Implanted medical devices are pacemakers, implanted defibrillators and similar. People with these devices may be particularly concerned about interference from EMFs, so we give quite a lot of detail here. See also a simpler summary and for information on how EMFs interfere with other equipment.

Advances in medical technology over the past 50 years have resulted in an increased number of patients who have active implantable medical devices (AIMDs). There are no longer the constraints there used to be on these patients and many are able to live active, full lives, including returning to full-time work. There are however electric and magnetic fields present in the environment, which can potentially interact with these devices.

What are Active Implantable Medical Devices?

An active implantable medical device (AIMD) is any medical device which is intended to be totally or partially introduced, surgically or medically, into the human body, and which is intended to remain after the procedure. The commonest are pacemakers and defibrillators (together described as "implanted heart devices") but there are others as well.

All usually comprise of a small battery-powered box with electronic circuitry and leads, electrodes and/or sensors, which detect a biological function or deliver a stimulus.

The rest of this page deals with pacemakers and defibrillators - see a separate page on cochlear implants.

Interference with pacemakers and intra-cardiac defibrillators (ICDs) 

The heart produces electrical signals or action potentials, which need to be reliably detected by pacemakers’ and ICDs’ sensing leads.  External electric and magnetic fields can induce signals on these sensing leads that prevent the device working properly. Any effects are temporary and manufacturers advise there should be no permanent harm to the device.

If this happens to a pacemaker, it usually reverts to constant pacing mode.  A defibrillator could in theory send a shock when one was not needed, or possibly be inhibited from providing a shock when one is needed (the evidence is divided on this).  See more on the consequences of interference if it does occur.  Any interference with an implanted heart device is potentially serious. 

Does interference occur in practice?

Neither the Medicines and Healthcare products Regulatory Agency (MHRA) nor National Grid are aware of any instance of a power line interfering with a correctly fitted modern electronic implantable device such as a pacemaker or ICD.  See more detail on this.

Thus there is considerable confidence in saying that based on the absence of reported incidents, power lines do not appear to interfere with implanted heart devices.

Can interference happen in theory?

Implanted medical devices are governed by Regulations and Standards.  These require the devices to be immune from interference up to, basically, the general public reference levels from the EU Recommendation on exposure limits.  Manufacturers typically test devices up to 100 µT and 6 kV/m.  This pretty well guarantees there will be no interference from magnetic fields, but leaves a theoretical possibility of interference from electric fields.  Scientists have produced interference in laboratory settings, as opposed to real-life settings.

Advice to patients from manufacturers

Manufacturers of potentially affected implanted devices often provide information on electromagnetic interference.  This typically covers a range of sources.  Advice often includes avoiding letting the implanted device get too close to certain sources of fields such as some household appliances, some walkie-talkies and similar transmitting devices, etc.  Some manufacturers’ literature does not mention high-voltage power lines, some say that exposure in public areas should not give interference, some advise not spending extended periods of time close to power lines.

For example, Medtronic state:

“Power lines - high voltage
Low risk of affecting Pacemaker or ICD when walking, driving underneath, or living in a house or building nearby. Individuals servicing high voltage power lines have the potential for Pacemaker reversion or ICD shock. For this work environment contact Medtronic Technical Services to review specific concerns”

No manufacturers appear to regard any hazard as sufficient to require a prohibition on approaching high-voltage power lines.

The regulatory position

The relevant UK regulatory body are the Medicines and Healthcare products Regulatory Agency (MHRA).  They do not regard power lines as a significant risk for people with implanted heart devices given the absence of any reports of interference occurring to date.

This conclusion is restated in the formal Government statement on policy for power lines, National Policy Statement EN-5:

"[MHRA] does not consider that transmission line EMFs constitute a significant hazard to the operation of pacemakers."

NPS EN-5 2.10.7

NPS EN-5 specifies that power lines must comply with the relevant exposure guidelines, but does not impose any extra requirements relating to implanted medical devices.