The three lines of ECG refer to three waves, which are P wave, QRS wave cluster and T wave.
1. P wave: represents the potential change of atrial muscle depolarization, the morphology of p wave is generally obtuse round, the time is generally less than 0.12s in normal people, the amplitude is less than 0.25mv in limb leads and less than 0.2mv in chest leads, the first half of p wave represents the agitation of the right atrium, and the second half of p wave represents the agitation of the left atrium. When there is atrial enlargement and abnormal conduction between the ventricles, the p-wave may show bimodal p or hyperacute p-wave.
2. QRS wave group: It represents the potential change of ventricular muscle depolarization. Normal QRS wave is usually no more than 0.11 seconds, and the V1 and V2 leads of chest lead are mostly rS type. When there is ventricular enlargement or hypertrophy, or right or left bundle conduction block, the QRS wave group will be broadened and time limit will be prolonged.
3. T wave: T wave represents the potential change of rapid repolarization of the ventricle. In normal people, T wave morphology is asymmetric in both limbs, with the first half of the wave being more gentle and the second half being steeper. When hyperkalemia occurs, the T wave will be high and pointed, and when hypokalemia occurs, the T wave will be low and flat.