• ECG
• arrhythmias
• artefacts
• cellular phone
• electromagnetic fields, emergency departments

A 44-year-old man presented to the emergency department with cocaine-induced chest pain. There was no previous cardiac history. His initial ECG was abnormal (figure 1A). On examination, he appeared well and a charging iPhone 4 was found beneath his forearm. The device was removed and another ECG was recorded (figure 1B).

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Figure 1

ECG acquired before (A) and after (B) removal of charging iPhone.

ECG interference can arise from numerous potential sources.AC interference is minimised using physical shielding and electrical filters, essential given that ECG voltages are in the order of millivolts compared with the mains supply (230 V). Direct contact with the device may have bypassed these measures, and figure 1A shows AC interference as the characteristic ‘thickened baseline’ with 2 sinusoidal waves every 1 small square (50 Hz).

Electromagnetic interference from mobile communication devices is common, hence restrictions on use in certain settings The GSM receiver has been shown to cause high-voltage spike at regular intervals.1 Figure 1A demonstrates such activity that resembles a pacing spike every 2 small squares caused by abnormal interpretation as genuine pacemaker pulses that are automatically expanded to allow better visualisation.

These two forms of interference need to be recognised given how often ECGs are recorded within the emergency department.