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Cleveland Clinic: mHealth Wearables Aren’t Reliable for Heart Rate

A Cleveland Clinic study of 4 activity trackers finds they don't measure heart rate accurately enough, especially during intense exercise, to be used in clinical situations.

By Eric Wicklund

- A Cleveland Clinic study of activity trackers has once again reinforced healthcare’s concern about wearables: They aren’t yet accurate enough for clinical use.

A study of four of the most popular fitness trackers found that they are 83 percent to about 90 percent accurate in measuring a use’s heart rate during rest or mild exercise. Those percentages dropped into the 80s, however, when the user started running.

“What we really noticed was all of the devices did not a bad job at rest for being accurate for their heart rate, but as the activity intensity went up, we saw more and more variability,” Gordon Blackburn, PhD, director of cardiac rehabilitation at Cleveland Clinic and one of the study’s authors, told Gadgets and Wearables. “At the higher levels of activity, some of the wrist technology was not accurate at all.”

"If my GPS gave me wrong results one in five times, I'd be a little disappointed," Marc Gillinov, MD, the study’s senior author, told Medscape.

By comparison, a Polar H7 chest-worn monitor also used in the study recorded a 99 percent accuracy rate, along with a standard ECG.

"If you really need to know your heart rate, either because you're using it to guide high-level athletic training or because you're a cardiac patient who's been given a 'safe range' for heart values, your best bet is with a chest-strap, electrically based monitor," Gillinov added.

Gillinov noted that the four wearables used in the study – the Apple Watch, Fitbit Charge HR, Mio Fuse and Basis Peak (which was recently recalled due to overheating issues) – all measure heart rate by blood flow in the wrist through optical sensors, instead of electrical activity, which is more accurate.

The study focused on 50 healthy adults, who were monitored while at rest and running on a treadmill for various distances. According to an analysis published in JAMA Cardiology, researchers gathered 1,773 data points from each device and found a wide range of variation, both in underestimating and overestimating heart rate.

In a response to the study, Fitbit officials said their own tests showed an accuracy rate of 94 percent. They also pointed out that activity monitors aren’t meant to be clinical devices – that’s not why they’re so popular with consumers.

“Unlike chest straps, wrist-based trackers fit comfortably into everyday life, providing continuous heart rate for up to several days without recharging (vs. a couple hours at a time) to give a much more informative picture of overall health and fitness trends,” the company said.

Satish Misra, MD, a cardiology Fellow at Johns Hopkins Hospital and managing editor of iMedicalApps, says many wearables include heart rate monitoring, but because they’re designed for health and wellness, they aren’t regulated as much as medical devices. Still, in conditions like atrial fibrillation, a wearable that can accurately track heart rate would be useful.

“Overall, it does serve as a useful reminder of the limitations of consumer health wearables that are worth considering if you’re going to incorporate them into recommendations for patients,” he wrote.

Dig Deeper:

Wearables Can Help People With Heart Conditions - If Only They’d Wear Them

Connected Health Technology - Just a Heartbeat Away

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