EM · ECG interpretation (approach)
The 12-lead ECG — the systematic emergency department interpretation approach
Also known as ECG interpretation · 12-lead ECG · ECG reading · Electrocardiogram
The systematic approach to the 12-lead ECG for the emergency medicine trainee — the rate, the rhythm, the axis, the intervals (PR 120 to 200 ms, QRS under 120 ms, a sex-specific rate-adjusted QT), the segments and waves (ST elevation with the gender-specific STEMI thresholds, ST depression, T-wave inversion, pathological Q), the chambers (atrial enlargement, ventricular hypertrophy with the Sokolow-Lyon and Cornell criteria), the blocks (AV block, bundle branch block), and a reproducible stepwise reading method. Includes the ECG-driven drug doses — adenosine 6 then 12 mg for SVT, atropine for bradycardia with pacing backup, treat wide-complex tachycardia as VT. ACEM-primary, globally tagged.
Checked against its sources on 5 Oct 2026
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Related topics
- Tachyarrhythmias in the emergency department
- Bradyarrhythmias and atrioventricular block in the emergency department
- Acute coronary syndromes (STEMI, NSTEMI and unstable angina)
- Syncope — the emergency department approach and risk stratification
- Electrolyte emergencies — potassium and sodium
- Cardiogenic shock in the emergency department
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Target exams
ACEMFRCEMABEMFRCPCCCFPEMEBEEM
Red flags
- A regular broad-complex tachycardia is ventricular tachycardia until proven otherwise — never give verapamil, which can collapse a failing ventricle
- In pre-excited atrial fibrillation (Wolff-Parkinson-White, an irregular broad-complex rhythm with a delta wave) atrioventricular-node blockers are contraindicated — they accelerate conduction down the accessory pathway to ventricular fibrillation
- Torsades de pointes is a polymorphic VT in the context of QT prolongation — give intravenous magnesium 1-2 g and stop the offending drug
- Mobitz II atrioventricular block, 2-to-1 block, and complete heart block need urgent cardiac pacing — do not assume a Wenckebach pattern
- A normal computer interpretation does not exclude occlusion myocardial infarction — read the ECG yourself, compare with the old one, and treat the patient
Meet the patient
A 58-year-old man presents with 45 minutes of heavy central chest tightness radiating to the jaw, diaphoresis, and nausea. He has a past history of hypertension and smokes 20 cigarettes a day. On arrival: BP 96/62, HR 52 (regular), SpO2 96 per cent on room air. The 12-lead ECG is performed within eight minutes and shows ST elevation of 2 mm in leads II, III, and aVF, with reciprocal ST depression in I and aVL — and the ST elevation in lead III is greater than in lead II.[12]
The question that decides his next hour is the question that decides every ECG in the ED: did you read it systematically, or did you jump to a pattern? The candidate who applies the seven-step sequence to every trace, names each compartment aloud, and then synthesises catches the occlusion equivalents the pattern-recogniser misses.[12][38]
References42ShowHide
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