Daily Heart Rate Per Step (DHRPS): A Wearables Metric Associated with Cardiovascular Disease in a Cross-Sectional Study of the All of Us Research Program.

Background: Simple biometrics such as peak heart rate and exercise duration remain core predictors of cardiovascular disease (CVD). Commercial wearable devices track physical and cardiac electrical activity. Detailed, longitudinal data collection from wearables presents a valuable opportunity to identify new factors associated with CVD.

Methods: This cross-sectional study analyzed 6,947 participants in the Fitbit Bring-Your-Own-Device Project, a subset of the All of Us Research Program. The primary exposure Daily Heart Rate Per Step (DHRPS) was defined as the average daily heart rate divided by steps per day. Our analysis correlated DHRPS with established CVD factors (type 2 diabetes, hypertension, stroke, heart failure, coronary atherosclerosis, myocardial infarction) as primary outcomes. We also performed a DHRPS-based phenome-wide association study (PheWAS) on the spectrum of human disease traits for all 1,789 disease codes across 17 disease categories. Secondary outcomes included maximum metabolic equivalents (METs) achieved on cardiovascular treadmill exercise stress testing.

Results: We examined 5.8 million person-days and 51 billion total steps of individual-level Fitbit data paired with electronic health record data. Elevated DHRPS was associated with type 2 diabetes (OR 2.03 [95% CI 1.70-2.42]), hypertension (OR 1.63 [95% CI 1.32-2.02]), heart failure (OR 1.77 [95% CI 1.00-3.14]), and coronary atherosclerosis (OR 1.44 [95% CI 1.14-1.82]), even after adjusting for daily heart rate and step count. DHRPS also had stronger correlations with max METs achieved on exercise stress testing compared to steps per day (∆ρ=0.04, p<0.001) and heart rate (∆ρ=0.31, p<0.001). Lastly, DHRPS-based PheWAS demonstrated stronger associations with CVD factors (p<1×10^-55) compared to daily heart rate or step count.

Conclusions: In the All of Us Research Program Fitbit Bring-Your-Own-Device Project, DHRPS was an easy-to-calculate wearables metric and was more strongly associated with cardiovascular fitness and CVD outcomes than daily heart rate and step count.