On a recent Saturday, my 87-year-old mother was feeling a bit woozy, so she pressed a button on the side of her Apple watch to reveal her ECG, a recording of her heart’s electric rhythm. Thirty seconds later, three messages appeared on the watch’s screen. One showed the characteristic zigzag spikes of the ECG, or electrocardiogram. The second revealed that her heart rate, usually 80 beats per minutes, was down to only 40. The third said the results were “inconclusive,” with the advice: “Call your doctor.”

My mother is a hardy octogenarian. She walks about a mile every day, works out with a trainer (currently via Zoom) three times a week and, as she often used to say, planks nearly as well as her former sorority sister, the late Ruth Bader Ginsburg.

After leaving a message with her doctor’s office, she called my brother, a doctor who lives nearby, and told him she was exhausted and “just not feeling right.” He came over immediately and took her to the emergency room.

There, the hospital’s electrocardiogram showed that the electrical signals in the top part of the heart were not being transmitted properly to the bottom. Her heart was beating, but too slowly. The staff rushed her to the cardiac care unit, where doctors implanted a pacemaker the next morning.

When she called a longtime friend to tell her the story, the friend responded that she’d likewise had a recent smartwatch scare: Her heart rate was sky-high, reaching 182. Her doctor had her wear a Holter monitor, a medical-grade portable ECG device that monitors heart rhythm continuously, for four days, and the report from the device revealed that everything was fine.

The advent of smartwatches that retrieve heart physiology both excite and worry physicians. For every story like my mother’s, there are many more like her friend’s, in which minor variations in heartbeats lead to needless work-ups, treatments with risky side effects and lots of unnecessary anxiety.

So are these wearables worth it?

Conclusive evidence about their accuracy is lacking, though an Apple-sponsored study from 2019 published in The New England Journal of Medicine suggested they may help to detect some kinds of abnormal heart rhythms, particularly in the elderly. A slew of additional studies are underway.

Most at-home ECG watches are designed to record heart rate and detect atrial fibrillation, the most common irregular heart rhythm, which affects up to six million Americans. A-fib, as it’s called, increases the risk of strokes, leading to 150,000 deaths and 450,000 hospitalizations a year. But doctors say that many people have an irregular heartbeat every now and then.

Most watches wait to send an alert until there have been about five abnormal beats within an hour or so, rather than after every altered rhythm. Still, that doesn’t mean the abnormality is dangerous.

“As a cardiologist, I really like at-home devices,” said Dr. Gary Rogal, medical director of cardiovascular services at RWJBarnabas Health in West Orange, N.J., whose team cared for my mother. But he clarified he likes them only for patients in whom he feels there’s an indication to look for something, such as those with an existing heart condition or a family history of heart disease. “I would never subscribe to the concept that everyone should be monitored. You’ll see stuff and it will make you crazy, but you’re probably fine.”

And doctors worry that as more and more people wear these devices, there could be a flood of unnecessary follow-up testing and too much treatment.

“That’s what keeps me up at night,” said Dr. Joseph Ross, a professor of medicine and public health at Yale, who is among a team of investigators conducting a randomized clinical trial that compares a group wearing the Apple watch to a control group wearing a smartwatch without the ECG app. “If someone with an occasional abnormal rhythm that would never have caused a stroke undergoes an extensive work-up or is put on a blood thinner, the risk of a dangerous bleed or other harm outweighs the benefits of potentially preventing a stroke.”

Two weeks after her surgery, my mother was doing her one-minute planks and lifting weights with her Zoom personal trainer. Maybe, without the watch, my mother would have been OK and just felt really tired until she called her doctor on Monday. Or maybe not.

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