US researchers have warned that the magnets in iPod headphones and those used by other MP3 devices "may interfere with heart pacemakers and implantable defibrillators".
A team led by Dr William Maisel of the Medical Device Safety Institute at Beth Israel Medical Center in Boston tested eight models of MP3 cans on 60 defibrillator and pacemaker patients by placing the headphones on their volunteers' chests, "directly over" the heart-assisting devices.
Reuters explains: "The headphones interfered with the heart devices in about a quarter of the patients - 14 of the 60 - and interference was twice as likely in those with a defibrillator than with a pacemaker."
In the case of pacemakers, the researchers elaborated, the magnet "could make it deliver a signal no matter what the heart rate is, possibly leading to palpitations or arrhythmia". An implantable cardioverter defibrillator, meanwhile, could be de-activated by a magnet, "making it ignore an abnormal heart rhythm instead of delivering an electrical shock to normalize it".
The risk is, however, a matter of close proximity - the headphones need to be within 1.2 inches of a pacemaker or defibrillator to threaten their smooth running. Maisel said: "The main message here is: it's fine for patients to use their headphones normally, meaning they can listen to music and keep the headphones in their ears. But what they should not do is put the headphones near their device."
Specifically, people "should not place the headphones in a shirt pocket or coat pocket near the chest when they are not being used, drape them over their chest or have others who are wearing headphones rest their head on the patient's chest", Maisel warned.
The team presented their findings to an American Heart Association shindig yesterday. The meeting heard that related research had concluded "cellular phones equipped with wireless technology known as Bluetooth are unlikely to interfere with pacemakers". ®