Acute and Chronic Myocardial Ischemia

Question 1

What defines myocardial ischemia?

Answer 1

When myocardial oxygen demands are greater than myocardial oxygen supply

Question 2

What percent of oxygen is extracted by myocardium from the coronary artery blood? Why is it significant?

Answer 2

90%
Under stress the blood flow must increase since the myocardium is already taking the maximum amount of oxygen from the blood

Question 3

What is the main control system of coronary blood flow?

Answer 3

Metabolic control (i.e. exercise, climbing stairs)

Question 4

How many beats can the heart make it before it runs out of stored ATP? CP?

Answer 4

3-4

8-12

Question 5

What occurs after the heart runs out of ATP?

Answer 5

Adenosine released and converted to inosine
Na/K pumps cease increased IC Na decrease IC K
Lactate production

Question 6

What occurs due to Na/K pumps no longer working?

Answer 6

Loss of resting MP

Question 7

What effect on an EKG does MI have?

Answer 7

ST segment changes
QRS widens
QT interval reduced

Question 8

Why does the ventricular AP shorten in MI?

Answer 8

To preserve intracellular potassium

Question 9

What K channels are activated in a MI?

Answer 9

IKatp

IkACH

Question 10

What do IKatp and IkACH channels do?

Answer 10

Open shortly to decrease the loss of intracellular K and shortens the AP

Question 11

What does acidosis cause?

Answer 11

Reduces L-type calcium entry and troponin Ca2+ sensitivity

Question 12

What is hypokinesis?

Answer 12

Reduced contraction

Question 13

What is akinesis?

Answer 13

Absence of contraction

Question 14

What is dyskinesis?

Answer 14

Stretching of myocardium during contraction

Question 15

What are three visible estimates of cardiac function?

Answer 15

LV wall thickness
Circumferential shortening
Ejection fraction

Question 16

What is cardiac stunning?

Answer 16

Short lived loss of cardiac contractile function (hypokinesis)

Question 17

What causes cardiac stunning?

Answer 17

Short term coronary artery insufficiency

Question 18

What is cardiac hibernation?

Answer 18

Long lived but reversible loss of contractile function (hypokinesis)

Question 19

What causes cardiac hibernation?

Answer 19

Long term coronary insufficiency

Question 20

What are the four different forms of reperfusion injury to the heart?

Answer 20

Reperfusion arrhythmia
Myocardial stunning
Microvascular injury
Acceleration of myocardial necrosis

Question 21

What are the oxygen derived free radicals seen with reperfusion?

Answer 21

Superoxide
Hydrogen peroxide
Hydroxyl radical
Hypochlorite
Singlet oxygen

Question 22

What are three sources of free radicals?

Answer 22

Mitochondrial respiration/uncoupling
Neutrophils
Xanthine oxidase

Question 23

What causes calcium overload?

Answer 23

Reduced SR uptake
NCX reversal
L-type reduced
Reduced sensitivity of contractile fibers to Ca (troponin C)

Question 24

What happens to adenosine?

Answer 24

It is released from myocardium becoming a substrate for xanthine oxidase

Question 25

What reduces the amount of free radicals?

Answer 25

Allopurinol and free radical scavengers

Question 26

What are two variants of myocardial ischemia?

Answer 26

Subendocardial ischemia

Transmural ischemia

Question 27

Is a subendocardial ischemia an NSTEMI or STEMI?

Answer 27

NSTEMI

ST depression

Question 28

What does NSTEMI stand for?

Answer 28

Non ST Elevation Myocardial Ischemia

Question 29

Is a transmural ischemia NSTEMI or a STEMI?

Answer 29

STEMI

Question 30

What does STEMI stand for?

Answer 30

ST Segment Elevation Myocardial Infarction