Wearable fitness and wellness trackers could interfere with some implanted cardiac devices such as pacemakers, according to a study.

Devices such as smartwatches, smart rings and smart scales used to monitor fitness-related activities could interfere with the functioning of cardiac implantable electronic devices (CIEDs) such as pacemakers, implantable cardioverter defibrillators (ICDs), and cardiac resynchronisation therapy (CRT) devices, the study published in the Heart Rhythm journal found.

Researchers found that the electrical current used in wearable smart gadgets during “bioimpedance sensing” interfered with proper functioning of some implanted cardiac devices from three leading manufacturers.

Bioimpedance sensing technology sends a small, imperceptible electrical current to measure the person’s body composition, including the level of body fat, muscle mass, level of stress and breathing rate. Wearable fitness trackers are able to record health-related metrics such as distance walked or the number of steps taken, heart rate, blood pressure, daily calories burned and sleep patterns using this technology.

“Bioimpedance sensing generated an electrical interference that exceeded Food and Drug Administration-accepted guidelines and interfered with proper CIED functioning,” said the lead researcher, Dr Benjamin Sanchez Terrones, of the University of Utah.

He said the results did not convey any immediate or clear risks to patients who wear the trackers. However, the different levels of electrical current emitted by the wearable devices could result in pacing interruptions or unnecessary shocks to the heart. Further research was needed to determine the actual level of risk, Sanchez said.

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“Our findings call for future clinical studies examining patients with CIEDs and wearables,” he added.

The interaction between general electrical appliances – including smartphones – and CIEDs has been studied in recent years, but this is the first study to look at devices that use bioimpedance sensing technology and their possible interference with CIEDs.

“Our research is the first to study devices that employ bioimpedance-sensing technology as well as discover potential interference problems with CIEDs such as CRT devices. We need to test across a broader cohort of devices and in patients with these devices. Collaborative investigation between researchers and industry would be helpful for keeping patients safe,” Sanchez said.

Most implantable cardiac devices warn patients about the potential for interference with a variety of electronics due to magnetic fields. For example, patients are warned about carrying a mobile phone in a breast pocket near a pacemaker.

Prof James Leiper, an associate medical director at the British Heart Foundation, said: “As more people wear smartwatches and other devices with body-monitoring technology, it is important to understand any potential interference they may cause with lifesaving medical devices like ICDs and pacemakers.

“This study is a first step in this process. However, more research needs to be done in this area to understand any effects in patients.”