The forebears of today's best fitness trackers and smartwatches may have been little more than tiny notification buzzers and step tracking novelties, but we’ve always known they had the potential to save lives and help us identify serious issues before they become irreversible. Last month, Google highlighted its work with machine learning algorithms to advance healthcare, and now the U.S. Food and Drug Administration just gave the go-ahead to roll out a new algorithm to Fitbit devices that will be even more effective at identifying people with atrial fibrillation (AFib), one of the leading signs that a person is at risk of a stroke.

This isn’t Fitbit’s first success story in the fight against irregular heart rhythms. Back in 2020, regulatory clearance was given to Fitbit for an app that could be used to perform spot checks. Users could begin a test and sit still for about 30 seconds while the built-in PPG (photoplethysmography) optical heart-rate sensor performed measurements and gave a reading.

The new algorithm goes a step further by automating the testing procedure to perform regular measurements while you’re asleep or at rest. By increasing the regularity of testing and expanding to different hours during the day, the odds of detecting occasional AFib episodes are greatly increased.

PPG works by measuring the size of the blood vessels in your body. Each heartbeat causes the vessels to expand and contract as blood is pushed through the body. By tracking irregularities in this pattern, it’s possible to identify signs of atrial fibrillation.

In a five-month study of 455,699 participants during 2020, Fitbit found that it could successfully identify AFib 98% of the time, and was 100% accurate in identifying participants with normal sinus rhythm.

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Fitbit is preparing to launch a new feature called Irregular Heart Rhythm Notifications based on its algorithm. This will be useful for alerting wearers to potential problems, which when used in tandem with the current ECG app to perform spot checks and record a trace, it’s possible to give healthcare professionals more data that they can use to reach an early diagnosis.

The Irregular Heart Rhythm Notifications feature will only be available in the US until regulatory approval is also granted in the EU and other countries. Fitbit’s blog post only specified that the feature will be available on “a range of heart-rate enabled devices,” but did not clarify if it would be available on current devices or only new models. However, the ECG app was made available to basically all compatible hardware, and it’s likely that this monitoring feature will work on all of the same hardware. Once this rolls out, it will match up with the AFib monitoring capabilities that are currently available on later models of the Apple Watch.