The relationship between heart rate variability and frailty in older adults: Systematic review and three-level...

Heart rate variability (HRV) is a potential biomarker for frailty, which is burdensome in older adults. However, existing studies report inconsistent findings regarding their relationship, and no meta-analysis has been conducted. This systematic review and meta-analysis aim to examine the association between HRV and frailty, as well as the boundary conditions that influence this relationship.

We systematically searched eight databases for studies examining three domains of HRV parameters - time-, frequency-, and nonlinear-domain - and their associations with frailty. Using a three-level random-effects meta-analytic model, we investigated the pooled effect sizes (Hedges' g) for short-term (≤ 5 minutes) and long-term (24-hour) HRV, and potential variables moderating the relationship between HRV and frailty.

We included 16 studies (n = 2365) in the review from 1132 records, and 13 of them were meta-analyzed (n = 1677) contributing 90 effect sizes. Both short-term (7 studies, 47 effect sizes) and long-term (6 studies, 43 effect sizes) models indicated lower HRV in (pre)frail individuals compared to their non-frail counterparts, while the effects were not statistically significant. For long-term HRV, the relationship was moderated by HRV domain: time-domain parameters exhibited a larger effect size (g = 2.097) than frequency-domain parameters (g = 1.698).

Our meta-analyses revealed a trend towards lower HRV in (pre)frail individuals; however, the effects in both models were not statistically significant. Although HRV may be a potential biomarker of frailty, the current evidence remains inconclusive. Further prospective studies are necessary, considering the heterogeneity and potential publication bias observed.