ECG Flashcards
what are the leads that should be placed for an ECG
right/left arm and leg
V1-6
where is V1
4th intercostal space to the right of the sternum
where is V2
fourth intercostal space at the left sternal border
where is V4
the midclavicular line at the 5th intercostal space
where is V3
midway between V4 and V2
where is V5
at the anterior axillary line in the 5th intercostal space
where is V6
at the midaxillary line at the 5th intercostal space
what forms ECG recordings
the electrical signals formed by action potentials in the heart
T/F a larger muscle will produce greater voltage and larger ECG waveform
true
scalar ECG
a recording of the potential differences between two points on the body surface
is an ECG an action potential?
elaborate
no
ECG reflects the cumulative effect of action potentials at skin level
what are the three main parts of an ECG wave
P wave
QRS complex
T wave
what electrical event does the P wave represent
atrial depolarization
what electrical event does the QRS complex represent
ventricular depolarization
what electrical event does the T wave represent
ventricular repolarization
why can’t you appreciate atrial repolarization on a normal ECG
because it is masked by the QRS
what part of an ECG would correspond with SA node firing
the isoelectric period prior to the P wave
at what point on an ECG would correspond with AV node firing
halfway through the P wave into the PR segment
what structures are depolarizing during the PR segment
AV node
Bundle of His
Bundle branches
Purkinje fibers
PR interval
the length between the begining of the P wave to the Q wave
PR segement
isoelectric portion of the ECG between the end of the P wave and the start of the QRS
what would a long PR segement indicate
slow AV conduction
ST segment
the isoelectric portion between the end of QRS and the start of the T wave
what two parts of the ECG should be isoelectric
PR segement and ST segment
what recordings are included on a 12 lead ECG
I, II, III
aVR, aVL, aVF
V1-6
what two limbs are used in lead I?
what is the direction of the force?
right and left arms
from right to left
what two limbs are used in lead II?
what is the direction of the wave
right arm and a leg
from the right arm down to the leg
what limbs are used in lead III?
what is the direction of the wave
left arm and lower limb
down and to the right
T/F the right arm is always a positive lead in ECG
false, it is always negative
what are the Dipolar leads in ECG?
why are they called that
Leads I-III
because there will always be two leads, one will be more negative to reflect the passing of an AP wave
what are the three augmented unipolar leads
aVL, aVR, aVF
what is the direction of aVR
from the heart toward the right arm
what is the direction of aVL
from the heart to the left arm
what is the direction of aVL
from the heart towards the legs
einthovens triangle
an imaginary triangle formed by the upper and lower limbs along with the pelvis used to measure the amplitude and direction of cardiac APs at the skin
what would be considered a left axis devation?
what would cause that
a heart vector that is from 0 to -90 degrees
left ventricular hypertropy or inferior MI
what would be considered right axis deviation?
what would cause this
heart axis shift to between 90 and 180 degrees
left bundle branch block, right ventricular hypertrophy
how can a cardiac AP be considred a wave
there is a wavefront of depolarized cells followed by hyperpolarizing cellls
what is the function of leads V1-6 on ECG
to observe the deoplarization wave in the frontal plane from a particular area of the heart
what is the standard paper speed of an ECG
25mm/sec
a standard paper speed, what are the x and y axes
x is time
y is voltage
on a standard ECG what are the units on the x axis? y axis?
x axis = .04seconds per division
y axis = .1mV per division
how should HR be calculated of ECG when the heart rate is constant
R-R distance
describe the process of calculating heart rate using R-R interval
measure the distance in mm between consecutive R waves
divide the paper length in 60s (1500mm) by the RR length
describe the process of calculating HR by RR interval
measure the interval of time between R waves
divide 60s by the RR time
how should HR be calculated if the HR varies
count the number of RR intervals in 10 seconds and multiply by 6
what is quick way to estimate HR on ECG if the rate is regular
1 space between R waves is 300bpm
2 = 150
3 = 100
4 = 75
5 = 60
what should a normal sinus rhythm look like on ECG
positive P waves in the leads I and II indicate rhythm from the SA node
what are three causes of arrhythmias
delayed after polarizations
conductions defects
circuit re-entry
two examples of delayed after polarization
ectopic beats
PVCs
two examples of conduction defects that would cause arrhythmias
heart block
bundle branch block
what happens during circuit re-entry that causes arrhythmia
conduction from the ventricle is looped around to cause an abnormal conduction and stimulation pattern
compensatory pause
what is the function
a prolonged isoelectric period following an ectopic beat and the resumption of sinus
allows the heart to reset
heart block/bundle branch block
failure of the AV node to conduct from the atria to the ventricles
what are two common causes of heart block
ischemic heart disease
valve fibrosis
what will an ECG look like with heart block
normally firing P waves from the SA node with missing QRS complexes
whatis ST segment depression/T wave inversion indicative of
signs of previous ischemia
what starts a ventricular fibrillation
R on T firing
R on T firing
ectopic APs that occur during the “vulnerable period” of the late T wave
what causes ventricular fibrillation to persist
re-entry of AP into the circuit, causing repeating circus pathways
