Guide: How to place electrodes for a resting ECG

Main functions of electrodes in an ECG

Detecting cardiac electrical activity

Each heartbeat generates electrical signals. This electrical signal is weak, only a few millivolts, but it travels through body tissues to the skin. The electrodes, placed on the skin, detect these signals at different points on the body.

Transmitting the signals to the ECG device

The signals are transmitted to the electrocardiograph, which converts them into a graphic trace. The device interprets them as a waveform, including P waves, QRS complexes, T waves, etc., corresponding to the electrical activity of the different parts of the heart.

Creating the 12 standard leads

With only 10 electrodes, 12 “views” of the heart, known as leads, can be obtained thanks to the different combinations between them.

Enabling a detailed analysis of heart function

This makes it possible to detect rhythm or conduction abnormalities, as well as signs of ischaemia or myocardial infarction.

How to place electrodes to obtain a 12-lead ECG

10 electrodes are used to record the heart’s electrical activity from 12 different angles.

An ECG device can measure a lead directly or derive electrical information. In other words, it measures a potential difference between two points on the body, or more simply, combines the signals from two electrodes.

1. Preparing the patient

Place the patient in a lying position, relaxed and bare-chested.
Clean the skin with alcohol or a wipe to remove excess sebum or sweat.
Shave hairy areas if necessary to ensure good adhesion. Use disposable razors or a surgical clipper.
If you are using disposable electrodes, check their expiry date.

2. Placing the limb electrodes

Red electrode, R or RA (Right Arm): inner side of the right forearm, or at wrist level or on the right shoulder

Yellow, L or LA (Left Arm): inner side of the left forearm, or at wrist level or on the left shoulder

Black electrode, N or RL (Right Leg): above the right ankle (neutral ground) or on the right iliac crest. This grounding electrode, also called the neutral electrode, is used in an ECG to stabilise the electrical signal and reduce electrical interference.

Green electrode, F or LL (Left Leg): above the left ankle or on the left iliac crest

These 4 limb electrodes alone make it possible to create 6 leads in the frontal plane:

Standard leads: I, II, III
Augmented leads: aVR, aVL, aVF
These 6 leads are calculated automatically by the machine by combining the signals from the limb electrodes.

3. Placing the precordial electrodes

The precordial electrodes are the 6 electrodes placed on the chest, from V1 to V6, or C1 to C6, to record the heart’s electrical activity in the horizontal plane.

V1: 4th intercostal space, right sternal border
V2: 4th intercostal space, left sternal border
V3: between V2 and V4
V4: 5th intercostal space, left midclavicular line (MCL)
V5: at the same horizontal level as V4, between V4 and V6
V6: at the same horizontal level as V4, midaxillary line (MAL)
These 6 chest electrodes (V1 to V6) provide a direct lead view of the horizontal plane:

These 6 electrodes provide a direct lead view of the horizontal plane and appear on the final trace as: V1, V2, V3, V4, V5, V6.

4. General advice

Make sure the electrodes are securely attached and properly connected.
Avoid interference: keep the patient calm and move phones and electrical sources away.
Start the recording once all checks have been completed.
If you are using pre-gelled electrodes that are dry, throw them away. They are probably expired or the pouch has been open for too long.

Why is correct electrode placement important during a resting ECG?

Correct electrode placement is essential to ensure a reliable ECG trace. It helps avoid false diagnoses, ensures accurate measurements, makes it possible to compare ECGs over time, and complies with medical standards. Incorrect placement can distort the results and lead to clinical errors.

Tag: Ecg

Posted in: Practical guides