TLOC that isn't syncope)

• Epileptic seizure
• Psychogenic pseudosyncope
• Hypoglycaemia, hypoxia, intoxication
• Falls without loss of consciousness
• TIA or stroke (vertebrobasilar ischaemia only rarely causes TLOC)

Focused history

• Before: posture, activity (exertion?), triggers, prodrome (warmth, sweating, nausea, tunnel vision), palpitations or chest pain.
• During (from a witness): duration, colour, movements, tongue biting, incontinence.
• After: speed and completeness of recovery, confusion, injury.
• Background: heart disease, medicines and recent changes, family history of sudden death under 40.

Seizure or syncope?

Favours seizure	Favours syncope
Lateral tongue bite	Prodrome of warmth, sweating, nausea
Head turning, unusual posturing	Triggered by standing, pain or emotion
Prolonged confusion afterwards	Rapid return to normal
Aura (déjà vu, rising epigastric feeling)	Pallor

Pitfall: brief myoclonic jerks are common in syncope (convulsive syncope). Incontinence doesn't discriminate.

Focused examination

• Lying and standing BP (at 1 and 3 minutes).
• Murmurs (aortic stenosis, HCM), signs of heart failure, carotid bruits.
• Neurological examination and injuries.
• Carotid sinus massage (ECG and BP monitored) in patients over 40 with unexplained syncope compatible with a reflex mechanism. Avoid it after a TIA or stroke in the past 3 months or with a carotid bruit, unless Doppler has excluded significant stenosis.

Red flags (high risk)

• Syncope during exertion or when lying down
• Sudden palpitations immediately before
• No or very brief prodrome
• Known structural heart disease, heart failure, low ejection fraction or previous MI
• Family history of sudden cardiac death at a young age
• Chest pain, breathlessness, abdominal pain or headache with the event
• ECG features: Mobitz II or third-degree block, bifascicular block, sinus bradycardia <40/min or pauses >3 s, VT, pre-excitation, Brugada type 1 pattern, long or short QT, features of ARVC or HCM

Investigations

• Everyone: 12-lead ECG, lying and standing BP, glucose. Hb if bleeding is possible.
• Suspected structural disease: echocardiogram.
• Rhythm monitoring by frequency of events:
  • Inpatient telemetry for high-risk patients
  • Holter (24 to 48 hours or longer) for frequent events, at least weekly
  • External event recorder for weekly to monthly episodes
  • Implantable loop recorder for recurrent, infrequent unexplained syncope
• Exercise testing if syncope occurs during exertion (after echo excludes significant aortic stenosis or HCM).
• Tilt testing in selected cases of suspected reflex syncope or orthostatic hypotension.
• Pitfall: CT brain and EEG have low yield in typical syncope. Order them only for focal signs, head injury or a suspected seizure.

Management

• Reflex syncope: reassurance and education, avoiding triggers, physical counter-pressure manoeuvres, fluids and salt if appropriate, review of hypotensive drugs.
• Orthostatic hypotension: stop or reduce culprit drugs, maintain hydration, rise slowly, compression garments. Fludrocortisone or midodrine in selected patients.
• Cardiac: treat the cause (pacing for conduction disease, ICD where indicated, valve intervention).

Driving

• Advise patients about driving restrictions after syncope. They depend on the cause and the licence class. Check the current Austroads Assessing Fitness to Drive standards.