Approach to Syncope
A board-focused framework for syncope: separate benign reflex and orthostatic causes from life-threatening cardiac syncope using history, exam, orthostatic vitals, and a mandatory 12-lead ECG, then apply next-best-step diagnosis and disposition rules.
The framework
Syncope is a transient loss of consciousness (TLOC) from global cerebral hypoperfusion, defined by rapid onset, short duration, and spontaneous, complete recovery. Separate it up front from mimics: seizure, hypoglycemia, and psychogenic pseudosyncope.
Every cause sorts into one of three mechanistic buckets:
- Reflex / neurally-mediated (vasovagal, situational, carotid sinus) — most common, benign
- Orthostatic hypotension — volume depletion, drugs, autonomic failure
- Cardiac — arrhythmic or structural/obstructive — least common but highest mortality
The board task is always the same: use history, exam, orthostatic vitals, and a 12-lead ECG in every patient to decide who has benign reflex syncope and can go home versus who has cardiac syncope and needs admission with a monitored workup.
- Syncope = brief TLOC from global cerebral hypoperfusion with full spontaneous recovery
- Order a 12-lead ECG in EVERY patient — cheap, mandatory first test
- Reflex (vasovagal) = most common; prodrome of nausea, warmth, diaphoresis, tunnel vision; triggered by pain, emotion, prolonged standing, heat
- Orthostatic = SBP drop ≥20 or DBP drop ≥10 within 3 min of standing; culprits: diuretics, alpha-blockers, nitrates, TCAs, volume loss
- Cardiac red flags: syncope during exertion or while supine, no prodrome ("drop attack"), palpitations/chest pain, known structural heart disease, abnormal ECG, family history of sudden cardiac death
- Exertional syncope + systolic murmur → aortic stenosis or HOCM until proven otherwise → echocardiogram
- Cardiac syncope carries the highest mortality → admit and monitor
Three buckets side by side
| Feature | Reflex / Vasovagal | Orthostatic | Cardiac |
|---|---|---|---|
| Trigger | Pain, emotion, standing, heat | Standing up, meds, dehydration | Exertion or none |
| Prodrome | Nausea, warmth, tunnel vision | Lightheaded on standing | Often none; palpitations/chest pain |
| Position | Upright | Within 3 min of standing | Any position, incl. supine |
| Recovery | Rapid, full | Rapid once supine | Rapid but may recur |
| Key test | Clinical ± tilt table | Orthostatic vitals | ECG, echo, rhythm monitoring |
| Risk | Benign | Low–moderate | High (mortality) |
A 68-year-old man passes out while climbing stairs. Exam: a harsh crescendo–decrescendo systolic murmur at the right upper sternal border radiating to the carotids, with a weak, delayed carotid pulse (pulsus parvus et tardus).
Dx: Aortic stenosis causing exertional syncope — one of the classic triad (angina, syncope, dyspnea) that signals severe disease.
Next best step: Transthoracic echocardiogram to confirm severity (valve area, mean gradient). Severe symptomatic AS → aortic valve replacement. Avoid preload/afterload reducers (nitrates, diuretics, vasodilators) — in fixed obstruction they can precipitate collapse.
A 17-year-old collapses during a basketball game; a cousin died suddenly at 20. Exam: a systolic murmur that increases with Valsalva and standing and decreases with squatting.
Dx: Hypertrophic cardiomyopathy (dynamic LVOT obstruction). Next step: echocardiogram (asymmetric septal hypertrophy, systolic anterior motion of the mitral valve) plus ECG (LVH, deep septal Q waves). Restrict competitive athletics. Exertional/unexplained syncope plus a family history of sudden death are themselves high-risk markers → ICD for sudden-death prevention.
Contrast: a 25-year-old faints after standing in a hot, crowded church, with preceding nausea and warmth, recovering in seconds. Dx: vasovagal syncope. Next step: normal ECG → reassurance, hydration, counterpressure maneuvers — no cardiac workup needed.
CHESS is the San Francisco Syncope Rule, a validated ED tool. Any single positive predictor flags high risk of a serious short-term (7-day) outcome → admit / monitor:
- C — Congestive heart failure history
- H — Hematocrit < 30%
- E — ECG abnormal (new changes or non-sinus rhythm)
- S — Shortness of breath
- S — Systolic BP < 90 mmHg at triage
All five negative → low risk, candidate for outpatient evaluation. Any positive → serious causes (arrhythmia, hemorrhage, PE, ACS) must be excluded before discharge.
Workup ladder and disposition
After history, exam, orthostatic vitals, and ECG, risk-stratify:
- Normal ECG + clear reflex features + young/healthy → discharge, no further testing.
- Murmur or suspected structural disease → echocardiogram (AS, HOCM, tamponade, low EF).
- Recurrent unexplained syncope, normal ECG/echo → ambulatory rhythm monitoring, matched to frequency: Holter (daily symptoms), event/patch monitor (weekly), implantable loop recorder (infrequent, unexplained episodes).
- Recurrent reflex syncope, diagnosis uncertain → tilt-table testing.
- High-risk features / suspected arrhythmia with structural heart disease → admit, telemetry, ± electrophysiology study.
- Older patient, unexplained, no carotid bruit or recent stroke/MI → carotid sinus massage to unmask carotid sinus hypersensitivity.
- Syncope: pallor and diaphoresis beforehand; brief (<15 s) myoclonic jerks that occur AFTER the fall (convulsive syncope); rapid, full recovery; a trigger/prodrome is common
- Seizure: preceding aura; lateral tongue biting; sustained tonic-clonic activity; prolonged postictal confusion (minutes); cyanosis
- Not discriminating (occur in both): urinary incontinence and a few brief jerks
- Next step: syncope → orthostatics, ECG, ± tilt; seizure → EEG and MRI brain
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