Cerebrovascular autoregultion and neurcardiogenic syncope

pp 619-624

Abstract

Head upright tilt table testing is often used to support the diagnosis of vasovagally mediated syncope. Transcraneal Doppler sonography studies have shown a minor increase in cerebrovascular resistance in patients without syncope. To determine the effect of vasovagally mediated syncope on the cerebral circulation, transcraneal Doppler was used to assess cerebral blood flow velocity during head upright tilt in patients with unexplained syncope or presyncope. Thirty patients were evaluated with an upright tilt table test for 60 minutes in an attempt to reproduce symptoms. Transcraneal Doppler sonography was used to assess mean middle cerebral artery velocity, and pulsatilly index (PI = Vs-Vd/Vmean) before, during and after head upright tilt. Syncope occurred in six patients (20%). In tilt positive patients transcraneal Doppler showed a 59% mean decrease in mean velocity and a 355% mean increase in pulsatilly index (p < 0.001), concomitant with the development of hypotension and bradichardia. In all cases there was an initial mean decrease of 24% in pulsatilly index. This last response was also observed in another 10 patients without syncope during head upright tilt table testing. These findings reflect an arteriolar vasodilatation distal to the insonation point of the middle cerebral artery, suggesting a derangement of cerebral autoregulation. The remaining 14 patients had an 11% mean increase in pulsatilly index during head up tilt table testing. Heart rate and blood pressure increase, in all groups, except during syncope. In conclusion, the use of transcraneal Doppler to measure blood flow velocity of the middle cerebral artery, identified alterations of the cerebral circulation before syncope and increased tilt table testing sensitivity.