Do you know the location of the ECG leads?

Electrocardiogram is a common examination item in our daily life. It will help us better understand our own physical condition and better detect diseases. Many people do not have a deep understanding of the position of electrocardiogram leads. In fact, it mainly includes ground lead, pressurized unipolar left/right upper limb lead, and unipolar chest lead. People should have a certain understanding of this.

1. Ground lead in ECG leads

In addition, when recording the electrocardiogram, the right leg will be connected to the ground wire of the electrocardiograph, which is called the ground lead.

2. Pressurized unipolar left/right upper limb leads in ECG leads

The pressurized unipolar limb lead places the exploration electrode on the right arm, so it is called the pressurized unipolar right upper limb lead (aVR), the exploration electrode is placed on the left arm, so it is called the pressurized unipolar left upper limb lead (aVL), and the exploration electrode is placed on the left leg, so it is called the unipolar pressurized left lower limb lead (aVF). The remaining two limb lead electrodes are connected together through 5000Ω resistors as indifferent electrodes. The electrocardiogram voltage recorded in this way is 50% higher than the voltage recorded by unipolar limb leads, which is conducive to observing the electrocardiogram.

3. Unipolar chest leads in ECG leads

Unipolar chest lead: The exploration electrode is placed on the chest wall in front of the heart to record the electrocardiogram, which is called unipolar chest lead. There are six common record locations. For the V1 lead, the exploration electrode is placed at the fourth intercostal space on the right edge of the sternum; for the V2 lead, the exploration electrode is placed at the fourth intercostal space on the left edge of the sternum; for the V4 lead, the exploration electrode is placed at the fifth intercostal space on the left midclavicular line; for the V3 lead, the exploration electrode is placed at the midpoint of the line connecting points V2 and V4; for the V5 lead, the exploration electrode is placed at the fifth intercostal space on the left anterior axillary line; and for the V6 lead, the exploration electrode is placed at the fifth intercostal space on the left midaxillary line. The electrodes of the left arm, right arm and left leg were connected together through 5000Ω resistors to serve as indifferent electrodes.

Lead V 1 is usually above the right ventricle and right atrium;

Leads V2 and V3 are usually located above the ventricular septum and close to the left ventricle;

Leads V4 to V6 are located above the left ventricle and left atrium.

Thus, the P wave in lead V1 (and occasionally in lead V2) is bidirectional because the depolarization begins in the right atrium (toward lead V1) and the second part of the P wave originates in the left atrium, away from lead V1. The P waves in leads V3 to V6 are usually positive because these leads are mostly over the left atrium, reflecting activation of the left atrium toward these leads. Based on the location of the V lead, there is an initial small positive wave (R wave) in lead V 1 , representing a septal depolarization from left to right (thus toward this lead). This is followed by a deep S wave representing left ventricular depolarization, which moves from right to left (away from this lead). In contrast, lead V6 has an initial negative-going waveform (Q wave) representing initial septal activation from left to right, i.e., away from this lead. This is followed by a high positive deflection (R wave) representing left ventricular depolarization, which is conducted from right to left and therefore in the direction of this lead. If you examine leads V1 to V6 (arranged from right to left on the chest wall), the amplitude of the R wave gradually increases, indicating that more left ventricular force is toward this lead; while the depth of the S wave decreases (indicating that the left ventricular force is away from this lead). Therefore, the gradual increase in the amplitude of the R wave is called the precordial progression of the R wave. This change (R/S ≥ 1) usually occurs between leads V3 and V4 (the normal transition zone).