UC San Diego

Background: We assessed the test validity of the Apple Watch’s measure of HRV by comparing it with HRV measured via Biopac 3 lead ECG.Methods: We recruited 58 young adults (aged 20- 51 years) from San Diego, CA, US. HRV was measured under the four following conditions during the visit: 1) at rest in a supine position, 2) sitting while talking, 3) sitting while watching a movie clip, and 4) sitting before and after walking. To guarantee the Apple Watch and Biopac 3 lead ECG recordings aligned, a synchronized countdown was conducted for each condition, with event markers electronically placed on the Biopac 3 lead ECG recording when the Apple Watch Breathe app began and ended. Test validity was assessed using the Bland-Altman method, and the combination of both precision and accuracy were estimated using Lin’s correlation coefficient. Results: The highest level of agreement and concordance between devices occurred during rest. Near perfect agreement was observed for measures of the R-R interval and BPM, with mean absolute percentage errors of 1.03% and 4.50 %, respectively. Moderate levels of agreement and concordance for N-N intervals, PNN50, and %PNN50 were only achieved at rest. Conclusion: The Apple Watch provides a high level of validity for measuring R-R intervals and BPM in healthy adults. More refined measures of HRV, such as N-N intervals, were only moderately acceptable when taken at rest. Further research is needed to determine if the Apple Watch’s HRV measures offer a significant opportunity for the surveillance of CVD risk.