electrical axis and chamber enlargement Flashcards
What is the direction of the normal QRS axis
- down and to the patients left
- between 0 degrees and +90 degrees
a good approximation of the mean QRS axis of the heart can be determined by looking at the QRS comples in what leads
- lead I
- aVF
if the predominant direction is positive in both of these leads, the axis is normal
Left axis deviation is a mean QRS axis between what degrees? Are lead I and aVF positive or negative?
0 degrees and - 90 degrees
- lead I: positive
- aVF: negative
Right axis deviation is a mean QRS axis between what degrees? Are lead I and aVF positive or negative?
- 90 and + 180
- aVF is positive
- lead I is negative
indeterminate (extreme) means axis is when lead I and aVF are positive or negative?
- lead I: negative
- aVF: negative
What does it mean for the axis if the QRS complex in one lead is isoelectric
- the axis is 90 degrees away (perpendicular) from the limb lead
- isoelectric: positive componenet = negative component
What determining mean QRS axis, which QRS should you pick
- look for the tallest QRS complex - the axis points in the direction of that lead
tall, thin individuals may have a heart in what direction? what does this do to the QRS axis?
- a more “vertical” heart
- shifts QRS axis toward + 90
obese or pregnant individuals may have a heart in what direction? what does this do to the QRS axis?
- a more “horizontal” heart
- shifts QRS axis more leftward
differentiate between hypertrophy and enlargement
- hypertrophy: thickening of wall of cardiac chamber
- usually due to increased work of heart against higher pressure (high BP, stenotic valve)
- enlargement -> dilation
- stretching of cardiac chamber from volume overload
hypertrophy and enlargement: which is more common in atria? in ventricles?
- atria tend to dilate
- ventricles -> hypertrophy
if assessing for atrial enlargement, which wave do you look at
P wave
if assessing for ventricular hypertrophy, which wave do you look at
QRS complex
normal amplitude and duration of P waves
- amplitude: 0.5 - 2.5 mm
- duration: 0.6-1.0 sex
list criteria for right atrial enlargement ? what leads are you looking at
- P wave > 2.5 mm tall
- if P is biphasic, the initial component is taller than the terminal component
- lead II and V1
List the criteria for left atrial enlargement
-
P wave duration > 0.10 sec, often with notching
- frontal plane (usu. lead II)
-
terminal portion of P wave in V1 is
- negative
- duration > or = 0.04 sec (one small block)
- depth > or = 1 mm (one small block)
why is the R wave in V1 normally small
- normal ventricular depolarization moves downward, to the left, and posterioly in the direction of the thicker left venticular muscle
- moves away from lead V1
List the criteria for right venticular hypertrophy
- Right axis deviation ( > +90)
- R wave > S wave in V1
- S wave > R wave in V6 (not required)
What happens to R wave progression from V1-V6 in RVH
- in normal R wave progression, R wave gets bigger from V1-V6 (pictured)
- in RVH, opposite occurs and V1 has the tallests R wave
