Heart

Question 1

0-4 hours

Answer 1

No. Visible change

Question 2

4-12 hours

Answer 2

Wavy fibers with narrow, elongated myocytes normal-appearing nuclei can be detected in infarcted myocardium

Question 3

12-24 hours

Answer 3

Myocyte hypereosinophilia with pyknotic (shrunken) nuclei

Question 4

1-3 days

Answer 4

Coagulation necrosis (loss of nuclei and striations)
- prominent neutrophilic infiltrate found at the border zone of infarcted myocardium

This acute inflammatory infiltrate becomes increasingly prominent over the next few days before receding around days 5-7.

Question 5

3-7 days

Answer 5

• disintegration of dead neutrophils and myofibers
• macrophage infiltration at border areas

Macrophage phagocytosis of infarcted myocardium begins at about 3 days postinfarction. The macrophages become laden with degenerating myoglobin pigment and hemosiderin (not foam cells, which are indicative of extensive lipid engulfment).

By day 10, the accumulated macrophages begin to be replaced by granulation tissue.

Question 6

7-10 days

Answer 6

• robust phagocytosis of dead cells by macrophages

- beginning formation of granulation tissue at margins

Question 7

10-14 days

Answer 7

Well-developed granulation tissue with neovascularization

Question 8

2 weeks to 2 months

Answer 8

Progressive collagen deposition and scar formation

decreased cellularity in the zone of infarcted myocardium

Fibrosis continues during weeks 2-8, resulting in a dense collagenous scar at about 2 months postinfarction.