In acute myocardial infarction, the first histologically detectable change on routine H&E staining typically appears at:
- A 12-24 hours: neutrophilic infiltrate
- B 3-7 days: granulation tissue and macrophages
- C 1-4 hours: wavy fibres and early coagulation necrosis ✓
- D 1-2 weeks: fibrosis and scar formation
Correct answer: C. 1-4 hours: wavy fibres and early coagulation necrosis
Explanation
The earliest H&E change in myocardial infarction appears at 1-4 hours as wavy fibres (lateral compression of myocytes by adjacent viable myocytes causing undulating contours) and early coagulation necrosis with nuclear pyknosis. These subtle changes reflect the onset of irreversible injury. Neutrophilic infiltration is maximal at 24-48 hours; macrophages and granulation tissue appear at days 3-7; and dense collagenous scar replaces the necrotic zone by weeks 3-8. This temporal sequence is critical for determining time-since-infarction at autopsy.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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