This is a record or graphical registration of electrical activities of the heart, which occur prior to the onset of mechanical activities. the summed electrical activity of all the cardiac muscle fibers when recorded extracellularly is called electrocardiogram.
Waves of normal electrocardiogram:
Normal electrocardiogram has the following waves namely P,Q,R,S and T. Willem Einthoven had named the waves of ECG starting form the middle of alphabet (P) instead of starting from the beginning (A).
P wave is the atrial complex.
QRST complex is the ventricular complex.
QRS complex is the initial ventricular complex.
T wave is the final ventricular complex.
1. 'P' wave: it is a positive wave and the first wave in ECG. it is also called as atrial complex.
Cause: This is recorded due to the depolarization of atrial musculature.
Duration: 0.1 second.
Amplitude: 0.1 to 0.12 mV
2. 'QRS' complex: This is also called the initial ventricular complex. Q wave is a small negative wave. it is continued as the tall R wave, which is a positive wave. R wave is followed by a small negative wave, the S wave.
Cause: QRS complex is obtained because of the depolarization of ventricular musculature. Q wave is due to the depolarization of basal portion of inter ventricular septum. R wave is due to the depolarization of the apical portion of ventricular muscle and S wave is due to the depolarization of basal portion of ventricular muscle near atrioventricular ring.
Duration: 0.8 to 0.10 second
Amplitude: Q wave : 0.1 to 0.2 mV
R wave : 1 mV
S wave : 0.4 mV
3. 'T' wave: it is the final ventricular complex and is a positive wave.
Cause: due to the repolarization of ventricular musculature.
Duration: 0.2 second.
Amplitude: 0.3 mV
Atrial repolarization is not recorded as a separate wave in ECG because, it is merged with QRS complex.
4. 'U' wave: it is a rare and insignificant wave of ECG. it is supposed to be due to repolarization of papillary muscle.
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Intervals and segment of ECG |
