Electromagnetic interference from smartphones can cause implantable cardioverter defibrillators to deliver a painful shock to the user, according to researchers.
The research is being presented at the joint meeting of the European Heart Rhythm Association (EHRA) of the European Society of Cardiology (ESC) and Cardiostim, taking place in Milan, Italy.
"Pacemakers can mistakenly detect electromagnetic interference (EMI) from smartphones as a cardiac signal, causing them to briefly stop working," reports study author Dr. Carsten Lennerz, of the German Heart Center in Munich, Germany. "This leads to a pause in the cardiac rhythm of the pacing dependent patient and may result in syncope."
These cardiac devices are used widely. According to a previous study, around 2.9 million patients received permanent pacemakers in the US between 1993 and 2009. Pacemakers are not the only cardiac device found to be affected by smartphones, however.
"For implantable cardioverter defibrillators (ICDs), the external signal mimics a life-threatening ventricular tachyarrhythmia, leading the ICD to deliver a painful shock," Dr. Lennerz adds.
For the study, researchers investigated whether the recommended safety distance of 15-20 centimeters between pacemakers or ICDs and mobile phones was still relevant with the latest models of cardiac devices and smartphones.
The current recommendations made by device manufacturers and institutions such as the US Food and Drug Administration (FDA) were made in light of studies conducted around 10 years ago that focused on pacemakers. Since these studies, technology on both sides has changed greatly.
To investigate, 308 participants - 147 with pacemakers and 161 with ICDs - were exposed to EMI from three modern smartphones that were in turn positioned on the skin directly above where the cardiac devices were implanted.
The researchers analyzed the effects of each part of the standard act of calling a smartphone - connecting, ringing, talking and disconnecting - on the cardiac devices. The calls were made using different network standards at both maximum transmission power and at 50 Hz, a frequency previously identified as one that can influence implanted cardiac devices.
Interference 'is uncommon but can occur'
Over 3,400 tests were performed, with electrocardiograms recorded continuously to track potential interference. Out of the 308 patients tested, just one (0.3% of participants) was affected by the EMI produced by the smartphones.
The patient was using an MRI-compatible ICD that misinterpreted EMI produced by two of the three common smartphones when operating on two of the three networks (GSM and UMTS) as intracardiac signals.
Despite how infrequently the study found EMI to affect the performance of the cardiac devices, the researchers believe that it is enough for current safety recommendations to be kept and followed.
"Interference between smartphones and cardiac devices is uncommon but can occur so the current recommendations on keeping a safe distance should be upheld," concludes Dr. Lennerz. "Interestingly, the device influenced by EMI in our study was MRI-compatible, which shows that these devices are also susceptible."
"Patients with a cardiac device can use a smartphone, but they should not place it directly over the cardiac device," advises study author Prof. Christof Kolb. "That means not storing it in a pocket above the cardiac device. They should also hold their smartphone to the ear opposite to the side of the device implant."
A separate study presented at the meeting found that the EMI from high voltage power lines - 230 Kilovolts (kV) and more - could also be problematic to people using cardiac devices. The researchers exposed 21 pacemakers and 19 ICDs to electrical fields of up to 20 kV/m in a laboratory.
The researchers found that pacemakers in bipolar mode with nominal settings were unaffected by EMI up to 8.6 kV/m and ICDs programmed to nominal parameters were unaffected up to 2.9 kV/m.
However, pacemakers with higher sensitivity levels or in unipolar mode were far more susceptible to EMI, with the threshold level as low as 1.5 kV/m in some of these devices.
"There is no significant concern for patients with pacemakers programmed in the usual configuration," states study author Dr. Katia Dyrda, a cardiologist at the University of Montreal, Canada. "For the minority of patients with devices in unipolar mode or with very sensitive settings, counseling should be given at implantation or at medical follow-up."