Introduction To 12-lead Electrocardiogram

As a non-invasive but most valuable diagnostic tool, 12-lead ECG records the electrical activity of the heart as a waveform. If a doctor can accurately interpret an ECG, it can detect and monitor a variety of heart conditions -- from arrhythmias to coronary heart disease to electrolyte imbalances. Much progress has been made in the recording and interpretation of electrocardiograms since the first one was published in 1903. Today, the 12-lead ECG remains a standard diagnostic tool for paramedics, EMTs, and hospital staff.

The 12-lead ECG records information from 12 different perspectives, giving a complete picture of the electrical activity of the heart. We can think of it as 12 different faces of an object interwoven, and we can interpret the ECG to tell a story about the heart. The 12 views collect information by placing electrodes or small sticky patches on the chest (pre-cardiac area), wrists and ankles. These electrodes are connected via an ECG wire to a machine that records the electrical activity of the heart.

Why do we need a 12-lead ECG

The primary purpose of a 12-lead ECG is to screen patients for possible cardiac ischemia. It can help hospital staff quickly identify patients suffering from myocardial infarction, or heart attack, and perform appropriate medical interventions based on initial readings.

12 lead electrocardiogram electrode placement

In order to accurately measure the electrical activity of the heart, it is essential to place the electrodes correctly. In a 12-lead ECG, 12 leads were calculated using 10 electrodes.

Chest (precardiac area) electrodes and placement

» V1 - Fourth intercostal space on the right margin of the sternum

» V2 -- Fourth intercostal space on the left margin of the sternum

» Between V3-V2 and V4

» V4 - Fifth intercostal area of the midclavicular line

» V5 - Anterior midaxillary line and V4

» V6-midaxillary line is at the same level as V4 and V5

Limb (limb) electrodes and placement

» RA(Right arm)- Any position between right shoulder and right elbow

» RL(Right leg)- Anywhere below the right torso and above the right ankle

» LA(Left arm)- Anywhere between left shoulder and left elbow

» LL (Left leg) - Anywhere below the left torso and above the left ankle

Instructions on placement of 12-lead ECG:

Limb leads can also be placed on the upper arms and thighs. However, the position should be uniform, that is, if the click is placed on the right wrist, the left should also be placed on the wrist,

For female patients, the V3-V6 lead was placed under the left breast.

Do not use the nipple as a reference point for placing male and female electrodes, as the nipple position varies from person to person.

12-lead transmitte

Leads are a glimpse of the electrical activity of the heart from a specific Angle. In short, a lead is a perspective. In a 12-lead ECG, 10 electrodes provide 12 perspectives of cardiac activity using different angles through two electrical planes (vertical and horizontal).

Vertical plane (front leads) :

By using four limb electrodes, six frontal leads that provide information about the vertical plane of the heart can be obtained:

I lead

Lead II

III lead

Lead aVR

Lead aVL

Of aVF lead

Leads I, II, and III require both negative and positive electrodes (bipolar) for monitoring. On the other hand, the enhanced leads -AVR, aVL, and aVF -are unipolar and require only one positive pole for monitoring.

The Einthoven Triangle

The Eindthoven triangle explains why there are six leads instead of four limb electrodes.

The principle behind the Einthoven triangle describes how electrodes RA, LA, and LL record cardiac electrical activity associated with themselves through leads aVR, aVL, and aVF, and how they correspond to each other to form leads I(RA to LA), II(RA to LL), and III(LL to LA).

As a result, they form an equilateral triangle. It is therefore known as the Einthoven triangle, after William Einthoven, who invented the first practical electrocardiogram. Where, RL is neutral (also known as the zero point of the measured current). The RL does not appear in ECG readings, but is considered a ground wire that helps reduce ECG artifacts.

Horizontal plane (transverse lead)

By using six chest electrodes, six transverse guide links are obtained that provide information about the heart level: V1, V2, V3, V4, V5, and V6. The transverse lead is unipolar and requires only one positive terminal. The negative terminal of all six leads is located in the center of the heart. The results were obtained by electrocardiogram calculation.

Preparation before ECG

1. Patient posture

l Remove electronic devices (e.g. smartphones) from the patient. These devices can create artifacts (interference) and cause problems with readings.

l Place client in supine or semi-Fowler position.

l With your arms flat at your side, have the patient relax his shoulders and keep his legs uncrossed.

l For patients who cannot lie comfortably on the bed or examination table due to their size, cross your arms over your abdomen to reduce muscle tension and movement.

l The patient should remain quiet throughout the test.

2. How to reduce significant artifacts

l Mild ECG artifacts are not uncommon. However, we can reduce further interference by taking the following steps:

l Turn off non-essential electrical equipment and equipment in the vicinity whenever possible.

Check cable loops and avoid laying cables near metal objects to avoid affecting the signal.

Check wires and cables for cracks or breaks. Replace as needed.

l If possible, use a current suppressor on the power supply.

l Ensure the connection between the patient's ECG cable and the device, carefully checking the gap between the connectors.

3. Prepare the skin

l Keep skin dry, hairless and oil free. Shave any hair that may interfere with electrode placement. The electrode should be in full contact with the patient's skin.

l To ensure electrode adhesion and reduce skin oil, alcohol gauze can be used to wipe the electrode placement area.

The electrical resistance is reduced by touching the soft skin before the electrode is placed, and this will help ensure that the electrical signal from the heart is transmitted to the electrode.

l To ensure the effectiveness of monitoring, it is necessary to maintain a quiet and temperature appropriate environment to prevent sweating.

4. Electrode application

l Ensure electrode conductive gel is fresh and well moistened. Dry electrodes with insufficient gel can reduce the conduction of ECG signals. Often, electrode gels dry out as a result of incorrect storage. Therefore, the electrode should be stored correctly according to the product instructions.

l Do not place electrodes on bones, incisions, irritated skin, and skin on body parts where there may be a lot of muscle movement.

l Use the same brand of electrodes. The different composition of the electrode sheet may prevent accurate ECG tracking.