A 62-year-old man with poorly controlled hypertension and smoking history dies suddenly at home. Autopsy reveals acute transmural myocardial infarction with a thrombus occluding a major epicardial coronary artery. What is the most common coronary artery involved in fatal acute myocardial infarction?

Explanation

## Most Common Coronary Artery in Fatal MI **Key Point:** The left anterior descending (LAD) artery is the most common coronary artery involved in fatal acute myocardial infarction, despite the inferior wall being the most common site of non-fatal MI. ### Why LAD Occlusion Is Most Lethal **High-Yield:** The LAD supplies the largest territory of the left ventricle, including: - Anterior wall of the left ventricle - Anteroseptal region - Apex - Anterior two-thirds of the interventricular septum Occlusion of the LAD results in the largest area of myocardial necrosis, leading to severe left ventricular dysfunction and cardiogenic shock—the leading cause of in-hospital mortality in acute MI. ### Coronary Artery Involvement in MI: Frequency vs. Mortality | Coronary Artery | Frequency of All MI | Frequency in Fatal MI | Territory Supplied | Mortality Risk | |-----------------|--------------------|-----------------------|-------------------|----------------| | **LAD** | **35–40%** | **40–50%** | Largest (anterior + septum + apex) | **Highest** | | RCA | 40–50% | 20–30% | Inferior wall + RV | Moderate | | LCx | 15–20% | 15–20% | Lateral wall | Lower | | Left main | <5% | 10–15% | Entire left ventricle | Extremely high | **Clinical Pearl:** LAD occlusion proximal to the first diagonal branch results in anterior wall MI with septal involvement, causing extensive myocardial loss and conduction abnormalities (complete heart block, severe bradycardia). This explains why LAD occlusion, though not the most frequent MI overall, is the most common cause of fatal MI. **Mnemonic:** **LAD = Largest Area of Damage** — remember that the LAD supplies the largest myocardial territory, making its occlusion the most lethal. ### Pathophysiological Consequence Large anterior wall infarctions with septal involvement lead to: 1. Severe reduction in left ventricular ejection fraction (LVEF < 30%) 2. Cardiogenic shock 3. Mechanical complications (ventricular rupture, papillary muscle rupture) 4. Arrhythmias (ventricular fibrillation) **Warning:** Do not confuse "most common site of MI" (inferior wall) with "most common artery in fatal MI" (LAD). The LAD supplies a larger territory, so its occlusion is more catastrophic despite being less frequent overall. [cite:Robbins 10e Ch 12]