Observations on EEG patterns in neurally-mediated syncope: an inspective and quantitative study.

We performed an observational EEG study in 43 patients with neurally-mediated syncope in basal condition and during hyperventilation (HV), and compared it with 32 healthy controls. On blind analysis at rest, EEG was classified as normal in 47% of patients (vs. 94% of controls, P < 0.001). More abundant and pronounced delta-theta activities and alpha slowing were found in patients than in control subjects on both visual inspection and quantitative spectral analysis. During prolonged HV, the EEG remained normal in 21% of patients only. Slow activities became more evident in patients than in control subjects, and intermittent rhythmic delta activity appeared in 40% of syncopal patients. These "pseudoparoxysmal" EEG changes differed from the common slowings induced by HV in adult subjects and were not observed in our control subjects. Moreover, these distinctive EEG changes, a common finding in syncopal patients, could not be confused with epileptiform activity of any kind. Further studies will clarify the pathophysiology of these EEG modifications.