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Myocardial Infarction (MI) - "What Kind of Case Is It?"
MI is a case of ischemic coagulative necrosis of the heart muscle. Here is a full breakdown:
Definition
MI (also called a "heart attack") is the necrosis (death) of cardiac muscle resulting from prolonged ischemia - an inadequate oxygen supply to myocardial tissue lasting long enough to cause irreversible cell death.
The 2018 universal definition (joint U.S./European Cardiology task forces) defines it as:
"The presence of acute myocardial injury detected by abnormal cardiac biomarkers in the setting of evidence of acute myocardial ischemia."
- Robbins & Kumar Basic Pathology, Robbins, Cotran & Kumar Pathologic Basis of Disease
What Type of Pathological Process?
| Category | MI is a case of... |
|---|---|
| Cell injury type | Ischemic coagulative necrosis |
| Mechanism | Prolonged oxygen deprivation to myocardium |
| Primary cause | Coronary artery atherothrombosis (plaque rupture + thrombus) |
| Part of | Ischemic Heart Disease (IHD) / Acute Coronary Syndrome (ACS) |
Pathogenesis (Step-by-Step)
- An atherosclerotic plaque is eroded or suddenly disrupted - by endothelial injury, intraplaque hemorrhage, or mechanical force
- Platelets adhere, aggregate, and release thromboxane A2, ADP, and serotonin, causing further aggregation and vasospasm
- Coagulation is activated by tissue factor exposure, growing the thrombus
- Within minutes, the thrombus completely occludes the coronary artery lumen
- Myocardium distal to the occlusion is deprived of oxygen → ischemic necrosis
Types of MI (ECG-Based Classification)
| Type | Description |
|---|---|
| STEMI (ST-Elevation MI) | Full-thickness (transmural) infarct; ST elevation on ECG; usually complete occlusion |
| NSTEMI (Non-ST-Elevation MI) | Subendocardial infarct; no ST elevation; partial occlusion or demand ischemia |
Universal Classification (Type 1-5)
| Type | Mechanism |
|---|---|
| Type 1 | Spontaneous - atherosclerotic plaque rupture/erosion with thrombosis |
| Type 2 | Supply-demand imbalance (e.g., tachycardia, hypotension, coronary spasm) without plaque rupture |
| Type 3 | Sudden cardiac death before biomarkers can be measured |
| Type 4a/4b | PCI-related / stent thrombosis |
| Type 5 | CABG-related |
MI in ~10% of Cases WITHOUT Atherothrombosis
- Coronary artery vasospasm (e.g., cocaine, ephedrine)
- Embolism - from left atrial mural thrombus (AF), valve vegetations, prosthetic material, or patent foramen ovale
- Small vessel disease - vasculitis, amyloid deposition, sickle cell disease
Key Facts
- ~800,000 MIs/year in the USA (nearly one every 40 seconds)
- 10% occur before age 40; 45% before age 65
- Men > women in reproductive years; gap narrows post-menopause
- IHD (of which MI is the most severe manifestation) is the most common cause of death in older adult women
In short: MI is a case of ischemic coagulative necrosis of the myocardium, most commonly caused by acute thrombotic occlusion of a coronary artery on top of an atherosclerotic plaque.
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