Theft-stoppers jam pacemakers, shockers.

Antitheft detectors in retail stores and elsewhere require patrons to pass through a portal that scans them with a magnetic field in search of stolen goods. New medical findings indicate that certain heart patients who linger near such portals may place themselves in harm's way. The reports find that the scanners' magnetic fields can interfere with implanted electronic devices, such as pacemakers and defibrillators, that control heartbeats.

Heart specialists, including the authors of the new reports, say that the consequences of interference can be life-threatening. However, disruptions occur so rarely and are so easily corrected by simply moving away from the portals that the likelihood of harm is very low. The specialists urge people with implanted heart controllers to walk normally through the scanning gates and then to move promptly away from the instruments.

In a laboratory study described in the October Pacing and Clinical Electrophysiology, researchers at the Heart Institute of St. Petersburg, Fla., tested the three types of antitheft portals commonly used in the United States. They report that the newest and fastest-growing version of the technology, known as acoustomagnetic surveillance, temporarily affected the functioning of pacemakers in 48 of 50 subjects tested. The other two classes of instruments had little or no effect.

None of the technologies disrupted defibrillators in 25 other volunteers. Implanted defibrillators monitor the heart for a potentially fatal, disorderly quivering known as ventricular fibrillation. They then correct it by delivering electric shocks to the organ.

Because acoustomagnetic detectors are effective over greater distances than competing devices and will work even if concealed, users of the systems are increasingly installing them out of sight in walls, ceilings, and floors. "I think there should be advisory signs," says cardiologist Michael E. McIvor, leader of the study.

Representatives of Sensormatic Electronics Corp. in Boca Raton, Fla., the sole manufacturer of the acoustomagnetic gates, dismiss the St. Petersburg group's results as no news at all. They say the potential for interference has been known, but extremely rarely seen, in the decade since acoustomagnetic scanners were introduced. In instruction manuals given to patients and doctors, defibrillator and pacemaker manufacturers have for years included warnings about lingering near antitheft scanners, they note. "This is a tempest in a teapot," says Douglas P. Zipes, chief of cardiology at the Indiana University School of Medicine in Indianapolis, who is conducting a Sensormatic-funded study of scanner impact on defibrillators.

Sensormatic's business rival, Checkpoint Systems in Thorofare, N.J., gave the lion's share of funding for the St. Petersburg study, but McIvor insists that his team maintained its independence and integrity. In an editorial accompanying the study, J. Warren Harthorne of Massachusetts General Hospital in Boston questions the medical significance of the study's results since "there are no reports in the real world of patient harm."

However, a pair of articles in the Nov. 5 New England Journal of Medicine now documents real-life instances of the effects. McIvor coauthors one correspondence that describes a 30-year-old woman with a pacemaker who had palpitations, nausea, and other symptoms while passing through a store's acoustomagnetic antitheft gate. In the other report, a team at Rush-Presbyterian-St. Luke's Medical Center in Chicago describes a near-fatal episode in which a 72-year-old man's implanted defibrillator-pacemaker misfired under the influence of an acoustomagnetic portal and temporarily shut off his heart.