## Inferior Wall STEMI: Culprit Vessel and Site **Key Point:** The right coronary artery (RCA) is responsible for approximately 80% of inferior wall STEMIs, with the proximal RCA being the most common occlusion site. ### Anatomical Basis of Inferior STEMI Inferior wall STEMI (ST elevation in II, III, aVF) indicates occlusion of a vessel supplying the inferior wall of the left ventricle: | Vessel | Blood Supply | Frequency in Inferior STEMI | |---|---|---| | **Right coronary artery (RCA)** | **Inferior LV, RV, AV nodal artery, SA nodal artery** | **~80%** | | Left circumflex artery (LCx) | Inferior LV (in left-dominant systems) | ~15–20% | | Left anterior descending (LAD) | Rarely causes isolated inferior STEMI | <5% | **High-Yield:** RCA dominance (present in ~70% of the population) makes RCA occlusion the most common cause of inferior STEMI. In right-dominant systems, the RCA supplies the inferior wall, posterior descending artery (PDA), and posterolateral branches. ### Proximal vs. Distal RCA Occlusion | RCA Occlusion Site | Clinical Features | Complications | |---|---|---| | **Proximal RCA** | ST elevation II, III, aVF + RV involvement | **Bradycardia, AV block, cardiogenic shock** | | Distal RCA (after RV branches) | ST elevation II, III, aVF only | Minimal RV involvement | **Clinical Pearl:** Proximal RCA occlusion is the most common site because: 1. Atherosclerosis burden is highest in proximal segments 2. Plaque rupture occurs more frequently at branch points 3. Proximal occlusion causes the largest infarct territory **Mnemonic:** **RCA = Right Coronary Artery = Responsible for 80% of inferior STEMI** — In a right-dominant system (70% of people), RCA supplies the inferior wall. ### Diagnostic Clue ST elevation in leads II, III, aVF with reciprocal ST depression in I and aVL = **RCA occlusion** (inferior STEMI). If RV involvement is present (ST elevation in V4R), this confirms proximal RCA occlusion.
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