Electromagnetic interference

This section summarises the safety guidance and information that we have issued on electromagnetic (EM) interference with medical devices. There are links to the original web pages and contact details for the relevant specialist.

 


EM interference may originate from a variety of sources including mobile phones, electronic article surveillance systems (EAS), radiofrequency identification devices (RFIDs), diathermy (electrosurgery) and magnets. (Note: electromagnets with an alternating current (AC) or radiofrequency (RF) feed may cause EM interference, but permanent magnets do not. Permanent magnets can affect pacemakers, but this is because they are used to trigger switching.)

A range of medical devices can be affected by EM interference, for example implantable pacemakers or defibrillators and sensitive electronic medical equipment used in intensive care and specialist baby units.

 

Mobile phones and other mobile communications
The MHRA does not recommend a blanket ban on the use of mobile phones in hospitals, however under certain circumstances, the electromagnetic interference from a mobile can affect the performance of some medical devices (see: FAQs, One Liner, Mobile communications interference)

The impact of radio communications on the safe use of medical devices (including pacemakers implanted in patients), both inside ambulances and at the scene of an accident in the vicinity of emergency vehicles, is discussed in Emergency service radios and mobile data terminals: compatibility problems with medical devices, DB 1999(02).

The compatibility of mobile communication equipment with medical devices is an area where much published information and guidance is conflicting. In 1997 the MHRA organised a large study, based on research conducted at 18 locations including hospitals and MDA evaluation centres (see Electromagnetic Compatibility of Medical Devices with Mobile Communications, DB 9702).
For further information contact Mel King, mel.king@mhra.gsi.gov.uk (020 3080 7286).


Effects on pacemakers and implantable defibrillators
Interference generated by monopolar surgical diathermy/electrocautery is more severe than bipolar and can be sufficient to temporarily inhibit pacemaker output, give rise to a temporary increase in pacing, or cause a loss of programmed settings (see Guidelines for implantable cardioverter defibrillators (ICDs) - pacemaker perioperative management).

Possible interference effects between electronic article surveillance security systems and implantable pacemakers/defibrillators are discussed in PTN No 74. Activation of magnetic reed-switches in implantable pacemakers and defibrillators from concealed magnets, especially in clothing and fashion accessories, can give rise to asynchronous mode pacing in pacemakers and inhibition of shock therapy in implantable defibrillators (PTN No 84).

For further information contact Simon Holmes, simon.holmes@mhra.gsi.gov.uk (020 3080 7240) or Guido Fumagalli, guido.fumagalli@mhra.gsi.gov.uk (020 3080 7144).

Personal music players such as iPods can have a temporary effect on the operation of implantable pacemakers, the MHRA has advised that patients with pacemakers or defibrillators can use personal electronic equipment with negligible risk, providing they are not placed directly over the implant, for example in shirt pockets etc (see Briefing on MP3 players and implantable pacemakers and defibrillators).

There is also a potential for interference between headphones (used with devices such MP3 players) and implantable pacemakers and implantable cardioverter defibrillators (ICDs) (see General implantable cardioverter defibrillators (ICDs) - pacemaker safety information). 


Radiofrequency identification systems
Radiofrequency identification (RFID) systems are used in healthcare establishments to trace and track equipment. The system consists of two parts, a tag (which may be active or passive) and a detector (‘reader’). The tags are small memory chips that store information (e.g. a serial number, date of next service) and are attached to the equipment. The readers can be hand-held or fixed at a particular location. Such a system can also be used to track the whereabouts of patients.

Concerns have been raised with the MHRA about the possibility of RFID systems interfering with electronic medical devices. Working out the risks of interference is not straightforward as there are many factors involved. These include:

  • type/power rating of reader
  • type/power rating of tag
  • distance between reader and medical device
  • location of use – eg store room = low/no risk; operating theatre = higher risk

Although the tags are directly attached to medical devices, they are very low power devices and so are unlikely to cause interference. The main risk comes from the RFID readers that tend to be higher powered, up to several watts, putting them in the same risk bracket as mobile phones.

We have studied a number of published papers and articles as part of our regular review of the risks of interference from mobile communications. The latest research from The Netherlands [1] indicated adverse interference at separations of less than one metre, which is similar to mobile phones.

At this stage it is reasonable to say that RFID readers should be treated like mobile phones and should be kept out of areas with sensitive electronic medical equipment, such as intensive care and specialist baby units. It may also be appropriate to avoid using the readers in operating theatres and critical care areas until further evidence is available.

The risk of interference will also depend on the type of reader and how it is used. If mobile readers are used in storerooms and non-clinical areas the chances of causing adverse incidents are remote. With portal readers, risks exist if they are used in close proximity to patients connected to critical care devices or who have an implanted active device.

Some systems appear to use wide area networks, to allow devices to be located anywhere within a hospital. These often require active RFIDs, but overall signal levels from the tag appear to be low.

The USA’s Food and Drug Administration (FDA) has also been undertaking a review of RFIDs in healthcare facilities and, like the MHRA, has not received any incident reports of electronic medical devices reacting to RFID tags or the readers.

At present we don't know enough about the extent and mode of use of RFIDs in UK healthcare establishments to fully assess the risks. However, like mobile phones, it is important not to lose sight of the benefits while warning of the hazards. The MHRA will continue to monitor the situation and we will provide updated information on RFIDs in healthcare as it becomes available.

Ref 1 Van der Togt, R, van Lieshout, EJ, Hensbroek, R, et al (2008) Electromagnetic interference from radio frequency identification inducing potentially hazardous incidents in critical care medical equipment, Journal of American Medical Association, 299 (24) pp. 2884-2890.

FDA page on Radiofrequency identification (RFIDs) (external link)


For further information contact Mel King, mel.king@mhra.gsi.gov.uk (020 3080 7286).

 
Diagnostic imaging rooms
There are potential EM interference issues in diagnostic imaging rooms and radiotherapy suites. For further information contact Brian Mansfield, brian.mansfield@mhra.gsi.gov.uk (020 3080 6233).


Airport security body scanners and implanted electronic medical devices such as pacemakers, implantable cardioverter defibrillators (ICDs) and neurostimulators
During their travels air passengers will encounter electromagnetic radiation from a number of sources, including body scanners, metal detectors and screening wands, as well as from the sun due to flying at high altitude. Electromagnetic radiation presents minimal risks to those with implanted electronic devices. The recently introduced airport security body scanners send high frequency electromagnetic waves over the body’s surface. These electromagnetic waves pass through clothing and are reflected by the skin and do not enter the body. The energy reflected back is used to create an image of the person’s body and items within their clothing. They are intended to detect items on the body’s surface, not within the body.

MHRA advice
The MHRA is not aware of any evidence of interference problems between airport security body scanners and implanted electronic medical devices. If you have an implanted pacemaker, ICD or neurostimulator you can use airport security body scanners. You should walk through metal detectors normally and not wait within the detection zone. As with mobile phones, you should maintain a distance of 6 inches (15 centimetres) between the screening wand and the implanted device. Patients are reminded to carry their registration card with their device details on to assist airport staff when passing through security checks. Although the flight itself does not present any increased risks of interference to the implant, be aware that you may find yourself in closer proximity to wireless technology on board an aircraft than you would on land. For further information relating to your own specific implanted device please contact your local cardiac centre, doctor or the manufacturer of your device.

Background information
There are two main types of body scanner in use at present: backscatter X-ray scanners, and terahertz or millimetre wave scanners.

Backscatter X-ray scanners
These systems use low energy X-rays that are reflected off the skin to form an image. The amount of radiation emitted during a body scan is typically 40 to 80 times less than the radiation experienced during the flight itself (depending on the length of the flight). This is approximately 100 times less than that from one day of natural background radiation [1], and around 1,000,000 times lower than that known to interfere with active implants [2,3].

Terahertz or millimetre wave scanners
These use radio waves, which can penetrate clothing. They can be either active or passive. Passive devices use the energy naturally emitted by the human body to form an image. Active devices produce radio waves that are reflected off the skin to form an image. The energy emitted by these systems is around 100,000 times less than a mobile phone transmission [4]. The frequency of the electromagnetic radiation used in terahertz or millimetre wave scanners and backscatter X-ray scanners does not pass through the skin and is not known to interfere with pacemaker, ICD or neurostimulator technology.

References
1 Health Protection Agency. Body scanning at airports. http://www.hpa.org.uk/Topics/Radiation/UnderstandingRadiation/UnderstandingRadiationTopics/BodyScanners/
2 Effects of CT Irradiation on Implantable Cardiac Rhythm Management Devices. Radiology: Volume 243: June 2007
3 Does High-Power Computed Tomography Scanning Equipment Affect the Operation of Pacemakers? Satoshi Yamaji, MD et al Circ J 2006; 70: 190-197
4 USA Homeland security. Privacy Impact Assessment for TSA Whole Body Imaging. http://www.dhs.gov/xlibrary/assets/privacy/privacy_pia_tsa_wbi.pdf

For further information contact Simon Holmes, Simon.holmes@mhra.gsi.gov.uk (020 3080 7240).


Page last modified: 20 August 2013