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?

Question

Accepted Answer

D. Atherosclerotic plaque rupture with superimposed thrombosis. ## 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

Answer

A. Coronary artery vasospasm without atherosclerosis

Answer

B. Spontaneous coronary artery dissection

Answer

C. Coronary embolism from a cardiac source

Explanation

Most Common Cause of Acute Myocardial Infarction

Pathophysiology of Plaque Rupture

Comparison of Causes of Acute MI

Pathological Timeline

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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