iPods can cause cardiac implantable pacemakers to malfunction by interfering with the electromagnetic equipment monitoring the heart, according to a study presented by a 17-year-old high school student to a meeting of heart specialists on Thursday.

The study tested the effect of the portable music devices on 100 patients, whose mean age was 77, outfitted with pacemakers. Electrical interference was detected half of the time when the iPod was held just 2 inches from the patient's chest for 5 to 10 seconds.

The study did not examine any portable music devices other than iPods, which are made by Apple.

In some cases, the iPods caused interference when held 18 inches from the chest. Interfering with the telemetry equipment caused the device to misread the heart's pacing and in one case caused the pacemaker to stop functioning altogether.

The study was held at the Thoracic and Cardiovascular Institute at Michigan State University. The results were presented at the Heart Rhythm Society annual meeting in Denver in the USA.

Jay Thaker, lead author of the study and a student concluded that iPod interference can lead physicians to misdiagnose actual heart function.

Thaker, whose father is an electrophysiologist and whose mother is a rheumatologist, said he asked his dad about a potential interaction between pacemakers and iPods.

"We looked online but didn't see anything. Then, one of his patients asked him if there would be a problem, so (my father) put me in touch with Dr. Krit (Jongnarangsin)," Thaker said in a telephone interview.

Jongnarangsin, a long-time friend of Thaker's father, is the senior author of the study and an assistant professor in the Division of Cardiovascular Medicine at the University of Michigan.

"Most pacemaker patients are not iPod users," Jongnarangsin said. For that reason, he said, it is unclear how often iPods cause misdiagnosis.

"This needs to be studied more," Jongnarangsin added.

Thaker said he is interested in doing a similar study about how implantable cardioverter defibrillators, known as ICDs, are affected by iPods.