A novel software algorithm compatible with a wide range of smartwatches and fitness trackers detected irregular heart rhythms and accurately identified undiagnosed atrial fibrillation (AFib) 98 percent of the time, according to research presented at the American Heart Association’s Scientific Sessions 2021.

Many smartwatches and fitness trackers can detect the wearer’s pulse rate using light sensors. Researchers developed a novel software algorithm to analyze pulse rate signals and infer the presence of atrial fibrillation on one brand of wearables. The algorithm operates during periods of inactivity and uses a process that examines continuous and overlapping episodes of pulse information from the wearable device to analyze for an irregular heart rhythm. The algorithm requires at least 30 minutes of sensing irregular heart rhythms to indicate the presence of possible atrial fibrillation.

“Undiagnosed atrial fibrillation can lead to strokes, and early detection of atrial fibrillation may allow doctors to prescribe medications that are effective at preventing strokes,” said Steven A. Lubitz, MD, MPH, Associate Professor of medicine at Harvard Medical School and cardiologist at the Massachusetts General Hospital in Boston.

In this study, conducted from May through October 2020, investigators from Massachusetts General Hospital and fitness wearable manufacturer Fitbit remotely enrolled more than 455,000 adult smartwatch or fitness tracker users in the United States. None of the study participants had a self-reported prior diagnosis of atrial fibrillation. The average age of the participants was 47 years; 71 percent were female; and 73 percent were white. The data from their devices were analyzed using the novel software algorithm.

Participants who had an irregular heart rhythm detected by the software algorithm were notified and invited to schedule a visit with a telehealth professional. After meeting with the telehealth doctor, participants received a one-week electrocardiogram (ECG) patch monitor to wear along with the smartwatch or fitness tracker.

The analysis found that the novel software algorithm was able to successfully detect atrial fibrillation, and the findings were consistent across age groups. Specifically:

  • Irregular heart rhythm detection occurred in 1 percent of individuals overall and 4 percent of adults older than 65 years.

  • Among individuals who received notification of an irregular heart rhythm, 32 percent had atrial fibrillation detected on a subsequent ECG patch monitor.

  • The ECG patch confirmed atrial fibrillation in 98 percent of individuals who had another irregular heart rhythm detection while wearing the ECG patch monitor.

  • For participants over 65 years old, a subgroup at elevated risk for stroke caused by atrial fibrillation, the algorithm corresponded to concurrent AFib 97 percent of the time.

The algorithm is currently being reviewed by the FDA for clearance and widespread use. The study did not test whether screening for atrial fibrillation leads to a reduction in strokes, which Lubitz noted is an opportunity for future research.

For more information, contact Bridgette McNeill at This email address is being protected from spambots. You need JavaScript enabled to view it..