⚠️ Must-Not-Miss Diagnoses
Ventricular tachycardia/fibrillation, complete heart block, STEMI, aortic stenosis, HCM, PE, aortic dissection, subarachnoid hemorrhage.
Differential Diagnosis by Key Features
| Clinical Feature | Think Of | Priority |
|---|---|---|
| Exertional syncope, family history of sudden death, young patient | Hypertrophic cardiomyopathy / structural | HIGH |
| Palpitations before syncope, rapid onset/offset | Arrhythmia | HIGH |
| Prodrome (nausea, diaphoresis, vision graying), prolonged standing, warm environment | Vasovagal | Low |
| Position change (lying → standing), antihypertensives, elderly | Orthostatic hypotension | Low-moderate |
| After coughing, micturition, defecation | Situational syncope | Low |
| Focal neuro deficit, headache before syncope | Neurologic cause (SAH, seizure) | Moderate |
Systematic Approach
History
Prodrome, circumstances, witnesses
The history is your most powerful diagnostic tool. Was there a prodrome (vasovagal) or no warning (arrhythmia)? What was the patient doing? What did witnesses observe? How quickly did they recover?
ECG
Obtain in every patient with syncope
ECG is mandatory. Look for: prolonged QT (Torsades risk), pre-excitation (WPW), Brugada pattern, heart block, ischemic changes, RV strain (PE).
Risk Stratify
ROSE or San Francisco Syncope Rule
High-risk features requiring admission: abnormal ECG, signs of heart failure, hematocrit <30, shortness of breath, SBP <90. Low-risk young patients with classic vasovagal story can often be discharged.
Orthostatics
Check in all patients
Measure BP lying and standing. Drop >20 mmHg systolic or >10 mmHg diastolic with symptoms = orthostatic hypotension. Review medications — antihypertensives and diuretics are common culprits.
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