ECG Flashcards
ECG definition?
A body surface recording of a change in electrical potential, which is a PROJECTION of the net potential changes occurring in the heart
ventricular depolarization - first things to contract?
interventricular septum and papillary muscles
on read out yo get a peak going up and one going down. what does this mean?
The depolarizations were paced from different areas - multple PVCs = compromise in circulation in those areas
vertical axis=
voltage
horiz axis=
time
10 mm is how many mvolts?
1.0mV
How many horiz lines will you pass on a EC chart in 1sec?
25mm per second= 25 lines (boxes)
How long to travel across 5 boxes? Dark line to dark line?
0.2 seconds since each 1mm box=.04seconds
PR interval shouldnt be longer than?
0.2 seconds
P-wave
- atrial depolarization
- Phase 0 of atrial muscle cells
range: 60msec to 110msec
P-R interval
- time for atrial depolarization and passage through the A-V node (to begining of QRS or ventricular depolarization)
- range: 120msec to 200msec
- onset of atrial depol to onset of ventricular depol
P-R segment
- passage of current through the A-V node
- base line!
QRS complex and components
- ventricular depolarization
- takes about 80 miliseconds (2 boxes) (30msec- 120msec)
- positive deflection = R wave of QRS
- negative deflection before R wave = Q-wave
- negative deflection after R-wave = S-wave
- Phase 0 of all ventricular muscle cells
S-T segment
- about at isoelectric line - 0 mV
- between depolarization and repolarization (between Phase 0 and phase 3 = refractory period –> the plateau PHASE 2)
T-wave
- repolarization - Phase 3 of all ventricular muscle cells
- length varies
- REPOL OF VENTRICLE
U-wave
- repolarization of purkinje or papillary muscles
- not really seeing it
isoelectric line
base- 0 milivolts
ATRIAL DEPOLARIZATION should be how long?
60-110msec
What happens to time of atrial depolarization if the left atrium is enlarged?
longer than 120msec
-usually due to stenosis and mitral regurg
QRS longer than #msec? ventricules should not take longer than how long to depolarize? what could be the problem?
- 120msec or 0.12seconds
- ectopic focus
- right or left bundlebranch block
S-T segment can indicate? (When the line is not flat at 0V)
- acute ischemia of the ehart (its fixable bc its still alive)
- shouldnt detect electrical activity at surface because during Phase 2 (ie STsegment) the voltage is at 0!)
- So problem injured or ischemic - the damaged area is at a different voltage that another part which will show up on the ECG
- ST-segment elevation from 0 = acute injury
- STsegment depression from 0 = ischemia without injury (need to open the vessel)
QT interval
- begining of QRS to end of T-wave (onset of vent depol to end of ventricular repolarization)
- varies with heartrate
- commonly changes with Rx drugs
what can cause U waves to get larger?
- electrochemical conditions of the heart
ex) hypocalcemia
If Pr interval is less than its min range - 120msec then this means/
-accessory pathway between atria and ventricules - bundle of kent
