093014 EKG Flashcards
P wave represents
atrial depolarization (first right, then left, but both are combined into the P wave)
if you prolong AP duration, what happens on the EKG?
prolongation of QT interval (QT interval changes can be arrhythmia-genic)
in the heart the sequence of repolarization is opposite to that of
depolarization, b/c AP duration is shorter near the outer epicardium (the last cells to depolarize)
so you get a positive T wave
precordial leads
in transverse plane (V1-V6)
limb leads
front plane leads
bipolar leads are leads
I, II, III
aVL’s degree deflection
-30 degrees
lead II’s degree deflection
60 deg
if you have RBBB, what will happen on EKG?
prolongation of total time to depolarize the two ventricles (the left will depolarize first and then the right)
this prolongation widens out the QRS
also, get deflection of electrical activity to the right
septal depolarization is from
left to right
as lateral wall of LV is depolarized, why is depolarization directed leftward as opposed to rightward?
bc electrical forces of thick LV outweigh those of RV
electrical forces of thick LV-depolarization is directed leftward and posteriorly toward V6
interpreting EKG-what to look for?
check voltage calibration check heart rhythm HR measure intervals (PR, QRS, QT) calculate mean QRS axis evaluate P wave evaluate QRS (hypertrophy, bundle branch block, infarction) evaluate ST/T wave
in standard cases along vertical axis 1 mm represents?
0.1 mV
time in standard horizontal axis on EKG-with recording speed of 25 mm/sec, 1mm = ?
0.04 seconds
PR interval should be btwn
120-200 ms
normal sinus rhythm criteria
every P followed by QRS
upright P in I, II, III
PR interval btwn 120 and 200 ms
HR btwn 60-100 bpm
how to calculate HR from EKG
1500/ number of small boxes between two beats
or
count off 300-150-100-75-60-50
if rhythm is irregular, can count number of QRS during 6 seconds and multiply by 10
corrected QT interval
measured QT/square of RR interval (seconds)
you do this because QT can vary with heart rate
other thing you can do–QT interval should normally be less of half of RR
mean QRS axis is defined as
average of instantaneous lectrical ofrces generated during ventricular depolarization in the frontal plane
normal mean QRS axis is
-30 to 90 deg
how do you roughly estimate the QRS mean axis?
look at leads I and II- if net deflection is positive in both of these leads, the mean QRS axis is within normal range of -30 to +90 degrees.
how to use geometric method to find mean QRS axis
pick any two frontal leads
draw perpendiculars from them and where they intersect is the mean axis
how to use inspection method to find mean QRS axis
look for isoelectric frontal lead, then draw a perpendicular line to this lead. this perpendicular line is the mean QRS axis, but to determine which direction it’s pointing, you need to look at another lead to determine which direction
if you have R atrial enlargement what would you see on P wave in leads II and V1?
in lead II-taller P wave
in lead V1-taller right atrium wave
L ventricle hypertrophy-what would you see in lead V1?
deeper S wave
L ventricle hypertrophy-what would you see in lead V6?
bigger QRS
if you have L atrial enlargement what would you see on P wave in leads II and V1?
in lead II-a second left atrium peak
in lead V1-a deeper left atrium depression
if you have R ventricular hypertrophy, what would you see on EKG?
in V1: increased R-R is greater than S
in V6: deep S
with fascicular blocks, QRS interval is
reasonably normal, as opposed to bundle branch block
with left anterior fascicle block, what is the direction of activation?
initial inferior followed by dominant superior direction of activation
with left posterior fascicle block, what is direction of activation?
initial superior followed by dominant inferior direction of activation
in bundle branch block, why is activation of the blocked part slow?
because relies on activation from cell to cell rather than rapidly conducting HIs purkinje system
in left bundle branch block, why does the Q wave disappear in V6?
because you don’t have the normal left to right ventricular septum depolarization
criteria for RBBB
QRS complex
RsR’ (M shaped ) QRS complex in lead I
widened or “slurred” S wave in leads I and V6
when you have ST segment elevation, can you have reciprocal ST depression in some leads for the case of myocardial infarction?
yes
