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İLGIN, N.,et al.: Brain Perfusion Assessed by 99mTc-ECD SPECT Imaging in Pediatric Patients with Neurally Mediated Reflex Syncope. Background:The involvement of cardiogenic and neurogenic mechanisms in neurally mediated reflex syncope is well documented. In our previous studies in patients with neurally mediated reflex syncope, we have found evidence for differential regulation of the noradrenergic receptors in tilt-positive and tilt-negative patients. The present work concentrates on the observations of differences in regional brain perfusion using brain SPECT via injecting the patient at the completion of the tilt test.Methods and Results:The following study was designed to assess the reduction and regional differences in cerebral blood flow by means of SPECT using technetium-99m labeled V-oxo-1,2-N1ethylenedylbisl-cysteine diethylester (ECD) in patients with an injection during tilt testing. Twenty patients with NMS were included in the study with a mean age of 12.2 years (age range; 8–16 years). HUT was positive in 10 patients and negative in 10 patients. When tilt (+) and tilt (−) were evaluated together, regional cortical/cerebellum ratios were ranging from 0.85 to 1.25 in different cortical areas with highest variability of perfusion index in left frontoparietal cortex. The lowest perfusion index values were observed in the left anterior frontal region followed by the left prefrontal-frontoparietal-anterior, parietal-orbito frontal, and anterior temporal regions where perfusion is predominantly supplied via the anterior and middle cerebral arteries, while these differences did not reach statistical significance in a single dominant region compared to the other regions examined using ANOVA (P>0.05) with this sample size.Decreases in[99mTc]ECD uptake were more widespread regionally on the left hemisphere than were decreases in right side of the brain. However when tilt– and tilt+ groups were compared, perfusion was significantly lower in the right periinsular posterior parietal and temporal regions (P<0.05) in tilt+ group.Conclusion:These tilt induced regional differences in brain perfusion suggest the distinct roles of middle cerebral artery dominant territory-related vasodepressor compensation mechanisms in neurally mediated reflex syncope phenomena where cerebral lateralization of cardiac control and insular ischemia may play an important role.(PACE 2005; 28:534–539) [ABSTRACT FROM AUTHOR]