In 2018, Apple irrevocably blurred the line between consumer technology and medical devices as it landed FDA approval for a pair of high-tech features. One allows the Apple Watch to perform on-the-spot ECGs, while the other continuously monitors a wearer’s heart rhythm in the background to spot signs of atrial fibrillation.
Two years later, Fitbit partially caught up to its competitor with a late 2020 regulatory OK for its eponymous smartwatch’s own ECG app. The Google-owned devicemaker further leveled the playing field this week, thanks to an FDA nod for an algorithm designed to passively check for afib around the clock.
Like its predecessor at Apple, the new algorithm is based on photoplethysmography (PPG) sensor technology. The optical sensor assesses changes in blood volume—which determine the heart’s rhythm—by observing blood vessels under the skin as they expand and contract. It looks through the heart rhythm readings for deviations from the norm that could potentially point to afib, then automatically sends a notification to the wearer if any irregularities are detected.
The algorithm was validated in the fully virtual Fitbit Heart Study in 2020, which recruited more than 455,000 participants who had never been diagnosed with afib. Data presented at the American Heart Association’s annual scientific sessions last November showed that the algorithm accurately identified irregular heart rhythms and helped diagnose previously undetected cases of afib.
Participants who received an irregular heartbeat notification from their Fitbit during the study were asked to wear an ECG patch for seven days. In the 32% of patients who were flagged by the smartwatch and then went on to receive another irregular pulse notification from the ECG patch, 98% were ultimately diagnosed with afib.
Additionally, in study participants over the age of 65—a group with a heightened risk of experiencing stroke caused by afib—the algorithm’s alerts corresponded to an afib diagnosis at a rate of 97%.
The PPG technology is designed to work in the background throughout the day and night when a wearer is still or asleep. It faces the same regulatory restrictions as the Apple Watch’s irregular heartbeat notifications, limiting its use only to those aged 22 and older.
In its announcement about the FDA clearance, Fitbit highlighted the algorithm’s far-reaching potential, singling out statistics showing that while often difficult to detect, afib affects as many as 33.5 million people around the world and ups their risk of stroke five times over.
“We want to make afib detection as accessible as possible to help reduce the risk of potentially life-threatening events—like stroke—and ultimately improve overall heart health for everyone,” the company said.