Reliability and validity of a smartwatch with a photoplethysmograph: Comparison with a Holter electrocardiograph

Although consumer-grade smartwatches with a photoplethysmograph (PPG) can measure heart rate, their reliability and validity in healthy participants under free-living conditions remain unclear. Therefore, this study compared the heart rates measured by a smartwatch with PPG and a clinically accepted Holter electrocardiograph in healthy adult participants under completely free-living conditions. Ten participants wore a Holter recorder on their left chest and a Garmin vivosmart 5 on their non-dominant wrist simultaneously for 72-96 h. Averages were calculated every 2 min from the data obtained, and timestamps were used for alignment. Agreement between the measurements taken by the two devices was verified using intraclass correlation and Bland-Altman analyses. Error trends for Garmin vivosmart 5 were examined using linear regression analysis. The overall intraclass correlation coefficient range was 0.819-0.937 (mean: 0.902), indicating strong agreement. The mean bias was 1.16 bpm, and the mean limit of agreement was ±12.4 (7.87-20.6) bpm. Furthermore, the linear regression line intercept was negative for all participants, indicating that Garmin vivosmart 5 tended to underestimate the heart rate; however, the slope was positive and close to 0. Overall, the smartwatch maintained a certain accuracy level under fluctuating heart rates and demonstrated reasonable reliability during sleep or daily activities.