LONDON -- People with pacemakers should walk quickly through shoplifting detectors at store entrances to avoid possible interference that could cause dizziness or fainting, an American cardiologist recommended Wednesday.
Dr. Michael E. McIvor, medical director of the Research Center at the Heart Institute of St. Petersburg, Fla., based his recommendation on a study that found that signals from some detectors caused pacemakers to emit extra heart beats or stop entirely.
"The risk is small," he told a conference on store security systems sponsored by the Center for Retail Research. "If you walk through the device and if you don't stop, you're probably not going to be hurt. But if you stand in the device, there is a potential for harm."
The study found that the most popular theft detection system used in the United States affected pacemakers in 96 percent of cases. Two other systems caused little or no interference, McIvor said.
Dr. Richard Sutton, a cardiologist who directs the pacemaker program at the Royal Brompton Hospital, said McIvor only cited four cases of people with pacemakers getting dizzy or fainting and accused him of exaggerating "the infinitesimal nature of the danger."
"You're making a huge song and dance of it which will undoubtedly ... make patients nervous," he said.
In the study, 50 volunteers with a variety of pacemakers were tested with different detectors, which set off an alarm if a person walks through with a tagged piece of merchandise. The volunteers first walked through the detector quickly, and then lingered for two minutes.
When they lingered, 48 of the 50 volunteers reacted to the acusto-magnetic detection system, which transmits signals in pulses and generates high voltage and very strong magnetic field.
McIvor said 69 percent had extra heart beats. Twenty-four percent had the signal turn their pacemaker off, and six percent experienced rapid heart beats. Several became dizzy and were moved away from the system so they wouldn't faint, he said.
The volunteers' pacemakers did not react to radio frequency detection systems, which use high frequencies and generate a weak magnetic field. And the pacemakers responded to only one brand of magnetic audio-frequency systems, which use extremely low frequencies and create a moderate magnetic field.
McIvor said a pacemaker battery is only 2.5 volts, so it was not surprising that it would get confused about what to do when it was penetrated by the acusto-magnetic system's stronger magnetic field of 3.7 volts.
"I'm not suggesting acusto-magnetic systems need to be withdrawn from the market. It's just they need to be used with more caution, more prudence," McIvor said.
Stores should use signs and voice warnings telling customers wearing pacemakers not to linger in the strong magnetic fields created by acusto-magnetic detectors, he said.
Detectors should also be placed away from cashiers and customers waiting in line at checkout counters, he said.
McIvor said the U.S. Food and Drug Administration is still studying the effects of shoplifting detectors on pacemakers, but he said the data from his study should not be ignored.
"Common sense precautions can keep anyone from getting hurt," he said.