Patients with implantable cardioverter-defibrillators or pacemakers should avoid placing the headphones from their MP3 players too close to their chests, researchers said.
That's because the magnets in portable headphones may cause the cardiac devices to temporarily malfunction, William Maisel, MD, MPH, of Beth Israel Deaconess Medical Center in Boston, and colleagues reported in the October issue of Heart Rhythm.
In a study of 100 patients with an implanted device, 30% had a clinically significant interaction when certain models of headphones were placed on their chests, including inhibition of tachyarrhythmia detection in ICDs and asynchronous pacing in pacemakers.
All interference occurred when the headphones were 2 centimeters or less from the skin surface, prompting Maisel and his colleagues to recommend telling patients who have these devices to keep portable headphones at least 3 centimeters (1.2 inches) from their chests.
"These patients should not be told that they cannot use headphones," Maisel said. "They just need to keep them at their ear level and not drape them over their device."
Laurence Epstein, MD, head of the cardiac arrhythmia service of Brigham and Women's Hospital, said the findings were not surprising.
"We have always advised patients to avoid placing any electronic equipment directly over their devices," said Epstein, who was not involved in the study.
Douglas Zipes, MD, editor-in-chief of Heart Rhythm and a former president of the American College of Cardiology, said "the significance of the article is to remind and warn physicians and patients that headphones have magnets that can influence pacemaker and defibrillator function when held very close to the implant."
Although the FDA concluded that electromagnetic interference from digital music players is unlikely to cause problems with implanted devices, there had been little known about the potential for portable headphones to affect the function of the devices, the researchers said.
To explore the issue, they evaluated the magnetic fields associated with eight headphone models -- two clip-on varieties and six ear buds -- and their effect on 55 patients with ICDs and 45 with pacemakers when placed on different parts of the chest.
When the headphones were placed directly on top of a Gauss meter, six of the eight had electromagnetic fields greater than 100 Gauss and five had fields greater than 200 Gauss.
A level of about 10 Gauss, which was exceeded by all eight headphone models, is sufficient to close the read switch and disable sensing in an implanted cardiac device.
The field strength quickly dropped off, however, as the headphones were moved away from the meter. At 2 centimeters, only the two clip-on models -- Sony MDR-Q22LP and Phillips SBC HS430 -- had a field strength greater than 10 Gauss.
All of the clinically important interference that occurred when the headphones were placed on the chests of the patients occurred with these two models.
Interactions were more common in patients with ICDs than in those with pacemakers (38.2% versus 20%, P=0.048).
For all but one of the patients who had an interaction, function of the implanted devices returned to normal immediately after removing the headphones from the chest.
In one patient who had a Medtronic Kappa 401 dual-chamber pacemaker, the device was permanently reprogrammed from DDD to DOO mode. The device could be reprogrammed to DDD mode with a programmer.
Maisel said he and his colleagues contacted Medtronic about the issue. He said the company indicated that it had received rare reports of this type of interaction with this specific model.
The magnetic fields of the headphones were the same regardless of whether the music player was turned on or whether the headphones were plugged in. The players themselves did not result in any interference with the implanted devices.
Only three of the patients in the study reported symptoms during the tests -- palpitations in two and lightheadedness and dizziness during asynchronous pacing in one.
The researchers said that they were not aware of any reports of adverse events associated with exposure to portable headphones in patients with ICDs or pacemakers.
"Nevertheless," they said, "given the millions of pacemaker and ICD patients and the ubiquitous presence of portable headphones, the potential for important clinical interactions exists."
They said the applicability of the findings to other models of headphones or to devices made by other manufacturers -- 84% of those in the study were made by Medtronic -- is uncertain.
The authors made no financial disclosures.