Depression and reduced heart rate variability after cardiac surgery: the mediating role of emotion regulation.

Heart rate variability (HRV), as an index of autonomic nervous system (ANS) functioning, is reduced by depression after cardiac surgery, but the underlying mechanisms of this relationship are poorly understood. Poor emotion regulation as a core symptom of depression has also been associated with altered ANS functioning. The present study aimed to evaluate whether emotion dysregulation could be a mediator of the postoperative depression-reduced HRV relationship. Self-reported emotion regulation and fourminute HRV were measured in 25 depressed and 43 nondepressed patients after cardiac surgery. Mediation analysis was conducted with emotion regulation scores as mediator of the depression-reduced HRV relationship. Compared to nondepressed patients, those with depression showed lower standard deviation of normal-to-normal (NN) intervals, root mean square successive difference of NN intervals, number of interval differences of successive NN intervals greater than 50 ms (NN50), and NN50-total number of NN intervals ratio (pNN50). Increased low frequency (LF) in normalized units (n.u.) and reduced high frequency (HF) n.u. were also found in depressed compared to nondepressed patients. Suppression of emotion-expressive behavior partially mediated the effect of depression on LF and HF. Results confirm that depression is associated with reduced HRV, especially reduced vagal tone and sympathovagal imbalance, after cardiac surgery. This study also suggests that increased suppression of expressive emotion may mediate the depression-related sympathovagal imbalance after cardiac surgery.