Acute and Chronic Myocardial Ischemia Flashcards
What defines myocardial ischemia?
When myocardial oxygen demands are greater than myocardial oxygen supply
What percent of oxygen is extracted by myocardium from the coronary artery blood? Why is it significant?
90%
Under stress the blood flow must increase since the myocardium is already taking the maximum amount of oxygen from the blood
What is the main control system of coronary blood flow?
Metabolic control (i.e. exercise, climbing stairs)
How many beats can the heart make it before it runs out of stored ATP? CP?
3-4
8-12
What occurs after the heart runs out of ATP?
Adenosine released and converted to inosine
Na/K pumps cease increased IC Na decrease IC K
Lactate production
What occurs due to Na/K pumps no longer working?
Loss of resting MP
What effect on an EKG does MI have?
ST segment changes
QRS widens
QT interval reduced
Why does the ventricular AP shorten in MI?
To preserve intracellular potassium
What K channels are activated in a MI?
IKatp
IkACH
What do IKatp and IkACH channels do?
Open shortly to decrease the loss of intracellular K and shortens the AP
What does acidosis cause?
Reduces L-type calcium entry and troponin Ca2+ sensitivity
What is hypokinesis?
Reduced contraction
What is akinesis?
Absence of contraction
What is dyskinesis?
Stretching of myocardium during contraction
What are three visible estimates of cardiac function?
LV wall thickness
Circumferential shortening
Ejection fraction
What is cardiac stunning?
Short lived loss of cardiac contractile function (hypokinesis)
What causes cardiac stunning?
Short term coronary artery insufficiency
What is cardiac hibernation?
Long lived but reversible loss of contractile function (hypokinesis)
What causes cardiac hibernation?
Long term coronary insufficiency
What are the four different forms of reperfusion injury to the heart?
Reperfusion arrhythmia
Myocardial stunning
Microvascular injury
Acceleration of myocardial necrosis
What are the oxygen derived free radicals seen with reperfusion?
Superoxide Hydrogen peroxide Hydroxyl radical Hypochlorite Singlet oxygen
What are three sources of free radicals?
Mitochondrial respiration/uncoupling
Neutrophils
Xanthine oxidase
What causes calcium overload?
Reduced SR uptake
NCX reversal
L-type reduced
Reduced sensitivity of contractile fibers to Ca (troponin C)
What happens to adenosine?
It is released from myocardium becoming a substrate for xanthine oxidase
What reduces the amount of free radicals?
Allopurinol and free radical scavengers
What are two variants of myocardial ischemia?
Subendocardial ischemia
Transmural ischemia
Is a subendocardial ischemia an NSTEMI or STEMI?
NSTEMI
ST depression
What does NSTEMI stand for?
Non ST Elevation Myocardial Ischemia
Is a transmural ischemia NSTEMI or a STEMI?
STEMI
What does STEMI stand for?
ST Segment Elevation Myocardial Infarction
