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
Phase 2:
A. by 3 hours: ??
B. by 6 hours: ??
C. by 24 hours: ??
A. 2/3 of myocardial well is necrotic
B. most of the myocardial wall (90%) is necrotic and evolution of MI is nearly complete
C. progression of necrosis from endocardium to epicardium is complete
Phase 3:
By 24-72 hrs,
- no ischemic tissue remains as most tissue is necrotic or recovered; acute inflammation and edema sets in and infiltration of inflammatory cells in necrotic tissue
Phase 4:
By 2-8 weeks, inflammation continues, and necrotic tissue is replaced with fibrotic connective tissue by week 8
Necrosis Diagnostic Q wave
- greater than 1 box wide
and - greater than 2 boxes deep
OR
- 25% of height of depth of R wave
The initial reightward ventricular activation may produce…
tiny insignificant q waves in leads where the QRS is usually upright
Window theory
positive electrode sees through the electrical void of an infarct
Sequence of depolarization overlying a LV lateral wall MI
(part 1-3 recorded by aVL)
- pathological Q wave develop in leads overlying infarcted tissue
- necrotic tissue does not depolarize, so Q wave represents the depolarization of the tissue on the opposite side of the heart
Sequence of depolarization overlying a LV lateral wall MI
(part 4 recorded by aVL)
terminal R wave reflects depolarization of remaining viable tissue beyond the infarcted region
Anterior Infarcts can be seen in leads…
V3 and V4
- as an ST elevation
Septal infarcts can be seen in leads…
V1 and V2
- as an ST elevation
Anteroseptal infarctions can be seen in leads…
V1, V2, V3, and V4
- as an ST elevation
Lateral infarctions can be seen on leads…
V5 and V6
- ST elevation
Inferior infarctions can be seen on leads…
I, II, and aVF
- ST elevation
In acute posterior infarction, there is ?? in ??.
- ST depression
- V1 or V2
