Lec 17 Pathology of Myocardial Infarction

Question 1

(T/F) Myocardial Infarction occurs spontaneously.

Answer 1

It does not occur spontaneously: first develops in the subendocardium and progresses as a WAVE FRONT of necrosis from subendocardium to subepicardium over several hours.

Question 2

The chief factor in the transmural progression of an infarct.

Answer 2

The volume of arterial collateral flow

Question 3

(T/F) An infarcted myocardium leads to hypertrophy of the heart.

Answer 3

TRUE.

Old fibrosis replaces infarcted myocardium -> Less contractility -> Myocardial cells around fibrosis start to hypertrophy to accommodate loss of myocardial celIs

Question 4

The relationship between coronary collateral circulation and progression of infarct:

a. direct: more collaterals, faster progression of infarct
b. Inverse: more collaterals, lesser progression of infarct

Answer 4

b. inverse: more collaterals, lesser progression of infarct.

Question 5

Coronary artery most prone to thrombosis, leading to MI.

Answer 5

LEFT ANTERIOR DESCENDING ARTERY

CORONARY ARTERY THROMBOSIS CAUSING M.I

• LAD(Left anterior descending artery) approximately

50%

• RCA (right coronary artery)approximately 35%
• LCA(left coronary artery)approximately 15%
• Secondary Subepicardial branches approximately 1%
• Intramyocardial branches- Never

Question 6

Myocyte injury becomes irreversible after how many minutes of ischemia?

Answer 6

30-60 minutes

• Summary of gross and microscopic changes in MI

4-24 Hours – coagulation necrosis, edema;

3-7 days – peak;

1-3 weeks – there is already healing;

3-6 weeks – fibrosis

Question 7

Occurs when there is massive influx of Ca++ into myocytes leading to hypercontraction.

Answer 7

CONTRACTION BAND NECROSIS

• This can happen during reperfusion of ischemic myocardium (REPERFUSION INJURY) when tissue where there is low oxygen is suddenly bombarded with high oxygen.
• Typically hemorrhagic.
• Therefore, we have to be careful with reperfusion of ischemic myocardium.
• It would look like as if an MI happened again.

Question 8

Interventions done to limit infarct size

Answer 8

1. Restoration of arterial blood flow
2. Thrombolytic enzymes shrink thrombus by lysing clots
3. Percutaneous transluminal coronary angioplasty 2 vessels or less
4. Coronary artery bypass grafting (CABG) more than 2 occluded vessels use of saphenous vein to bypass blocked coronary arteries

Question 9

This happens when the free wall of the myocardium is ruptured leading to blood filling up the pericardial space and compression of the heart.

Answer 9

Cardiac Tamponade

Question 10

A complication of MI that occurs if there is a loss of at least 40% of left ventricular mass and if the LAD artery is blocked.

a. Arrythmia & Sudden Death
b. LV failure and cardiogenic shock
c. LV aneurysm
d. Mural thrombosis and embolism

Answer 10

b. LV failure and cardiogenic shock
- heart may not be able to pump more efficiently;

systolic and diastolic functions affected

• 44% of short-term deaths after Acute Myocardial

Infarction (AMI)

Question 11

A complication of MI that occurs especially when the SA node is affected.

a. Arrythmia & Sudden Death
b. LV failure and cardiogenic shock
c. LV aneurysm
d. Mural thrombosis and embolism

Answer 11

a. Arrythmia & Sudden Death
- occurs in 25% of MI cases
- paths of electrical conduction along the heart are blocked by ischemic / scar tissue

Question 12

True or false aneurysm: necrosis thins out the ventricular wall causing the myocardium to balloon out

Answer 12

TRUE ANEURYSM

False aneurysm, a hematoma blocks a ventricular wall rupture - LV aneurysms in MI are usually false aneurysms

Question 13

The most sensitive and also the reference biomarker for the detection of myocardial injury, risk stratification in ACS (acute coronary stenosis) and for the diagnosis of acute MI.

Answer 13

Cardiac Troponin (I or T) - Troponin I and T are parts of the troponin complex

I: binds to actin in thin myofilaments to hold the actin-tropomyosin complex in place.

T: binds to tropomyosin, interlocking them to form a troponin-tropomyosin complex.

• Cardiac Troponins therefore help regulate calcium-mediated contraction of cardiac and skeletal muscle.

Question 14

restoration of coronary flow (reperfusion) is usually done by:

Answer 14

Thrombolysis & Balloon angioplasty

• helps salvage myocardium and limit infarct size
• however, these interventions may lead to reperfusion injury