Localizing the infarct by lead territory and naming the likely culprit artery
Interactive · Localize the STEMI
Pick a wall. Watch its leads light up, and see the artery most likely to blame.
The 12-lead
Select a wall above — the leads that see it will light up, and the likely culprit artery appears here.
Localization is a probability, not a promise — dominance varies and lateral/inferior overlap is common. Always confirm with the whole picture.
Once you've confirmed real elevation, the next question is where. The leads that light up tell you which wall is infarcting, and the wall tells you which artery is likely to blame. That matters because it changes what you anticipate — RV involvement, posterior extension, which complications to watch.
The territory map
Each lead looks at the heart from a fixed angle. Group them by wall:
| Territory | Leads | Likely culprit artery |
|---|---|---|
| Septal | V1–V2 | LAD |
| Anterior | V3–V4 | LAD |
| Anteroseptal | V1–V4 | LAD |
| Lateral | I, aVL, V5–V6 | LCx or diagonal |
| High lateral | I, aVL | LCx / first diagonal |
| Inferior | II, III, aVF | RCA (most), sometimes LCx |
| Extensive anterior | V1–V6, I, aVL | Proximal LAD / left main |
The three arteries in plain terms
- LAD (left anterior descending) — the front and the septum. "Widowmaker" when it's proximal, because a big LAD occlusion takes out a huge chunk of left ventricle. Think V1–V4, often spilling into the lateral leads.
- LCx (left circumflex) — the lateral wall, and in a lot of people the posterior wall. Circumflex MIs are the ones that hide, because the standard 12-lead barely looks at that real estate.
- RCA (right coronary artery) — the inferior wall in the roughly 85–90% of people who are "right dominant," plus the right ventricle and a lot of the conduction system (why inferior MIs bring bradycardia and AV blocks).
How to use it
Name the wall first from the leads, then predict the artery. It's a probability, not a promise — dominance varies, and lateral/inferior overlap is common. But the reflex — inferior means think RCA and check the right side; anterior means think LAD and big territory — is what turns a pattern into a plan before you ever reach the cath lab.
Key takeaways
- Leads name the wall; the wall predicts the artery.
- LAD = anterior/septal (V1–V4); LCx = lateral/posterior; RCA = inferior + RV in most people.
- Inferior MIs are usually RCA — anticipate bradycardia, blocks, and RV/posterior extension.
- Localization is a strong probability, not a guarantee — confirm with extra leads.
You just localized a STEMI. The course does this for every rhythm, block, and 12-lead you'll face.
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