Zurich, Switzerland - Magnets are everywhere, and some that patients with implantable cardioverter defibrillators (ICDs) or pacemakers could encounter every day are strong enough to interfere with the devices, changing their settings, with consequences ranging from negligible to life-threatening, according to a report scheduled for the January 2007 issue of Heart Rhythm [1].

The potential for magnetic interference is a long-recognized problem for ICDs and pacemakers, but less appreciated, according to Dr Thomas Wolber (University Hospital, Zurich, Switzerland) and colleagues, is that small but surprisingly strong magnets are increasingly appearing in products worn on the body.

The reason: growing and widespread commercial use of inexpensive neodymium-iron-boron (NdFeB) magnets. These "rare-earth" magnets are common in hard drives and other computer components, audio and video electronics, laboratory equipment, eyeglasses and jewelry, toys, clothes, workplace identification badges, and many other products. They are frequently hidden from view or exposed but not obvious.

"Magnetic toys and NdFeB magnets for home and office use should be handled with caution in patients with pacemakers and ICDs," Wolber et al write. "The use of name tags, jewelry, or reading glasses containing NdFeB magnets should generally be considered to be contraindicated."

The group tested the effects of a magnetic name tag and different-sized spherical NdFeB magnet beads placed, in varying orientations and distances from the skin surface, over the pectoral implantation sites of 41 patients with pacemakers and 29 with ICDs. Magnetic interference was observed at skin-to-magnet distances of up to 3 cm, with a mean maximum interference distance of 2.1 cm for pacemakers and 1.7 cm for ICDs (p=0.007).

None of the patients experienced symptoms during magnet testing, and the devices resumed normal function after the magnets were removed. There were no interference-distance differences by device manufacturer. Interference strength depended on the magnets' size, shape, and orientation on the chest. "Only small magnets weighing up to 8 g were tested. Larger NdFeB magnets are likely to cause interference at greater distances," the group writes.

In an accompanying editorial [2], Dr Huagui Li (Minnesota Heart Clinic, Edina) writes that "unintentional magnet interference of implantable devices may be much more common than expected." He cites observational data suggesting it occurred at a rate of 11% in a patient cohort followed for 84 patient-years.

"Persistent magnet interference of a pacemaker can deplete the battery and cause undesirable hemodynamic effects because of rapid pacing at the magnet rate," he writes. More rarely, according to Li, magnetic interference could cause asynchronous pacing that promotes ventricular arrhythmias.

In ICDs, he writes, magnetic interference could disable arrhythmia detection and treatment functions, leaving the patient vulnerable to sudden death.

Manufacturers that incorporate NdFeB magnets in their clothes, jewelry, or other items that could be worn or placed close to an implanted device, Li writes, "should be required to put warning labels on their products to avoid serious health consequences for pacemaker or ICD patients."

In addition, Li told heartwire, "The physician community should be aware that some decorative products may have magnets in them, and, when they have discussions with their patients with implantable devices, tell them they should check any decorations they put on their body to make sure they don't contain magnets."

Device manufacturers often put warnings about magnetic exposure in their patient-education literature, he observed, but it would be helpful if they also emphasized how common magnets are in products worn on the body.