Dr William Maisel

"Because exposure of a pacemaker or defibrillator to portable headphones can result in interaction between the two, we recommend that pacemaker or defibrillator patients not allow portable headphones to be near their device," senior author Dr William Maisel (Beth Israel Deaconess Medical Center, Boston, MA), told heartwire. "Enough headphones have enough magnetic field strength that we believe that our recommendations apply to all portable headphones; they do not apply to one particular brand or one particular model."

But authors of the study, who spoke with heartwire during the American Heart Association 2008 Scientific Sessions, say that the problems arise only if people place the headphones directly over their devices, less than 3 cm away.

"So patients shouldn't place them in a front shirt pocket or in a front jacket pocket, and they shouldn't allow someone wearing headphones to rest their head on their chest," Maisel commented. "But if the headphones are kept a reasonable distance away, we found no interaction. . . . It's fine for patients; in fact we encourage patients to enjoy their music and listen to it in their ears, but they shouldn't take off their headphones and drape them around their necks so that the earbuds dangle over the chest."

Maisel, with first investigator Dr Sinjin Lee (Beth Israel Deaconess Medical Center) said they were motivated to look at iPod headphones in the wake of stories in 2007 addressing the potential interference caused by iPods and other MP3 players. "We were skeptical that there would be an interaction between MP3 players and defibrillators, but we also know that portable headphones contain magnets—magnets are used in speakers to vibrate and make noise that we listen to," and magnets are a known cause of device interference," Maisel said.

Dr Sinjin Lee

What they found is that while two iPod brands (the Shuffle and the Nano) caused no interference with either pacemakers or ICDs, 14 out of 60 patients (23%) experienced device interference from close contact with headphones. Types of interference ranged from inappropriate (asynchronous) pacing in four out of 27 pacemaker patients to inhibition of ICD detection in 10 out of 33 ICD patients. Close contact with headphones actually caused device reprogramming in one patient.

Of note, measured magnetic field strength varied considerably between headphone brands and was highest with clip-on type headphones such as the Sony MDR Q22 LP and Phillips SBC HS430. For the Sony clip-on headphones, the magnetic field strength at 2 cm was 20 G and over 300 G at 0 cm; a magnetic field strength of just 10 G can interact with a pacemaker or defibrillator, Maisel noted.

The key, said Maisel, is that magnetic field strength falls off very rapidly with distances, although physicians and patients should be aware that headphone magnetic field strength is "on" whether the MP3 player is on or off and whether the headphones are attached to the MP3 player or not.

But he also emphasized that as long as patients are aware that headphones contain magnets, the risk is minimal. "Pacemaker and defibrillator patients are told when they get their device and they are repeatedly reminded not to expose their device to magnets. So they're used to that message. The real message here is that portable headphones have magnets in them, and if that message got out, patients and doctors would know what to do from there. So I don't think patients are particularly alarmed, nor do I think they should be," Maisel said. "The other thing to remember is that as soon as the headphones are removed from the device, the device function returns to normal."

First author Lee also added that just because patients with these types of devices tend to be older, physicians shouldn't assume they're not hip enough to have an iPod or other MP3 player. "We became interested in this because a lot of patients do ask us about these things. A lot of our patients are older, but a lot of people do have [digital music players] or they have family members and grandchildren who use them a lot."

Commenting on the study for heartwire, Dr Kenneth A Ellenbogen (Medical College of Virginia, Richmond) also urged an appropriate reaction from patients with cardiac devices. "It's not a real issue, clinically speaking. Yes, the magnetic field that headphones make—some brands from some manufacturers—can be significant, but you have to take your headphones off your ears and put them right over your device. If somebody falls asleep and happens to have one of these earphones and puts them over their device and then sleeps for a couple of hours, this could potentially be a problem. But the take-home message is, wear your headphones on your head, and don't put them in your breast pocket."