A 58-year-old man with a 10-year history of hypertension and dyslipidemia presents with acute anterior wall myocardial infarction. Coronary angiography reveals a critical stenosis in the left anterior descending artery. Which of the following is the most common cause of acute myocardial infarction in this patient?

## Most Common Cause of Acute Myocardial Infarction **Key Point:** Atherosclerotic plaque rupture with superimposed thrombosis accounts for approximately 80–90% of acute myocardial infarctions, particularly in the setting of pre-existing coronary artery disease. ### Pathophysiology of Plaque Rupture 1. **Vulnerable plaque characteristics:** - Thin fibrous cap (< 65 μm) - Large lipid-rich necrotic core - Increased macrophage infiltration - Positive remodeling of the vessel 2. **Rupture mechanism:** - Mechanical stress on the fibrous cap - Inflammatory cell-mediated weakening - Exposure of tissue factor and collagen 3. **Thrombotic cascade:** - Platelet adhesion and aggregation - Thrombin generation - Fibrin deposition - Coronary occlusion ### Comparison of Causes of Acute MI | Cause | Frequency | Risk Factors | Clinical Features | |-------|-----------|--------------|-------------------| | Atherosclerotic plaque rupture + thrombosis | 80–90% | Hypertension, dyslipidemia, smoking, diabetes | Typical presentation, ST elevation or NSTEMI | | Coronary vasospasm (Prinzmetal's) | 5–10% | Smoking, cocaine use, young age | Chest pain at rest, transient ST elevation | | Spontaneous coronary artery dissection | 1–4% | Pregnancy, connective tissue disorders, female | Sudden onset, often young patients | | Coronary embolism | 1–5% | Atrial fibrillation, endocarditis, prosthetic valve | Embolic phenomenon, often no prior CAD | **High-Yield:** In a patient with established risk factors (hypertension, dyslipidemia) and angiographic evidence of stenosis, atherosclerotic plaque rupture with thrombosis is overwhelmingly the most likely mechanism. **Clinical Pearl:** The presence of risk factors like hypertension and dyslipidemia in this patient strongly supports chronic atherosclerotic disease with acute plaque rupture rather than vasospasm, dissection, or embolism. ### Pathological Timeline ```mermaid flowchart TD A[Chronic atherosclerotic plaque formation]:::outcome --> B[Plaque becomes vulnerable]:::outcome B --> C{Triggering event?}:::decision C -->|Plaque rupture| D[Tissue factor exposure]:::action D --> E[Platelet aggregation]:::action E --> F[Thrombin generation]:::action F --> G[Fibrin deposition]:::action G --> H[Coronary occlusion]:::urgent H --> I[Myocardial infarction]:::outcome ``` **Mnemonic:** **RUPTURE** = Rupture of plaque → Underlying tissue exposure → Platelet activation → Thrombin generation → Ulceration extends → Reocclusion → Embolization