Headphones may hinder pacemakers

The MP3 players themselves posed no threat to pacemakers and defibrillators, used to normalize heart rhythm. But strong little magnets inside the headphones can foul up the devices if placed within 1.2 inches 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.