Resting Heart Rate and Associations With Clinical Measures From the Project Baseline Health Study: Observational Study

Abstract

Background: Though widely used, resting heart rate (RHR), as measured by a wearable device, has not been previously evaluated in a large cohort against a variety of important baseline characteristics.

Objective: This study aimed to assess the validity of the RHR measured by a wearable device compared against the gold standard of ECG (electrocardiography), and assess the relationships between device-measured RHR and a broad range of clinical characteristics.

Methods: The Project Baseline Health Study (PHBS) captured detailed demographic, occupational, social, lifestyle, and clinical data to generate a deeply phenotyped cohort. We selected an analysis cohort within it, which included participants who had RHR determined by both ECG and the Verily Study Watch (VSW). We examined the correlation between these simultaneous RHR measures and assessed the relationship between VSW RHR and a range of baseline characteristics, including demographic, clinical, laboratory, and functional assessments.

Results: From the overall PBHS cohort (N=2502), 875 (35%) participants entered the analysis cohort (mean age 50.9, SD 16.5 years; n=519, 59% female and n=356, 41% male). The mean and SD of VSW RHR was 66.6 (SD 11.2) beats per minute (bpm) for female participants and 64.4 (SD 12.3) bpm for male participants. There was excellent reliability between the two measures of RHR (ECG and VSW) with an intraclass correlation coefficient of 0.946. On univariate analyses, female and male participants had similar baseline characteristics that trended with higher VSW RHR: lack of health care insurance (both P<.05), higher BMI (both P<.001), higher C-reactive protein (both P<.001), presence of type 2 diabetes mellitus (both P<.001) and higher World Health Organization Disability Assessment Schedule (WHODAS) 2.0 score (both P<.001) were associated with higher RHR. On regression analyses, within each domain of baseline characteristics (demographics and socioeconomic status, medical conditions, vitals, physical function, laboratory assessments, and patient-reported outcomes), different characteristics were associated with VSW RHR in female and male participants.

Conclusions: RHR determined by the VSW had an excellent correlation with that determined by ECG. Participants with higher VSW RHR had similar trends in socioeconomic status, medical conditions, vitals, laboratory assessments, physical function, and patient-reported outcomes irrespective of sex. However, within each domain of baseline characteristics, different characteristics were most associated with VSW RHR in female and male participants.

Trial registration: ClinicalTrials.gov NCT03154346; https://clinicaltrials.gov/study/NCT03154346.

Keywords: PBHS; Project Baseline Health Study; Verily Study Watch; cohort study; eHealth; electrocardiogram; electronic health; heart rate; laboratory assessments; medical condition; observational study; physical function; physiology; regression analyses; remote monitoring; resting heart rate; socioeconomic status; vital signs; wearable devices; wearables.

Figure 1

Verily Study Watch resting heart rate (VSW RHR) determination during the Project Baseline Health Study (PBHS) procedures. (A) Relative placement in time of the 2-minute VSW data acquisition window against the backdrop of the 10-second ECG acquisition window. (B) Flowchart showing the processing steps to calculate the VSW RHR for each participant. ECG: electrocardiogram; SW: study watch; PPG: photoplethysmography; IBI: interbeat interval; VSW: Verily Study Watch; RHR: resting heart rate.

Figure 2

Analysis cohort flowchart. This flow chart details the creation of the eventual analysis cohort (n=875), originating from the full PBHS cohort. PBHS: Project Baseline Health Study; ECG: electrocardiogram; PPG: photoplethysmography; IBI: interbeat interval; VSW: Verily Study Watch.

Figure 3

Correlation between baseline ECG-based and Study Watch measured RHR in this analysis cohort (within the PBHS) for (A) all participants and (B) male (left) and female (right) participants separately. Each dot corresponds to one participant. There is excellent overall reliability between ECG RHR and VSW RHR (ICC=0.946) and within each of the male (0.942) and female (0.949) subgroups. BPM: beats per minute; ECG: electrocardiogram; ICC: intraclass correlation coefficient; RHR: resting heart rate; SW: study watch.

Figure 4

Baseline study watch resting heart rate by age and sex in this analysis cohort (within the PBHS). A U-shaped curve was observed for both female and male participants when Verily Study Watch resting heart rate (VSW RHR) was plotted against age. The lines show fitted quadratic models for female and male data separately. The shaded areas show the 95% CIs of the models. BPM: beats per minute; RHR: resting heart rate.

Figure 5

LASSO (least absolute shrinkage and selection operator) regressions. Regression analyses performed in this cohort (within the PBHS) suggest that, within each domain, different baseline characteristics are most associated with resting heart rate. All continuous measurements, ie, laboratory, vital, and physical function variables, were transformed by the Box-Cox method before analysis. All variables were standardized as required for penalized regression methodology. Within each domain of baseline characteristics, there were some characteristics that were more associated with RHR in female participants and others that were more associated with male participants. A higher-resolution version of this image is available in Multimedia Appendix 2.