ECG- Ischemia and Infarction Flashcards Preview

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Flashcards in ECG- Ischemia and Infarction Deck (19):
1

1. Explain the cellular changes that occur in ischemic myocytes during phase 4.

decreased O2 supply and pH
[H+] activated K+ opens and depletes local gradient
resting potential becomes less negative
Na+/K ATPase pumps slow, further depleting gradient

2

1. Explain the cellular changes that occur in ischemic myocytes during phase 0/1.

decrease in resting potential (potential becoming more positive) causes a decrease in Na+ channel availability and slower upstroke

because to the slower depolarization rate, overshoot is also decreased

3

1. Explain the cellular changes that occur in ischemic myocytes during phase 2/3

plateau is lower and shorter due to less L type Ca+++ channels active and K+ dominating

depolarization (3) is quicker and occurs earlier

4

What is systolic gradient?

the difference in AP that appears when healthy and ischemic cells co-exist

not an analogous diastolic gradient occurs because of less- negative resting membrane potential, but its effectively normalized by the ECG, making the ST effect more significant

5

What electrical consequence do you see based on a partially ischemic heart (healthy and ischemic tissue right next to each other)

because there is a voltage potential between the normal and ischemic tissue, there is a baseline shift

6

Which direction does the cardiac muscle cell depolarize and re-polarize?

depolarize endo --> epi
re-polarize epi --> endo (T wave in same direction as QRS wave

the peak of the wave represents the point of largest potential between the cells in the wall (endo v. epi)

7

3. ST elevation is characteristic of what types of ischemia?

epicardial ischemia (pericarditis commonly) or transmural ischemia

8

3. ST depression is characteristic of what type(s) of ischemia?

typical subendocardial ischemia

9

4. What leads give the myocardial distribution for left anterior descending artery?

V1-4 (lateral anterior wall, may wrap around inferior point) anterior infarction

10

4. What leads give the myocardial distribution for circumflex artery?

V3-6, I and aVL (wraps around posterior side of heart) lateral wall infarction

11

4. What leads give the myocardial distribution for posterior descending artery?

2, 3, aVF ( anterior, wrapping around to posterior side) inferior wall infarction

12

Unipolar leads use what calculated reference point?

Wilson Central Terminus

13

What is T wave inversion indicative of?

develops in leads with ST elevation or on leads near the border zone of injury; mechanistically caused by the AP of partially ischmic cells is shortened and depolarizes earlier than in normal myocardium; is not specific to myocardial infarction can be caused by some drugs, drinking a cold glass of water

14

What is a Q wave, and what is diagnostic of?

in infarcted tissue, depolarization no longer proceeds into the infarcted zone but precedes away from the infarct, producing a negative deflection of the Q wave on leads overlying the area of infarction

15

7. How long to changes in an EKG last after MI?

ST elevation usually diminishes within 3-7 days
T wave inversion resolves over a few weeks but can remain biphasic or inverted chronically
Q waves usually persist as a chronic EKG findings but may decrease in intensity

16

What are acute MI EKG findings (very early)

peaked T waves, ST elevation, T inversion begins

17

What could persistent ST elevation be consistent with (less common)?

aneurism of heart wall

18

A non-Q wave MI would have which clinical signs?

no Q-wave, but ST depression and T inversion
positive biomarkers
chest pain

19

Name 4 diagnostic criteria for pathologic Q waves

depth >1mm
duration >40ms
seen in 2 or more anatomically adjacent leads
associated with acute ischemic ST and T changes