NEW ORLEANS—It might not be music to your ears, but headphones for MP3 players placed within an inch of pacemakers and implantable cardioverter defibrillators (ICDs) may interfere with the devices, according to a poster presentation on display Sunday at the American Heart Association (AHA) Scientific Sessions.
Researchers investigated the effects of MP3 player headphones, most of which contain the magnetic substance neodymium, on the operation of implantable cardiac devices (abstract P662). Earlier this year, an FDA report concluded that interactions between MP3 players, such as the popular iPod, and implanted cardiac devices are unlikely to occur.
“We became interested in knowing whether the headphones which contain magnets—not the MP3 players, themselves—would interact with implanted cardiac devices,” said the study’s senior author William H. Maisel, MD, director of the Medical Device Safety Institute at Beth Israel Medical Center in Boston.
He said doctors traditionally use magnets in the clinical setting to test pacemakers. ICDs near magnets may temporarily stop looking for abnormal heart rhythms. Implanted cardiac devices that react in these ways to magnets outside the clinical setting can be potentially dangerous for patients, who rely on the lifesaving technologies.
Researchers tested eight different models of MP3 player headphones with iPods on 60 defibrillator and pacemaker patients.
“We placed the headphones on the patients' chests, directly over where their devices are located, monitoring them for evidence of an interaction,” Maisel said.
The researchers found a detectable interference with the device by the headphones in 14 patients (23 percent). Specifically, they observed that 15 percent of the pacemaker patients and 30 percent of the defibrillator patients had a magnet response, Maisel said.
“Exposure of a defibrillator to the headphones can temporarily deactivate the defibrillator,” he said. In most cases, removal of the headphones restores normal device function.
The researchers also tested the magnetic field strengths of each of the headphone models using a gauss meter, which measures the units of magnetic charge produced. Field strength of 10 gauss at the site of the pacemaker or defibrillator has the potential to interact with the implantable device. Maisel and colleagues found that some of the headphones had field strengths as high as 200 gauss or more.
“Even at those high levels, we did not observe any interactions when the headphones were at least 3 cm, or about 1.2 inches, from the skin's surface,” Maisel said. “Patients should not focus on the brands we tested, but instead should simply be instructed to keep their headphones at least 3 cm from their implantable devices."