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Clinical Exercise Physiology > Myocardial Ischemia and Infarction > Flashcards

Myocardial Ischemia and Infarction Flashcards

1
Q

2 Coronary arteries

A
  • left (main) coronary artery
  • right coronary artery
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1
Q

The coronary arteries arise from the base of ?? and encircle the outside of the ??.

A
  • aorta
  • myocardium
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2
Q

The coronary arteries supply blood to myocardium during…

A

diastole

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3
Q

Myocardial Ischemia

A

transient decrease or absence of oxygenated blood to myocardial tissue that fails to meet the tissue’s need for oxygen

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4
Q

During myocardial ischemia, lack of oxygen can result in some delay of cells to ?? and ??, but it is completely ??.

A
  • depolarize
  • repolarize
  • reversible
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5
Q

Myocardial Injury

A

prolonged ischemia

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6
Q

Myocardial injury results in
1. ??
and is usually
2. ??

A
  1. loss of cells to conduct impulses and contract normally
  2. reversible upon re-oxygenation
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7
Q

Myocardial Infarction (MI)

A

irreversible injury

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8
Q

Myocardial Infarction is due to…

A

severe prolonged ischemia resulting in necrosis (death of tissue)

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9
Q

4 Coronary mechanisms of Ischemia/Injury/Infarction

A
  1. coronary thrombosis
  2. coronary artery spasm
  3. decreased coronary artery blood flow
  4. myocardial O2 demand (MVO2) > myocardial O2 (blood) supply
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10
Q

Coronary thrombosis

A

blood clot in an already narrowed artery following rupture of an atherosclerotic plaque
- most common cause of MI

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11
Q

Coronary Artery spasm

A

constriction of artery at site of atherosclerotic plaque

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12
Q

Decreased coronary blood flow
(other than thrombus or spasm)

A

from low CO related to arrhythmia, hypotension, or shock

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13
Q

Demand > blood supply

A

O2 supply is inadequate to match MVO2 demand

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14
Q

Myocardial Ischemia on ECG

A
  • T wave inversion
  • ST segment depression
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15
Q

Ischemia induced T wave inversion…

A
  • usually appear within seconds of onset
  • due to delay in repolarization
16
Q

Ischemia induced ST segment depression…

A
  • usually from severe subendocardial ischemia
  • leading to delayed repolarization in subendocardium
  • sometimes associated with inverted T waves but not always
17
Q

Ischemic depression of ST segment in mm below PQ segment (baseline).

A

0.08 msec (2 small boxes) after the J point

18
Q

3 key ST segment characteristics to determine:

A
  1. Magnitude: in mm (severity of ischemia)
  2. Distribution: # of leads
  3. Slope of ST depression is important
19
Q

Slope of ST depression meanings.

A
  • downsloping = severe ischemia
  • horizontal = moderate ischemia
  • ## upsloping = non-diagnostic ischemia
20
Q

An ST elevation indicates…

A

transmural ischemia (from endo to epicardium)

21
Q

An ST elevation results in…

A

high grade narrowing of coronary artery from thrombus via ruptured plaque or spasm

22
Q

If there is ST elevation, this indicates that the infarction is…

A

acute

23
Q

Phase 1:
A. within seconds: ??
B. 20-24 minutes: ??
C. 30 minutes: ??
D. By 1 hour: ??
E. By 2 hours: ??

A

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

24
Q

Phase 2:
A. by 3 hours: ??
B. by 6 hours: ??
C. by 24 hours: ??

A

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

25
Q

Phase 3:

A

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

26
Q

Phase 4:

A

By 2-8 weeks, inflammation continues, and necrotic tissue is replaced with fibrotic connective tissue by week 8

27
Q

Necrosis Diagnostic Q wave

A
  • greater than 1 box wide
    and
  • greater than 2 boxes deep

OR

  • 25% of height of depth of R wave
28
Q

The initial reightward ventricular activation may produce…

A

tiny insignificant q waves in leads where the QRS is usually upright

29
Q

Window theory

A

positive electrode sees through the electrical void of an infarct

30
Q

Sequence of depolarization overlying a LV lateral wall MI
(part 1-3 recorded by aVL)

A
  • 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
31
Q

Sequence of depolarization overlying a LV lateral wall MI
(part 4 recorded by aVL)

A

terminal R wave reflects depolarization of remaining viable tissue beyond the infarcted region

32
Q

Anterior Infarcts can be seen in leads…

A

V3 and V4
- as an ST elevation

33
Q

Septal infarcts can be seen in leads…

A

V1 and V2
- as an ST elevation

34
Q

Anteroseptal infarctions can be seen in leads…

A

V1, V2, V3, and V4
- as an ST elevation

35
Q

Lateral infarctions can be seen on leads…

A

V5 and V6
- ST elevation

36
Q

Inferior infarctions can be seen on leads…

A

I, II, and aVF
- ST elevation

37
Q

In acute posterior infarction, there is ?? in ??.

A
  • ST depression
  • V1 or V2

Clinical Exercise Physiology (9 decks)

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