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Key words: electromagnetic compatibility, EMC, electronic article surveillance, EAS, pacemakers, electromagnetic fields
The FDAs Medical Device Report (MDR) system includes a number of reports of serious problems with implanted cardiac pacemakers due to interference from electronic article surveillance (EAS) systems. Both clinical and laboratory studies in the United States and Europe show that the pulsed magnetic fields from certain EAS systems can interfere with the normal operation of most models of pacemakers. Interactions reported include inhibition, reversion to fixed-rate pacing, atrial oversensing resulting in EAS induced tachycardia, asynchronous pacing, ventricular oversensing, and EAS induced pacing.
To address this issue, OST scientists acquired seven samples of EAS systems that represent the more popular EAS systems and technologies in use today. A unique, 3D scanning system with a nonmetallic arm was used to map the electric and magnetic fields generated by the units. This computer-controlled scanning system is capable of mapping EM fields at any point in a volume measuring 2 meters x 2 meters x 1 meter.
Figure 10 shows a sample magnetic field map from an EAS system, and Figure 11 shows the location of the plane in which the field was measured. The purpose of the EM field mapping was to help to quantify the magnitude of EM fields to which the persons can be exposed when walking through the EAS system. CDRH also worked with the FDAs Winchester Engineering and Analytical Center (WEAC) in Massachusetts to provide technical advice and support for their survey of EM fields generated by EAS units installed in local commercial establishments and hospitals.
Figure 10- Sample Magnetic Field Map of EAS System
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Figure 11- Locator of Measurement Plan in EAS Experiment
OST also developed a patient-simulating model for in vitro testing of the effects on various pacemakers from actual EAS systems. In this model, a pacemaker with its leads are fixed in a predetermined configuration and excited by a simulated cardiac wave-form until the pacemaker responds to the excitation as it would in a patient. Then the pacemaker is exposed to fields emitted from EAS systems. The response of the pacemaker to the EM fields is noted for a given orientation and distance from the EAS system transmitter. The first pacemaker was tested in this system in FY 97, and some unintended interactions were noted. OSTs EM field data plots provide a means to determine the field strengths that cause these interactions with pacemakers.
The data from these laboratory studies, along with data from MDR reports and clinical studies of this problem are being used by a CDRH ad hoc committee to assess the risk that EAS systems pose to the pacemaker patient. Based on the findings of these studies, OST will participate in the development of CDRH recommendations for pacemaker wearers and facilities utilizing EAS systems.