ECG reference
STEMI mimics.
Six ECG patterns that look like a STEMI on the monitor. Learn them and stop the false alarms.
LBBB (Left Bundle Branch Block)
Wide QRS with discordant ST changes that mimic infarction. Use Sgarbossa criteria: concordant ST elevation ≥ 1 mm (5 pts), concordant depression V1–V3 (3 pts), discordant elevation ≥ 5 mm (2 pts). ≥ 3 pts = high specificity for MI.
LVH with strain
Deep S waves lateral leads, tall R waves V5–V6, with ST depression and T inversion laterally + ST elevation V1–V3. Voltage criteria: S in V1 + R in V5/V6 > 35 mm. Look for prior ECGs.
Benign Early Repolarization (BER)
Young healthy patients, notched J-point, concave ST elevation, prominent T waves. No reciprocal changes. Chronic and unchanged.
Pericarditis
Diffuse concave ST elevation, PR depression (Spodick's sign), no reciprocal changes (except aVR/V1). Sharp pleuritic pain, worse supine, better leaning forward.
Wellens' syndrome
Deeply inverted (Type A) or biphasic (Type B) T waves in V2–V3 during a pain-free window after chest pain. Not a STEMI — but predicts imminent LAD occlusion. Cath lab, not thrombolytics.
Hyperkalemia
Peaked T waves, widened QRS, loss of P waves. Can look like a huge STEMI. Check the potassium.
Field rule
When in doubt, transmit. Modern receiving hospitals would rather cancel a cath than miss one — a "false-positive STEMI alert" is far less harmful than a missed occlusion.
Frequently asked
- What are the most common STEMI mimics?
- LBBB, LVH with strain, benign early repolarization, pericarditis, and hyperkalemia. Wellens' pattern is a critical near-mimic — it's not a STEMI but predicts imminent LAD occlusion.
- How do you diagnose STEMI in the setting of LBBB?
- Use the Sgarbossa criteria: concordant ST elevation ≥ 1 mm (5 pts), concordant ST depression V1–V3 (3 pts), or discordant ST elevation ≥ 5 mm (2 pts). ≥ 3 points is highly specific.
- What defines Wellens' syndrome?
- Deeply inverted (Type A) or biphasic (Type B) T waves in V2–V3 during a pain-free interval after chest pain. Highly specific for critical LAD stenosis.
- How can you tell pericarditis from STEMI?
- Pericarditis: diffuse ST elevation across multiple territories, PR depression, no reciprocal changes, positional/pleuritic pain, possible friction rub.
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