People with implantable pacemakers may want to be cautious when listening to tunes on their iPods. Interference from the portable music player could cause pacemakers to malfunction, a study suggests.

Electrical devices such as cellphones, appliances and microwave ovens can cause interference, leading doctors to advise heart patients not to place the devices over pacemakers.

Jay Thaker, a 17-year-old high school student, wondered if iPods cause a similar effect. To find out, he tested iPods on 83 people with pacemakers, with an average age of 77.

When an iPod was held above five centimeters from the chests of the patients for five to 10 seconds, electrical interference was detected in about half of the 800 trials.

Pacemakers misfired because they may have mistaken electronic signals from iPods as a rhythm problem, said Thaker.  

The experiment was done at Michigan State University. Dr. Krit Jongnarangsin, a professor in cardiovascular medicine at the University of Michigan in Ann Arbor and a friend of Thaker's family, was the senior author.

Since pacemakers keep a record of heart rhythms, it's possible that interference could lead doctors to misdiagnose a patient, but more research is needed on whether that happens, Jongnarangsin said.

While people with pacemakers may not commonly use iPods, they should be aware of the potential risks given the popularity of the music players, the team said.

The research was presented Thursday at the Heart Rhythm Society annual meeting in Denver.

The team did not specify what model of iPod they used, and other brands of portable music players were not tested.