Flashcards in ECG- Ischemia and Infarction Deck (19):
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
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
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
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
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
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)
3. ST elevation is characteristic of what types of ischemia?
epicardial ischemia (pericarditis commonly) or transmural ischemia
3. ST depression is characteristic of what type(s) of ischemia?
typical subendocardial ischemia
4. What leads give the myocardial distribution for left anterior descending artery?
V1-4 (lateral anterior wall, may wrap around inferior point) anterior infarction
4. What leads give the myocardial distribution for circumflex artery?
V3-6, I and aVL (wraps around posterior side of heart) lateral wall infarction
4. What leads give the myocardial distribution for posterior descending artery?
2, 3, aVF ( anterior, wrapping around to posterior side) inferior wall infarction
Unipolar leads use what calculated reference point?
Wilson Central Terminus
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
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
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
What are acute MI EKG findings (very early)
peaked T waves, ST elevation, T inversion begins
What could persistent ST elevation be consistent with (less common)?
aneurism of heart wall
A non-Q wave MI would have which clinical signs?
no Q-wave, but ST depression and T inversion