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Patients with pacemakers and implantable cardioverter defibrillators (ICDs) should keep their smartphones away from their hearts to avoid electromagnetic interference, according to a German study.

However, the risk for interference was small, occurring in one of 308 patients (0.3%) tested, reported , of the German Heart Care Center in Munich, and colleagues at the in Milan.

Lennerz and colleagues wanted to determine if current safety recommendations from the FDA and other regulatory organizations, based primarily on 10-year-old research, were still relevant to today's smart phones and mobile networks.

"Interference between smartphones and cardiac devices is uncommon but can occur, so the current recommendations on keeping a safe distance should be upheld," Lennerz said in an accompanying press release.

"Pacemakers can mistakenly detect electromagnetic interference from smartphones as a cardiac signal, causing them to briefly stop working. This leads to a pause in the cardiac rhythm of the pacing-dependent patient and may result in syncope. For implantable cardioverter defibrillators, the external signal mimics a life threatening ventricular tachyarrhythmia, leading the ICD to deliver a painful shock," Lennerz explained.

The patients in the study included 147 with pacemakers and 161 with ICDs. These patients were exposed to the electromagnetic fields of three common smartphones: the Samsung Galaxy 3, Nokia Lumia, and HTC One XL.

The phones were placed on the patients' skin, directly above their cardiac device, and connected to a radio communication tester, which works like a mobile network station. The investigators then put the phones through a standardized protocol that included connecting, ringing, talking, and disconnecting.

"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," Lennerz said.

The phones were operated on standard mode and at 50 Hz. The tests were repeated using multiple current mobile phone standards, which include

During all tests, a 6-lead electrocardiogram was continuously recorded and monitored for abnormalities.

One patient's ICD detected and misinterpreted electromagnetic waves from the Nokia and HTC smartphones as intracardiac signals, resulting in ventricular and atrial oversensing. The interference occurred when the smartphones were operated at GSM and UMTS, but not LTE.

"Interestingly, the device influenced by electromagnetic interference in our study was MRI compatible which shows that these devices are also susceptible," Lennerz said.

"Nearly everyone uses smartphones and there is the possibility of interference with a cardiac device if you come too close. Patients with a cardiac device can use a smartphone but they should not place it directly over the cardiac device," said lead author , also of the German Heart Center, in a press release.

The FDA declined to comment on the study results, but an FDA spokesperson provided the following statement which includes their

"FDA continues to monitor the use of cell phones for possible interactions with other medical devices. Should harmful interference be found to occur, FDA will conduct testing to assess the interference and work to resolve the problem. Based on current research, cell phones would not seem to pose a significant health problem for the vast majority of pacemaker wearers. Still, people with pacemakers may want to take some simple precautions to be sure that their cell phones don't cause a problem."

The FDA recommendations state that the phone should be held to the ear opposite the side of the body where the pacemaker is implanted to add some extra distance between the pacemaker and the phone. Also, the user should avoid placing a turned-on phone next to the pacemaker implant ("e.g., don't carry the phone in a shirt or jacket pocket directly over the pacemaker").

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