Smartphones could cause pacemaker wearers to experience painful shocks and even pauses in the device's function.

The European Society of Cardiology is urging people who wear cardiac devices to keep a safe distance from smartphones.

"Pacemakers can mistakenly detect electromagnetic interference (EMI) 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 (ICDs) the external signal mimics a life threatening ventricular tachyarrhythmia, leading the ICD to deliver a painful shock," Carsten Lennerz, first author and cardiology resident in the Clinic for Heart and Circulatory Diseases, German Heart Centre.

Device manufacturers and regulatory institutions including the US Food and Drug Administration (FDA) are recommending a safety distance of five to seven inches between pacemakers and smart phones.

To determine the safety distance, a team of researchers looked at 308 patients: 147 of which had pacemakers; 161 had cardioverter defibrillators (ICDs); and 65 used cardiac resynchronisation therapy (CRT). The patients were exposed to the electromagnetic field of three common smartphones (Samsung Galaxy 3, Nokia Lumia, HTC One XL) which were connected to radio communication tester. Only one of the patients was affected by the EMI fields.

"Interference between smartphones and cardiac devices is uncommon but can occur so the current recommendations on keeping a safe distance should be upheld. Interestingly, the device influenced by EMI in our study was MRI compatible which shows that these devices are also susceptible," Lennerz said.

The findings were presented at the EHRA EUROPACE -- CARDIOSTIM 2015 meeting.