Syncope
Syncope and presyncope deserve similar concern: a near-miss can share the same dangerous cardiac or neurologic cause as a complete loss of consciousness.
ABCs
- A–B–C, lay flat, check glucose immediately, IV access, full vitals + SpO₂ + monitor
- if still unresponsive → treat as reduced GCS, not simple syncope (airway, call for help)
- presyncope gets the same workup, not a lesser one
- focused cardiovascular and neurological exam, medication review, history from the patient and any witness: before, during, and after the event
cardiac syncope until proven otherwise
- syncope on exertion (think aortic stenosis, hypertrophic cardiomyopathy, pulmonary hypertension) or while supine
- no prodrome (“found on the floor”), or palpitations immediately before
- chest pain or dyspnea with the event
- family history of sudden cardiac death at a young age
- known structural heart disease, heart failure, or prior ventricular arrhythmia
- abnormal ECG: high-grade AV block, significant bradyarrhythmia, ventricular arrhythmia, pre-excitation, long QT, Brugada pattern, ischemic changes, or findings suggesting structural / cardiomyopathic disease
- hypotension or vital signs that stay abnormal, rather than a single event with full recovery
- significant anemia or active bleeding where clinically suspected (GI bleed, heavy menstrual bleeding, anticoagulated patient, postoperative bleeding) → GI bleed if that is the source
- new, unexplained murmur
- severe injury caused by the fall itself
risk features to weigh together, not one universal admission rule
definitions
- syncope = transient LOC from global cerebral hypoperfusion, with rapid onset and full spontaneous recovery
- not everything that drops a patient is syncope: separate seizure, hypoglycemia, intoxication, mechanical fall (tripped, no LOC), vertigo, psychogenic event, stroke / arrhythmia
three buckets of true syncope
| type | clues |
|---|---|
| reflex (vasovagal) | recognizable trigger (prolonged standing, heat, pain, emotion, micturition); prodrome (nausea, warmth, diaphoresis, visual dimming); rapid recovery, no prolonged postictal state |
| orthostatic | on standing; drugs (antihypertensives, diuretics, vasodilators), dehydration, bleeding, autonomic failure |
| cardiac | the dangerous one, see escalate now above |
workup
- ECG on everyone
- orthostatic BP: after ≥ 5 min supine, measure within 3 min of standing; positive if drop ≥ 20 systolic or ≥ 10 diastolic mmHg (≥ 30 systolic if supine hypertension)
- look for a cause: diuretics, vasodilators, antihypertensives, dehydration, bleeding, autonomic dysfunction
- does not exclude a coexisting dangerous cause
- CBC if anemia or bleeding suspected; electrolytes and renal function if dehydration, medication effect, or metabolic/arrhythmia risk; glucose if not already checked
- troponin: only if ischemic symptoms, ECG changes, or suspected myocardial injury → chest pain
- D-dimer / PE workup: only if PE is suspected, driven by validated pre-test probability, not because syncope occurred → dyspnea
- CT head: not routine; only for focal deficit, significant head trauma, or suspected intracranial pathology
- monitoring: telemetry if a cardiac / arrhythmic cause is suspected; one normal ECG does not exclude intermittent arrhythmia
- ambulatory monitoring (loop recorder, implantable if infrequent) by expected symptom frequency
- echo if structural heart disease suspected or ECG abnormal
- active arrhythmia → palpitations
Canadian Syncope Risk Score
Canadian Syncope Risk · MDCalc ↗︎
estimates 30-day serious-outcome risk in adults presenting within 24 hr of true syncope with no clear cause on initial assessment. Not validated for witnessed seizure, prolonged LOC, or major trauma. Supports judgment; an obvious high-risk presentation overrides it.
syncope vs seizure
- lateral tongue bite, sustained witnessed tonic-clonic activity, prolonged post-ictal confusion → seizure
- brief jerks after collapse, rapid recovery with no prolonged postictal state → likely convulsive syncope
- urinary incontinence does not distinguish the two: it occurs in convulsive syncope as well as seizures; never use it alone
- if seizure is the more likely diagnosis, full workup and management on seizures
treat
- treat the cause; review medications: hypotension, volume depletion, bradycardia, QT prolongation, arrhythmia, hypoglycemia. Hold the offending drug
- clear low-risk reflex / vasovagal: education, hydration, trigger avoidance, physical counter-pressure maneuvers (leg or arm tensing) at the next prodrome
- higher risk: suspected cardiac / arrhythmic cause, concerning ECG, structural heart disease, exertional or supine syncope, persistent abnormal vitals, significant bleeding, or serious injury → urgent monitored evaluation (telemetry) and specialist review
- low risk: reflex / orthostatic with a clear benign story and no red flags → reassure, optimise meds, safety-net
- persistent hemodynamic instability beyond the transient event → Advanced: Shock, or Advanced: Cardiogenic Shock if cardiac
MOC+ Volume 2 · Cardiopulmonary covers syncope & collapse. order here.
evidence
| source | type |
|---|---|
| 2017 ACC/AHA/HRS syncope guideline | international guideline |
| 2018 ESC syncope guideline | international guideline |
| Consensus definition of orthostatic hypotension (American Autonomic Society / AAN) | consensus statement |
| Canadian Syncope Risk Score validation studies | validated prognostic tool |
free the on-call checklist covers the whole shift on one printable page.
studying for the IM exam? the IM Rapid Review covers syncope in the same format. see the sample chapter.
updated Sep 2026file complaint/syncope