Protecting the Beat of Life

As electronic components become smaller and smarter, they allow development of increasingly sophisticated pacemakers, implantable defibrillators and other medical devices that have already improved life for more than a million people worldwide. At the same time, growing concern about theft from retail stores has led to widespread use of electronic article surveillance (EAS) systems that generate fields of electromagnetic energy while in operation.

Those electromagnetic fields can potentially interfere with operation of the sensitive medical devices, causing concern for some store customers using pacemakers or implantable defibrillators.

Test Center helps Manufacturers avoid Potential Problems

Researchers at the Georgia Tech Research Institute(GTRI) are working with manufacturers of both types of equipment to understand - and therefore help prevent - potentially harmful interactions. The work takes place at the EAS/Medical Device E3Test Center, a unique facility supported by manufacturers of the electronic article surveillance systems.

"As both groups of manufacturers learn more about one another, there will be fewer and fewer potential interactions," said GTRI Senior Research Engineer Jimmy A. Woody, manager of the test center. "What's unique here is that the manufacturers of the energy source and the manufacturers of the medical devices are cooperating to set up and use a test center that benefits both groups."

Support to set up the test center came from the International Electronic Article Surveillance Manufacturers Association (IEASMA), which estimates that 400,000 EAS systems are used worldwide. Typically placed near store exits and entrances, the EAS systems use electromagnetic energy to detect special tags placed on items stores wish to protect.

Devices Studied with Representative Sample of EAS Systems

The resulting data is used by the manufacturers' design and quality assurance departments to improve their products, if necessary. Thus, this data helps the manufacturers ensure that interference, which could cause harm to the wearers of medical devices, is not experienced.

Testing takes place with the devices submerged in a tank of saline solution that simulates the electromagnetic behavior of the human torso. Using a computer-controlled positioner, the tank containing the medical device is moved through each merchandise control system in a manner that simulates the way customers might walk through such systems in retail stores. The test protocol also simulates customers standing in a checkout line near equipment used to deactivate the control tags.

Because of a nondisclosure agreement, Woody and Herkert provide the data they generate only to the manufacturers who submit the devices. The researchers do not have medical training, so they do not render judgements about the health implications of the data they measure.

Devices are Designed to Handle Interference

"All of the responses we have seen are temporary in nature," he said. "As soon as the devices are moved out of the interfering field or the field is turned off, they return to the operational mode they were in before the test started."

Ironically, the features of a pacemaker or defibrillator that allow it to respond to the specific needs of an ailing heart make it potentially vulnerable to outside electromagnetic interference. Modern pacemakers and implantable defibrillators sense the body's heartbeat. When they detect an abnormal rhythm, the devices produce electrical pulses to restore a normal heartbeat. But electronic equipment can generate signals similar to those of the heart itself.

Woody explained,

"In any electromagnetic environment, the field or its modulation could mimic a heartbeat. The pacemaker could detect that signal as a heartbeat and be confused. That's why historically medical device manufacturers have tested their devices in various electromagnetic environments prior to submission to the U.S. Food and Drug Administration (FDA)."

To counter the potential interference, manufacturers include filters that keep out most of these external signals. In addition, modern pacemakers also include a "noise" mode that temporarily shifts the devices to a generic heartbeat pacing rate when they receive confusing signals. This mode keeps a heart beating until the interference is removed.

Woody and Herkert have tested more than 120 medical devices since the center opened in 1995. The testing includes both prototype and pre-production devices.

Potential Interference Studied for More Than 30 Years GTRI researchers have been studying the potential interactions between medical devices and other equipment for more than 30 years. Woody said the devices have improved dramatically during that time.

"Thirty years ago, it was not uncommon to expose a pacemaker to an electromagnetic field and have it stop pulsing," he said. "Nowadays, the results tend to be much less dramatic."

Electronic article surveillance systems are not the only potential sources of interference. GTRI also tests the effects of microwave ovens, military radar systems, cellular telephones, electric power equipment and radio broadcasts. Over the past 30 years, more than 1,600 medical devices have been tested.

As medical research produces new implantable devices, such as nerve stimulators and insulin pumps, Woody expects a steady demand for testing services.

We thank Jane Sanders, Editor, Research Horizons for permission to publish this article. Jane can be contacted at Research News & Publications Office, Georgia Institute of Technology, Atlanta, GA 30-332-0640, USA.
Tel: +1 404 894 2214 or +1 770 975 1014
Email: jane.sanders@edi.gatech.edu
Web site: www.gtri.gatech.edu/res-hor/