Thursday, November 5, 1998 Published at 22:29 GMT
Security gates pose threat to heart devices
Electronics stores often have anti-theft devices by the exit
The magnetic fields generated by anti-theft gates at shop exits can affect pacemakers and other devices with potentially fatal results, doctors have warned.
The warning comes in two reports published in the New England Journal Of Medicine.
Many shops now use such devices to deter shoplifters. The devices sense the presence of a magnetic security strip on products being illicitly removed from the store and sound an alarm.
But the reports indicate that they can also trick a pacemaker or defibrillator - which regulate the heartbeat - into thinking the patient is suffering an attack of some sort.
The device then applies unnecessary electric shocks to the heart.
In the first report, a 72-year-old man, who had a defibrillator to automatically shock his heart whenever it beats irregularly, suffered four unnecessary shocks as he stood close to an anti-shoplifting gate in a bookshop.
A nurse pulled him away from the gate and probably saved his life, said the report's author, Dr Peter Santucci of the Rush-Presbyterian-St. Luke's Medical Centre in Chicago.
He said: "A registered nurse also shopping in the bookstore noticed the man was being shocked and pulled him away from the electronic anti-theft surveillance equipment.
"This situation could have been life-threatening if she hadn't pulled the man away."
The man's defibrillator can record abnormally slow and fast rhythms.
Dr Santucci used this information to establish what had happened.
"In addition to the patient's normal heart rhythm, we saw a flurry of electrical spikes that were too fast to be his normal rhythm," he said.
He performed tests to confirm that the surveillance equipment was the cause of the interference.
He used an anti-theft device of the same model and a defibrillator that was tested to ensure it was functioning properly.
At a distance of one foot, electromagnetic interference affected the defibrillator on three occasions.
In the other case, two doctors looked at the reasons behind a 30-year-old woman with a pacemaker's problem.
She felt nauseous, breathless, and dizzy whenever she passed through electronic surveillance gates at shops.
They discovered that the anti-theft devices made her pacemaker send out the wrong signals.
One of the doctors involved in the study, Dr Michael McIvor of the Heart Institute of St Petersburg, Florida, pointed out that not all types of anti-theft surveillance systems create the type of magnetic interference that can disrupt pacemakers.
However, he said "patients with pacemakers, particularly those who are dependent on them, should take care to minimise their contact" with such systems "by passing quickly through the gates".
Even then symptoms can occur, he warned.
Newer systems "can be unobtrusive, located behind walls or beneath flooring," Dr McIvor said.
He called on shops to mark clearly areas where there are strong magnetic fields.
Dr Santucci's team advised that "merchandise should not be displayed next to electronic surveillance equipment".
They said: "With the increasing use of both implantable defibrillators and anti-theft surveillance devices, potentially serious interactions may be more common in the future unless preventive measures are undertaken."
It is estimated that 400,000 electronic anti-theft surveillance devices are present in stores, libraries and other locations worldwide.
Other sources of electromagnetic interference, such as slot machines and remote control devices for toys, are also known to disrupt devices designed to sense and correct erratic heart rhythms.