A 52-year-old woman with diabetes mellitus and hyperlipidemia is admitted with acute anterior wall STEMI. Coronary angiography is performed. What is the most common site of occlusion in acute anterior wall myocardial infarction?

Explanation

## Anterior Wall STEMI — LAD Dominance **Key Point:** Anterior wall STEMI (ST elevation in V1–V4, often extending to V5–V6 and/or I, aVL) is most commonly caused by occlusion of the **left anterior descending (LAD) artery**, particularly at the **proximal segment before the first diagonal branch**. ### Epidemiology Anterior STEMI accounts for approximately 40–50% of all acute MIs, and LAD occlusion is responsible for the vast majority of these cases, making it the single most common cause of acute MI overall. ### LAD Territory and Occlusion Sites | LAD Segment | Branches | Territory Supplied | Clinical Consequence | |---|---|---|---| | **Proximal (before D1)** | Septal, diagonal | **Anterior wall, septum, apex** | **Largest infarct; highest mortality** | | Mid | Diagonal branches | Anterior wall, lateral extension | Moderate infarct | | Distal | Diagonal, septal | Anterior wall, apex | Smaller infarct | **High-Yield:** Proximal LAD occlusion (before the first diagonal branch) causes the largest anterior wall infarction and carries the worst prognosis because it occludes the vessel before major collateral branches arise. ### ECG Localization in Anterior STEMI **Mnemonic: STEMI Leads by Artery** - **LAD:** V1, V2, V3, V4 (± V5, V6, I, aVL) - **RCA:** II, III, aVF - **LCx:** I, aVL, V5, V6 ### Why Proximal LAD? 1. **Vessel Dominance:** The LAD is the largest coronary artery and supplies the largest territory (anterior wall, septum, and apex). 2. **Collateral Supply:** Proximal occlusion (before D1) deprives the myocardium of collateral circulation from diagonal and septal branches, resulting in maximal myocardial damage. 3. **Clinical Severity:** Proximal LAD occlusion often leads to cardiogenic shock, left ventricular dysfunction, and mechanical complications (papillary muscle rupture, VSD). **Clinical Pearl:** Anterior STEMI with hemodynamic instability or cardiogenic shock should raise suspicion for proximal LAD occlusion with extensive myocardial involvement. **Warning:** Do not confuse proximal LAD occlusion (most common anterior STEMI) with left main occlusion (rare, <5%, causes diffuse ST elevation and profound shock). [cite:Harrison 21e Ch 297]