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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
Key points
- Three main categories: reflex/vasovagal (most common, ~60%), orthostatic (~15%), cardiac (~15%)
- Cardiac syncope is the most dangerous — suspect if: exertional, associated with palpitations, abnormal ECG, structural heart disease, family history of SCD, older patient without prodrome
- Initial workup for ALL syncope: detailed history, orthostatic vitals, 12-lead ECG. Echocardiogram if cardiac cause suspected
- Red flags for admission: abnormal ECG, structural heart disease, exertional syncope, syncope causing significant injury, family history of SCD, recurrent without explanation
- Vasovagal: reassurance + counterpressure maneuvers (leg crossing, squatting). Tilt-table for recurrent unexplained episodes
Overview
Syncope is a transient loss of consciousness due to global cerebral hypoperfusion, characterized by rapid onset, short duration, and spontaneous complete recovery. It must be distinguished from seizure, hypoglycemia, and other non-syncopal causes of transient LOC. The three main categories are: reflex (vasovagal, situational, carotid sinus hypersensitivity), orthostatic hypotension (volume depletion, autonomic failure, medications), and cardiac (arrhythmia or structural). Cardiac syncope carries the highest mortality risk and must be identified early.
Clinical Features
Symptoms
Vasovagal: prodrome of warmth, nausea, diaphoresis, tunnel vision, triggered by prolonged standing, pain, emotional stress, crowded/warm environments. Rapid recovery
Orthostatic: occurs on standing, associated with volume depletion or autonomic dysfunction (diabetes, Parkinson, medications)
Cardiac (arrhythmic): sudden onset without prodrome, may occur supine/exertional, associated palpitations. Brief loss of consciousness
Cardiac (structural): exertional syncope — AS, HCM, PE, pulmonary HTN, cardiac tamponade
Signs
Orthostatic hypotension: SBP drop >=20 mmHg or DBP >=10 mmHg within 3 minutes of standing
Murmur of AS, HCM, or other structural disease on cardiac exam
Abnormal neurological exam suggests an alternative diagnosis (stroke, seizure)
Tongue bite (lateral = seizure, tip = syncope with fall)
Investigations
First-line
Detailed historyMost important diagnostic tool: triggers, prodrome, witnesses (movements during LOC, duration, recovery), position, exertional, family history of SCD, medications, cardiac history
Orthostatic vitalsBP and HR lying, sitting, standing at 1 and 3 minutes
12-lead ECGLook for: AV block, bundle branch block, long QT, short QT, Brugada pattern, WPW, Q waves (prior MI), epsilon waves (ARVC), LVH (HCM/AS), AF. ECG is diagnostic in ~5% and suggestive in ~10%
Basic labsCBC (anemia), BMP (electrolytes, glucose), troponin if cardiac suspected
Second-line
EchocardiogramIf cardiac cause suspected: assess LVEF, valvular disease (AS, HCM), RVSP (pulmonary HTN), pericardial effusion
Continuous ECG monitoringTelemetry inpatient if high-risk; Holter or event monitor outpatient for recurrent unexplained syncope
Implantable loop recorderFor recurrent unexplained syncope after initial workup negative — continuous monitoring for up to 3 years
Specialist
Tilt-table testingFor recurrent syncope suspected vasovagal when diagnosis unclear from history alone. Patient tilted 60-70 degrees for 20-45 min; positive if reproduces symptoms with hypotension/bradycardia
EP studyIf arrhythmic cause suspected with non-diagnostic monitoring (structural heart disease + syncope)
Management
2017 ACC/AHA/HRS Syncope Guideline1
Vasovagal syncope
- Education and reassurance (excellent prognosis)
- Avoid triggers: prolonged standing, warm environments, dehydration
- Counterpressure maneuvers: leg crossing + tensing, squatting at prodrome onset
- Adequate hydration and salt intake (if not hypertensive)
- Midodrine (alpha-1 agonist): for recurrent refractory vasovagal — second-line
- Fludrocortisone: volume expansion — second-line
- Pacemaker: very rarely indicated, only for cardioinhibitory vasovagal with documented prolonged asystole (>6 sec) and recurrent severe episodes
2
Orthostatic syncope
- Treat underlying cause: volume repletion, review/reduce offending medications (diuretics, alpha-blockers, antihypertensives)
- Rise slowly from supine/seated, sleep with head of bed elevated
- Compression stockings, abdominal binders
- Midodrine or droxidopa (for neurogenic orthostatic hypotension)
3
Cardiac syncope
- Treat underlying cause: pacemaker for bradycardia/heart block, ICD for VT/VF, AVR for severe AS, septal reduction for obstructive HCM
- See individual condition pages for specific management
USMLE Step 2 CK Exam Tips
- 1Exertional syncope = cardiac until proven otherwise: think AS, HCM, arrhythmia, pulmonary HTN
- 2Young person + syncope after prolonged standing + prodrome of warmth/nausea = vasovagal (most common type)
- 3Syncope + family history of sudden death in young relative = HCM, Long QT, Brugada, ARVC — get ECG + echo + consider genetic testing
- 4Syncope without prodrome in an elderly patient = arrhythmic cause (especially if structural heart disease)
- 5ECG is the single most important test after history in syncope evaluation — look for Long QT, Brugada, WPW, AV block, prior MI
- 6Orthostatic hypotension: SBP drop >=20 or DBP >=10 within 3 min of standing. Always check in syncope patients
- 7Lateral tongue bite strongly suggests seizure, not syncope
practicetest your knowledge on SyncopeApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — Cardiovascular and beyond.
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