For ECG, 4 color-coded electrode clips and 6 color-coded electrode balls are fixed on the body. 4 clips are fixed on the limbs, of which red is fixed on the right wrist, yellow is fixed on the left wrist, black is fixed on the right ankle, and green is fixed on the left ankle. 6 electrode balls are placed in the following order: red is fixed on the right edge of the sternum 2cm aside at the fourth rib cage, yellow is fixed on the left edge of the sternum 2cm aside at the fourth rib cage, green is placed at the midpoint of the line connecting the yellow ball and the brown ball, black ball is placed at the intersection of the horizontal line of the brown ball and the anterior axillary line. The six electrodes were placed in the following order: red was fixed at the right edge of the sternum 2cm away from the fourth intercostal space, yellow was fixed at the left edge of the sternum 2cm away from the fourth intercostal space, brown was placed at the junction between the fifth intercostal space and the lower left nipple, green was placed at the mid-point of the line connecting the yellow ball and the brown ball, black was placed at the intersection between the horizontal line of the brown ball and the anterior armpit line, and purple was placed at the intersection between the horizontal line of the brown ball and the mid-axillary line.