A large study suggests that Apple Watch can detect an extremely irregular heartbeat at least sometimes – but experts say more work is needed to tell about using portable technology to help monitor heart problems.
More than 419,000 Apple Watch users signed up for the unusual study, making it the biggest ever exploring screening apparently healthy people for atrial fibrillation, a condition that if not treated, they can eventually trigger strokes.
Stanford University researchers reported Saturday that the clock did not panic flocks of people, warning only half of the participants – about 2,100 – that they might have a problem.
But even among those marked, "it's not perfect," warned Dr. Richard Kovacs of the American College of Cardiology, who was not involved in the study.
People who received a warning should consult a physician via telemedicine and then have ECG patch measurement cardiac activity next week to determine the accuracy of the clock. Some skipped the virtual check-up to hear their own doctors; Overall, about 57 percent seek medical help.
Among those who received ECG monitoring through the study, one-third had atrial fibrillation, according to preliminary results, presented at an American College of Cardiology Conference in New Orleans.
A-fib tends to come and go, and a week's monitoring may have missed some cases, said Stanford's leading researcher. Mintu Turakhia. But if the clock discovered another irregular heartbeat while someone was wearing the ECG patch, 84 percent of the time corresponded to the a-fib.
"This study we believe provides very encouraging evidence that a device, Apple Watch, can be used to detect a-fib and to point to people when additional monitoring or testing may be needed," Dr. Lloyd Minor, Stanford's Dean of Medicine.
Other heart experts said that the study, funded by Apple, suggests that screening with portable technology may be technically feasible in the end, but requires much more research.
"I wouldn't advise this to the general population," Dr said. Valentin Fuster, director of Mount Sinai Heart in New York and a former US Heart Association president who was not involved in the study. Instead, he would like to see it tested in seniors with risk factors such as high blood pressure.
What is atrial fibrillation?
A-fib occurs when the upper chambers of the heart, called the atriums, come out of synchronization with the bottom chambers' pumping. Sometimes patients feel a flat or a racial heart, but many times they are not aware of an episode.
Sometimes the heart gets back in the rhythm alone. Other patients are given an electric shock to return to the rhythm or prescribe blood thinners to counteract the blood clots that cause strokes that untreated α-fib can induce. A-fib causes 130,000 deaths and 750,000 hospitalizations per year in the United States
How do the doctors control it?
A-fib is most common in older adults, and other risks include high blood pressure or a family history of arrhythmias. However, routine screening is not recommended for people without symptoms. Studies have not yet proven that early detection from screening would prevent enough strokes to outweigh the risks of unnecessary testing or over-treatment.
How does Apple control it?
A mobile app uses the optical sensor on some versions of the clock to analyze pulse data. If it detects sufficient variation from beat to beat over a 48-hour period, the user receives an irregular heartbeat warning.
The latest version of Apple Watch also allows users to press a button to take ECG and share the reading with doctors. Saturday's survey did not include watches with that ability.
Does the new study show mass screening a good idea?
No. The study was designed to tell how the watch compared to a week of standard ECG monitoring – not if the wearer's health improved because the screening revealed the arrhythmia. To prove whether detecting a-fib early lowers the risk of stroke, it would require many years of study.
And since the study did not have a comparison group that received routine ECGs, there is no way of knowing whether the clock missed heartbeat problems, giving a false sense of security, Kovacs said.
The astonishingly low number of alarms may be due to the fact that most participants were young or middle-aged, not the seniors most at risk of a-fib, he said.
Lauran Neergaard, The Associated Press
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