A patient dies 4 days after a large anterior STEMI. Autopsy shows a soft, gelatinous, yellow-tan zone of myocardium with scattered neutrophilic infiltrates and beginning macrophage infiltration. What is the key structural change that poses the greatest risk for mechanical complications at this time?

• A Early granulation tissue formation with angiogenesis but insufficient collagen deposition to withstand ventricular wall stress
• B Coagulative necrosis with maximal neutrophil infiltration and collagenolytic MMP activity causing myocardial softening, risking free-wall rupture, papillary muscle rupture, or VSD ✓
• C Complete fibrosis replacing necrotic myocardium with mature collagen scar providing structural integrity
• D Edema and early hyperemia with contraction band necrosis as the predominant histological pattern at 4 days

Explanation

The period of 3–7 days post-MI represents the phase of maximum myocardial softening and thus the highest risk for mechanical complications. At this stage, neutrophils have infiltrated and are being replaced by macrophages that phagocytose necrotic debris; critically, neutrophil-derived and macrophage-derived matrix metalloproteinases (MMPs) digest collagen and fibronectin in the extracellular matrix, maximally weakening the necrotic zone. Free-wall rupture (hemopericardium, tamponade), interventricular septal rupture (acquired VSD), and papillary muscle rupture (acute mitral regurgitation) all peak at 3–7 days. Granulation tissue with early angiogenesis begins after 7 days. Mature fibrous scar is complete by 6–8 weeks. Contraction band necrosis is seen at reperfusion or at early stages (1–3 days), not at 4 days as the dominant pattern.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.