WASHINGTON: Headphones used with MP3 digital music players like the iPod may interfere with heart pacemakers and implantable defibrillators, US researchers said on Sunday.

The MP3 players themselves posed no threat to pacemakers and defibrillators, used to normalise heart rhythm. But strong little magnets inside the headphones can foul up the devices if placed within 3cm of them, the researchers told an American Heart Association meeting in New Orleans.

Dr William Maisel of the Medical Device Safety Institute at Beth Israel Medical Center in Boston led a team that tested eight models of MP3 player headphones, including clip-on and earbud types, in 60 defibrillator and pacemaker patients.

They placed the headphones on the patients’ chests, directly over the devices. 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.

Another study presented at the meeting showed that cellular phones equipped with wireless technology known as Bluetooth are unlikely to interfere with pacemakers.

A pacemaker sends electrical impulses to the heart to speed up or slow cardiac rhythm. The magnet, however, could make it deliver a signal no matter what the heart rate is, possibly leading to palpitations or arrhythmia, the researchers said.

An implantable cardioverter defibrillator signals the heart to normalise its rhythm if it gets too fast or slow. A magnet could de-activate it, making it ignore an abnormal heart rhythm instead of delivering an electrical shock to normalise it.

The devices usually go back to working the right way after the headphones are removed, the researchers 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,” Maisel said in a telephone interview.—Reuters