Every breath you take, every move you make
Authors: None The Lancet Digital Health
Journal: The Lancet Digital Health (2020)

The wearables are coming. In September 2020, Fitbit received US Food and Drug Administration clearance and CE marking for its new electrocardiogram (ECG) app to assess heart rhythm for atrial fibrillation. This announcement comes almost 2 years after the Apple Watch Series 4 was awarded the same clearance. But are we really any closer to general use of consumer cardiac monitoring that will yield reliable health benefits? Wearable fitness monitors enable users to track a range of health metrics, such as physical activity, quality of sleep, and heart rate. Combined with user demographics and medical history, they might herald a personalised approach to promoting health and preventing illness, including cardiovascular disease. Promising results in this area have been published in The Lancet Digital Health. Aravind Natarajan and colleagues extracted data from a population of Fitbit users and analysed changes in heart rate variability (HRV) metrics. Consistently low HRV is known to be associated with fatal and non-fatal cardiovascular events, such as congestive heart failure, but the authors found an increase in step count improves HRV metrics. This is one of the largest HRV analyses to date, with data from more than 8 million Fitbit users across 74 countries. By illustrating the potential of remote monitoring to optimise health, it could be seen as advancing wearables into the mainstream of cardiovascular health. First author of the paper Aravind Natarajan, a Staff Data Scientist (Research) for Fitbit, says, “The widespread availability of heart-rate enabled, wrist-worn devices have made metrics that were previously difficult to obtain, such as resting heart rate and HRV, available to researchers at scale.” But as wearables become more ubiquitous worldwide, are they helping to bridge health inequities by making health monitoring more accessible to all, or are they widening the digital divide? Most consumers are young (aged 25–34 years), but as cardiovascular diseases are more common in older individuals the gain for these younger consumers—who are probably in good health—is likely incremental. Conversely, individuals older than 55 years make up the smallest percentage of users. “Certainly, there are limitations,” says cardiologist Emma Svennberg from the Karolinska Institutet and Karolinska University Hospital, Sweden. “I think at present that most of the owners are younger and in better socioeconomic circumstances. Also, the accuracy and diagnostic abilities vary between devices.” Indeed, the evidence base is mixed and incomplete. Accuracy differs between devices, and current wrist-worn wearables can only record single-lead ECGs and so provide just a fraction of the view produced by the cardiology gold standard 12-lead ECG. Also, although the largest Apple Watch study thus far revealed an 84% concordance between watch notifications and atrial fibrillation, the findings should be validated through a randomised clinical trial. Even if their outputs are clinically acceptable, are wearables appealing enough to consumers for consistent use? If not, what are the concerns? Data privacy is a major issue. In the USA alone, 35% of adults do not approve of wearables data being shared with medical researchers for the purpose of cardiovascular disease research, and those older than 50 years—who would probably generate meaningful data—make up the bulk of this percentage. Finally, although touted as non-invasive, wearables are not passive and can be counterproductive. As highlighted by neurologist Guy Leschziner, our tendency to constantly monitor—or metricise—our lives can directly affect the variables being observed and cause anxiety. Today's wearables have potential, but to fulfil this potential some legitimate concerns must be addressed. Equitability should be built in from the start, ensuring they meet societal needs for people of all ages and economic backgrounds. Further rigorous testing of these devices through randomised clinical trials is an absolute must. Data security must be placed at the heart of the design, and if users consent to their data being shared, this sharing should occur under tight regulation with clear privacy policies in place. The public also need realistic guidelines on their usage to prevent unnecessary anxiety and to manage user expectations. A multidisciplinary approach is needed—with input from tech companies, health professionals, data protection experts, and users from a wide demographic. But until these concerns are addressed, wearables should continue to be used as an adjunct to clinicians and gold standard tests—not a replacement. Heart rate variability with photoplethysmography in 8 million individuals: a cross-sectional studyDiverse metrics of cardiac autonomic health can be derived from wrist-worn trackers. Empirical distributions of heart rate variability can potentially be used as a framework for individual-level interpretation. Increased physical activity might yield improvement in heart rate variability and requires prospective trials for confirmation. Full-Text PDF Open Access