ECG- Ischemia and Infarction Flashcards
- 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
- 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
- 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)
- ST elevation is characteristic of what types of ischemia?
epicardial ischemia (pericarditis commonly) or transmural ischemia
- ST depression is characteristic of what type(s) of ischemia?
typical subendocardial ischemia
- What leads give the myocardial distribution for left anterior descending artery?
V1-4 (lateral anterior wall, may wrap around inferior point) anterior infarction
- What leads give the myocardial distribution for circumflex artery?
V3-6, I and aVL (wraps around posterior side of heart) lateral wall infarction
- 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
- 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
