ECG artefacts in emergency medicine

Artefacts are technical errors on electrocardiogram that may be present in all leads or in some of them or in just one. They may be subtle with no interference with correct interpretation, but they can also be significant enough to make ECG recording absolutely useless and delay diagnose and timely therapy. On the other hand, artefacts can be misinterpreted and that way patient can be exposed to unnecessary or risky therapeutic procedures. There are two groups of ECG artefacts: the first group originates from external causes and the second group originates from patient's body. The first group can be caused by electromagnetic interference (alternating current from electrical installation, electrical devices in/on patient, light) or by malfunction of the cables and/or electrodes (damaged cables and electrodes, their movement during transport, wrong connecting, 'offset signals', detached electrodes, gel lacking or inappropriate filters). The second group comes from muscles, skin and adnexa. Muscle contractions are often the cause of artefacts, voluntary movements as much as involuntary. Skin and adnexa can cause ECG artefacts in two ways: through poor contact with electrodes or through simple stretching of the epidermis which generates electric potential (turning of the patient in bed for example). Rare form of artefact caused by radial artery pulsations directly under the electrode was also described; it is so called electromechanical association. Artefacts can present in different ways on ECG recording. The ECG line can be thick, irregular, discontinued, wandering or pseudo isoelectric. Artefacts can imitate any of the ECG waves, extra systoles, tachycardia of narrow or wide complexes, long QT interval, and elevation/depression of the ST segment or T wave changes. Removal of the artefacts requires manipulating with patient, auxiliary equipment and ECG machine itself.