An electrocardiogram (ECG) is a simple test that can be used to check heart's rhythm and electrical activity.
The general principle of ECG is that, the body is an electric conductor in which the heart, as electric generator, generates a current field, which is manifested on the skin as potential difference (PD). It is recorded by means of two electrodes kept at different places over the skin, and a curve is produced showing the course of PD between the electrodes.
When a muscle cell is at rest, the potential of cell content will be negative and the surface potential is positive. This PD is called as membrane potential (MP). The approximate voltage of MP is 100 mV. If the same negative charge is fed to the cell surface, then the MP drops about a third, then a further discharge, 'depolarization', will occur spontaneously. The heart muscle cell reacts to this by contraction. After depolarization the cell is repolarized, and return to the resting. The return to resting state, 're-polarization', takes place much slower.
General characteristics of E.C.G. are-
1. 1mm vertical corresponds to 0.1 mV.
2. 1-mm horizontal corresponds to 0.04 second.
3. Positive deflections are upwards and negative deflections are downwards.
4. P-wave:- Depolarization of the auricles. Normal duration 0.11 second (less than 3 mm) Maximum normal height 2.5 mm.
5. QRS Complex:- Depolarization of the ventricles.
Normal duration 0.05 to 0.10 second (less than 2.5 mm).
The initial negative wave is called a 'Q' wave. The first positive deflection is the 'R' wave. Any negative wave preceded by an 'R' wave is known as an 'S' wave.
6. T-wave:- Repolarization of the ventricles.
7. P-Q or P-R segment:- The normally occurring isoelectrical part of the tracing, which lies between the termination of the P wave and the start of the QRS complex.
8. S-T segment:- The iso electrical part of the tracing between the end of the QRS complex and the start of the T wave. Both S-T segment and T wave corresponds to the repolarization of the ventricles.
9. T-P segment:- The horizontal part of the tracing between the termination of the T wave and the start of the P wave of the next heart beat.
10. P-R and P - Q interval:-It is measured from the start of the P wave to the start of the QRS complex, and represents the time required for depolarization of the auricles as well as that involved in the conduction delay in the A-V node.
11. QRS interval:-This interval measures the time in which ventricular depolarization is accomplished. Maximum duration less than 0.10 sec- ond (2.5 mm).
12. Q-T interval:-The interval between the start of the QRS complex to the end of the T wave. It denotes the time elapsing during depolarization and repolalrization of the ventricles.
(ref.-AYURVEDIC MANAGMENT FOR HEART DISEASE - Dr. J.L.N. Sastry & Dr.K.Nisteswar)
for more information about health, stay connected with us.
