ECG VI: Myocardial ischemia and infarction Flashcards
what layer of the heart is most susceptible to ischemia?
subendocardial
what are the three main determinants of myocardial oxygen consumption?
HR
contracility
myocardial wall tension
what is the appearance of the ST segment in myocardial ischemia if blood flow is normal?
remains isoelectric
in what situation does the ST segment remain isoelectric during myocardial ischemia?
if blood flow is normal
how does the T wave change in myocardial (subendocardial) ischemia?
inverted T wave in relation to QRS
what is the best indicator for myocardial ischemia?
ST segment shift
how does the T wave change in myocardial (full thickness) ischemia?
hyperacute - tall and peaked
in which situation is ST elevation observed as related to ischemia?
transmural ischemia - coronary flow is lost due to occlusion
what % of patients have an RCA that supplies the right inferior wall?
90%
is it possible for the QRS complex to be affected by ischemia?
yes
what part of the ECG is most helpful during MI?
QRS complexes
what are the initial changes seen during MI? late changes?
initial - injury (ST elevation)
late - necrosis (Q waves)
what causes Q waves in MI?
myocardial activation in segments away from the affected area
pathologic Q waves are defined as being what duration?
greater than 0.03 s
Q waves are abnormal is they are seen in what leads?
V1-3
