A 62-year-old man with acute myocardial infarction undergoes primary PCI 3 hours after symptom onset. Histopathology of the infarcted myocardium at 24 hours shows coagulation necrosis with contraction band necrosis at the border zone and early neutrophilic infiltration. Which of the following is the most common morphological pattern of cell death in the necrotic core at this stage?

Explanation

## Morphological Pattern of Necrosis in Acute MI at 24 Hours ### Histopathology of MI: Temporal Evolution **Key Point:** Coagulation necrosis with preserved tissue architecture is the hallmark of acute myocardial infarction, distinguishing it from other forms of necrosis. ### Morphological Features of Coagulation Necrosis in MI | Feature | Coagulation Necrosis (MI) | Apoptosis | Liquefactive Necrosis | |---------|---------------------------|-----------|----------------------| | **Cell membrane** | Lost early | Preserved initially | Dissolved | | **Nuclear changes** | Pyknosis, karyorrhexis | Fragmentation into apoptotic bodies | Dissolution | | **Tissue architecture** | Preserved (ghost cells) | Minimal disruption | Destroyed; cavity formation | | **Inflammation** | Marked, early (neutrophils) | Minimal; macrophages only | Marked; abscess formation | | **Timing in MI** | 0–12 hours (acute phase) | 12–72 hours (reperfusion phase) | Not typical in MI | ### Histological Timeline in Acute MI ```mermaid flowchart TD A["Coronary occlusion<br/>0 hours"]:::outcome --> B["0-4 hours<br/>No light microscopy changes<br/>EM: mitochondrial swelling"]:::outcome B --> C["4-12 hours<br/>Coagulation necrosis visible<br/>Neutrophil infiltration begins"]:::action C --> D["12-24 hours<br/>Peak coagulation necrosis<br/>Contraction band necrosis at border<br/>Acute inflammation maximal"]:::action D --> E["24-72 hours<br/>Apoptosis in border zone<br/>Macrophage infiltration"]:::action E --> F[">3 days<br/>Fibroblast proliferation<br/>Granulation tissue"]:::outcome ``` ### Why Coagulation Necrosis at 24 Hours? 1. **Ischemic injury dominates** — Acute phase (0–12 hours) is characterized by ATP depletion and necrosis 2. **Contraction band necrosis** — Hypercontraction of myofibrils at the border zone due to calcium influx; pathognomonic for MI 3. **Neutrophilic infiltration** — Begins at 4–6 hours; maximal by 24 hours (acute inflammatory response to necrotic debris) 4. **Preserved ghost cells** — Outline of dead myocytes remains visible, distinguishing coagulation from liquefactive necrosis **High-Yield:** At 24 hours post-MI, the necrotic core shows **coagulation necrosis** while the border zone shows **contraction band necrosis**. Apoptosis becomes prominent only after 12 hours in the reperfusion zone. ### Contraction Band Necrosis: A Hallmark of MI **Clinical Pearl:** Contraction band necrosis (hypercontraction of myofibrils with wavy fibers) is virtually pathognomonic for myocardial necrosis and indicates that the tissue was viable at the time of injury. It is NOT seen in ante-mortem ischemia or sudden cardiac death without infarction. ### Why Other Options Are Incorrect - **Apoptosis** — Becomes significant only after 12 hours, particularly in the border zone during reperfusion. At 24 hours, apoptosis is secondary to the dominant coagulation necrosis. - **Liquefactive necrosis** — Characteristic of bacterial infection (abscess) or CNS infarction due to high lipid content and enzymatic digestion. NOT typical of MI, which preserves tissue architecture. - **Caseous necrosis** — Seen in tuberculosis with granulomatous inflammation. Not a feature of acute MI. **Mnemonic:** **COAGULATION** = **C**oronary occlusion → **O**xygen depletion → **A**TP loss → **G**host cells (preserved outline) → **U**ncontrolled **L**ysis → **A**cute **T**issue necrosis → **I**nflammatory **O**utpouring → **N**eutrophils → **D**ebris clearance.