Acute Myocardial Ischemia / Infarct (AMI)

General:

Gross: The appearance of the heart during or following AMI is dependent on extent and time since the injury. A commonly accepted progression of grossly apparent changes in the setting of an infarct is (with some degree of overlap and roughly defined timelines):

• 0-12 hours = No apparent changes.
• 12-24 hours = Pallor and blotchiness.
• 24-72 hours = Pale yellow, soft.
• 3-10 days = Yellow with hyperemic border.
• Weeks = Pale grey to white, firm, well demarcated.
• Long term = White scar.

Microscopic: The microscopic appearance of the myocardium following AMI is also heavily dependent on time since the injury. A commonly accepted progression of microscopic changes following an infarct is (with some degree of overlap and roughly defined timelines):

• 1-3 hours = Wavy myocardial fibers.
• 2-3 hours = Staining defect with tetrazolium or basic fuchsin dye.
• 4-12 hours = Early hypereosinophilia H and E, which fades over time. Coagulation necrosis with loss of cross striations, contraction bands, edema, hemorrhage, and early neutrophilic infiltrate.
• 18-24 hours = Continuing coagulation necrosis, pyknosis of nuclei, and marginal contraction bands.
• 24-72 hours = Total loss of nuclei and striations along with heavy neutrophilic infiltrate.
• 3-7 days = Macrophage and mononuclear infiltration begin, fibrovascular response begins. Few dead myofibers and lingering neutrophils.
• 10-21 days = Fibrovascular response with prominent granulation tissue.
• About 7 weeks to months = Replacement of granulation tissue with fibrosis.

Stains:

• Positive:
• Negative:
• Suggested, focused panel:

(Burke, Allen P, and Renu Virmani. “Pathophysiology of acute myocardial infarction.” The Medical clinics of North America 91, no. 4 (July 2007): 553-72; ix.)

Images:

Cases: