## Diagnosis: Inferior Wall STEMI ### ECG Interpretation **Key Point:** ST-segment elevation in the inferior leads (II, III, aVF) with reciprocal ST depression in the anterior leads (I, aVL) is pathognomonic for inferior wall myocardial infarction. **High-Yield:** The inferior wall of the left ventricle is supplied by the right coronary artery (RCA) in approximately 80% of the population. Occlusion of the RCA causes ST elevation in leads II, III, and aVF. ### Coronary Anatomy and Lead Correlation | Coronary Artery | Leads with ST Elevation | Reciprocal Changes | Wall Affected | |---|---|---|---| | Left anterior descending (LAD) | V1–V4, I, aVL | II, III, aVF | Anterior | | Right coronary artery (RCA) | II, III, aVF | I, aVL | Inferior | | Left circumflex (LCx) | V5, V6, I, aVL | II, III, aVF | Lateral | ### Clinical Correlation **Clinical Pearl:** Inferior wall MI may be complicated by right ventricular (RV) infarction (occurs in ~30% of inferior MI cases). Always check lead V4R for ST elevation to identify RV involvement, as these patients are preload-dependent and may deteriorate with nitrates or diuretics. **Warning:** Do not give nitrates or diuretics empirically in inferior MI without ruling out RV infarction first — hypotension may worsen. ### Why the Presentation Fits 1. **Acute chest pain** with diaphoresis = acute coronary syndrome 2. **Elevated troponin** = myocardial necrosis confirmed 3. **ST elevation in II, III, aVF** = inferior wall territory 4. **Reciprocal changes** = confirms acute transmural injury **Mnemonic:** **"Inferior = II, III, aVF"** — remember the Roman numeral II and the F in aVF both relate to the foot/inferior position on the body. [cite:Harrison 21e Ch 297] 
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