Investigation of an estimate of daily resting heart rate using a consumer wearable device

Resting heart rate is accepted as a valid overall indicator of cardiovascular risk and is a low-cost easy-to-measure metric that can be collected in both home and clinical settings. Wearable devices such as smartwatches and trackers can measure heart rate continuously using optical technology. This study reports initially on the agreement between the resting heart rate reported by a wearable device (Fitbit Charge HR and Fitbit Blaze) and a chest-based consumer electrocardiogram (Polar H7). In 45 subjects, the reported resting heart rates agreed within 0.89 bpm over a resting period of 5 mins. The same device and algorithm was then used in a population of 168 subjects (45.9{+/-} 15.6 yrs) who were asked to collect their resting heart rate for four days under seven different conditions and times (at wake sitting/lying down, pre-breakfast, pre-lunch, pre-dinner, and before bed sitting/lying down). The reported values were compared with the Daily Resting Heart Rate (DRHR) reported by the wearable device. The measurement lying down before wake were closest to the DRHR (mean error of 0.0 bpm with a 25-75th percentile spread of {+/-}3.5bpm. There was a significant circadian variation in the reported resting heart rate across subjects, with the highest values reported in the middle of the day. Within individual subjects, the median standard deviation of heart rate at rest was 3-5bpm even measured under nominally similar conditions over four days.