ECG I and II: Basic principles Flashcards
where does the first depolarization event occur?
high left septum
the depolarization of the entire conduction system occurs in what segment of the ECG?
PR interval
does the SA node depolarization inscribe a surface ECG wave?
no
what does the PR interval reflect?
time of impulse conduction from AV junction to ventricular myocardium
why is the T wave upright at the same time the QRS complex is upright?
opposite event traveling in the opposite direction
two negatives make a positive
what is reflected by the QRS complex?
summation of all depolarization forces throughout both ventricles
what is reflected by the T wave?
summation of all repolarization events in both ventricles
ST segment corresponds to what phase of the cardiac AP?
phase 2
what is the standard paper speed?
25mm / sec
small squares count how much time?
0.04 s
large squares count how much time?
0.20 s
5 large squares count how much time?
1 s
what is a normal HR?
60-100 bpm
how do you check regularity? (2 methods)
- R-R interval
2. same number of P waves as QRS complexes
what factors are checked to determine waves and complexes? (4 methods)
duration
amplitude
morphology
vector
what do the P waves record?
both atrial depolarizations
in which direction do the atria depolarize?
top right to lower left
what is the polarization of the P wave in avR (for normal sinus rhythm)?
negative
what is the normal duration of P waves?
less than 0.12 s
what is the typical voltage of P waves?
less than 25 mV
what is the best lead to look at P waves?
lead 2
the PR interval records events from what areas?
atrium through:
AVN
His
bundle branches
Purkinje fibers
what is the normal duration of the PR interval?
0.12 - 0.20 s
a PR interval over 0.20 s indicates what condition? is it pathologic?
first degree AV block
not necessarily pathologic; increases with age
