## Inferior Wall STEMI — RCA Dominance **Key Point:** Inferior wall STEMI (ST elevation in leads II, III, aVF) is most commonly caused by occlusion of the **right coronary artery (RCA)**, which is the dominant coronary vessel in approximately 80% of the population. ### Anatomical Basis The RCA supplies the inferior wall of the left ventricle via its marginal and posterior descending branches. In a right-dominant system (the norm), the RCA also perfuses the sinoatrial node and atrioventricular node. ### ECG Localization of STEMI | Coronary Artery | ST Elevation Leads | Wall Affected | Frequency | |---|---|---|---| | **Right Coronary Artery** | **II, III, aVF** | **Inferior** | **~40–50%** | | Left Anterior Descending | V1–V4 (± V5, V6) | Anterior | ~40–50% | | Left Circumflex | I, aVL, V5–V6 | Lateral | ~10–15% | | Left Main | Diffuse ST elevation | Extensive anterior + lateral | <5% | **High-Yield:** Inferior STEMI is the second most common type of acute MI overall, and RCA occlusion accounts for the vast majority of these cases. ### Clinical Correlates of RCA Occlusion **Warning:** RCA occlusion may cause: - Bradycardia and heart block (due to AV nodal ischemia) - Right ventricular infarction (if RCA occlusion is proximal) - Hypotension (especially with RV involvement) **Clinical Pearl:** Always check the right-sided leads (V4R) in inferior STEMI to detect concurrent RV infarction, which alters fluid management (avoid diuretics; use IV fluids cautiously). ### Why RCA and Not LAD? Although LAD occlusion causes anterior STEMI (the most common overall type of STEMI), the **specific ECG pattern of leads II, III, aVF** is pathognomonic for inferior wall involvement, which is RCA territory in the dominant system. [cite:Harrison 21e Ch 297]
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