A 58-year-old man with a 10-year history of hypertension and dyslipidemia presents to the emergency department with acute chest pain radiating to the left arm. Electrocardiography shows ST elevation in leads II, III, and aVF. What is the most common site of myocardial infarction in acute coronary syndrome?

Explanation

## Most Common Site of Myocardial Infarction **Key Point:** The inferior wall of the left ventricle is the most common site of acute myocardial infarction, accounting for approximately 40–50% of all transmural MIs. ### Anatomical Basis The right coronary artery (RCA) supplies the inferior wall of the left ventricle in approximately 80% of the population (right-dominant circulation). Occlusion of the RCA results in inferior wall MI, which is the most frequent presentation. ### Frequency Distribution of MI Sites | Site | Frequency | Coronary Artery | ECG Leads | |------|-----------|-----------------|----------| | **Inferior wall** | **40–50%** | RCA (80%) or LCx (20%) | II, III, aVF | | Anterior wall | 30–40% | LAD | V1–V4 | | Anterolateral wall | 10–15% | LAD + LCx | V1–V4, I, aVL | | Posterior wall | 5–10% | RCA or LCx | V7–V9 | **High-Yield:** The ST elevation pattern in leads II, III, and aVF (inferior leads) is pathognomonic for inferior wall MI, confirming RCA or LCx occlusion. ### Clinical Pearl Inferior wall MIs often present with bradycardia and hypotension due to RV involvement and increased vagal tone. Right-sided ECG leads (V4R) should be obtained to assess RV infarction, which carries prognostic implications for fluid management and hemodynamic support. **Mnemonic:** **LAD-Anterior, RCA-Inferior, LCx-Lateral** — remember the three main coronary territories and their corresponding wall distributions. [cite:Robbins 10e Ch 12]