Myocardial Infarction

Question 1

What are the gross manifestations of MI w/in 0-4 hrs

Answer 1

None

Question 2

What are the LM findings of MI w/in 0-4 hrs?

Answer 2

None

Question 3

What complications of MI may arise w/ in first 0-4 hrs?

Answer 3

Arrythmia, HF, cardiogenic shock

Question 4

What are the gross manifestations of MI w/in 4-24hrs

Answer 4

Dark mottling, pale w/ tetrazolium stain.

Question 5

What are the light microscope findings of MI w/in 4-24 hrs?

Answer 5

Early coagulative necrosis (no nuclei)
Release of necrotic contents into blood: Edema, hemorrhage, wavy fibers
Neutrophils begin to appear

Question 6

What is reperfusion injury?

Answer 6

1) Reactive oxygen species

2) Huge Ca2+ influx in irreversibly damaged cells leads to hypercontraction of myofibrils

Question 7

What is the light microscope finding associated with reperfusion injury?

Answer 7

Contraction bands due to free radical damage and hypercontraction

Question 8

What are the gross manifestations of MI w/in 1-3 days?

Answer 8

Hyperemia - yellowish pallor due to WBC infiltration of myocardium

Question 9

What are the light microscope findings of MI w/in 1-3days?

Answer 9

Extensive coagulative necrosis.

Tissue surrounding infarct shows acute inflammation with neutrophils

Question 10

What complications may arise w/in 1-3 days following MI?

Answer 10

Post-infarction fibrinous pericarditis

Question 11

What are the gross manifestations of MI w/in 3-14 days?

Answer 11

Hyperemic border - central yellow-borwn softening, maximally yellow and soft by 10 days. Red border will emerge as granulation tissue appears.

Question 12

What are the light microscope findings of MI w/in 3-14days?

Answer 12

Macrophages, then granulation tissue at margins (plump fibroblasts, collagen, blood vessels).

Question 13

What complications may arise w/in 3-14 days following MI?

Answer 13

This is the weakest time of myocardium, as macs are at work.
- Free wall rupture can lead to cardiac tamponade
- Papillary muscle rupture and lead to MR
- Interventricular septal rupture can lead to shunt
Venticular pseudoaneursym formation - contained free wall rupture.

Question 14

What are the gross manifestations of MI w/in 2 weeks to several months?

Answer 14

Gray-white scar

Question 15

What are the light microscope findings of MI w/in 2 weeks to several months?

Answer 15

Contracted scar complete: fibrosis.

Question 16

What complications may arise w/in 2 weeks to several monthsdays following MI?

Answer 16

• Dressler syndrome: transmural infarct exposes pericardial antigens to immune system.
• Ventricular aneurysm (risk of mural thrombus)

Question 17

When is the heart at greatest risk of a subsequent structure rupture?

Answer 17

3-14 days due to macs.

Question 18

What does ventricular free wall rupture cause?

Answer 18

Cardiac tamponade

Question 19

What does papillary muscle rupture cause?

Answer 19

MR

Question 20

What does interventricular septum rupture cause

Answer 20

VSD –> shunt

Question 21

When does ventricular true aneurysm form? When is it most prominent?

Answer 21

2weeks-months afterwards. Outward bulge during contraction - dyskinesia.