Marcio Jose Sanchez / AP

The new Apple Watch, unveiled yesterday in Cupertino, California, possesses a new and startling capability: It can monitor the electrical pulses that drive the heart’s activity, and proactively alert users who it has determined might have a condition called atrial fibrillation. The FDA has voiced its approval, Apple said, and the new product goes on sale this fall.

Reaction was predictably positive: Atrial fibrillation is the most common type of heart arrhythmia in the United States, and the most common cause of embolic stroke. The president of the American Heart Association graced the stage at the company’s product announcement. People tweeted about Apple saving lives. “It won’t catch every instance of [atrial fibrillation], but we believe this is going to help a lot of people who didn’t otherwise know they had an issue,” said Apple COO Jeff Williams onstage of the feature, which is opt-in.

It seems like the most obvious thing in the world: Generating more data about how your heart is working must be good, right? But in many cases—prostate cancer being the most famous example—checking (and monitoring and treating) people for a disease does not make their health outcome better. Screening can lead to overdiagnosis and overtreatment, and all medical interventions come with their own set of risks, especially in a health-care system as expensive and inefficient as ours. At the very least, it can provoke unneeded panic. Counterintuitively (at least to those in Silicon Valley), sometimes it is better not to know.

Last November, when a company called AliveCor released a heart-monitoring Apple watchband, the cardiac electrophysiologist John Mandrola worried about the ways the technology would intersect with a medical system that does not serve everyone well. “At least in the U.S., the upcoming watch-driven explosion of AF diagnoses will happen in a fee-for-service environment that pays doctors and hospitals to test and treat,” Mandrola wrote in the trade publication Medscape. Diagnosis by watch not only generates an expensive trip to the doctor, he argued, but introduces the possibility that a person will proceed unnecessarily down the medicalization path.

“Every time a person with a watch-driven encounter with the medical establishment suffers a complication from downstream testing or treatment, this acts as a drag on the net benefits for screening. Turning people into patients should be done with great caution,” Mandrola concluded.

And there will be complications, as we’ve seen in other areas where medical screenings have expanded. “Diagnosis is not prevention. Diagnosis might be the first step to prevention, but there are more steps, and they have their own risks,” says Ziggy Whitman, a cardiac electrophysiologist and an assistant professor at the Lewis Katz School of Medicine at Temple University. “It’s not like, ‘Oh! My doctor knows I have atrial fibrillation, I’m safe.’”

For many young and healthy people—that is, the kind of people most likely to purchase Apple Watches—atrial fibrillation may not actually be a problem. Whitman says that this heart arrhythmia is really only a concern for two reasons: One, it may be a sign of trouble for people who have a substantially elevated risk of stroke because of their age, excessive drinking, or other factors, and two, atrial fibrillation itself causes some patients pain and discomfort.

“If you are young and healthy, like most people wearing an Apple Watch, and you have asymptomatic atrial fibrillation, I don’t care,” Whitman says. “I will put you on no medication and I will do nothing for you. It might be a great watch for an 80-year-old, maybe not a great watch for you.”

A 2016 review of mobile-health technology in the Journal of the American Heart Association did see some potential for sensors like the ones in the new watch. “If these previously uncollected streams of continuous data can be translated into actionable information and presented at meaningful decision points, patients and their providers may be better able to achieve health goals and manage chronic conditions,” the review concluded.

But consider the if there. The data, in and of itself, even when combined with algorithmic screening for conditions like atrial fibrillation, must be integrated into actual medical practice. “There really is great utility in this. Don’t lose sight of that,” Whitman says. “It just needs to be with the right person under the guidance of a doctor who is able to interpret the data.”

Imagine getting a ping from your new watch that says, “You may have atrial fibrillation, a heart condition.” How will people around the world respond to such a notification sitting in between Slack messages and tweets and news alerts from The Washington Post? Is there any way to deliver that message in a don’t-freak-out kind of way?

“This is going to create such a massive headache” for physicians, Ethan Weiss, an associate professor at the Cardiovascular Research Institute at the University of California at San Francisco, told us, adding that he’s not “an alarmist” about unnecessary tests.

“I’m dealing with a number of patients who were found to have certain conditions because of inappropriate screening,” he said. “Maybe we are saving that person’s life. But we don’t know that, and what we do know is that we’re causing them this stress. Every worried [healthy] Tom, Dick, and Harry are going to be freaking out about every blip thing that shows up on their Apple Watch.”

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