Download EKG Lab Update

EKG Lab Update
In the interest of allowing more time for student questions and practice EKG recording and reading, this
page has been created and replaces pages 95-100 in the survival guide.
QRS Axis:
The QRS complex represents the depolarization of the ventricular myocardium. The mean QRS vector
normally points downward and to the patient’s left because this is the general direction of ventricular
depolarization.
If you would like to check if
your patient’s mean QRS is
downward and to the left,
then you will need to observe
the EKG from more than one
lead. Lead I and Lead AVF
can be used to check the
lower left quadrant quickly
(“Double thumbs up.”)
Notice how right axis deviation (R.A.D.) and left axis deviation (L.A.D.) would lead to different EKG
results. What are some reasons that a person’s mean QRS vector would move out of the normal
quadrant?
Several examples of abnormal rhythm strips are shown below. Note in the first example that the activity
of the ventricle started early; it started from a location other than the AV node, so the mean QRS axis is
expected to be abnormal.
We cannot make the usual inferences about R.A.D. or
L.A.D. when the ventricle’s depolarization starts at an
unusual location. You could look at the beats proceeding
or following the abnormal beat -- assuming these beats
resulted from normal AV node activity, of course.
Here are several additional examples.
Remember, a P-wave normally precedes each
QRS complex.
The long P-R interval of first-degree block
suggests slow conduction through the AV
node and/or AV Bundle (“Bundle of His.”) A
QRS follows each P-wave, but the QRS is
always tardy.
These examples of second-degree heart block
all have regular P-P intervals, but some QRS
complexes are missing. The “lost” QRS may
occur rarely (i.e., a skipped QRS), or it may
occur after every other P-wave, or it may
occur after every third P-wave.
Third-degree (“complete”) heart block
describes a condition in which the P wave is
regularly paced, and the QRS complex is
regularly paced, but the two are independent.
The atria and ventricles have independent
pacing mechanisms so the coordination
between atrium and ventricle is “completely”
lost.