Psychophysiological evaluation of patients with transient loss of consciousness of uncertain origin

Background: Psychological profile (PsyP) of patients with transient loss of consciousness (TLoC) is evidence of high prevalence of anxiety and depression. However, the mechanistic link between abnormal PsyP and TLoC is still unclear. Aim: This study aimed to evaluate: 1) prevalence of abnormal PsyP in TLoC patients; 2) cardiac autonomic response to head-up tilt test (HUTT) in patients with (PsyP+) or without abnormal PsyP (PsyP–), developing syncope (HUTT+) or not (HUTT–). Methods: Forty-one patients (66% female, mean age 36 ± 15 years), with history of TLoC, underwent PsyP before HUTT. Short-term heart rate variability analysis was carried out under baseline rest condition and at peak heart rate and/or onset of syncope induced by nitroglycerine (NTG), during HUTT. Results: HUTT+ occurred in 17/41 patients, more frequently in females, who had higher levels of anxiety (p < 0.0001). PsyP+ was prevalent in 70.5% of HUTT+ patients (p < 0.05). Among PsyP+ patients HUTT+ had dominant sympathetic modulation (DSM) at rest, which increased at the onset of syncope, whereas in HUTT patients vagal modulation was prevalent at rest. Among NTG-induced HUTT+ patients, fourfold higher increases of very low frequency (VLF) power were found in PsyP– compared with PsyP+. Conclusions: 58% of patients with history of TLoC were PsyP+. In PsyP+ patients, DSM at rest correlates with higher probability of NTG-induced syncope, which occurs with 60% increment of low frequency and 530% increment of VLF power. Conversely, in patients with prevalent vagal modulation at rest and a decrease in VLF power after NTG, syncope did not occur. This supports interpretation of VLF power as an index of stress-induced sympathetic activity.