Heart patients with pacemakers are being advised to keep their distance from smartphones. New research out of Germany suggests mobile phones can interfere with the functions of cardiac devices that could lead to painful shocks or pauses in function.

The study — presented this week at a meeting of the European Heart Rhythm Association of the European Society of Cardiology and Cardiostim in Milan — found electromagnetic pulses from smartphones can cause pacemakers and other implantable heart-regulating devices to malfunction or stop working.

“Pacemakers can mistakenly detect electromagnetic interference [EMI] from smartphones as a cardiac signal, causing them to briefly stop working,” said lead researcher Carsten Lennerz, a cardiology resident in the Clinic for Heart and Circulatory Diseases of the German Heart Centre in Munich, Germany.

Device manufacturers and regulatory institutions including the U.S. Food and Drug Administration recommend a safety distance of at least six inches between pacemakers and mobile phones. The advice is based on studies performed primarily in pacemakers 10 years ago.

The current study evaluated whether the recommended safety distance was still relevant with the new smartphones, networks, and cardiac devices. A total of 308 patients were exposed to the electromagnetic field of three common smartphones (Samsung Galaxy 3, Nokia Lumia, HTC One XL) which were placed on the skin directly above the cardiac device.

“From earlier studies we know that the most vulnerable phases of a call are ringing and connecting to the network, not talking, so it was important to analyze these separately,” Dr. Lennerz said. “More than 3,400 tests … were performed. One out of 308 patients [0.3 percent] was affected by [electronic signals from] smartphones.

“Interference between smartphones and cardiac devices is uncommon but can occur so the current recommendations on keeping a safe distance should be upheld.”