Exploring heart rate variability as a biomarker for frailty: A narrative review.

Abstract

<h4>Background</h4>Frailty is defined as a state of increased vulnerability to stressors resulting from reduced physiological homeostasis. The need to identify biomarkers capable of offering insight into the biological underpinnings of frailty and supporting early detection, diagnosis, and prognostic evaluation has grown in recent years. Heart rate variability (HRV), defined as the temporal variability between consecutive R waves of the electrocardiogram (R-R intervals), has emerged as a promising physiological biomarker in this context.<h4>Methods</h4>We conducted a narrative review of studies to synthesize evidence on HRV and frailty, examining analytical domains of HRV and situating findings within the current biomarker framework. Relevant literature was assessed across time-domain, frequency-domain, geometric and non-linear measures of HRV, together with reported associations involving clinical, functional and cognitive outcomes.<h4>Results</h4>Within the landscape of frailty biomarkers, HRV provides a non-invasive index of autonomic nervous system function. Reduced HRV has been associated with frailty status, diminished physiological reserve, adverse clinical outcomes, and cognitive decline, with particularly notable findings when assessed during physiological challenges rather than at rest. It should be noted, however, that the literature is heterogeneous and methodologically inconsistent, especially regarding recording duration and the specific HRV parameters analysed.<h4>Conclusions</h4>HRV is a highly promising physiological biomarker in the context of frailty, but further research is needed to clarify several aspects of its role. Its potential integration with other biomarkers may help confirm its validity and could contribute to identifying biomarker clusters relevant to personalized approaches.