Depression and heart rate variability in cardiac surgery patients

Depression is a significant and independent risk factor for cardiovascular diseases, cardiac morbidity, and fatal cardiac events after cardiac surgery. Although the physiological mechanisms underlying depression as a risk factor for developing cardiovascular diseases are still debated, an altered autonomic tone has been frequently implicated in the relationship between depression and cardiovascular morbidity or mortality. Indeed, it is well-established that depression is related to autonomic nervous system (ANS) dysregulation, and particularly, increased sympathetic nervous system activity and/or reduced vagal tone on heart rate. ANS dysregulation, in turn, may predispose patients to cardiovascular diseases such as ventricular tachycardia, ventricular fibrillation, and sudden cardiac death. Based on these considerations, the main aim of the current study was to examine the association between depression symptoms and heart rate variability (HRV), a measure which reflects cardiac vagal modulation, in patients who underwent first-time cardiac surgery. 20 patients with depressive symptoms and 22 patients without depressive symptoms, who underwent first-time cardiac surgery, were sequentially enrolled in the study. In all patients, blood volume pulse was recorded at rest. Beat to beat intervals were derived from blood volume pulse, and HRV was obtained through a Fast Fourier analysis on beat to beat intervals. Patients with depressive symptoms showed significantly reduced parameters of HRV compared to patients without depressive symptoms. Specifically, standard deviation of N-to-N intervals (SDNN), root mean square successive difference of N-to-N intervals (rMSSD) and high frequency (HF) power were reduced in patients with depressive symptoms. Consistent with these findings, correlations revealed that depressive symptoms were inversely associated with SDNN, rMSSD but not with other HRV parameters. These findings add to the literature on physiological mechanisms underlying the association between cardiovascular disease and depression by showing that the relationship between depression and reduced HRV extends to cardiac surgery patients. The current study suggests the usefulness of biobehavioral interventions after cardiac surgery, such as HRV biofeedback, aimed at treating physiological correlates of depressive symptoms, which, in turn, are relevant and independent risk factors for cardiac morbidity and mortality in patients after cardiac surgery.