Axis refers to the ________ of depolarization as it passes through the heart.
We can demonstrate the general direction of the movement of depolarization by using a ______.
Vectors can represent both _______ and _______ of depolarization.
direction and magnitude
Where in the heart does ventricular depolarization begin and where does it proceed to? (review from previous chapter)
it begins at the endocardial lining of the ventricles and proceeds through the thickness of the ventricular wall
If we add up all the small vectors of ventricular depolarization (considering both direction and magnitude), we have one large "______ ___ ______" that represents the general direction of ventricular depolarization.
"Mean QRS Vector"
Where does the Mean QRS Vector originate from?
the AV node
Depolarization is an advancing wave of _____ ions.
The "axis" of the heart is simply the Mean QRS Vector when located by degrees in the _______ plane.
frontal plane (the normal vector points downward and to the patient's left, that is, between 0 and +90 degrees)
If the heart is rotated toward the patient's right side, the Mean QRS Vector moves toward the patient's _______ side. (common in tall, slender people) In very obese people the diaphragm is pushed up (and also the heart), so the Mean QRS Vector may point directly to the patient's ______.
In a hypertrophied ventricle, is there an increase or decrease in depolarization?
(so, since there is more depolarization, the Mean QRS Vector deviates more toward the ventricle that is hypertrophied)
In myocardial infarction, the necrotic (dead) area of heart has an increase or decrease in depolarization?
decrease (it doesn't depolarize at all)
(so, the unopposed vectors from the other side of the heart draw the Mean QRS Vector away from the infarct)
Which lead is the best for determining Right Axis Deviation?
If the QRS is negative in lead I, what does this signify?
Right Axis Deviation
If the QRS in the AVF lead is positive, then which way does the vector point?
If the QRS in Lead I is positive and the QRS in AVF is positive, what does this mean?
(two thumbs way up!)
If the QRS in Lead I is positive and the QRS in AVF is negative, what does this mean?
Left Axis Deviation
If the QRS in Lead I is negative and the QRS in AVF is negative, what does this mean?
Extreme Right Axis Deviation
When depolarization moves in a direction perpendicular to the orientation of a lead, the deflection is minimal and is called "__________".
(an isoelectric QRS records equal magnitudes of upward and downward deflection)
To locate the position of the Vector (axis) more precisely (ie. in degrees) in the frontal plane, what are the two steps?
1st: locate the axis quadrant
2nd: note the limb lead in which the QRS is most isolelectric
Although the axis may "deviate" in the frontal plane, the vector is said to "______" in the horizontal plane.
The orientation of chest lead V2 makes it the most informative lead for the determination of what?
both anterior and posterior infarction
Axis ________ is in the frontal plane. Axis ________ is in the horizontal plane.
deviation = frontal plane
rotation = horizontal plane