The Food and Drug Administration (FDA) has issued an advisory to physicians on electromagnetic interference (EMI) from anti-theft systems and metal detectors to implanted pacemakers, defibrillators and spinal cord stimulators. "The number of reported significant patient injuries is very low," the September 28 letter emphasizes. Still, "to be on the safe side," the FDA's Center for Devices and Radiological Health (CDRH) suggests the following "simple precautions" for people with implanted medical devices:
** Do not stay near the system longer than necessary, and do not lean against it. ** Ask security personnel not to hold hand-held metal detectors near implanted devices. ** Be aware that anti-theft systems at store entrances may be hidden or not obviously visible.
"We do not think that we have a major public health problem at this time," said Dr. Elizabeth Jacobson, CDRH's deputy director for science, "but we would like it to stay that way." Jacobson pointed out that implanted devices are becoming more common, and that the use of "more and more sophisticated microcircuitry" makes them more vulnerable to interference. She spoke at a September 24, 1998 meeting of FDA's Technical Electronic Product Radiation Safety Standards Committee (TEPRSSC) in Gaithersburg, MD. At the TEPRSSC meeting, Dr. Michael McIvor of the Heart Institute of St. Petersburg in Florida reported that acoustomagnetic anti-theft systems caused EMI among 48 of 50 volunteers with implanted pacemakers. He found that swept RF devices produced no interactions. There was no EMI to defibrillators. The FDA considers McIvor's study to be "the single most comprehensive study on the issue," said Mitchell Shein of the CDRH. McIvor's findings appear in the October issue of PACE (Vol.21, pp.1,847-1,861, 1998). He first presented them at a conference last year (see MWN, S/O97). McIvor's findings are "of no consequence whatsoever," Dr. Warren Harthorne of Massachusetts General Hospital in Boston told TEPRSSC. "In over 30 years of experience of treating thousands of pacemaker recipients," Harthorne said, "I am not aware of any patient who has been harmed or injured by [anti-theft] devices." In an editorial in the same issue of PACE, Harthorne argues that three of the four types of EMI observed by McIvor are "of no clinical relevance." The fourth, in which a pacemaker fails to fire, could cause some symptoms-but only "if the patient lingered long enough in the field." Serious symptoms are rare, McIvor said, but not impossible. He described a 28-year-old man who passed out in an anti-theft system's gates: "When he fell down, he fell out of the magnetic field, so he woke up. He stood up. He passed out. He stood up. He passed out-until a nurse came by and dragged him out." McIvor points to acoustomagnetic anti-theft systems as the source of most serious EMI and calls for posting warning signs. But Harthorne argues that, "If you start placing signs in stores, you're going to have a rash of hysterical patients who will then have symptoms that they never would have had otherwise." "Whose responsibility is it to get the message out to patients?" asked TEPRSSC's Dr. Victoria Marx of the University of Michigan, Ann Arbor. Dr. Victor Parsonnet of Newark Beth Israel Medical Center in New Jersey answered that he would not bring up anti-theft systems with his patients, and, if asked, would tell them simply not to worry about it. "You don't want to alarm them," he explained. Parsonnet and Harthorne are both consultants to Sensormatic, a leading maker of security systems. "We were never intending to send this advisory directly to patients --it would only scare them," FDA's Jacobson told Microwave News. She stressed that it was addressed to physicians "to make sure that the appropriate information is out there." Jim Putzke of the Health Industry Manufacturers Association said that the most common neurostimulators today are spinal-cord stimulators that control pain. But, he added, devices are now being used to treat Parkinson's disease, tremors, urinary incontinence and more. "Almost everything that you can possibly imagine" is being experimented with, he said. CDRH's Jon Casamento said that the FDA had received several reports of EMI from security systems to spinal-cord stimulators: "Most of these interactions were very painful, and patients even reported being jolted or thrown to the floor." Jacobson said that the FDA does not know of any ongoing studies of EMI with spinal-cord stimulators. The FDA's advisory can be found on the Internet at:
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Charges that Sensormatic tried to suppress Dr. Michael McIvor's research results are detailed in the November/December 1998 issue of Microwave News. The first few paragraphs of this story, "Corporate Interference Charged over Disclosure of EMI to Pacemakers," are on the Microwave News Web site: www.microwavenews.com.
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