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  • William R. Lewis
    Correspondence
    Address reprint requests and correspondence: Dr. William R. Lewis, MetroHealth Campus, Case Western Reserve University, Division of Cardiology, H350, 2500 MetroHealth Drive, Cleveland, Ohio, 44109-1998
    Affiliations
    MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio
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Published:October 19, 2009DOI:https://doi.org/10.1016/j.hrthm.2009.10.018
      If you drove to work on a toll road today, you may have paid the fee automatically without stopping, using a device attached to your windshield. Radiofrequency identification devices (RFIDs) are increasingly being used to track inventory, provide security, and prevent theft. Hospitals also use these systems to control inventory, track expensive medical devices, locate employees to optimize staffing, and calculate patient wait times in emergency rooms. These tags are small enough to implant in a surgical sponge to assure that none are left in an operating room patient. The systems are composed of two parts: a tag attached to the item of interest and a reader that collects information from the tag. Active systems contain a battery that is the source of energy for the tag's antenna and circuitry. In a passive system, the tag contains no battery, but an antenna coil in the tag is energized by radio waves emitted by a transmitter located in the reader. These radio waves are a potential source of electromagnetic interference (EMI).
      EMI from RFIDs has the potential to interfere with medical equipment. A group from the Netherlands demonstrated that RFIDs were capable of interfering with infusion pumps and temporary external pacemakers. In addition, an RFID turned off a ventilator in one case and changed the ventilator settings in another.
      • van der Togt R.
      • van Lieshout E.J.
      • Hensbroek R.
      • Beinat E.
      • Binnekade J.M.
      • Bakker P.J.
      Electromagnetic interference from radio frequency identification inducing potentially hazardous incidents in critical care medical equipment.
      EMI with pacemakers and implanted defibrillators has been demonstrated by portable media players,
      • Thaker J.P.
      • Patel M.B.
      • Jongnarangsin K.
      • Liepa V.V.
      • Thakur R.K.
      Electromagnetic interference with pacemakers caused by portable media players.
      mobile phones,
      • Naegeli B.
      • Osswald S.
      • Deola M.
      • Burkart F.
      Intermittent pacemaker dysfunction caused by digital mobile telephones.
      and induction cooktops.
      • Irnich W.
      • Bernstein A.D.
      Do induction cooktops interfere with cardiac pacemakers?.
      In this issue of Heart Rhythm, Seidman and colleagues studied the effect of 13 RFID devices on 15 implantable cardioverter-defibrillators (ICDs) and 15 pacemakers.
      • Seidman S.J.
      • Lewis B.M.
      • Guag J.
      • et al.
      In vitro tests reveal sample radio frequency identification readers inducing clinically significant electromagnetic interference to implantable pacemakers and implantable cardioverter defibrillators.
      They used a mechanical arm to move the RFID device from 1 m to 2.5 cm away from the device, which was immersed in saline in a polyethylene plastic box to simulate a human torso. A simulated cardiac signal was applied to the system, and a bipolar pacing lead was used to monitor the output of the device being tested. The RFID systems they tested included low-frequency, high-frequency, and ultra-high-frequency passive devices. They classified device interactions as clinically significant (including permanent programming changes, ventricular inhibition for greater than 3 seconds, or inappropriate delivery of tachycardia therapy in a defibrillator) or clinically insignificant (including inappropriate pacing, ventricular inhibition for less than 2 seconds, atrial inhibition, and noise reversion). When pacemakers were studied, low-frequency RFIDs caused the greatest degree of interaction, with 67% of tests resulting in a reaction. Thirty-nine percent of tests caused clinically significant reactions. In contrast, 6% of tests using the high-frequency RFID resulted in an interaction, and only 4% were clinically significant. There were no reactions to the ultra-high-frequency RFIDs. In the ICD tests, clinically significant reactions occurred in 46% of the low-frequency tests, whereas no clinically significant reactions were observed with the high-frequency systems. Again there were no reactions to the ultra-high-frequency RFID devices. The probability of an interaction was inversely proportional to the distance from the RFID device. All clinically significant reactions were observed within 40 cm of the reader.
      The present study emphasizes two important concepts. First, with respect to implantable pacemakers and defibrillators, ultra-high- and high-frequency RFIDs should be preferentially used especially for medical applications. The authors state that ultra-high frequency cannot be used in patient applications due to the fact that human tissue absorbs radiofrequency in this range. Second, maintaining distance from the reader is critical to avoiding clinically significant reactions.
      Overall, this study was well designed and carefully executed. It sheds new light on the potential importance of environmental EMI to pacemaker and ICD patients. Yet despite the high number of clinically significant reactions demonstrated in this study, the authors state that there have been no reports to the Food and Drug Administration of EMI related to RFIDs. The reason for this discrepancy is not known. It is not clear that the authors' human torso model is valid. Several factors, including torso size, alter the degree of susceptibility to EMI.
      • Joosten S.
      • Pammler K.
      • Silny J.
      The influence of anatomical and physiological parameters on the interference voltage at the input of unipolar cardiac pacemakers in low frequency electric fields.
      The results of this study differ from the findings of van der Togt and colleagues,
      • van der Togt R.
      • van Lieshout E.J.
      • Hensbroek R.
      • Beinat E.
      • Binnekade J.M.
      • Bakker P.J.
      Electromagnetic interference from radio frequency identification inducing potentially hazardous incidents in critical care medical equipment.
      where more incidents of interference with medical equipment were observed using the ultra-high-frequency RFID compared with the low-frequency device. That study differs significantly from the present study, however. In the study by van der Togt et al,
      • van der Togt R.
      • van Lieshout E.J.
      • Hensbroek R.
      • Beinat E.
      • Binnekade J.M.
      • Bakker P.J.
      Electromagnetic interference from radio frequency identification inducing potentially hazardous incidents in critical care medical equipment.
      the low-frequency device was an active system and the ultra-high-frequency device was a passive system. Additionally, both systems were used at maximum power. Another factor may also explain the different findings between the studies. Filtering in pacing and defibrillation systems likely offers some protection from high- and ultra-high-frequency EMI from RFID. Other medical devices likely do not have such protection. Because of these differences, studies on other medical equipment should not be extrapolated to pacing and ICD systems.
      Pacemakers and defibrillators are designed to minimize EMI using shielding and signal filtering. Nevertheless, EMI is ubiquitous, and device patients and their physicians should be aware of its sources and consequences. If patients and physicians are aware of the potential sources of EMI in the patient's home and work environment, appropriate precautions can be taken and the consequences of EMI can be avoided. Pacemaker and defibrillator interactions often are exaggerated and sensationalized, causing potential patients to refuse such life-preserving therapy. In one study, 56% of pacemaker patients in India felt it was unsafe for them to flip a light switch.
      • Aqeel M.
      • Shafquat A.
      • Salahuddin N.
      Pacemaker patients' perception of unsafe activities: a survey.
      However, an informed patient can be reassured that significant interactions can be avoided with simple precautions. No clinically significant interactions in the present study occurred when the reader was at arm's length or greater.
      RFID technology has the potential to improve efficiency and outcomes in health care. However, if the benefits of RFID technology in health care are to be reaped, further studies are needed to evaluate its safety with pacemakers, ICDs, and other medical equipment. These studies should include a variety of frequencies, active and passive devices, and various distances. Such studies should include clinical data to supplement the bench research.

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