Heart rate variability: Can it serve as a marker of mental health resilience? Special Section on Translational and Neuroscience Studies in Affective Disorders Section Editor, Maria Nobile MD, PhD

Background: Stress resilience influences mental well-being and vulnerability to psychiatric disorders. Usually, measurement of resilience is based on subjective reports, susceptible to biases. It justifies the need for objective biological/physiological biomarkers of resilience. One promising candidate as biomarker of mental health resilience (MHR) is heart rate variability (HRV). The evidence for its use was reviewed in this study. Methods: We focused on the relationship between HRV (as measured through decomposition of RR intervals from electrocardiogram) and responses to laboratory stressors in individuals without medical and psychiatric diseases. We conducted a bibliographic search of publications in the PubMed for January 2010-September 2018. Results: Eight studies were included. High vagally mediated HRV before and/or during stressful laboratory tasks was associated with enhanced cognitive resilience to competitive/self-control challenges, appropriate emotional regulation during emotional tasks, and better modulation of cortisol, cardiovascular and inflammatory responses during psychosocial/mental tasks. Limitations: All studies were cross-sectional, restricting conclusions that can be made. Most studies included only young participants, with some samples of only males or females, and a limited array of HRV indexes. Ecological validity of stressful laboratory tasks remains unclear. Conclusions: Vagally mediated HRV may serve as a global index of an individual's flexibility and adaptability to stressors. This supports the idea of HRV as a plausible, noninvasive, and easily applicable biomarker of MHR. In future longitudinal studies, the implementation of wearable health devices, able to record HRV in naturalistic contexts of real-life, may be a valuable strategy to gain more reliable insight into this topic.