EKG - Ischemia Flashcards
Coronary Artery Disease
Coronary Artery Disease (CAD) is the
development of atherosclerotic plaques in
the walls of the coronary arteries.
CAD leads to stenosis of these very
important arteries, which can result in
_____
decreased blood supply to the area of the
myocardium supplied by that artery.
____ is the single largest killer of men and
women in the United States
Coronary artery atherosclerosis
The normal ST segment should be in line with _____
the isoelectric line and is the
starting point of early ventricular repolarization.
ST Segment Elevation
○ Defined as elevation of 1 mm (1 small
box) or more above the isoelectric line.
○ Elevation may suggest infarction,
pericarditis, hypothermia, etc
ST Segment Depression
○ Defined as depression of 1 mm (1 small box) or more below the isoelectric line.
○ Depression may suggest reciprocal changes of infarction, acute ischemia, digoxin toxicity,
hypokalemia, etc
If the T wave is inverted, this may suggest
■ Ischemia
■ Infarction
■ Drug effects
A twelve-lead EKG recorded during an anginal, ischemic event may show
ST Segment Depression and/or T Wave Inversion.
ST Depression has several different appearances
Although the resting EKG may be normal, increased demands
of exercise may bring out evidence of ischemia and subclinical CAD with _____
Stress testing
Infarction on EKG
Infarction occurs when ischemia becomes so significant that myocardial cell death starts to occur due to lack of oxygen and nutrients
● In most infarctions, the EKG will initially reveal the diagnosis
● Some of the characteristic EKG changes during infarction include T Wave
changes, ST Elevation, reciprocal ST changes, and pathologic Q Waves.
Some of the characteristic EKG changes during infarction include
T Wave changes, ST Elevation, reciprocal ST changes, and pathologic Q Waves
The Evolution of EKG Changes During an AMI:
A- Normal EKG prior to the onset of arterial
blockage.
B- Hyperacute T Waves can occur early
during the MI. If only T Wave inversion is
seen, this only indicates ischemia and is
not diagnostic of acute MI.
C- ST Segment Elevation develops. This
signifies myocardial injury
D- ST Elevation starts to decrease.
E- Q Waves are present, ST Segment has returned to
normal, and T Waves are inverted.
F- T Waves may return to normal over months-years.
Normal vs Pathologic Q Waves:
○ Small Q Waves can be seen in the left lateral leads (I, AVL, V5, V6) and occasionally in the inferior leads (esp II and III) in perfectly normal hearts.
○ Pathologic Q Waves generally signify history of infarction and are wider/deeper.
■ Must be greater than 1 mm wide and at least ⅓ the height of the total QRS amplitude
STEMI
○ Full-thickness, transmural infarction of the wall.
○ Causes ST elevation in the acute stages.
○ Most result in the development of pathologic Q Waves after (which is why they are also referred
to as Q Wave Infarctions).
○ Will cause elevation of Cardiac Enzymes
Non-STEMI
○ Partial-thickness, subendocardial infarction.
○ Does not cause ST Segment elevation, but instead generally presents with persistent ST Depression and T Wave Inversion.
○ Most of the time, there is not enough injury to cause the development of
pathologic Q Waves (So also referred to as Non-Q Wave Infarctions).
○ More difficult to diagnose because not as apparent as ST elevations. Need to
rely more on H&P and Cardiac Enzymes
In order to diagnose an MI, EKG changes of infarction must be seen in
____ or more anatomically contiguous leads
two
Anatomically contiguous leads
■ Lateral: I, AVL, V5 and V6
■ Inferior: II, III, and AVF
■ Septal: V1 and V2
■ Anterior: V1, V2, V3, and V4
■ Posterior: V7, V8, and V9, or
reciprocal changes in V1-V3
■ Right Ventricle: V4R *
If ST changes in just V1 and V2, it is MI of the ____
interventricular septum
If the blockage is at the bifurcation of the Left Main, you may see changes
in ____ (anterolateral MI, which is a huge MI).
any of V1-V6
Anterior MIs may also show ____ in the precordials
Poor R Wave Progression
Limitations of the EKG in diagnosing an infarction
Any underlying cardiac condition that masks the possibility of ST segment changes or development of a pathologic Q Wave by distorting the ST segment and QRS complex will render EKG diagnosis of infarction pretty much impossible
■ Two such conditions exist: Wolff-Parkinson-White Syndrome and Left
Bundle Branch Block.
T/F : In the presence of WPW or LBBB, the diagnosis of MI
cannot be reliably made by EKG
T
