This document defines and describes several normal interval values in an electrocardiogram (ECG). It discusses the RR, PP, PR, QRS, and QT intervals which measure the timing of electrical signals in the atria and ventricles. It also describes ventricular activation time, normal ECG segments including the PR, RST, and TP segments, and provides information on what can be determined from an ECG reading such as the site of the pacemaker, heart rate, rhythm, and potential in diagnosing heart conditions.

1. Normal Interval Values
These are Normal Interval Values :
1- RR Interval.
It is distance b/w two successive R- waves.
RR interval indicate the ventricle depolarization
rhytmically.
2- PP Interval.
It is the distance b/w two successive P- waves.
Equal intervals in next successive stages
indicate rhytmical depolarization of atrium.

2. 3- PR Interval.
This is interval from the onset of P to that of QRS
complex.
The more accurate term of PR interval is PQ interval.
During it the cardiac impulse travels from S.A node to
ventricles.
Its duration ranges b/w 0.12 to 0.20 or even 0.22 sec.
Longer interval of PR show impaired conduction through
the bundle, e.g, During Rheumatic fever.
Variable PR interval in successive stages indicate A.V
dissociation which indicate that ventricles beat without
influence of S.A node.

3. 4- QRS interval.
It measure the total ventricular depolarization time.
It is measured from the onset of Q- wave to end of S-
wave.
Its varies from 0.08 to 0.1 sec.
5- QT interval.
It measure the ventricular total systolic time.
It is generally measured from the onset of Q- wave to the
end of T- wave.
Its duration is 0.36 sec.

4. VAT ( Ventricular Activation Time )
It is represented by the interval b/w the onset of
Q- wave and the peak of R- wave.
Normal Segments.
1- PR segment.
It extends from the end of P to the onset of QRS
complex.
It is shorter than P.

5. 2- RST segment.
It also calls as J- point.
This indicate myocardial damage or hypoxia.
3- TP segment.
It extends from the end of T to the beginning of
the next P- wave.
It represents the resting state (repolarization
state ) of the atria and ventricle.
Its duration varies inversely with heart rate.

6. Significances of E.C.G.
Site of pace maker is recorded.
Heart rate can be calculated.
Rhythm of heart can be recognized.
Voltage produced due to potential change in
heart can be calculated.
Help in diagnosing of heart disease.
If Q- wave is not present causes of heart attack
increases.

7. If P- wave is inverted it indicates atrial fibrillation
or atrial hypertrophy.
If T- wave is prominent it indicate myocardial
infarction.
U- wave absence indicates hypokalemia.