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TUESDAY, Oct. 6 (HealthDay News) -- A U.S. study offers more evidence that portable headphones can create magnetic interference that might make implanted defibrillators and pacemakers malfunction.

Using the headphones over the ears doesn't appear to be a problem, but storing them in a shirt or jacket pocket near the chest or allowing them to hang near the heart could spell trouble, researchers found.

The findings should encourage doctors to spend more time talking to their patients about the possible risks of headphones, which could disrupt signaling and threaten lives, the study authors said in a report published in the October issue of the HeartRhythm Journal.

The researchers examined several kinds of portable headphones in 100 patients. They found the level of magnetic interference they emit may be enough to disrupt the devices' ability to detect problems in the heart's rhythm. In other words, the devices could miss an abnormal heart rhythm and fail to reset it to a proper pace.

"As digital music devices continue their current popularity, the risk of device interaction from portable headphones should be accounted for in patients with implantable cardioverter-defibrillators and pacemakers," lead author Dr. William H. Maisel of Beth Israel Deaconess Medical Center at Harvard University, said in a news release from the Heart Rhythm Society. "This study reinforces the need for a doctor-patient dialogue that includes warnings against certain scenarios, such as hanging headphones around the neck or storing them inside a front shirt pocket or jacket pocket."

The headphones caused interference whether or not they were connected to a music player. But the devices worked properly when the patients took off the headphones.

Of the 100 patients studied, 55 had implantable cardioverter-defibrillators and 45 had pacemakers.

A study last year found similar results, although researchers didn't think they would be life-threatening.

More information

Learn more about pacemakers from the American Heart Association.