A 60-year-old man dies 5 days after an acute myocardial infarction. Autopsy reveals a soft, yellowish area in the left ventricle with a thin, friable wall. Microscopically, abundant neutrophil infiltration was seen 2 days ago. What is the predominant cellular change seen at day 5 post-MI that creates the highest risk of ventricular free wall rupture?
- A Re-entry of coagulative necrosis with wavefront progression
- B Macrophage and granulation tissue ingrowth causing enzymatic dissolution of necrotic myocytes ✓
- C Calcification and fibrosis stiffening the necrotic wall
- D Haemorrhagic infarct expansion due to reperfusion injury
Explanation
The highest risk of mechanical complications (free wall rupture, papillary muscle rupture, VSD) in myocardial infarction is between days 3 and 7, coinciding with the phagocytic phase when macrophages infiltrate and enzymatically remove (via collagenases, metalloproteinases) the necrotic myocardium, producing a soft, maximally weakened zone. At day 5, macrophage-dominated removal of dead myocytes creates the 'yellow softening' phase before fibroblast proliferation and collagen deposition (beginning at 1–2 weeks) restore tensile strength. This interval represents the window for catastrophic wall rupture.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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