About the 12-Lead EKG Simulator
A free interactive tool for visualizing how acute coronary artery occlusion changes the 12-lead electrocardiogram. Choose a coronary lesion site and see the predicted ST-segment changes lead-by-lead, watch ST-elevation myocardial infarction (STEMI) evolve through hyperacute, acute, subacute, and chronic phases, and explore high-yield patterns that don't always meet classic STEMI criteria.
STEMI localization by coronary territory
The 12-lead EKG localizes the culprit vessel before the cath lab activation. The simulator covers the major occlusion sites:
- Proximal LAD — anterior STEMI (V1–V4) with reciprocal change in the inferior leads. Wraparound LAD lesions extend ST elevation to V5–V6 and the inferior wall.
- Mid/distal LAD — anteroseptal or apical pattern with less reciprocal change.
- RCA (right-dominant circulation) — inferior STEMI (II, III, aVF) with reciprocal depression in I and aVL. Always check right-sided leads (V4R) for RV infarct, and posterior leads (V7–V9) for posterior involvement.
- Left circumflex — lateral or posterior pattern. The LCx is the classic "electrocardiographically silent" vessel; a posterior MI may appear only as ST depression in V1–V3.
- Left main — diffuse ST depression with ST elevation in aVR > V1, often with hemodynamic instability.
STEMI equivalents and special patterns
Not every occlusion shows ST elevation. The simulator includes:
- Wellens syndrome — biphasic (Type A) or deeply inverted (Type B) T-waves in V2–V3 in the pain-free state, signaling critical proximal LAD stenosis.
- De Winter T-waves — upsloping ST depression at the J-point with tall, symmetric T-waves in V1–V6, a STEMI-equivalent for proximal LAD occlusion.
- Posterior MI — ST depression in V1–V3 with prominent R-waves; obtain V7–V9 to confirm.
- RV infarction — ST elevation in V4R, often with inferior STEMI; preload-sensitive, avoid nitrates.
- Sgarbossa criteria — diagnosing acute MI in the setting of left bundle branch block (LBBB) or ventricular pacing using concordance and discordance rules; the modified Smith criteria add proportionality.
MI evolution over time
Coronary occlusion produces a characteristic time-course on the surface EKG: hyperacute T-waves within minutes, ST elevation within the first hour, Q-wave development over hours to days, T-wave inversion as the infarct matures, and eventual normalization or persistent Q-waves and T-wave changes in the chronic phase. The simulator lets you scrub through these phases for any coronary territory.
Who this tool is for
Built for cardiology fellows, internal medicine and emergency medicine residents, medical students preparing for boards, and any clinician reviewing high-yield ECG patterns. It is an educational visualization, not a diagnostic device — always correlate with clinical presentation, troponin, and imaging.