The Apple Watch heart monitor sends too many people to the doctor.

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Only a handful of people the watch flagged actually had a heart problem.

The heart monitoring feature on the Apple Watch may lead to unnecessary health care visits, according to a new study published this week. Only around 10 percent of people who saw a doctor at the Mayo Clinic after noticing an abnormal pulse reading on their watch were eventually diagnosed with a cardiac condition.

The finding shows that at-home health monitoring devices can lead to over-utilization of the health care system, said study author Heather Heaton, an assistant professor of emergency medicine at the Mayo Clinic College of Medicine, in an email to The Verge. That may be expensive for patients and for the system as a whole, and it may take up doctor and patient time unnecessarily.

Heaton and the study team scanned patient health records at every Mayo Clinic site, including offices in Arizona, Florida, Wisconsin, and Iowa, for mentions of the term “Apple Watch” over a six-month period from December 2018 to April 2019. The window came just after Apple introduced a feature to detect abnormal heart rhythms and after publication of a study tracking how well the watches could detect atrial fibrillation.

They found records of 264 patients who said their Apple Watches flagged a concerning heart rhythm. Of that group, 41 explicitly mentioned getting an alert from their watch (others may have had an alert, but it wasn’t mentioned specifically in their health record). Half of the patients already had a cardiac diagnosis, including 58 who’d been previously diagnosed with atrial fibrillation. About two-thirds had symptoms, including lightheadedness or chest pain.

Only 30 patients in the study got a cardiac diagnosis after their doctors visit. Most of the concerning heart monitor data, then, were probably false positives, the study concluded. False positives, even though the patient ends up being healthy, can still cause problems: they can push patients to get unnecessary health care and cause stress and anxiety. Even people who don’t have symptoms, like some people in this study, may still feel the need to talk to a doctor about an abnormal flag on a device like an Apple Watch.

Some of these trends aren’t new. For years, doctors have watched patients come into their offices after researching medical conditions online, Heaton said. Smartwatches, though, passively monitor people who aren’t necessarily looking for a diagnosis. And Apple isn’t the only company flagging users with what its products pick up as abnormal heart rhythms: Samsung’s Galaxy Watch 3 has an EKG feature, as does Fitbit’s Sense smartwatch. While the percentage of people who get an abnormal heart reading on one of these devices could be low (a study of the Apple Watch found that less than 1 percent of users had an alert), millions of people use these products — so there could still be thousands of additional people going to the doctor based on them.

These types of products “blur the line between rigorously-studied medical devices and wellness tools,” Wyatt said. People may not understand how well they actually work and what they should actually be used for. People who already have an atrial fibrillation diagnosis, for example, aren’t supposed to use the Apple Watch feature — but over 20 percent of the people in the Mayo Clinic study did have that diagnosis already. The feature also isn’t supposed to be used by anyone under 22 years old, but nearly two dozen people with records in the study were below that cutoff.

Smartwatches might be useful ways for people to monitor their health on their own, at home, but it’s still not clear what their utility could be. Most of the research done on the Apple Watch, for example, focuses on how well it can detect atrial fibrillation, but it doesn’t track how well it can actually be used as a screening tool in the context of the health care system. Without that information, doctors like Heaton worry that the devices could cause unnecessary confusion and stress for patients. “Understanding context and the nuances of illness is important and at this point cannot be fully understood purely by a wearable medical device,” she said.

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