A new “red flag-raising” study has provided benchmark data on the safety of smart scales, watches and rings with bioimpedance technology for patients with cardiovascular implantable electronic devices (CIEDs). Discussing the research, principal investigator Benjamin Sanchez Terrones (University of Utah, Salt Lake City, USA) spoke to Cardiac Rhythm News about the underexamined technology and the potentially serious “adverse events” it could cause, suggested by their data.
Theirs, they posit, is the first study to evaluate the functioning of CIEDs from Medtronic, Boston Scientific, and Abbott, while applying an electrical current used to mimic bioimpedance sensing. Commonly used to measure levels of stress, breathing rate or vital signs in wearable smart devices such as the Samsung Galaxy Watch 4 or the Fitbit Aria 2 smart scale, bioimpedance emits a small, imperceptible current of electricity which then flows through the body.
Delineating two key parts to their study, Sanchez first outlines the benchtop testing which meant connecting an impedance analyser to a tissue-equivalent interface circuit defined by the ISO 14117 standard—a test protocol for implantable cardiac devices. Addressing the second part of the study, he elaborates on the male and female “simulations” they generated, “[bridging] the gap” between benchtop testing and a clinical trial. They created an “idealised” environment in which to change and measure the frequency, amplitude of the signal and signal measurement duration at each frequency, giving the investigators “total control” over their instruments—unlike deploying smart watches or scales—which is salient in the context of their investigation.
In the USA, wearable consumer devices which are not medical products are not required to be approved by the US Food and Drug Administration (FDA). “Companies have disclaimers on their websites to prevent the use of certain wearables in patients with implantable electronics, and now we have a better idea of the influence that some of these devices could have in this population.”
Measuring the effect of CIEDs at different current and frequency levels for each of the three manufacturers, their simulations showed evidence of interference with voltages exceeding specified threshold values in the ISO 14117 standard. The authors note that the level of interference did vary with the frequency and amplitude of the bioimpedance signal between male and female models. Additionally, their results show that the level of interference generated with smart scales and rings was seen to be lesser than that of smart watches.
Citing the effects of their simulated bioimpedance across device manufacturers, Sanchez Terrones notes that all three showed susceptibility to oversensing and pacing inhibition at different signal amplitudes and frequencies. For patients reliant on these implantable devices to live, repeated or prolonged bioimpedance interference could cause serious “adverse events” say Sanchez Terrones et al, asserting that these events may occur “without forewarning” in patients with CIEDs, causing further interference to lifesaving therapy.
Sanchez Terrones goes on to clarify that a “one-size-fits-all” approach to determining which wearable device is safe to pair with which CIED will not be sufficient, noting that clinical testing will need to be done on an individualised, on a “case-by-case” basis.
Admitting certain limitations of the study, Sanchez Terrones went on to discuss his awareness that a larger cohort of patients with variations beyond benchtop male and female models is needed to translate their observations to a clinical setting. Equally, the importance of understanding individuals who may be at higher risk of CIED bioimpedance interference by wearable smart devices is also essential—Sanchez Terrones highlighted that their simulation cannot account for individuals with “pre-existing conditions” or variations in age.
Fundamentally, their research is the first step for further study, Sanchez Terrones says, concluding that the present findings do not recommend the use of smart devices with bioimpedance sensing in patients with CIEDs. Their results additionally call for a review of the ISO 14117 standard to define new, specific tests for devices with bioimpedance technology.
For the broader population of smart device wearers who do not have CIEDs, Sanchez Terrones believes their results do not provide concrete evidence for immediate concern. When asked about the benefits smart watches, scales and rings can have for the general public, Sanchez Terrones comments on the “blurry” usefulness of some of the features, which the clinical utility might be unclear.
Wearable smart devices of the future have the potential to measure health parameters that could give doctors a clearer image of patient health between visits, Sanchez Terrones projects, “where they can fill those gaps—that is where they have a lot of potential”.
Continuing, he points to fluid accumulation detection as an “exciting” future application in patients with chronic heart failure. “A wearable device with bioimpedance sensing that is able to monitor the accumulation of fluid would be invaluable to help manage heart failure patients”, Sanchez Terrones opines, however he counterbalances this with a catch-22—most patients with heart disease often have a pacemaker.
“Healthy people do not accumulate fluid in the limbs and would not need a pacemaker, but the most essential use of a wearable device would be for patients with heart disease. So you first need to show that they do not cause [bioimpedance] interference.”
Rounding off, Sanchez Terrones states that discussions on the significance of health metrics provided by wearable smart devices is “neverending”, but he goes on to confirm the potential they have to become more “clinically actionable”. However, within the realm of the study concerning individuals with CIEDs, Sanchez Terrones concludes “safety questions must first be answered” to ensure the health of patients.