We discuss the issues of Active Implanted Medical Devices (AIMDs, including pacemakers) and possible interference from EMFs on another page. Here, we give details of the various standards that relate to this issue.
In summary, the relevant European Directive creates an obligation on designers and manufacturers of AIMDs to make them immune to interference in "reasonably foreseeable" circumstances. The CENELEC standards interpret this as meaning that devices should be immune up to the general public reference levels as set by ICNIRP. This largely explains why in practice, power lines are not observed to interfere with implanted heart devices.
All new such devices are subject to the Active Implantable Medical Devices Directive (90/385/EEC, first established in 1990 with subsequent amendments, though the amendments do not affect the provisions we are talking about here). This includes the following provision:
I. GENERAL REQUIREMENTS
Devices must be designed and manufactured in such a way as to remove or minimize as far as possible:
risks connected with reasonably foreseeable environmental conditions such as magnetic fields, external electrical influences, electrostatic discharge, pressure or variations in pressure and acceleration”
The European Directive is transposed into UK law by the Medical Devices Regulations 2002. These state:
"... no person shall place on the market or put into service a relevant device unless that device meets those essential requirements set out in Annex 1 [of the Directive] which apply to it."
Part III 22 (1)
CENELEC, the European electrical standards organisation, produce standards covering this issue. These automatically become British Standards, so have "BS EN" numbering.
The specific standards
So far, they have produced:
BS EN 45502-1: 1998
Active implantable medical devices Part 1. General requirements for safety, marking and information to be provided by the manufacturer
BS EN 45502-2-1: 2003
Active implantable medical devices Part 2-1. Particular requirements for active implantable medical devices intended to treat bradyarrhythmia (cardiac pacemakers)
BS EN 45502-2-2: 2008
Active implantable medical devices Part 2-2. Particular requirements for active implantable medical devices intended to treat tachyarrhythmia (includes implantable defibrillators)
note: EN 45502 replaced an earlier EN 50061, known in the UK as BS 6902, which was withdrawn in 2004
BS EN 50527-1:2010
Procedure for the assessment of the exposure to electromagnetic fields of workers bearing active implantable medical devices. General
BS EN 50527-2-1:2011
Procedure for the assessment of the exposure to electromagnetic fields of workers bearing active implantable medical devices -
Part 2-1: Specific assessment for workers with cardiac pacemakers
What these standards say
These are quite complicated to piece together, but is summarised:
"The risk assessment is based on the approach that AIMDs are expected to work uninfluenced as long as the General Public Reference levels of 1999/519/EC (except for static fields) are not exceeded..."
BS EN 50527-1 2010 5.1.2
"Under normal circumstances, if the fields are below the reference levels then the voltage [induced at the sensing terminals of the AIMD] is low enough that there are no electromagnetic interference effects. For higher fields the voltage can cause electromagnetic interference effects but often this is not clinically significant (see also D.7) and transient exposure can be permitted."
BS EN 50527-1 2010 D.4.1
Although not applicable in the UK, there is also an American standard dealing with the same issues, ANSI/AAMI PC69:2007. This has been superseded by ISO 14117, “Active implantable medical devices – Electromagnetic compatibility – EMC test protocols for implantable cardiac pacemakers, implantable cardioverter defibrillators and cardiac resynchronization devices.”
What does mean in practice?
The Directive requires immunity from interference in normally foreseeable circumstances. CENELEC interprets this as, broadly speaking, immunity up to the general public reference levels from the EU Recommendation, which are 100 µT and 5 kV/m. In fact, several manufacturers say they test for immunity up to 100 µT and 6 kV/m.
Medical devices other than pacemakers and defibrillators
The commonest active medical devices are pacemakers and defibrillators. But there are plenty of other devices - neurostimulators, cochlear implants, insulin pumps, etc. Some are implanted, some are body-worn.
- The Medical Devices Regulations apply to all devices and require immunity for reasonably foreseeable environmental conditions - but don't specify what these reasonably foreseeable conditions are.
- CENELEC 50527-1 applies to all Active Implanted Medical Devises and interpret "reasonably foreseeable environmental conditions" as fields up to the general public reference levels, 5 kV/m and 100 µT.
- CENELEC are writing a sequence of standards - 50527-2 - that apply to specific devices and give more detail. But so far, the only one published is for pacemakers, with a similar one for defibrillators well on the way.
So, most particularly for pacemakers and defibrillators, but also for all active implanted devices, the standards dictate immunity up to 5 kV/m and 100 µT. The same thing can be assumed to apply to body-worn devices as well, but that has not been made explicit yet.
For all practical purposes, power lines never exceed 100 µT or even approach it, so it is safe to say interference from magnetic fields should never happen. But some power lines can under some circumstances exceed 5 or 6 kV/m. So there is theoretical scope for interference from electric fields. We know that such interference has never been observed in practice. The explanation is two fold.
- First, most implanted devices are immune to rather higher fields than the minimum level required in the tests.
- And secondly, the circumstances where power lines do exceed 5 or 6 kV/m are not that common. It is not every span that can do so; even when a span can do so, it is only over a limited area towards the middle of the span; it may happen only for limited periods of time depending on the operation of the electricity system and other factors such as the weather; and additionally electric fields are very easily screened by most objects, for example bushes and hedges, reducing the fields further.