[Cerebral blood flow during neurocardiogenic syncopes in children]

Neurocardiogenic syncope, the most common episodic event in children results from global cerebral hypoperfusion. Monitoring of the blood flow during head-up tilt-induced syncope resulted in registration of preferential reduction of end-diastolic velocities in middle cerebral arteries (MCA). The significance of those changes was however not explained. The aim of this retrospective research was to establish the significance of visual inspection of spectra changes of cerebral blood flow in MCA during presyncope and syncope in children.

The diagnostic head-up tilt test (TT) was conducted in 276 children with neurocardiogenic syncopes. The group consisted of 211 girls and 65 boys aged 8 to 18 years (mean age 14 years). 30 healthy volunteers were enrolled as a control group. During rest in supine position and during tilting upright to 70 degree at the tilt table, the blood flow was monitored in MCA using Nicolet Companion III in order to perform transcranial Doppler ultrasonography.

During passive TT symptoms of syncope were observed in 31 girls and 10 boys after 3 to 30 min (mean 13.7 min) of tilting, and mild presyncopal signs in other 9 children. The most typical change of the blood flow in MCA registered during vasovagal syncope was a preferential decrease of end-diastolic velocities. In one patient two TT were performed, both examinations were positive, however during the second TT wave reflection during early diastole in MCA was registered. In one child from the control group result of TT was false positive, with the same pattern of blood flow spectra, as in children from the syncope group. During hyperventilation the reduction of velocities of the blood flow in MCA was detected, mainly diastolic.

The registration of reduced velocities of the blood flow in middle cerebral arteries during diastole may allow to earlier termination of tilting in order to prevent a loss of consciousness. One of important prophylactic actions related to syncope is to counteract hyperventilation. The pattern of high resistance spectrum of blood flow in MCA, with a backward direction of early diastolic flow during syncope may suggest that wave reflection may play a significant role.