Heart Rate Variability Analysis: How Much Artifact Can We Remove?

Abstract

Objective: Heart rate variability (HRV) evaluates small beat-to-beat time interval (BBI) differences produced by the heart and suggested as a marker of the autonomic nervous system. Artifact produced by movement with wrist worn devices can significantly impact the validity of HRV analysis. The objective of this study was to determine the impact of small errors in BBI selection on HRV analysis and produce a foundation for future research in mental health wearable technology.

Methods: This was a sub-analysis from a prospective observational clinical trial registered with clinicaltrials.gov (NCT03030924). A cohort of 10 subject's HRV tracings from a wearable wrist monitor without any artifact were manipulated by the study team to represent the most common forms of artifact encountered.

Results: Root mean square of successive differences stayed below a clinically significant change when up to 5 beats were selected at the wrong time interval and up to 36% of BBIs was removed. Standard deviation of next normal intervals stayed below a clinically significant change when up to 3 beats were selected at the wrong time interval and up to 36% of BBIs were removed. High frequency HRV shows significant changes when more than 2 beats were selected at the wrong time interval and any BBIs were removed.

Conclusion: Time domain HRV metrics appear to be more robust to artifact compared to frequency domains. Investigators examining wearable technology for mental health should be aware of these values for future analysis of HRV studies to improve data quality.

Keywords: Artifact; Heart rate variability; Mental health; Suicidality.

Conflict of interest statement

The authors have no potential conflicts of interest to disclose.

Figures

Figure 1.

Mean Square of Successive Differences (RMSSD). A: For shift, mean absolute percent difference stays below 5% until about 5 samples for a random shift and about 5 samples for a shift to the right. B: For percent of beats removed, mean absolute percent difference is always below 5% (up to 36 % of beats removed). It's about the same for removal randomly versus consecutively.

Figure 2.

Standard Deviation of NN intervals (SDNN). A: For shift, mean absolute percent difference stays below 5% until about 3 samples and then dramatically increases. It's about the same for random shift versus right shift. B: For percent of beats removed, mean absolute percent difference is always below 5% (up to 36% of beats removed). It's about the same for removal randomly versus consecutively.

Figure 3.

Mean number of times in which the difference in NN intervals is greater than 50 milliseconds (pNN50). A: PNN50 is very sensitive to shifting. No amount of shifting keeps the average absolute percent difference less than 5%. B: For beats removed, mean absolute percent difference is below 5% until about 4% of beats for randomly or consecutively removed beats.

Figure 4.

Low Frequency (LF). A: For shift, mean absolute percent difference stays below 5% until about 2 samples, hovers around 5% until about 6 beats, and then dramatically increases. For a right shift, no amount of shift makes the mean absolute percent difference rise above 5%. LF if very robust to shifting samples right. B: For beats removed, LF is very sensitive with the mean absolute percent difference staying below 5% for only 2% of beats removed. It’s the same regardless of random versus consecutive removal.

Figure 5.

High Frequency (HF). A: For shift, mean absolute percent difference stays below 5% until about 2 samples for a random shift. For a right shift, it mean absolute percent difference remains below 5% until about 8 samples shifted. B: For beats removed randomly, HF is very sensitive with the mean absolute percent difference always being greater than 5% with any amount of beats removed. For beats removed consecutively, that hovers around 5% mean absolute difference until 8% of beats removed.