Emergency Medicine Emergency Medicine · Cardiology

Syncope Causes

Syncope is transient loss of consciousness due to global cerebral hypoperfusion. Stratifying cardiac from non-cardiac causes is the central task — cardiac syncope carries significantly higher mortality.

✦ The Mnemonic

"CARDIAC Syncope vs VASOVAGAL Syncope"

Cardiac (high risk) vs Neurally mediated (benign) vs Orthostatic

V Vasovagal (reflex) Most common overall; triggered by pain, emotion, prolonged standing; prodrome; complete recovery

Or Orthostatic hypotension Fall in SBP ≥20 mmHg or DBP ≥10 mmHg on standing; dehydration, drugs, autonomic failure

BR Bradyarrhythmia Complete heart block (Stokes-Adams), sinus arrest, sick sinus syndrome — no prodrome

TA Tachyarrhythmia VT (structural heart disease), SVT (rarely causes syncope unless rapid), AF with fast rate

ST Structural HOCM (exertional), severe aortic stenosis, massive PE, tension pneumothorax

Si Situational reflex Cough, micturition, defecation, swallowing — vagal-mediated

CS Carotid sinus Pressure on carotid sinus (tight collar, head turning) — bradycardia + hypotension

📚 Clinical Breakdown

High-risk features warranting hospital admission and urgent cardiology review: exertional syncope, syncope in supine position, no prodrome, syncope with palpitations, family history of SCD, abnormal ECG (QT prolongation, Brugada pattern, pre-excitation, Q waves, LBBB), known structural heart disease, or cardiac biomarker elevation.

EGSYS score (Evaluation of Guidelines in SYncope Study) distinguishes cardiac syncope from neurally mediated: palpitations before syncope (+4), abnormal ECG (+3), syncope during effort (+3), syncope supine (+2), prodrome (+1), predisposing/precipitating factors (−1). Score ≥3 suggests cardiac cause.

Tilt-table test: used to diagnose vasovagal syncope and orthostatic hypotension when the diagnosis is uncertain. Patient tilted to 70° for 20–45 minutes. Positive if syncope/presyncope + haemodynamic response (cardioinhibitory, vasodepressor, or mixed) reproduced.

Most common cause Vasovagal — emotional/pain trigger + prodrome

Cardiac syncope marker No prodrome; exertional; supine; family history SCD

High-risk ECG finding QT prolongation, Brugada, pre-excitation, Q waves

Orthostatic threshold SBP drop ≥20 mmHg on standing

⭐ Clinical Pearl

Carotid sinus massage: gentle massage of the carotid sinus for 5 seconds (with cardiac monitoring and resuscitation equipment available) — positive if ventricular pause >3 seconds or BP drop >50 mmHg. Contraindicated if carotid bruit present or recent TIA/stroke. A positive response diagnoses carotid sinus hypersensitivity — consider pacemaker.

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