Inflammation III - Myocardial Infarction

  • Hypoxia = no oxygen = no ATP
  • Na+/K+ ATPase fails, Ca2+ pump fails

>20 mins

  • Mild, short-lived damage does not always result in tissue death - reversible
  • No microscopic changes to myocardium

After 20 mins

  • Cell death - results in necrosis
  • Cells shrink and become red

24 hours

  • Cell contents leaked
  • Complement cascade initiated
  • Acute inflammation
  • Necrosis - mostly coagulative

24-72 hours

  • Total loss of nuclei and striations
  • Heavy neutrophilic infiltrate

3-7 days

  • Heart is weakest - most vulnerable to cardiac rupture
  • Neutrophils fade away and are replaced by macrophages - chronic inflammation

2-6 weeks - restitution

  • Macrophages fade away, replaced by fibroblasts
  • Fibroblasts lay down collagen - scarring (poor blood supply)
    • Scar tissue means heart can’t pump as well
    • Nerve bundles may also be damaged

6 weeks +

  • Can’t date MI if took place longer than 6 weeks ago - just scar tissue