ECG signal quality: how to identify and correct artefacts before repeating the recording

This guide offers a structured way to identify the cause, change one variable at a time and review the result before accepting the electrocardiogram. It is not intended to interpret the trace or replace local protocols, instructions for use or clinical judgement.

An artefact is not a clinical finding

In electrocardiography, an artefact is an alteration in the trace that does not originate from the heart’s actual electrical activity, but arises during signal acquisition or processing. It may appear as baseline drift, fine rapid noise, spikes, interruptions or a missing signal. Its appearance can guide the investigation, but rarely identifies a single cause on its own.

It is worth distinguishing terms that are often treated as interchangeable. Noise describes an unwanted component that contaminates the signal; interference points to a disturbance, usually from an external source; and an artefact is the alteration that ultimately appears in the recording. Not every technical error is an artefact either: incorrect electrode placement can change morphology without producing an obviously noisy trace.

This distinction matters. A clean signal does not mean that the ECG is normal, and a noisy signal does not prove that there is a cardiac abnormality. The first question is whether the recording is technically acceptable. A suitably qualified professional can then interpret it alongside the patient’s other clinical information.

For readers who first need to review the purpose of the test, Equimed explains what an electrocardiogram is and what it records. The focus here is narrower: preventing a technically poor acquisition from compromising the subsequent review.

The table is intended to help decide where to look first, not to diagnose a device fault or a clinical condition. If the problem continues after the approved procedure has been followed, the device or accessory should be managed in accordance with the organisation’s technical protocol.

ECG signal quality starts with the patient

In everyday practice, a short explanation can change the recording. Telling the patient what will happen, protecting their privacy and asking them to remain still and avoid speaking can make it easier to relax. The ELI® 280 user manual also emphasises that the patient should be lying down and comfortable before acquisition begins.

Some situations need a little more time: cold, tremor, pain, anxiety, breathing difficulty or a poorly supported position. Their effect should not simply be hidden on the screen. They should be addressed within the clinical limits of the case, the environment adapted where possible and anything that may affect the recording documented.

Skin and electrode form a single interface

Electrode-to-skin contact needs to remain stable. Hair, skin oils, moisture, product residue, dry skin or deteriorated adhesive may increase impedance or cause the contact to change with movement. Correct preparation is not a universal recipe: it depends on the electrode, its instructions for use, the condition of the skin and the approved protocol.

It is therefore unwise to improvise with products or techniques that have “always worked”. Recommendations may vary between consumables and institutions. For frail or older patients, and for anyone with vulnerable skin, preparation requires particular care to avoid discomfort or injury.

How to identify the cause without repeating blindly

When a technical alteration appears, changing everything at once makes it impossible to know what solved it. A short sequence and one change at a time are more useful. If correcting the contact of one electrode removes the problem, the team has learnt something. If ten electrodes are repositioned, the filter changed and the cable replaced at the same time, the second ECG may be clean, but the healthcare team will not know why.

1. Stop the recording from being accepted. Do not confirm or send it while a relevant technical doubt remains.
2. Assess the extent. Determine whether the artefact appears in one lead, a particular group or all leads.
3. Return to the patient. Check position, movement, speech, tremor and comfort.
4. Follow the physical path. Review the skin, electrode, connector and cable for the affected leads.
5. Confirm placement. Use anatomical landmarks rather than the position used for a previous ECG or a visual approximation.
6. Review the settings. Check speed, gain and filters against the protocol. Do not use them to disguise poor acquisition.
7. Acquire again and compare. Assess whether the change corrected the pattern before moving to another possible cause.

The affected leads can help focus the investigation

The trace does more than show that an alteration is present; it can sometimes narrow down where to look. The ELI® 280 manual relates certain combinations of affected limb leads to the electrode or limb that should be checked. This is a practical troubleshooting aid, not a rule for clinical interpretation.

The value of this approach lies in reducing the field of investigation. If the alteration is concentrated in leads I and II, there is little point in starting by replacing every precordial electrode. Begin with what those leads have in common and then assess the effect of the correction.

A filter can clean up the appearance and alter the signal

Filters are necessary for managing unwanted signal components, but they are not a harmless eraser. The AHA, ACC and HRS scientific statement on ECG standardisation explains that certain filters can reduce baseline drift or high-frequency noise while also altering the fidelity of parts of the trace. The setting used should therefore be visible, understood and consistent with the procedure.

If the recording only appears acceptable after changing filters without correcting the physical cause, the acquisition still deserves further review.

The ELI® 280 allows the mains interference filter to be configured at 50 or 60 Hz and offers 40, 150 and 300 Hz print filters. The manual explains that these selections attenuate different frequencies and affect the fidelity of the displayed and printed trace. There is therefore no single setting that should be applied automatically in every situation. The organisation should define it for the intended use and retain that information with the recording.

How the ELI® 280 can support quality control

Preparation and placement remain human tasks, but the electrocardiograph can make certain problems visible before the examination is accepted. Equimed’s page for the ELI® 280 resting electrocardiograph documents simultaneous display of all twelve leads, connection confirmation, lead-fail indication and detection of possible lead reversals.

The device also includes Best 10. When the function is active, it analyses segments held in a five-minute buffer and selects ten seconds on the basis of high- and low-frequency noise. The manual also states that Best 10 is unavailable while certain lead-fail conditions remain. The sequence makes sense: resolve the connection first, then select the segment.

Best 10 can support review and reduce avoidable repeats, but it cannot turn incorrect placement into correct placement or replace professional assessment. It is one aid within a wider quality chain. Equimed’s guide to choosing a 12-lead electrocardiograph explores how these functions fit into clinical workflow, connectivity and organisational support.

Reducing repeat recordings takes more than training one person

When the same type of artefact appears repeatedly across different departments or shifts, the problem may not be an individual mistake. Electrodes may be stored poorly, cables replaced too late, settings left unstandardised or preparation performed differently by each professional. At that point, the question changes from “Who recorded this ECG?” to “Which part of the system is creating the variation?”

Checklist before accepting the recording

• The patient identity and request match.
• The patient is informed, comfortable and as still as their condition allows.
• The skin has been prepared in accordance with the protocol.
• The electrodes are intact, adherent and within their conditions of use.
• The cables are connected, supported and free from tension.
• The leads follow the intended anatomical landmarks.
• Speed, gain and filters are authorised for the examination.
• All twelve leads are present and warnings have been resolved.
• Relevant changes have been documented.
• The recording has been reviewed before transmission or archiving.

A good signal is achieved by correcting, not simply repeating

The most reliable way to reduce artefacts is not to pursue a perfect-looking screen, but to make acquisition reproducible. Patient, skin, electrodes, cabling, placement and settings should be reviewed in the same order, even when the department is under pressure.

This method saves repeat recordings, but offers something more valuable: it makes it possible to explain why a recording was accepted, what was changed and what should be reviewed if the problem appears again. Technology helps professionals see and manage the signal. Quality emerges when that support is integrated into a procedure that people can apply and verify.