TORONTO - Headphones for portable MP3 players can interfere with pacemakers and defibrillators implanted in patients' chests to control heart rhythm problems and should be used with care, a study has found.
U.S. researchers tested the headphones for eight different brands of portable music players, placing them over the chests of 60 patients with either an implanted pacemaker or defibrillator.
In one in four patients, the headphones interfered with the cardiac devices, which are used to maintain a normal heart rhythm.
"Portable headphones have powerful magnets in them," said senior investigator Dr. William Maisel, director of the Medical Safety Device Institute at Beth Israel Medical Center in Boston.
"And patients with pacemakers and defibrillators should not allow the portable headphones to get close to their device."
Maisel said the results don't mean that people with pacemakers or defibrillators can't use MP3 players to enjoy music, but tests showed they should keep headphones at least three centimetres away from the cardiac devices.
"They should not take them out of their ears and rope them over their chest," he said from Boston. "And they shouldn't take them off and wrap them up and store them in their front shirt pocket, shouldn't put them in a front coat pocket that would leave the headphones very close to their device."
As well, people with implanted cardiac devices should avoid having another person wearing headphones rest against their chest.
"As long as you keep the headphones a short distance from the chest, there's no interaction," said Maisel, who presented the study's findings Sunday at the American Heart Association meeting in New Orleans.
The researchers also measured the magnetic field strength of the various headphones.
They found that some had batteries that produced magnetic field strengths that were 20 times higher than the minimum needed to interfere with implanted cardiac devices.
In the case of pacemakers, which are used to increase the heart rate when it gets dangerously slow, the headphones can cause the heart "to beat without regard to the patient's underlying heart rhythm," he said.
"So somebody could have a perfectly sufficient heart rate and you put a magnet over their pacemaker, it will cause the heart to beat even faster. It can also cause it to beat irregularly."
Implanted defibrillators are designed to shock the heart into a normal rhythm if it stops beating properly, which can be a precursor to a cardiac arrest.
"And if a defibrillator is deactivated, then theoretically a patient could have a cardiac arrest and it would not be recognized or treated by their defibrillator if a magnet were on top of it," Maisel said. "Theoretically, that could be fatal."
In testing, the researchers found that the effect of the headphones was temporary: as soon as they were removed a safe distance, the cardiac devices' function returned to normal.
Dr. Eugene Crystal, a cardiologist and electrophysiologist at Toronto's Sunnybrook Health Sciences Centre, said he is not surprised at the findings.
"We know there's a lot of interference between electromagnetic devices of different kinds and the pacemakers, because pacemakers are simply acting like antenna, and with a certain frequency and amplitude of the signal, they will recognize (it) as a potential signal from the heart."
Crystal, who was not involved in the study, said a defibrillator may react to the magnet and shock a patient inappropriately, even when the heart's rhythm is normal.
"We usually advise our patients that anything that is electronic should not be put close to the (cardiac) device, so not in the front pocket of your shirt, for example."
Maisel said the researchers don't want to discourage people with pacemakers or defibrillators from enjoying portable music players.
"It's fine for patients to use them, they just need to be judicious."
