Myocardial Ischemia

Question 1

1. Increasing levels of adenosine occurs in ischemia is indicative of what process?

Answer 1

aerobic metabolism slows with ischemia and ATP is degraded successively to ATP, AMP and then adenosine, loss of ATP also leads to increased creatine phosphate and slowing Na/K ATPase.

Question 2

1. How does Katp channel act in cellular protection from ischemia?

Answer 2

low ATP concentration can trigger Katp channel to shuttle K+ out of the cell causing hyperpolarization of the membrane

hyper polarization causes cell to loose contractile force but does result in self-preservation by inactivating many other channels

Question 3

3. Describe the progression of damage in the electrical and pump actions of the heart due to ischemia.

Answer 3

because there is ion channel dysfunction there is further dysfunction of sinus or AV notes leading to changes in conduction velocity (arrhythmias)

ion channel dysfunction also leads to (1) impaired relaxation and (2) impaired contraction

Question 4

2. How does reperfusion cause cellular injury?

Answer 4

increased O2 leads to radicals which reduce NO

abrupt rise in intracellular Ca+++ from damage to sarcolemmal membrane and SR due oxidative stress

rapid return to normal pH facilitates hypercontracture (Kapt channels close, removing local protection)

Question 5

4. How is myocardial tissue “stunned” and what does this mean for the tissue?

Answer 5

prolonged ischemia (20min) with restored blood flow can cause alterations in troponin response to Caa++ and reduce cellular function

cells can repair damage over the course of 7-14 and can restore their functionality

Question 6

What is the cause of “no reflow”?

Answer 6

microvascular injury means the structural components of the vessel have been damaged to such an extent that they can no longer perfuse the tissue

Question 7

Why might arrhythmia after reperfussion be a good thing regarding the myocardial tissue?

Answer 7

repercussion can causes electrolyte imbalance after a thrombolytic agent busts a clot, it is usually a signal that the blood flow has been restored to the tissue

Question 8

What is the effect of stuttering angina to protect the heart in MI?

Answer 8

short periods of ischemia may help to condition the heart before a major MI and limit the damage due to ischemia

Question 9

4. What is cardiac hibernation?

Answer 9

chronic partial occlusion can result in “hibernation” that reduce myocyte function but keep cells alive, this is different from stunning because is longer but is caused by ischemia not infarction

characteristically, it is muscle that would work better if it had better blood flow (still viable) and its function will increase if blood flow improves

Question 10

4. Contrast stunning and hibernation.

Answer 10

stunning is transient total occlusion

hibernation is constant partial flow

Question 11

4. List 4 factors that can lead to no re-flow.

Answer 11

vascular occlusion due to debris
vascular constriction in response to debris
destruction of ischemic tissues
tissue edema

Question 12

5. Name 4 ways to test for ischemia while at rest.

Answer 12

measure electrical impact with ECG (ST seg)
observe wall function with Echo
evaluate perfusion with nuclear imaging
evaluate anatomical structures with CT or angiogram

Question 13

5. Name 3 ways to test for ischemia caused by stress.

Answer 13

induce stress by (and measure response):
exercise (ECG +/- echo or nuclear)
vasodilator (nuclear medicine)
beta agonist (echo)

Question 14

5. Discuss 4 key changes of the heart that can be used in diagnosis of MI.

Answer 14

electrical changes (EKG)
anatomic changes in wall (Echo, MRI)
functional changes (Echo/ventriculogram)
perfusion changes (nuclear imaging)