Understanding pacemaker interference
By Dr Tony Maisey and Anne Silk, 22 February 2012
How interference from mobile devices can affect pacemakers. By Dr Tony Maisey and Anne Silk
There are more than 240,000 people in the UK and more than 3m worldwide who have been fitted with pacemakers for diagnosed cardiac problems.
Many have been in situ for several years and cause no problems at all, provided medical aftercare checks are maintained. Pacemakers restore quality of life to countless people of all age groups.
As technology moves so rapidly, it is not surprising to find unexpected problems and risks emerging. With the rapidly ageing population, more pacemakers will be fitted, so it is timely to draw attention to these caveats.
Depending on the type of implant, interference effects can occur from mobile communication devices if the device is held too close to the chest, for example, if it is carried in the left breast pocket over the pacemaker.
Here we discuss radio frequency interference (RFI), well known to the electronics industry and well covered by manufacturers in their patient handbooks and websites. RFI may be noticed in everyday situations such as your car radio switching stations, or burglar alarms going off for no apparent reason.
The effect on pacemakers
Pacemakers listen out constantly for all electrical signals, however sourced. All electronic devices are liable to produce artefacts – known as electromagnetic interference (EMI). EMI can (a) cause pulses to be delivered to the pacemaker irregularly; (b) cause the pacemaker to ignore the heart's own natural rhythm and then deliver pulses at a fixed rate; and (c) stop the pacemaker from delivering pulses as regulated.
The electrical properties of biological tissue are all frequency dependent and thus depending on amplitude (strength) and waveform, interference effects can be produced.
The term 'artefact' is used in this context to mean any electrical signal not originating from nerve or muscle. Also, demodulation of a digital mobile phone signal can create a very low frequency signal (2Hz or 4Hz), which can be mistaken by the device for normal heartbeat.
Not all pacemaker implants will react adversely and not all mobile phones will cause problems. Newer pacemaker units now have inbuilt shielding for radio frequency signals in the form of a thin incorporated ceramic panel.
What a patient will notice
The symptoms may sound puzzling but are consistent throughout global clinical reports.
The symptoms described include sensations, such as feeling 'spaced out', 'weird' or 'poorly', with nausea, head pain, disorientation, weakness, fibrillation, dizziness, confusion, shortness of breath, palpitations and syncope.
The new digital (pulsed) signals pacemakers use have now largely taken over from analogue signals, with implications for RFI.
Neither you nor your patient should assume a device is safe to use if it is known to cause anomalous response in the implant.
If in doubt, keep all mobile devices at least 15cm from the left chest – roughly the distance from outstretched thumbtip to little fingertip.
Manufacturers' advice leaflets are updated as new technology enters the marketplace. Check that your patient's advice leaflet is up to date. New devices mean new warnings. The patient's cardiac unit will happily update with a new leaflet.
European pacemaker patient identification card
Everyone with an implant will have been given a European pacemaker patient ID sheet with the name of their cardiologist and emergency phone numbers. In cases of doubt, these contact details can be used.
- Dr Maisey is a retired GP in Princes Risborough, Buckinghamshire. Anne Silk is a health researcher, chair of the NHS DenDron Steering Committee, member of the Public and Patient Initiative Group, NHS London, and a former member of the HPA Electromagnetic Field Discussion Group
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