Pacemakers and medical devices
Medical devices which use an energy source are known as active implantable medical devices (AIMDs). This term covers a broad range of devices, including pacemakers, defibrillators and neurostimulators.
AIMDs usually comprise of a small battery-powered box with electronic circuitry and leads, electrodes, and/or sensors, which detect a biological function and/or deliver a stimulus. The most common types of AIMDs are pacemakers and defibrillators, and this page concentrates on those. If you have questions about any other device, please contact our helpline.
Can power lines cause interference with pacemakers and intra-cardiac defibrillators (ICDs)?
The heart produces electrical signals, which need to be reliably detected by pacemakers’ and ICDs’ sensing leads. External electric and magnetic fields can induce signals on these sensing leads which could prevent the device working properly.
Given we are all surrounded by EMFs in our daily lives, the Medical Devices Regulations enforce an obligation on designers and manufacturers of AIMDs to make them immune to interference in "reasonably foreseeable" circumstances. This means that devices should be immune up to the public reference levels as set by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). Immunity tests are performed by the device manufacturers to ensure devices remain unaffected by external fields up to 100 µT and 5 kV/m for the most common ‘factory setting’. These are the minimum immunity requirements. Many devices can be exposed to much higher fields without experiencing interference.
This largely explains why in practice, power lines are not observed to interfere with implanted heart devices. Interference is a well-known issue with some other sources of EMFs (e.g., shop security devices, some DIY power tools, etc.) - but there has been no recorded case in Britain of a patient coming to harm because of fields produced by the power system.
Does interference occur in practice?
The relevant UK regulatory body is the Medicines and Healthcare Products Regulatory Agency (MHRA). The MHRA does 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 (2024)
Patients with specific warnings
Most devices are fitted using ‘standard settings’, meaning that they are, as a minimum immune to interference up to the ICNIRP public reference levels. However, on rare occasions, cardiologists may need to adjust these settings, which can result in them being more susceptible to interference from EMFs.
If this is the case, the patient will be given a specific warning about the possibility of increased interference, along with additional guidance. In these circumstances, additional care may need to be taken around sources of EMFs. If effects were to occur, they would be temporary, and manufacturers advise there should be no permanent harm to the device.
What about working near a substation or overhead line with an AIMD?
If your place of work is near to an overhead line or substation, as long as you are in publicly accessible areas, the advice above will apply, and interference is unlikely.
If you access areas within a substation or climb pylons, additional risk assessments will need to be carried out.