Friday, January 8th, 2010 | Posted by Reik Read

Cardiac Implantables Show Reaction to RFID, But Mitigation Factors Do Exist

Two new studies, which will be published in the near future, suggest electromagnetic interference (EMI) of pacemakers and implantable cardiac defibrillators (ICDs) can be caused by RFID readers at LF and HF, while UHF results are more mixed. The conclusion of these studies differ somewhat, but both suggest process-related protections be implemented, and longer term, that the implantable and RFID manufacturers should work to mitigate interference in future product sets. The conclusion from one study states that RFID interference is not a public health risk.

We are pleased to see that these two studies are in-depth, followed a test protocol and evaluated the impact of RFID at varying frequencies. As we noted in “Medical Standards Need More Work,” published in the August edition of RFID Monthly, the work to date has been limited in testing RFID and its impact on medical equipment with only one European study conducted at the Academic Medical Centre at the University of Amsterdam in 2006. More of this type of work will supply healthcare providers with parameters towards selecting and implementing RFID systems. In our view, this helps reduce uncertainty associated with RFID, which in turn helps improve the acceptability of the technology.

Results Summary
Of the studies to be published, one was conducted by the U.S. Food and Drug Administration (FDA), while the other is from the University of Hokkaido in Japan. Results from the FDA study show a reaction observed with LF (ISO 11785) on 67% of pacemakers and 47% from ICDs. At LF, the maximum distance for a reaction was 60 centimeters for a pacemaker and 40 centimeters for an ICD. At HF (ISO 18000-3, mode 1), reactions occurred in 6% of pacemakers and 1% of ICDs. At HF, the maximum distance for a reaction was 22.5 centimeters for a pacemaker and 7.5 centimeters for an ICD. At UHF (ISO 18000-6B) no reactions were observed for either pacemakers or ICDs. The conclusion of the study stated, “We do not believe the current situation reveals an urgent public health risk.” The Hokkaido study showed similar results for LF and HF, but unlike the FDA, also showed some reactions to UHF.

Overview of Key Issue – EMI
At issue for these types of implantable devices is the impact from EMI, which can be caused by RFID readers. These implantable devices are generally sensitive and can misinterpret outside EMI as a physiological signal from the body, which can cause the device to act in a different manner than the prescribed treatment. These devices have been improved over the years with more external noise rejection filters and improved on board software, which has reduced the EMI impact from microwaves, cell phones and other commonplace devices that emit EMI. However, EMI can still cause issues depending on several factors, including frequency, field strength, duty-cycle, proximity and duration of exposure. LF caused the most reactions as that frequency tends to defeat the feedthrough filters of the implantable. According to the FDA study, “UHF signals are filtered most effectively, followed by HF…”

Synopsis of Test Methodology
Both the FDA and Hokkaido tests used a similar methodology that was largely a modified version of the AAMI PC69 Standard, which is used for developing in vitro test protocols for implantable pacemakers and ICDs. A human torso simulator (or torso phantom), essentially a box with a 0.18% saline solution, was used to house the implantable, while a reader was attached to non-conducting material on a robotic arm. The saline solution is consistent with the electrical properties of body tissue. Testing equipment was set up to read any reactions by the implantable. Most of the test procedures used a conservative approach, for example, the implantable was set to maximum sensitivity.

For the FDA Study, the RFID reader was placed 100 centimeters away, and moved toward the torso simulator that contained the implantable at a constant rate of speed until reaching 2.5 centimeters. Once a reaction was observed the test protocol required the reader to be moved outside of the range and then again moved towards the torso simulator, this time at set intervals of 2.5 centimeters, which included a pause of 10 seconds at each level. All reactions were recorded. The FDA tested 15 pacemakers and 15 ICDs using 13 readers. The study recorded 1,091 tests between June 2006 and August 2008. The wide number of tests came from using different readers and different settings on the implantable. “Reactions from the implantable pacemakers and ICDs included pacing inhibition, inappropriate pacing, noise reversion mode, changed pacing rates, inappropriate delivery of ATP (anti-tachycardia packing), inappropriate delivery of high voltage shocks and a device programming change (specifically a change from bipolar to unipolar pacing).”

Conclusions
The studies did show reactions in pacemakers and ICDs from EMI induced by LF and HF readers, which is concerning. However, the FDA does not see an immediate public health threat on cardiac implantables from the use of RFID. Instead, the study made several recommendations to ensure that RFID and its associated benefits can be used in healthcare settings, while continuing to protect patient health.

With this data in mind, consideration should be given to the potential EMI impact between cardiac implantable devices and RFID. Processes should be enacted to maintain separation between implantables and RFID readers to help diminish the impact of EMI.
Manufactures for both medical implantables and readers need to work together to understand the key issues in order to improve equipment designs. The FDA noted that implantable providers are already working to develop industry design requirements. This will be an important process as the FDA noted, “With so many promising healthcare applications for RFID it is inevitable that RFID and medical devices will increasingly function in close proximity.”
Where close proximity is likely, consideration needs to be given to the type of technology employed. As evidenced by the study, some technologies caused greater reactions than others.

This study was conducted by the FDA’s Center for Devices and Radiological Health (CDRH) and included support from the Association for the Advancement of Medical Instrumentation (AAMI) Cardiac Rhythm Management Devices (CRMD) Electromagnetic Compatibility (EMC) Task Force. The full study will be published in HeartRhythm Journal in January.

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