Myocardial Ischemia and Infarction Flashcards
2 Coronary arteries
- left (main) coronary artery
- right coronary artery
The coronary arteries arise from the base of ?? and encircle the outside of the ??.
- aorta
- myocardium
The coronary arteries supply blood to myocardium during…
diastole
Myocardial Ischemia
transient decrease or absence of oxygenated blood to myocardial tissue that fails to meet the tissue’s need for oxygen
During myocardial ischemia, lack of oxygen can result in some delay of cells to ?? and ??, but it is completely ??.
- depolarize
- repolarize
- reversible
Myocardial Injury
prolonged ischemia
Myocardial injury results in
1. ??
and is usually
2. ??
- loss of cells to conduct impulses and contract normally
- reversible upon re-oxygenation
Myocardial Infarction (MI)
irreversible injury
Myocardial Infarction is due to…
severe prolonged ischemia resulting in necrosis (death of tissue)
4 Coronary mechanisms of Ischemia/Injury/Infarction
- coronary thrombosis
- coronary artery spasm
- decreased coronary artery blood flow
- myocardial O2 demand (MVO2) > myocardial O2 (blood) supply
Coronary thrombosis
blood clot in an already narrowed artery following rupture of an atherosclerotic plaque
- most common cause of MI
Coronary Artery spasm
constriction of artery at site of atherosclerotic plaque
Decreased coronary blood flow
(other than thrombus or spasm)
from low CO related to arrhythmia, hypotension, or shock
Demand > blood supply
O2 supply is inadequate to match MVO2 demand
Myocardial Ischemia on ECG
- T wave inversion
- ST segment depression
Ischemia induced T wave inversion…
- usually appear within seconds of onset
- due to delay in repolarization
Ischemia induced ST segment depression…
- usually from severe subendocardial ischemia
- leading to delayed repolarization in subendocardium
- sometimes associated with inverted T waves but not always
Ischemic depression of ST segment in mm below PQ segment (baseline).
0.08 msec (2 small boxes) after the J point
3 key ST segment characteristics to determine:
- Magnitude: in mm (severity of ischemia)
- Distribution: # of leads
- Slope of ST depression is important
Slope of ST depression meanings.
- downsloping = severe ischemia
- horizontal = moderate ischemia
- ## upsloping = non-diagnostic ischemia
An ST elevation indicates…
transmural ischemia (from endo to epicardium)
An ST elevation results in…
high grade narrowing of coronary artery from thrombus via ruptured plaque or spasm
If there is ST elevation, this indicates that the infarction is…
acute
Phase 1:
A. within seconds: ??
B. 20-24 minutes: ??
C. 30 minutes: ??
D. By 1 hour: ??
E. By 2 hours: ??
A. subendocardial ischemia
B. reversible myocardial injury occurs
C. necrosis of subendocardium as injury spreads toward epicardium
D. necrosis has spread through 1/3 of myocardium
E. necrosis has spread through 1/2 of myocardial wall from endocardium to epicardium
