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.
avr
right arm (wrist) positive. angle -150.
avf
left leg positive. angle 90.
v1
4th intercostal space to the right of sternum.
v2
4th intercostal space to the left of sternum.
v3
halfway between v2 and v4.
v4
5th intercostal space midclavicular line.
v5
halfway between v4 and v6. anterior axillary line.
v6
mid-axillary line. even w v4.
ekg changes w ischemia
will appear only the ischemic area.
lateral leads
1, avl, v5, v6.
inferior leads
2, 3, avf.
anterior leads
v2, v3, v4.
normal qrs axis
0-90 degrees.
qrs axis shifts right if
smoker or mi.
qrs axis shifts left if
left ventricular hypertrophy.
cor pulmonale
right axis deviation. lead 1 is negative. avf is positive.
myocardial infarction has four stages
acute hyperacute t waves.
t wave inversion - indicative of ischemia.
st segment elevation - injury to muscle.
q waves - dx of mi. after st segment returns to normal. must be 0.04 seconds or 1/3 the height of the qrs complex.
nstemi
non st segment elevation mi.
st segment elevation for 48 hours.
s/s mi: hurting, increased troponin, nausea, infarcting.
right coronary artery
right coronary and posterior descending.
left coronary artery
left circumflex, left anterior descending.
main branch of left anterior descending is
diagonal.
main branch of left circumflex is
obtuse marginal.
extra branch from left coronary artery
ramus.
acute coronary syndrome
any group of clinical symptoms compatible w acute myocardial ischemia.
increased potassium
makes p wave taller in all leads.
decreased potassium
st segment depression. flattened t wave. u wave.
to determine ventricular rate
divide the number of small boxes between two qrs complexes into 1500.
calcium effects
qt interval. decreased prolongs and could cause VTach or torsades de pointe. increased shortens.
hypothermia
sinus bradycardia. prolonged intervals. dysrhythmias. <30 centigrade.
lanoxin
normal asymmetric st segment depression. will be in all leads. inverted t wave. conduction blocks. tachycardia. bradycardia.
increase force of contraction by decreasing heart rate.
take a pulse. iv push only in emergencies.
could cause vasoconstriction = heart attack.
0.125-0.25 over 5 minutes.
sinus node and atrial arrhythmias originate
above the junctional tissue.
can’t treat ____ w meds
sinus tachycardia. must test cause of tachycardia.
normal sinus rhythm
origin is sa node. fires between 60-100 beats per minute. r-r interval of 3-5 big boxes.
sinus tachycardia
sa node origin but over 100 beats per minute.
sinus bradycardia
sa node origin but less than 60 beats per minute.
sinus arrhythmia
result of respiratory cycle influences on the sa node. rate faster during inspiration. slower during expiration.
sinoatrial block
failure of the sa impulse to exit the sa node. only a single missed beat. appears as a straight line. may evoke an impulse from an ectopic site.
sinus arrest
sa node ceases to function. will show a straight line as long as the event persists.
sinus arrest will lead to
sa node resuming pulsing at normal rhythm. an ectopic site becoming a pacemaker. or death.
atrial arrhythmias
ectopic site in the atria acts as a pacemaker.
premature atrial condition
irritable atrial ectopic focus may fire before sa node and act as pacemaker for one or more beats.
no compensatory pause.
characteristics of PAC
early p wave - caused by premature ectopic impulse.
abnormal p wave - bc different site of origin.
different pr interval - ectopic focus at dif distance than sa node or because av conduction time is altered.
normal qrs - bc av node conducts impulse normally.
atrial tachycardia
several pacs found in a group. usually at a rate of 150-200 beats per minute but commonly around 180 beats per minute.
p wave may be in the preceding t wave.
atrial tachycardia w block
several pacs but av node av node impulses. will have an excess of p waves.
atrial tachycardia w regular block
will have a steady ratio. 2:1, 3:1, 4:1.
atrial tachycardia w irregular block
will have 4:1, 3:1, and 2:1 all in one strip.
wandering atrial pacemaker
new pacemaker site wanders throughout atria. dif p waves result bc location and distance to the av node change. varying distances alter the pr interval. qrs is unchanged.
afib
ectopic focus in the atrium fires and an extremely rapid rate.
will have small, fibrillatory waves - f waves.
av node can’t conduct all impulses so there’s a totally irregular ventricular response.
absence of repitition and absence of p waves.
aflutter
will have sawtooth waveforms instead of p waves - F waves.
usually one ventricular response to every 4 F waves.
can be regular or irregular.
supraventricular tachycardia
when there are no identifiable p waves, the origin of the tachycardia is in doubt.
junctional arrhythmias
arise from the av node. occur when the sa impulse is blocked.
premature nodal contraction
av node triggers only an occasional beat. occurs when an impulse arises from the av node and is conducted through the usual pathway to the ventricles. activation may spread back over the atria - will have inverted p wave.
characteristics of pnc
pr interval is shorter than normal - distance is shorter than normal.
qrs is normal.
ectopic impulse from upper av node will have inverted p before qrs.
ectopic impulse from lower av node will have inverted p after qrs.
ectopic impulse from middle of av node may have hidden p wave in qrs.
nodal tachycardia
nodal rhythm w a rate of over 100 beats per minute. pnc w a rate of over 100 beats per minute.
