Accuracy of wearable heart rate monitors in cardiac rehabilitation

Background: To assess the accuracy of four wearable heart rate (HR) monitors in patients with established cardiovascular disease enrolled in phase II or III cardiac rehabilitation (CR). Methods: Eighty adult patients enrolled in phase II or III CR were monitored during a CR session that included exercise on a treadmill and/or stationary cycle. Participants underwent HR monitoring with standard ECG limb leads, an electrocardiographic (ECG) chest strap monitor (Polar H7), and two randomly assigned wrist-worn HR monitors (Apple Watch, Fitbit Blaze, Garmin Forerunner 235, TomTom Spark Cardio), one on each wrist. HR was recorded at rest and at 3, 5, and 7 minutes of steady-state exercise on the treadmill and stationary cycle. Results: Across all exercise conditions, the chest strap monitor (Polar H7) had the best agreement with ECG (r(c)=0.99) followed by the Apple Watch (r(c)=0.80), Fitbit Blaze (r(c)=0.78), TomTom Spark (r(c)=0.76) and Garmin Forerunner (r(c)=4.52). There was variability in accuracy under different exercise conditions. On the treadmill, only the Fitbit Blaze performed well (r(c)=0.76), while on the stationary cycle, Apple Watch (r(c)=4.89) and TomTom Spark (r(c)=4.85) were most accurate. Conclusions: In cardiac patients, the accuracy of wearable, optically based HR monitors varies, and none of those tested was as accurate as an electrode-containing chest monitor. This observation has implications for in-home CR, as electrode-containing chest monitors should be used when accurate HR measurement is imperative.