The 12 leads are 6 for the limb leads and 6 for the chest leads. The position of the limb leads: are 4 electrodes attached to the leads, and the electrodes are placed at the end of each limb, that is, the wrist of the left upper limb, the ankle of the left lower limb, the wrist of the right upper limb and the ankle of the right lower limb. Lead I, lead II, lead III, AVR lead, AVL lead and AVF lead were recorded separately, and the chest lead referred to six leads V1-V6. If V7, V8, V9, V3R, V4R, V5R leads are added, it becomes 18 leads. v1: 4th intercostal space on the right edge of the sternum, v2: 4th intercostal space on the left edge of the sternum, v3: midpoint of the line connecting V2 and V4 on the left edge of the sternum, v4: 5th intercostal space on the left midclavicular line, v5: same level as V4 on the left anterior axillary line, v6: same level as V4 and V5 on the left midaxillary line, v7: Left posterior axillary line at the same level as V4 and V6, V8: Left scapular line at the same level as V4-V7, V9: Left paravertebral line at the same level as V4-V8. V3R: Right chest wall corresponding to V3, V4R: Right chest wall corresponding to V4, V5R: Right chest wall corresponding to V5.