The Principle of Electrocardiogram Generation

The myocardial cell membrane is a semi-permeable membrane. In the resting state, a certain number of positively charged cations are arranged outside the membrane, and the same number of negatively charged anions are arranged inside the membrane. The external potential of the membrane is higher than the inside of the membrane, which is called the polarization state.

In the resting state, since the myocardial cells in all parts of the heart are in a polarized state, there is no potential difference, and the potential curve recorded by the current recorder is flat, which is the equipotential line of the body surface electrocardiogram. When the cardiomyocytes are stimulated by a certain intensity, the permeability of the cell membrane changes, and a large number of cations flood into the membrane in a short period of time, causing the potential in the membrane to change from negative to positive. This process is called depolarization.

For the whole heart, the potential change of myocardial cells during the depolarization process from the endocardium to the epicardium. The potential curve traced by the current recorder is called the depolarization wave, which is the P wave of the atrium and the ventricle on the surface electrocardiogram. QRS wave. After the depolarization of the cell is completed, the cell membrane discharges a large amount of cations, which causes the potential in the membrane to change from positive to negative and return to the original polarization state. This process proceeds from the epicardium to the endocardium, which is called repolarization. Similarly, the potential changes during the repolarization of cardiomyocytes are called repolarization waves as recorded by the current recorder. Since the repolarization process is relatively slow, the repolarization wave is lower than the depolarization wave. The repolarization wave of the atrium is low and buried in the depolarization wave of the ventricle, and the electrocardiogram of the body surface is not easy to identify. The repolarization wave of the ventricle appears as a T wave on the surface electrocardiogram.

After the entire cardiomyocytes were completely repolarized, the polarization state was restored again, there was no potential difference between the cardiomyocytes at various parts, and the electrocardiogram of the body surface recorded the equipotential line.