Evolution of MI

Question 1

0-4 hrs: gross/light/complications

Answer 1

No gross findings
No light microscope findings
Complications: arrhythmia, HF, cardiogenic shock, death.

Question 2

4-12 hours:

Answer 2

Gross: occluded artery, infarct, dark mottling; pale with tetrazolium stain
Light: early coagulative necrosis, release of necrotic cell content into blood; edema, hemorrhage, wavy fibers
Complications: Arrhythmia, HF, cardiogenic shock, death.

Question 3

12-24 hours:

Answer 3

Gross: occluded artery, infarct, dark mottling; pale with tetrazolium stain
Light: neutrophil migration starts. Reperfusion injury may cause contraction bands (due to free radical damage)
Complications: Arrhythmia, HF, cardiogenic shock, death

Question 4

1-3 days:

Answer 4

Gross: hyperemia
Light: Extensive coagulative necrosis. Tissue surrounding infarct shows acute inflammation with neutrophils.
Complications: Fibrinous pericarditis

Question 5

3-14 days:

Answer 5

Gross: hyperemic border; central yellow-brown softening - maximally yellow and soft by 10 days
Light: Macrophages, then granulation tissue at margins
Complications: Free wall rupture –> tamponade; papillary muscle rupture –> mitral regurg; interventricular septal rupture due to macrophage-mediated structural degradation.
LV pseudoaneurysm (mural thrombus “plugs” hole in mycardium –> “time bomb”)

Question 6

2 weeks to several months

Answer 6

Gross: recanalized artery; Gray-white
Light: Contracted scar complete
Complications: Dressler syndrome, HF, arrhythmias, true ventricular aneurysm (outward bulge during contraction, “dyskinesia”)