Wrist-Worn Heart Rate Monitors Show Variable Accuracy

Most-popular monitors don’t measure up to chest ECGs

In a study published online in JAMA Cardiology, researchers at the Cleveland Clinic assessed the accuracy of four popular wrist-worn heart rate (HR) monitors under conditions of varying physical exertion.

While the accuracy of chest-strap, electrode-based HR monitors has been confirmed, the accuracy of wrist-worn, optically based HR monitors is uncertain. Assessment of the monitors’ accuracy is important for individuals who use them to guide their physical activity and for physicians to whom these individuals report HR readings.

The new study included 50 healthy adults (average age, 37 years). Twenty-eight participants were women. The subjects wore standard electrocardiographic limb leads and a Polar H7 chest-strap monitor. Each subject was randomly assigned to wear two different wrist-worn HR monitors. Four wrist-worn monitors were assessed: Fitbit Charge HR (Fitbit), Apple Watch (Apple), Mio Alpha (Mio Global), and Basis Peak (Basis). HR was assessed with subjects on a treadmill at rest and at 2, 3, 4, 5, and 6 mph. Participants exercised at each setting for three minutes to achieve a steady state; and HR was recorded instantaneously at the three-minute point. After subjects completed the treadmill protocol, HR was recorded during 30, 60, and 90 seconds of recovery.

A total of 1,773 HR values were recorded across all four devices. The investigators found that, when compared with an electrocardiogram, the HR monitors had variable accuracy. While the Basis Peak overestimated HR during moderate exercise, the Fitbit Charge HR underestimated HR during more-vigorous exercise. Variability occurred across the spectrum of midrange HRs during exercise. The Apple Watch and Mio Fuse had 95% of values within –27 bpm and +29 bpm of the electrocardiogram, whereas Fitbit Charge HR had 95% of values within –34 bpm and +39 bpm, and the corresponding values for the Basis Peak were within –39 bpm and +33 bpm.

“We found variable accuracy among wrist-worn HR monitors; none achieved the accuracy of a chest strap-based monitor. In general, accuracy of wrist-worn monitors was best at rest and diminished with exercise,” the authors wrote.

“Electrode-containing chest monitors should be used when accurate HR measurement is imperative. While wrist-worn HR monitors are often used recreationally to track fitness, their accuracy varies; two of four monitors had suboptimal accuracy during moderate exercise. Because cardiac patients increasingly rely on these monitors to stay within physician-recommended, safe HR thresholds during rehabilitation and exercise, appropriate validation of these devices in this group is imperative.”

Source: Medical Xpress; October 12, 2016.