Myocardial Infarction

Question 1

What is a myocardial infarction?

Answer 1

cardiac muscle cell necrosis from ischemia

Question 2

What are three causes of MI?

Answer 2

1) atherosclerosis
2) hemorrhage
3) vasospasm

of a coronary artery

Question 3

What is the pathophysiology of an MI?

Answer 3

• atherosclerosis occurs over time in a coronary artery
• a complicated lesion develops, occludes the vessel
• occlusion causes ischemia to tissue it supplies
• ischemia causes hypoxia
• cells switch to anaerobic metabolism
• if the ischemia isn’t temporary… metabolic acidosis
• this can cause arrhythmias and affect heart function
• if ischemia continues, cells die = infarction (and related loss of function)

Question 4

What factors affect the size of infarct in an MI?

Answer 4

1) affected vessel (how much tissue does it perfuse?)
2) extent of the occlusion (partial or full?)
3) duration
4) status of the heart (what is its metabolic demand at the time?)
5) heart rate, blood pressure, heart rhythm
6) existence of collateral vessels

Question 5

What are the two types of infarcts?

Answer 5

1) subendocardial
- inner 1/3-1/2 of ventricular wall affected
- caused by a distal occlusion (smaller vessel)

2) transmural
- entire ventricle wall affected
- caused by proximal occlusion in one artery

Question 6

What are the manifestations of MI?

Answer 6

• chest pain, can radiate to neck, shoulder, back, fingertips
• anxiety
• tachycardia
• nausea and vomiting
• fatigue

Question 7

Why do patients with severe pain have nausea?

Answer 7

theory = nausea centre in brain close to pain centre

Question 8

How is an MI diagnosed?

Answer 8

1) ECG (look for ST elevation or depression)
2) angiogram
3) serum markers (troponin I and T, myoglobin, CKmb)

Question 9

How is an MI treated?

Answer 9

drugs:

• thrombolytics to break up clot (careful it doesn’t get lodged in a smaller vessel)
• anti-arrhythmic
• anticoagulant (prevent further coagulation at thrombus)

oxygen for hypoxia
morphine for pain

post stabilization:

• IV drugs to reduce heart workload
• inotrope
• vasodilator

revascularization surgery

• angioplasty
• bypass

Question 10

What is an eluting stent?

Answer 10

stent put in that emits drugs to prevent platelet aggregation on the stent