Association between depressive symptoms and reduced cardiac vagal modulation in patients after cardiac surgery

Several lines of evidence indicate that depression is a relevant and independent risk factor for cardiovascular diseases. Reduced heart rate variability (HRV), which reflects altered autonomic nervous system activity, has been suggested as a potential factor linking depression to cardiovascular diseases. While several studies have investigated the association between depression and reduced HRV in patients with cardiovascular diseases, to our knowledge, this relationship has not yet been studied in patients after cardiac surgery. Therefore, the main aim of this study was to examine whether postoperative depressive symptoms could be related to reduced HRV. Patients with depression and without depression, who had undergone cardiac surgery, were enrolled postoperatively. In all patients, HRV was derived from a four-minute blood volume pulse recording at rest. Analyses of covariance and partial correlations, while controlling for anxiety, were used to examine the association between postoperative depression and HRV parameters. The two groups of patients (i.e., with depression and without depression) were comparable in terms of demographic, biomedical and surgical characteristics. Compared to non-depressed patients, patients with depression showed significantly lower standard deviation of N-to-N intervals (SDNN), root mean square successive difference of N-to-N intervals (rMSSD), and high frequency power. Partial correlation analyses showed that depression was inversely related to SDNN, rMSSD, and high-frequency power, whereas it was unrelated to other HRV parameters. Discussion: These novel findings add to the literature on physiological mechanisms underlying the association between depression and cardiovascular disease by showing that a depression-reduced HRV relationship extends to patients after cardiac surgery. Also, our study suggests that postoperative depression is more likely to be associated with reduced cardiac vagal modulation rather than excessive sympathetic influence. Conclusion: Reduced HRV, especially an altered vagal tone, may be considered as a potential mechanism underlying the link between postoperative depression and subsequent risk for cardiac events or mortality after surgery. In particular, the present study suggests that, in addition to cardiac surgery itself, depressive symptoms may further affect HRV in the early postoperative period, potentially contributing to adverse outcome in patients after surgery.