Combined transcranial Doppler and EEG recording in vasovagal syncope

Background: In neurally mediated syncope a ‘typical’ EEG pattern during hyperventilation (HV) may be observed. This study aimed to investigate transcranial Doppler (TCD) and EEG variations in response to hyper- and hypocapnia using simultaneous recording. Methods: Syncope patients with a typical EEG pattern during HV (SEEG+, n = 15) and those without abnormalities (SEEG–, n = 16) were compared with healthy controls (n = 20). Simultaneous TCD and EEG recordings were performed at rest (baseline), during 2 apnea tests and during HV. Cerebrovascular vasoreactivity, index for hypocapnia, total vasomotor reserve and time to flow velocity normalization after HV (t-norm) were recorded. Results: With TCD, a reduction in Vasomotor reserve was observed in SEEG+ compared with the other 2 groups (control: 67 ± 8%; SEEG–: 67 ± 10%; SEEG+: 57 ± 8%; p < 0.0001). t-norm was longer in all syncopal patients and in particular in SEEG+ (control: 20.2 ± 3 s; SEEG–: 40 ± 7 s; SEEG+: 123 ± 45s; p < 0.0001). Quantitative EEG showed an increase in slow bands in all subjects during HV, small and nonsignificant in controls and SEEG–, higher and significant in SEEG+, related with flow reduction. Conclusions: Changes in the sympathetic modulation of cerebral vasoconstriction may explain both the pathophysiology of vasovagal syncope and the typical paroxysmal EEG findings.