How to recognize a STEMI on an ECG
Other platforms explain it with text and video. In VMS you practice it on the patient.
A STEMI means a coronary artery is likely blocked and heart muscle is dying. Finding it on the first ECG starts the fastest path to opening the artery.
Step by step
Get the ECG fast
Obtain a 12-lead ECG within 10 minutes of first contact for chest pain or anginal symptoms. [1]
Measure at the J point
Measure ST elevation where the QRS ends, compared with the baseline before the P wave. [2]
Use the size rules
STEMI needs new elevation in two neighboring leads: at least 1 mm in most leads, and larger in V2 and V3 (2 mm in men 40 and older, 2.5 mm in younger men, 1.5 mm in women). [2]
Find the territory
Group the leads to see which wall and artery are involved, as in the table below. [2]
Look for reciprocal changes
ST depression in the opposite leads supports a true STEMI. [2]
Do not miss hidden STEMIs
ST depression in V1 to V3 can be a posterior MI; check leads V7 to V9. In inferior MI, check right-sided lead V4R. [2]
Rule out mimics and act
Consider pericarditis, early repolarization, bundle branch block and LVH. If STEMI is likely, activate the cath lab without waiting for troponin. [1]
Common errors
- Waiting for troponin before activating the cath lab.
- Missing a posterior MI shown only as ST depression in V1 to V3.
- Calling diffuse pericarditis changes a STEMI.
Leads and territories [2]
| Leads | Heart wall | Usual artery |
|---|---|---|
| II, III, aVF | Inferior | Right coronary (sometimes circumflex) |
| V1 to V4 | Septal and anterior | Left anterior descending |
| I, aVL, V5, V6 | Lateral | Circumflex or diagonal branch |
| V7 to V9 (ST depression V1 to V3) | Posterior | Circumflex or right coronary |
Practice it in VMS
In VMS you do this on the patient, not on paper: every step goes on the checklist with a score, and in Teach mode Blocky tells you what comes next.
VMS cases that train this skill
Sources
Facts and steps follow AAMC Core Entrustable Professional Activities (Core EPAs); NCCPA PANCE Content Blueprint. VMS is not affiliated with these organizations. Updated: 2026-10-11.