ABSTRACT
External electrical interference seldom causes difficulties when recording electrocardiogram (ECG) in hospital. However, for general practitioners who sometimes record ECGs in patients’ homes, 50 Hz electrical interference from domestic appliances has been reported as a major cause of ECG artefact, and this can make the ECG difficult or even impossible to interpret correctly. Every ECG must include a calibration mark so that the gain setting can be checked. Sometimes it is necessary to alter the gain setting, particularly if the QRS complexes are so big at the standard setting that they will not fit clearly on the paper. The ECG records the electrical activity of the heart, but this is not the only source of electrical activity in the body. Skeletal muscle activity is also picked up on the ECG, and it is important for patients to lie still and relaxed while an ECG is being recorded.
