A standard lead
Lead IIIIII is called standard limb lead, or standard lead for short. The standard lead uses the potential difference between the two limbs as the obtained body surface ECG signal. The electrode placement position and the connection with the amplifier are:
Lead I: The left upper limb (LA) is connected to the positive input terminal of the amplifier, and the right upper limb (RA) is connected to the negative input terminal of the amplifier; it reflects the potential difference between the left upper limb and the right upper limb,
Lead II: The left lower limb is connected to the positive input terminal of the amplifier, and the right upper limb is connected to the negative input terminal of the amplifier; it reflects the potential difference between the left lower limb and the right upper limb.
Lead III: The left lower limb is connected to the positive input terminal of the amplifier, and the left upper limb is connected to the negative input terminal of the amplifier; it reflects the potential difference between the left lower limb and the left upper limb.
When using standard leads, the right lower limb is always output and indirectly grounded. Its characteristic is that it can more truly reflect the general condition of the heart, such as posterior myocardial infarction, arrhythmia and other symptoms.
Two unipolar leads
To use an electrocardiograph to detect potential changes in a certain area of the heart, one electrode can be placed on the chest wall close to the heart, and the other electrode can be placed on the limb away from the heart. The change in the location of the probe electrode is the change in the local potential of the heart. The reference electrode is always maintained at zero potential during the measurement, which is called the electrode limb lead, or unipolar lead for short.
Three compression leads
The unipolar chest lead ECG signal obtained by the above method is real, but the obtained unipolar limb lead ECG signal is weakened due to the existence of resistance R. In order to facilitate detection, the Wilson resistance network has been improved. When recording the unipolar lead ECG waveform of a limb, the balance resistance between the limb and the center point is disconnected, and the lead form is improved to increase the voltage amplitude, which is called the unipolar limb compression lead , Referred to as compression lead.
Four chest leads
Chest leads are divided into unipolar chest leads and bipolar chest leads. In addition to the standard twelve leads, there is also a bipolar chest lead. Bipolar chest lead ECG is to measure the ECG potential difference between a specific part of the human chest and three limbs, that is, the probe electrode is placed at six specific points on the chest, and the reference click is connected to the three limbs.
