Early Repolarization vs. Acute Myocardial Infarction: ECG Differentiation

Definition and Epidemiology

Early repolarization is a benign normal ECG variant characterized by stable ST‑segment elevation without reciprocal changes, evolving Q waves, or elevated cardiac biomarkers, as described by the American College of Cardiology and the American Heart Association. [1][2]
The pattern is present in up to ~13 % of the general population and is especially common among young males and athletes (American Heart Association). 2

ST‑segment elevation above the isoelectric baseline occurs in the absence of chest pain and remains a chronic, stable finding (American Heart Association). 2
The elevation is frequently accompanied by terminal QRS notching or slurring (J‑point abnormalities) (American Heart Association). 2
The ECG pattern is stable over months to years and does not evolve into pathologic Q waves or T‑wave inversions (American College of Cardiology). 1
Early repolarization most often involves the inferior leads (II, III, aVF) and lateral/precordial leads (V4‑V6) (American Heart Association). 2

Acute MI produces reciprocal ST‑segment depression in leads opposite the injury vector, a finding absent in early repolarization (American College of Cardiology). [3][1]
Dynamic ECG evolution—progressive ST elevation followed by normalization—is typical of acute MI (American Heart Association). 2
T‑wave inversions that develop after the acute phase are characteristic of MI (American Heart Association). 5
Elevated cardiac biomarkers (troponin or CK‑MB above the 99th percentile) are required for the diagnosis of MI (American Heart Association). 5
Clinically, acute MI presents with prolonged chest pain (>20 min) unresponsive to nitroglycerin and often with autonomic symptoms (European Society of Cardiology). 6

Early repolarization is usually discovered incidentally in asymptomatic individuals, whereas acute MI is associated with acute chest pain and systemic symptoms (European Society of Cardiology). 6

Hyperkalemia can produce peaked T waves and modest ST elevation (American Heart Association). 2
Acute myocarditis may present with diffuse ST elevation and concurrent troponin rise (American College of Cardiology). 3
Takotsubo cardiomyopathy shows characteristic apical ballooning on echocardiography together with ST changes (American Heart Association). 7

Do not assume all ST elevation equals MI; early repolarization accounts for a substantial proportion of ST‑elevations in the community (American Heart Association). 2
Serial ECGs are essential: acute MI demonstrates dynamic changes, whereas early repolarization remains static over time (European Society of Cardiology; American Heart Association). [6][5]
When ST elevation is seen in V4‑V6, obtain posterior leads (V7‑V9) to exclude a posterolateral MI (American Heart Association). 7