Wearable Irregular Heart Rhythm Detection Recurrences and Electrocardiographic Atrial Fibrillation Confirmation: The Fitbit Heart Study

BACKGROUND: Wrist-worn wearables can detect irregular heart rhythms using photoplethysmography, but ECGs are required to confirm atrial fibrillation (AF). We sought to determine the frequency of a recurrent irregular heart rhythm detection (IHRD; ≥30 minutes of an irregular rhythm), estimate the potential diagnostic yield of different electrocardiographic monitoring strategies for confirming AF, and identify predictors of recurrent IHRDs. METHODS: The Fitbit Heart Study enrolled wrist-worn photoplethysmography device users without diagnosed AF. Of 455 699 participants, 1057 who wore and returned a 1-week ECG patch monitor after receiving an IHRD were analyzed. Baseline clinical data, device-derived metrics, IHRDs during follow-up, and electrocardiographic patch data were used for analysis. RESULTS: A total of 570 (53.9%) participants were aged 40 to 64 years, 422 (39.9%) were aged ≥65 years, and 510 (48.2%) were women. Median follow-up after ECG patch initiation was 80 days (interquartile range, 45–122 days). The frequency of another IHRD was 57.2% (95% CI, 53.1%–60.9%) at 3 months. After an initial IHRD, the estimated diagnostic yield for AF with a 10-second ECG was 7.6% (95% CI, 6.2%–9.0%), twice-daily 30-second ECGs over 1 week 19.0% (95% CI, 16.7%–21.2%), 24-hour monitor 17.4% (95% CI, 15.5%–19.3%), 1-week monitor 32.2% (95% CI, 29.4%–35.0%), 2-week monitor 46.8% (95% CI, 42.7%–50.8%), and 4-week monitor 60.8% (95% CI, 56.5%–65.1%). The risk of a recurrent IHRD was greater with older age ( P <0.001), male sex ( P =0.001), vascular disease ( P =0.03), longer initial runs of consecutive IHRDs at detection ( P =0.02), and less nightly sleep ( P =0.03). CONCLUSIONS: Irregular heart rhythms are common after initial detection using a wrist-worn wearable device. Longer electrocardiographic monitoring periods increase the likelihood of confirming AF. REGISTRATION: URL: https://www.clinicaltrials.gov ; Unique identifier: NCT04380415.