Interactions Between Surveillance Systems and ICDs
Abstract & commentary
Synopsis: It is generally safe for a patient with an ICD to walk normally through an electronic surveillance system.
Source: Groh WJ, et al. Circulation 1999;100:387-392.
Groh and colleagues performed a study to assess the effects of commercial electronic surveillance systems used for antitheft applications in commercial stores on the function of detection systems in implantable cardioverter defibrillators (ICDs). Three participating centers recruited 170 individuals with ICDs. The patients were left with their tachyarrhythmia detection algorithms as clinically programmed but delivery of therapy was inactivated. The patients’ electrocardiograms were continuously monitored during the testing procedure to minimize risk that they might have either a device-induced or spontaneous episode of arrhythmia while the therapy function of their device was inactivated. Three types of electronic surveillance systems were tested. Three different commercial systems were studied: a pulsed acoustomagnetic system (Ultra-Max) and two different electromagnetic systems (Aislekeeper and P-Magnetic). These electronic surveillance systems are commonly used worldwide and are representative of the types of installations in common use.
Patients were exposed to the systems in three different protocols. In the routine exposure protocol, subjects were asked to walk through the middle of the gates over a 10-15 second period. This was thought to mimic typical exposure by an elderly individual entering a store. For an extreme exposure, subjects were told to stand within six inches of the gate transmitter of the surveillance system for two minutes. Subjects either turned or leaned on the gate transmitter to ensure exposure from different directions. Finally, extreme exposure format was repeated with pacing, since activation of pacing changes the sensitivity for detecting cardiac arrhythmias in many types of ICD systems.
The patients had ICDs made by five different manufacturers. They included patients with 26 different ICD models, including both abdominal and pectoral implants and several different sensing configurations (endocardial tip to ring, endocardial tip to coil, and bipolar epicardial sensing).
During routine exposure, no alteration in baseline cardiac arrhythmia was observed with gate transit. There was also no indication of ICD reprogramming. In three subjects undergoing extreme exposure, inappropriate tachyarrhythmia detection was observed. These three detections occurred with use of the pulsed acoustomagnetic system, Ultra-Max, and would have resulted in shocks if therapy had been programmed on. The extreme exposure resulted in continuous noise that was detected by the ICD as ventricular fibrillation. These inappropriate detections were observed in one Medtronic model (7219) and two Cardiac Pacemaker, Inc., model 1746 defibrillators. During extreme exposure with pacing, 19 of 126 subjects showed evidence of oversensing. No ICD reprogramming was observed. In 12 subjects, the interaction was not clinically significant, consisting of only an intermittent delay in pacing caused by noise-augmented T-wave oversensing. In seven subjects, however, the interactions were clinically relevant. Complete pacing inhibition occurred with surveillance system exposure in five patients. In two additional subjects, prolonged pacing inhibition, but not complete cessation of pacing, was observed.
Groh et al conclude that it will be generally safe for a patient with an ICD to walk normally through an electronic surveillance system. Patients should be cautioned not to linger in a doorway where such a system may be in use and certainly should not stop completely in immediate proximity to the gate transmitter.
Comment by John P. DiMarco, MD, PhD
Within the last year, a number of interactions of electronic devices commmon in the environment have been reported with both pacemakers and defibrillators. Interference may occur with cellular telephones, particularly digital models, diagnostic or therapeutic medical devices, strong magnetic fields from radio transmitters, and now electronic antitheft surveillance systems. The latter interaction may be particularly significant since these devices are ubiquitous in the environment and are often not immediately obvious to someone entering a store or business establishment. This article demonstrates that although technical problems with these devices should be rare, they can occur particularly if the patient makes an unusually close approach to the transmitter.
It is likely that similar interactions will occur more frequently in the future. One would also like to have standards developed within the industry that might prevent further increases in the electronic output from these devices. Levels of energy that might be safe for normal individuals could increase the exposure risk in patients with implantable devices that depend on sensing small amplitude electrical events. For now, Groh et al’s suggestions seem reasonable. Patients should be aware that an interaction is possible but need to eliminate only a few specific and unusual activities. (Dr. DiMarco is Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville.)
Patients with ICD should be advised regarding electronic surveillance systems to:
a. walk normally through them.
b. not linger in them.
c. not get close to the transmitter.
d. All of the above
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