The following originally appeared on The Upshot (copyright 2018, The New York Times Company).
The newest version of the Apple Watch will feature a heart monitor app that can do a form of an electrocardiogram. Many have greeted this announcement as a great leap forward for health. The president of the American Heart Association even took part in the product launch.
For a more measured response, it’s worth looking at potential downsides, and it turns out there are a few.
The upside potential is twofold. First, doctors could monitor — at a distance — how patients with known heart problems are functioning outside the office. Second, the device could diagnose heart problems in people who don’t know they have them, picking up abnormal heart rhythms earlier than would otherwise be possible.
With respect to monitoring from a doctor, the Food and Drug Administration “cleared” the app — an easier hurdle to surmount than “approval.” But it specifically said people with diagnosed atrial fibrillation, one of the most common heart arrhythmias, should not be using the app.
If that’s the case, the major potential for the device — which will arrive later this year — is to pick up arrhythmias in otherwise healthy people. That’s still a big selling point. Picking up abnormal function earlier could theoretically lead to improvements in health, such as reductions in strokes.
But just because something seems like a good idea doesn’t mean it is. No screening test is perfect. In the simplest sense, whenever we consider the results of medical tests, they can be “positive” or “negative.”
In general, we would like people who are sick to have a positive screening result, and people who are well to have a negative result. Unfortunately, people who are sick sometimes have a negative result. Those are false negatives. People who are well sometimes have a positive result. Those are false positives.
Both of these outcomes are worrisome. A false negative might leave someone who needs medical help with a mistaken sense of assurance. Given that relatively few people have serious, undiagnosed arrhythmias with no symptoms (if people did, we would be screening for this more often), this isn’t the major concern. False positives are, because they cost us time and money, as well as cause emotional distress.
The health care system is already busy, if not overloaded. No physician wants to field calls from patients who have no problems. Such patients will require visits and further testing, and will potentially receive interventions. They’ll generate bills and harms without benefits.