## Coronary Anatomy and Inferior STEMI **Key Point:** The right coronary artery (RCA) is the dominant coronary vessel in approximately 80% of the population and is responsible for the blood supply to the inferior wall of the left ventricle. ### Inferior Wall Infarction — ECG Localization Inferior wall myocardial infarction is identified by ST-segment elevation in the **inferior leads**: II, III, and aVF. These leads directly face the inferior surface of the left ventricle. ### Coronary Artery Distribution | Coronary Artery | Territory Supplied | Infarction Pattern | |---|---|---| | **Right coronary artery (RCA)** | Inferior wall, RV (80% of cases) | Inferior STEMI (II, III, aVF) | | Left anterior descending (LAD) | Anterior wall, anteroseptal | Anterior STEMI (V1–V4) | | Left circumflex (LCx) | Lateral wall, posterolateral | Lateral STEMI (I, aVL, V5–V6) | | Left main | Left anterior descending + circumflex territory | Extensive anterior + lateral | **High-Yield:** In dominant RCA systems (80%), the RCA also supplies the AV node and SA node, making inferior STEMI prone to conduction disturbances (heart block, bradycardia). **Clinical Pearl:** Right ventricular involvement occurs in 30–50% of inferior STEMIs. Check leads V4R and V5R for RV infarction, which contraindicates nitrates and requires fluid resuscitation. ### Why RCA is Most Common 1. RCA is the dominant coronary in ~80% of individuals (right-dominant system) 2. RCA directly perfuses the inferior wall and AV nodal artery 3. Inferior STEMI is the second most common STEMI pattern after anterior (LAD), and nearly all inferior STEMIs are RCA occlusions **Mnemonic:** **RCA = Right wall = Inferior** (RCA supplies the right and inferior territories in a dominant system).
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