Transcript Electrocardiographs ECG part2

Electrocardiographs
ECG
part2
Elements of the ECG:
P wave: Depolarization of both atria;•
Relationship between P and QRS helps distinguish various cardiac •
arrhythmias
Shape and duration of P may indicate atrial enlargement•
PR interval: from onset of P wave to onset of QRS•
Normal duration = 0.12-2.0 sec (120-200 ms) (3-4 horizontal boxes)•
Represents atria to ventricular conduction time (through His bundle)•
Prolonged PR interval may indicate a 1st degree heart block•
QRS complex: Ventricular depolarization•
Larger than P wave because of greater muscle mass of ventricles•
Normal duration = 0.08-0.12 seconds•
Its duration, amplitude, and morphology are useful in diagnosing cardiac •
arrhythmias, ventricular hypertrophy, MI, electrolyte derangement, etc.
Q wave greater than 1/3 the height of the R wave, greater than 0.04 sec are •
abnormal and may represent MI
ST segment:
Connects the QRS complex and T wave•
Duration of 0.08-0.12 sec (80-120 msec)•
T wave:
Represents repolarization or recovery of ventricles•
Interval from beginning of QRS to apex of T is referred to •
as the absolute refractory period
QT Interval
Measured from beginning of QRS to the end of the T •
wave
Normal QT is usually about 0.40 sec•
QT interval varies based on heart rate•
Standard Lead System
Lead I
Lead II
Lead III
Lead I:
LA- RA
Lead :
LL - RA
Lead III: LL - LA
V1-V6: Locations of
chest electrode:
Lead aVR
Lead aVL
Lead aVF
V1-V6
ECG Machines
It Consists of
* electronic part
1-Preamplifier
2-Power amplifier to move the galvanometer pen
3- 1 mv calibration source
4- Protecting circuits
* Stylus
1 mV
Lead
selector
Amplifier
Stylus
Gear Train
Motor
Galvanometer
Patient cables
• Most important part
• Most frequently at fault.
• There are several different cables:
Some constructed of two pieces: more expensive
but more economical in the long run
• One piece construction
• Most ECG cables are made of shielded wire
Standard cable color code
AN/MS Plug
Pins
A
Goes to
RA
Electrode Color
Code
White
B
LA
Black
C
LL
Red
D
C
Brown
E
RL
Green