Lead composition:
1. Limb leads
This includes standard limb leads I, II, III, and pressurized unipolar limb leads aVR, aVL, and aVF.
(1) Standard limb lead: also known as bipolar lead, reflects the potential difference between two limbs.
(2) Pressurized unipolar limb lead: It is a technique in which only one electrode displays a potential, while the potential of the other electrode is equal to zero, in two electrodes. At this point, the amplitude of the waveform formed is small, so pressurization is used to increase the measured potential for easy detection.
(3) In clinical practice, when recording electrocardiograms, there are four colors of limb lead exploration electrodes, and their placement positions are: the red electrode is located on the right upper limb wrist, the yellow electrode is located on the left upper limb wrist, the green electrode is located on the left lower limb ankle, and the black electrode is located on the right lower limb ankle.
2. Chest lead
Belongs to unipolar leads, including V1~V6 leads. During the detection, the positive electrode should be placed at the designated location on the chest wall, and the three electrodes of the limb lead should be connected to the negative electrode through a 5K resistor to form the central electrical terminal.
During routine electrocardiogram examination, a total of 12 leads including bipolar, pressor unipolar limb leads, and V1-V6 can meet the requirements. If there is suspicion of right-sided heart, right ventricular hypertrophy, or myocardial infarction, V7, V8, V9, and V3R leads should be added, with V7 at V4 level on the left posterior axillary line; V8 is at the level of V4 on the left scapular line; V9 is at the level of V4 on the left spinal sideline; V3R is located in the corresponding area of V3 on the right chest.