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

Background: 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 symptomof depression has also been associatedwith altered ANS functioning. The present study aimed to examine whether emotion dysregulation could be a mediator of the depression-reduced HRV relationship observed after cardiac surgery. Methods: Self-reported emotion regulation and four-minute HRV were measured in 25 depressed and 43 nondepressed patients after cardiac surgery. Mediation analysis was conducted to evaluate emotion regulation as a mediatorof the depression–reduced HRV relationship. Results: Compared to nondepressed patients, those with depression showed lower standard deviation of normal-to-normal (NN) intervals (p < .05), root mean square successive difference of NN intervals (p < .004), and number of interval differences of successive NN intervals greater than 50 ms (NN50) (p < .05). 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 (p's < .01). Mediation analysis revealed that suppression of emotionexpressive behavior partially mediated the effect of depression on LF n.u. and HF n.u. Conclusions: Results confirmed previous findings showing that depression is associatedwith reduced HRV, especially a reduced vagal tone and a sympathovagal imbalance, after cardiac surgery. This study also provides preliminary evidence that increased trait levels of suppression of emotion-expressive behavior may mediate the depression-related sympathovagal imbalance after cardiac surgery.