A study that involved 60 pacemaker and defibrillator patients has claimed that Magnetic interference from iPod headphones could bear a risk to patients with surgically implanted heart monitoring devices.

The research team said, "Interference from MP3 player headphones could prove fatal by temporarily deactivating the device. Patients should keep headphones more than 3cm away from their pacemaker or defibrillator."

William Maisel, director of the medical device safety institute at Beth Israel Medical Centre in Boston, Massachusett, said "For family members or friends of patients with implantable defibrillators, they should avoid wearing headphones and resting their head right on top of someone's device."

He added, "Patients themselves should avoid keeping headphones in a chest pocket or draping them over the chest."

Eight different models of headphones, including clip-on and ear-bud varieties were tested by Maisel and his team. A majority of headphone types have small amounts of the magnetic metal neodymium.

The headphones were placed on the skin above the implanted device of 60 defibrillator and pacemaker patients and an impact on the device's operation was detected in
14 patients.

Maisel added, "When a magnet is placed on a defibrillator, it temporarily deactivates the device. In other words the defibrillator stops looking for dangerous fast heart rhythms, and if a patient had a life-threatening heart rhythm problem while the magnet was over the device, it would not treat it."

Maisel reported, "Pacemakers, on the other hand, are designed to treat slow heart rhythms. They are meant to send signals to the heart when the heart rate slows, but magnetic interference can cause a pacemaker to start pacing without regard to the patient's underlying heart rate. This can cause palpitations (a feeling of heart irregularity) or can rarely induce an abnormal heart rhythm - although we did not observe any of these in our study."

However, no magnetic interactions were discovered by the team after they placed headphones 3cm or more from the device.

The study was presented by Maisel at the American Heart Association's meeting in New Orleans yesterday, where he also said that he did not know of any cases in which headphones had caused death or injury.