Vectors and ECG Flashcards
action potentials along the heart cause an electrical signal where that is recorded on ECG w/ leads
body surface
p wave
atria depolarization
PQ segment (PR)
conduction through AV node, but too small to yield signal (baseline);entire atria depolarized
QRS complex
ventricular depolarization
ST segment
entire ventricle depolarized and has surface voltage of zero (baseline)
T wave
repolarization of ventricles
electrical depolarization of atria aka
wave of depolarization
wave of depolarization is detected as - signal coming towards positive electrode on skin surface, but what is actually happening inside the heart
positive charge is taking over (Na influx) and pushing - charge out
depolarization stimulus moving toward a positive skin electrode causes an _________ wave to be recorded on ECG
upward wave (positive wave—-positive deflection)
seen in #1
3
isoelectric (biphasic deflection)
4
negative deflection
happens when signal moves away from positive electrode on surface of skin
negative deflection
what happens to the strength of signal when there is a bigger mass of tissue
makes signal larger
a wave of REPOLARIZATION traveling toward a positive electrode
negative deflection
a wave of REPOLARIZATION traveling away from positive electrode
positive deflection
standard limb leads
Lead I: 0
Lead II: 60 degrees
Lead III: 120 degrees
augmented limb leads
aVR= -150 degrees
aVL= -30 degrees
aVF= 90 degrees
normal axis is between what 2 degrees
+90 and -30 degrees
normal axis deviation
Right axis deviation
Left axis deviation
Extreme axis deviation
where is the mean vector
lead III big + deflection so points towards it
where is the mean vector
lead III major - deflection so points opposite from it
leads helpful in detecting Myocardial Infarction
chest leads (precordial leads)
chest leads are showing us what
how the heart is functioning taken at different angles
size of small box
0.04
size of big box
0.2
first negative deflection following P wave
Q wave
first positive deflection following P wave
R wave
negative deflection following R wave
S wave
voltage that goes positive after an S wave
R’
example of R’ (positive voltage after S wave)
RBBB (right bundle branch block)
what happens if the P-R interval (time from start of P to start of QRS complex) is longer than normal
would mean conduction through AV node is slow—-> 1st degree heart block
time to depolarize entire ventricle
QRS interval
happens if QRS interval is longer than normal
heart hypertrophy or failing ventricle
depolarization + repolarization of ventricle
Q-T interval
long Q-T syndrome is associated with what
increased risk of sudden death
what 2 things decrease Q-T interval (normal)
exercise and sympathetic input
why should PR and ST segments be isoelectric (baseline)?
b/c there is no charge difference (the atria and ventricles are completely depolarized)
how to calculate rate on ECG
count of method: R wave to next R wave (QRS to QRS)
1st QRS complex to end of first large box=300
2nd large box=150
3rd large box=100
4th=75
5th=60
6th=50
