FDA Clears Fitbit Algorithm to Detect Atrial Fibrillation

"Most of the episodes of undiagnosed atrial fibrillation detected occurred during sleep, and we suspect that these episodes were asymptomatic."

FitBit today received clearance from the US Food and Drug Administration (FDA) for its photoplethysmography-(PPG) based algorithm to detect atrial fibrillation (Afib).

The algorithm, the company stated in its announcement, passively assesses heart rhythm while an individual is still or even asleep. Any rhythm suggestive of Afib will trigger FitBit’s Irregular Heart Rhythm Notifications feature, providing the FitBit wearer with the option to speak to a health care provider or seek further assessment to avoid a significant event, eg, stroke. 

The agency’s clearance was based on results from the landmark 2020 FitBit Heart Study, the FitBit statement says. The original data were presented at the American Heart Association Scientific Sessions in November 2021.

As reported then on Patient Care, FitBit Heart enrolled 455 669 US adults aged ≥22 years (median age, 47 years; 71% women; 73% White) with a compatible Fitbit fitness tracker or Android or iOS smartwatch with the FitBit app and had no prior diagnosis of AF or atrial flutter or use of oral anticoagulation or implantation of a pacemaker or defibrillator; investigators reported the positive predictive value of the algorithm for concurrent AF on the ECG patch monitor was 98.2%.

Given that Afib presentation can be sporadic, optimal screening is through technology that continues to track heart rate and rhythm when the body is in a resting state, according to the statement. The device's 24/7 heart rate tracking potentially shortens time to arrhythmia identification with consistent long-term rhythm assessment.

Meanwhile, a spot-check approach with the FitBit’s ECG app allows wearers to proactively screen themselves for AF and share ECG tracings with health care providers.

FitBit Heart Study lead author Steven Lubitz, MD, associate professor of medicine at Harvard Medical School and cardiac electrophysiologist at Massachusetts General Hospital, said during the AHA 2021 meeting that while a FitBit wearer is inactive, the algorithm continuously samples pulse data in 5-minute tachograms overlapping by 50%, and flags an irregular heart rhythm if 11 consecutive tachograms are irregular.

During the study, Lubitz explained, “most of the episodes of undiagnosed atrial fibrillation detected occurred during sleep, and we suspect that these episodes were asymptomatic. Since the algorithm is most active when wearers are physically inactive, the wearable should be worn during sleep for the greatest benefits.”

Irregular heart rhythm detection occurred in 1% of Fitbit Heart Study participants overall and in 4% of those aged ≥65 years, according to the study. Lubitz and colleagues reported that 32.3% of participants with IHRD detection who after submitting ECG readings had confirmed AF. Those with confirmed AF had a median AF burden of 7%.

“The Fitbit PPG-based algorithm and Irregular Heart Rhythm Notifications feature will soon be available to consumers in the U.S. across a range of heart-rate enabled devices,” the company says.