Phase shift in transmitted electrocardiograms: a cautionary tale of distorted signals.

We describe how a routine manufacturer's upgrade of equipment designed to record and transmit electrocardiograms inadvertently introduced the potential for artefact that simulated the ST segment elevation of myocardial infarction. Whilst this type of artefact from a phenomenon known as phase shift is likely to be rare, the possibility should be recognised. Any doubt about the veracity of ST segment elevation from this phenomenon can be tested by introducing test signals from a simple pulse generator.