Heart doctors always warn patients with electronic implants to avoid close contact with magnetic fields. But patients may not recognize that the jewelry they receive as a gift -- or the name badge they get at a conference -- could carry magnets far stronger than their size would suggest.
These aren't your average refrigerator magnets. The newer magnets are made from neodymium-iron-boron, or NdFeB. Dozens of brightly colored, pea-size NdFeB magnets can be placed together in various intriguing shapes -- without strings or clasps.
Is this really a problem? Minnesota Heart Clinic cardiologist Huagui Li, MD, PhD, recalls an urgent call from a 64-year-old woman whose implantable cardioverter defibrillator, or ICD, began beeping.
The beeping stopped when she took off her blouse -- to which a magnetic brooch was attached.
"It is those magnets that are not easy to identify that become a problem," Li tells WebMD. "Most people don't feel the difference right away."
Magnets an Inch From Trouble
Thomas Wolber, MD, of University Hospital, Zurich, tested NdFeB magnets on 41 patients with pacemaker implants and 29 patients with ICDs, which are designed to detect a dangerous heart rhythm and shock it back into normal rhythm.
Wolber and colleagues used four different NdFeB magnets: a sphere less than a third of an inch in diameter, a sphere less than a half-inch in diameter, a necklace made up of 45 small spherical magnets, and a magnetic name badge.
Under close medical supervision, they exposed the patients to the magnets.
None of the magnets affected patients' implants -- until they got within 1.2 inches of the patient's skin. Then the magnets switched off ICDs and affected the speed at which pacemakers ran.
None of the patients had any symptoms during the tests. And their devices resumed normal function once the magnets were removed.
"Notably, only small magnets were tested," Wolber and colleagues observe. "Larger NdFeB magnets are likely to cause interference at greater distances."
Wolber and Li agree that while the magnets affect pacemakers, their effects are potentially much more serious for ICD patients.
"The ability of ICDs to detect and treat life-threatening arrhythmias is temporarily suspended as long as the magnet switch of the device is activated," Wolber tells WebMD. "This may put the patient at substantial risk if the device is inactivated for a longer period of time, as might be the case with nametags, necklaces, and brooches worn close to the device."
Wolber advises heart patients with electronic implants to be on the lookout for jewelry, accessories, or even clothing that may carry NdFeB magnets. And he warns patients not to test magnets by themselves.
What about patients who discover they have been wearing magnets?
"Don't panic, use common sense. Removal of the magnet resolves the problem immediately," Wolber says.
Wolber's study -- and an editorial by Li -- appear in the December issue of Heart Rhythm.