Heart Rate Variability as a Digital Biomarker in Adolescents and Young Adults Receiving Hematopoietic Cell Transplantation.

Introduction: Adolescents and young adults (AYAs) receiving hematopoietic cell transplantation (HCT) are at high risk for poor psychosocial outcomes. Heart rate variability (HRV), a surrogate for autonomic nervous system activity, is a promising digital biomarker that has been linked to important outcomes. The objectives of this study were to prospectively describe the trajectory of HRV among AYAs receiving HCT and explore the association between HRV and patient-reported outcomes (PROs).

Methods: This was a multi-site study embedded in a randomized trial among AYAs receiving HCT (NCT03640325). We collected sequential 24-h HRV metrics, including the standard deviation of normal-to-normal beats (SDNN), root-mean-square of successive differences (RMSSD), as well as frequency domain measures. PRO surveys queried anxiety, depression, quality of life, hope, and resilience at baseline and 3 months. We summarized outcomes using descriptive statistics, and Pearson correlation coefficients were used to examine the relationship between HRV and PROs.

Results: Thirty-nine HRV recordings were collected from n = 16 participants aged 12-21 years. There was a moderately strong correlation between inferior baseline HRV and higher anxiety and depression (anxiety: r = -0.35 (p = 0.18) for SDNN, r = -0.47 (p = 0.07) for RMSSD; depression: r = -0.26 (p = 0.34) for SDNN, r = -0.39 (p = 0.14) for RMSSD). Among participants with elevated baseline anxiety, higher HRV suggested greater improvement in anxiety over time (r = -0.66 (p = 0.08) for SDNN, r = -0.31 (p = 0.45) for RMSSD).

Conclusions: There was a correlation between HRV and PROs in this study, and among those with elevated anxiety, HRV predicted improvement over time. Digital biomarkers may augment behavioral intervention design and implementation.