Depression is associated with reduced HRV and EEG alpha in patients after cardiac surgery

Depression is an independent risk factor after cardiac surgery and autonomic nervous system (ANS) dysregulation, as indexed by reduced Heart Rate Variability (HRV), has been indicated as a mechanism underlying the relationship between depression and cardiac risk. Depression has also been associated with altered electroencephalographic (EEG) patterns, mostly hypoactivation, as indicated by overall increased alpha power spectrum. The association between HRV and EEG alpha activity has not yet been studied in patients after cardiac surgery. The present study aimed at examining a) HRV and EEG alpha power, and b) their association, in depressed and nondepressed patients after first time cardiac surgery. Five minute rest HRV and EEG (Fz, Cz, Pz) were measured in 15 depressed and 21 nondepressed patients. Compared to nondepressed patients, those with depression showed reduced cardiac vagal control (root mean square successive difference of NN intervals, rMSSD; numbers of couples of adjacent NN intervals differing by more than 50 ms, NN50) and reduced alpha power spectrum. Moreover, while a significant positive correlation between NN50 and alpha power emerged in nondepressed patients, depressed patients showed no correlation between HRV and EEG indexes. These results indicate that depression after cardiac surgery is associated to impaired vagal modulation on the heart, and, contrary to the main literature in this field, reduced EEG alpha activity. Further studies are needed to determine whether these alterations may lead to increased risk in depressed patients after cardiac surgery.