Is cardiac autonomic control affected in major depressive disorder? A systematic review of heart rate variability studies

INTRODUCTION: Major depressive disorder (MDD) is a heterogeneous psychiatric disorder that is a risk factor for cardiovascular diseases. Autonomic dysregulation, estimated as an important orrelated pathophysiological cause, was investigated in many studies mainly through a quantitative evaluation of the heart rate variability (HRV). AIM: The objective of this review was to provide any reproducible insights on autonomic regulation characteristics of MDD through the selection, revision, and joint interpretation of a restricted sample of studies based on systematic criteria. METHODS: The literature research resulted in thirty eligible articles that reported the comparison of short-term resting-state HRV measures between drug-free MDD patients and healthy controls, excluding subjects affected by cardiovascular diseases. RESULTS: Most of the reviewed studies reported significant differences between MDD patients and controls in the investigated HRV measures, especially for those that mainly reflect vagal activity. Nonlinear measures, although computed by fewer studies, seem to be more sensitive in detecting autonomic changes in MDD. CONCLUSIONS: Our findings can be considered as evidence that the intrinsic autonomic state of MDD is characterized by decreased parasympathetic tone, which, interpreted in the context of the polyvagal theory, might be associated with impaired emotion regulation and flexible adjustment in MDD.