Myocardial Infarction

Question 1

Definition

Answer 1

irreversible necrosis of heart muscle due to prolonged ischemia

Question 2

How long prolonged ischemia for MI to happen?

Answer 2

greater than 20 minutes

Question 3

Why is thrombolytic therapy or angioplasty still worth doing b/w 20 minutes and 6 hours after the onset of ischemia?

Answer 3

MI occurs in wavefront starting in subendocardial region and not complete until 6 hours after it started

Question 4

Why doesn’t chronic ischemia automatically cause MI?

Answer 4

• -repeated episodes of ischemia too brief to cause infarction OR
• -inadequate perfusion that is low enough to injure but not low enough to kill myocytes

Question 5

What causes 90% of MIs?

Answer 5

coronary atherosclerosis

Question 6

What are some other causes of MIs?

Answer 6

• -coronary vasculitis
• -coronary emboli from endocarditis
• -vasospasm (esp. with cocaine)
• -hypercoagulable states (esp. w/ antiphospholipid syndrome and surgery)
• -blood hyperviscosity
• -congenital anomalies
• -ect.

Question 7

What does transmural infarction involve?

Answer 7

full thickening of heart wall

Question 8

What are transmural infarctions usually associated with?

Answer 8

occlusive thrombosis superimposed on atherosclerotic plaque that undergoes acute change (usually disruption of unstable vulnerable plaque by ulceration or rupture)

Question 9

What do subendocardial infarctions involve?

Answer 9

inner portion of heart wall

Question 10

Differences b/w transmural and subendocardial infartions

Answer 10

subendocardial infarcts are:

• -more likely to be patchy
• -more likely to have episodes of extension with additional infarction at periphery
• -becoming more common than transmurals