EKGs. Flashcards
EKG
electrical recording of the heart.
polarization
cell is resting, potassium leaks out. inside is more negative than outside.
depolarization
cardiac cells lose internal negativity. if all works right, it causes contraction. occurs in a wave.
repolarization
relaxation. restoration if resting polarity. occurs in a wave.
pacemaker cells
generate electrical impulse. have automaticity. small cells located in the upper righty atrium. depolarize spontaneously at a rate of 60-100 beats per minute.
SA node
biggest clump of pacemaker cells. rate varies with autonomic nervous system.
vagal stimulation (parasympathetic)
slows heart rate.
electrical/conduction cells
carry the current rapidly and efficiently. long and thin cells. all cells of the heart have this property.
myocardial/contractile cells
do the work. contract only after stimulated.
conduction pathway
SA node. right and left atrium. AV node. bundle of His. bundle branches. purkinje fibers.
SA node fires at
60-100 beats per minute.
AV node fires at
40-60 beats per minute.
purkinje fibers fire at
20-40 beats per minute.
p wave
shows current moved from right atrium to left atrium. uniform. symmetrical. small.
electrical silence after p wave
bc of barrier in av node. slows down for 0.01 second to allow atria to fully empty into ventricle.
av node
electrical impulse between the atria and ventricles. cells in the floor of right atrium. vulnerable to blocks in conduction
bundle of His, bundle branches, purkinje fibers
ventricular depolarization. qrs complex.
bundle branch block
conduction delayed to the right or left bundle.
left bundle branch
3 fascicles: septal, anterior, posterior.
q wave
if the first deflection is negative.
r wave
first positive deflection.
r’ wave
second positive deflection, if its there.
s wave
first positive deflection following a negative deflection.
t wave
ventricular repolarization. ventricles regain internal negativity.
absolute refractory period
onset of the qrs until the peak of the t wave. heart muscle can’t respond to another stimulus.
relative refractory period
midpoint of the t wave until the end of the t wave. the heart muscle has not yet fully recovered and can be depolarized again if a wrong enough impulse is received.
increase the refractory period to
decrease extra beats.
measure the qt interval when giving drugs that increase refractory period
if the interval increases by more than half, stop med bc of risk of arrhythmia.
segment
straight line that connects two waves.
pr interval lasts
less than 0.20 seconds
represents time it takes the atria to depolarize.
qt interval
time it takes the ventricles to depolarize and repolarize.
qrs complex
between 0.10 and 0.12 seconds.
lead 1
left arm positive. right arm neg. angle 0.
lead 2
left leg positive. right arm negative. angle 60.
lead 3
left leg positive. left arm negative. angle 120.
avl
left arm (wrist) positive. angle -30.