ELECTROENCEPHALOGRAPHIC CORRELATES OF VASOVAGAL SYNCOPE INDUCED BY HEAD-UP TILT TESTING

Background and Purpose-We sought to determine whether the introduction of EEG monitoring during head-up tilt testing could significantly imp rove the understanding of the cerebral events occurring during tilt-in duced vasovagal syncope and the potential danger to the patient of thi s diagnostic procedure. Method;-EEG monitoring was performed during he ad-up tilt testing in a group of 63 consecutive patients (27 males and 36 females; mean age, 41.5 years) with a history of recurrent syncope of unknown origin despite extensive clinical and laboratory assessmen t. Results-Syncope occurred in 27 of 63 patients (42.8%) during head-u p tilt testing and was found to be cardioinhibitory in 11 of 27 (40.7% ) and vasodepressor in 16 of 27 (59.3%). All patients with a negative response to head-up tilt testing showed no significant EEG modificatio ns. In patients with vasodepressor syncope, a generalized high-amplitu de, 4- to 5-Hz (theta range) slowing of EEG activity appeared at the o nset of syncope, followed by an increase of brain-wave amplitude with the reduction of frequency at 1.5 to 3 Hz (delta range). The return to the supine position was associated with brain-wave amplitude reductio n and frequency increase to 4 to 5 Hz, followed by restoration of a no rmal EEG pattern and arousal (mean total duration of syncope, 23.2 sec onds.). In patients with cardioinhibitory syncope, a generalized high- amplitude EEG slowing in the theta range was noted at the onset of syn cope, followed by a brain-wave amplitude increase and slowing in the d elta range. A sudden reduction of brain-wave amplitude then ensued, le ading to the disappearance of electrocerebral activity (''flat'' EEG). The return to the supine position did not allow either the immediate resolution of EEG abnormalities or consciousness recovery, both of whi ch occurred after a further time interval (mean total duration of sync ope, 41.4 seconds.). Conclusions-EEG monitoring during head-up tilt te sting allowed recording and systematic description of electrocerebral abnormalities developing in the course of tilt-induced vasovagal synco pe.