Cardiovascular · Topic 46 of 48
Syncope
Cardiovascular · syncope
Syncope
Most syncope is benign reflex fainting; the ECG, orthostatic vitals and high-risk cardiac features decide who is admitted and monitored.
Key numbers
Orthostatic hypotension: SBP falls ≥ 20 mmHg standingSBP drop ≥ 20 mmHg
Canadian Syncope Risk Score ≤ 0: safe dischargeCSRS ≤ 0 → < 1% risk
01 · Do12-lead ECG and orthostatic vitals for everyone
Every patient with syncope gets a careful history (ideally with a witness), examination, orthostatic blood pressure and heart rate (supine, then after 3 minutes standing) and a 12-lead ECG.
02 · RiskExertional or supine syncope: think cardiac
Red flags for cardiac syncope: onset during exertion or lying down, no prodrome or sudden palpitations, structural heart disease or heart failure, abnormal ECG, family history of sudden death, older age, injury.
03 · DoAdmit for a serious suspected cause
Admit for monitoring and evaluation when the initial assessment finds a serious possible cause — heart failure, structural heart disease, an abnormal ECG, family history of sudden death, suspected arrhythmia, or persistently abnormal vital signs.
01
What it is
Core ideaSyncope: brief loss of consciousness, spontaneous recovery must knowSyncope is a sudden, brief loss of consciousness and postural tone from transient global cerebral hypoperfusion, with spontaneous complete recovery; near-syncope has the same causes and gets the same evaluation.
02
Causes & risk factors
Why it happensThree types: reflex, orthostatic, cardiacSyncope is classified as reflex (neurally mediated: vasovagal, situational, carotid sinus), orthostatic hypotension, or cardiac (arrhythmia or structural obstruction); vasovagal syncope is the most common cause.
03
Presentation
What you'll seeVasovagal: trigger, prodrome, upright, slow recoveryVasovagal syncope follows a trigger (pain, fear, sight of blood, prolonged standing) while upright, with prodromal nausea, sweating and lightheadedness; recovery is prompt but not immediate, often 5–15 minutes.
04
Diagnosis & monitoring
Work-upOrthostatic hypotension: SBP falls ≥ 20 mmHg standingOrthostatic measurements are diagnostic when standing SBP falls by 20 mmHg or more or drops below 90 mmHg; a heart rate rise of 30 or more without hypotension suggests postural tachycardia syndrome.
San Francisco rule: any CHESS finding is high-riskSan Francisco Syncope Rule (CHESS): congestive heart failure, hematocrit < 30%, abnormal ECG, shortness of breath, or systolic BP < 90 mmHg — any one marks high risk for a serious short-term outcome.
Canadian Syncope Risk Score ≤ 0: safe dischargeA Canadian Syncope Risk Score of 0 or less predicts under 1% serious 30-day outcomes, so these patients can be discharged from the ED; scores of 4 or more carry 19–51% risk.
05
Do right now
In this orderFirst moves
1
→Witnessed collapse: check a pulse first
2
→12-lead ECG and orthostatic vitals for everyone
3
→Exertional or supine syncope: think cardiac
4
Admit for a serious suspected cause
Why each step
Witnessed collapse: check a pulse firstIn witnessed syncope, check the pulse at once: no pulse means CPR; treat severe bradycardia with atropine or transcutaneous pacing and unstable tachyarrhythmia with synchronized cardioversion; lay the patient flat with legs raised.
12-lead ECG and orthostatic vitals for everyoneEvery patient with syncope gets a careful history (ideally with a witness), examination, orthostatic blood pressure and heart rate (supine, then after 3 minutes standing) and a 12-lead ECG.
Exertional or supine syncope: think cardiacRed flags for cardiac syncope: onset during exertion or lying down, no prodrome or sudden palpitations, structural heart disease or heart failure, abnormal ECG, family history of sudden death, older age, injury.
Admit for a serious suspected causeAdmit for monitoring and evaluation when the initial assessment finds a serious possible cause — heart failure, structural heart disease, an abnormal ECG, family history of sudden death, suspected arrhythmia, or persistently abnormal vital signs.
06
Management
OrdersEcho for murmur or exertional syncopeOrder echocardiography when structural heart disease is suspected — a murmur, exertional syncope, heart failure, or unexplained syncope after history, exam and ECG — to find aortic stenosis, HCM, tamponade or LV dysfunction.
Match rhythm monitoring to symptom frequencyChoose rhythm monitoring by how often episodes occur: Holter up to 72 hours, external loop recorder 4–6 weeks, implantable loop recorder up to 3 years for infrequent, recurrent unexplained syncope.
Carotid massage positive: pause over 3 secondsCarotid massage (age over 40, suspected carotid sinus syncope) is positive with asystole over 3 seconds or an SBP fall of ≥ 50 mmHg; avoid it with a carotid bruit or TIA/stroke within 3 months.
Vasovagal: education and counterpressure maneuversTreat vasovagal syncope with reassurance, trigger avoidance and physical counterpressure maneuvers (leg crossing, squatting, muscle tensing) at prodrome onset; beta-blockers and fludrocortisone show little benefit.
07
The rules
Know theseNo routine labs, head CT or EEGRoutine laboratory panels, head CT, EEG and carotid ultrasound have low yield and are ordered only when the history or exam points to them; women of childbearing age get a pregnancy test.
08
Vasovagal or cardiac syncope?
Commonly confused| Trigger | Pain, fear, sight of blood, prolonged standing |
|---|---|
| Position | Upright |
| Warning | Nausea, sweating, lightheadedness |
| Recovery | Prompt but not immediate (5–15 minutes) |
| Disposition | Reassure; discharge if low risk |
09
Commonly confused
Tell apartSeizure: prolonged jerking, tongue bite, postictal confusionConvulsions lasting more than a few seconds, tongue biting, incontinence and postictal confusion point to seizure; a few brief myoclonic jerks can occur with true syncope.
10
Teach & follow up
Patient educationNo driving until the cause is foundIf a benign cause is not clear, prohibit driving and operating machinery until the cause is identified and treated — the next episode of unrecognized cardiac syncope may be fatal.
11
More detail
ReferenceShow 9 reference facts
Orthostatic syncope is managed by stopping or reducing offending drugs, increasing fluid and salt, slow position changes, head-of-bed elevation and compression; midodrine or fludrocortisone if needed.
A harsh late-peaking basal murmur radiating to the carotids suggests aortic stenosis; a systolic murmur louder with Valsalva and softer with squatting suggests hypertrophic cardiomyopathy.
Drugs that cause syncope: AV-nodal blockers and amiodarone (bradycardia), QT-prolonging drugs (torsades), and antihypertensives, diuretics, nitrates, tricyclics and antipsychotics (orthostatic hypotension).
In older adults syncope is often multifactorial, and postural hypotension from stiff arteries, inactivity and medications is the most common cause.
Arrhythmias cause syncope when the rate is too fast to fill the ventricles (about 150–180/min or more) or too slow to sustain output (about 30–35/min or less).
Hypoxemia during or right after syncope suggests pulmonary embolism and calls for CT pulmonary angiography; troponin and serial ECGs are added when MI is suspected.
Syncope risk scores may be reasonable adjuncts (ACC/AHA/HRS class IIb), but clinician judgment performs at least as well; no score replaces a careful history, exam and ECG.
Permanent dual-chamber pacing reduces recurrence in severe asystolic reflex syncope; paroxetine is reserved for patients with coexisting psychiatric disease.
Syncope that begins and ends abruptly, with quick recovery, is typical of a cardiac cause, most commonly an arrhythmia; vasovagal syncope has a prodrome and slower recovery.
Faints with a warning while standing are usually vasovagal; collapse without warning, on exertion or lying down is cardiac until proven otherwise.
Sources · Merck Manual Professional — Syncope · Runser LA et al. Syncope: Evaluation and Differential Diagnosis. Am Fam Physician 2017;95(5):303–312 · Canadian Syncope Risk Score: A Validated Risk Stratification Tool. Am Fam Physician 2021;103(6):375–376 · emDocs — Syncope: ED Updates from the 2017 AHA/ACC/HRS Clinical Policy · Shen WK et al. 2017 ACC/AHA/HRS Guideline for the Evaluation and Management of Patients With Syncope. J Am Coll Cardiol 2017;70(5):e39–e110 · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).