Modified electrode placement must be recorded when performing 12-lead electrocardiograms.

BACKGROUND

Local observation has suggested that placing limb leads on the torso when recording the standard 12-lead resting electrocardiogram (ECG) has become commonplace. This non-standard modification has the important advantages of ease and speed of application, and in an emergency may be applied with minimal undressing. Limb movement artefact is also reduced. It is believed that ECGs obtained with torso electrodes are interchangeable with standard ECGs and any minor electrocardiographic variations do not affect diagnostic interpretation.

STUDY DESIGN

The study compared 12-lead ECGs in 100 patients during routine electrocardiography, one being taken in the approved way and one taken with modified limb electrodes.

RESULTS

It was found that the use of torso leads produced important amplitude and waveform changes associated with a more vertical and rightward shift of the QRS frontal axis, particularly in those with abnormal standard ECGs. Such changes generated important ECG abnormalities in 36% of patients with normal standard ECGs, suggesting "heart disease of electrocardiographic origin". In those with abnormal standard ECGs, moving the limb leads to the torso made eight possible myocardial infarcts appear and five inferior infarcts disappeared. Twelve others developed clinically important T wave or QRS frontal axis changes.

CONCLUSIONS

It is vital that ECGs should be acquired in the standard way unless there are particular reasons for not doing so, and that any modification of electrode placement must be reported on the ECG itself. Marking the ECG "torso-positioned limb leads" or "non-standard" should alert the clinician to its limitations for clinical or investigative purposes, as any lead adaptation may modify the tracing and could result in misinterpretation.