摘要Background Syncope is common in children and adolescents, with 15% estimated to have had at least one syncopal episode by age 18. In recent years, an increasing number of children, especially girls at their school age,have developed unexplained syncope. The mechanism of an unexplained syncope exhibited by children is incompletely studied; the association between different hemodynamic patterns and clinical features is also not clear. The aim of the study was to investigate the hemodynamic patterns of children with unexplained syncope and to examine the clinical relevance.Methods Two hundred and eight children [87 boys, 121 girls, aged 3-19 years, mean (11.66±2.72) years]were selectively recruited from May 2000 to April 2006 when they presented syncope as their main complaint at the Multi-center Network for Childhood Syncope in Beijing, Hunan Province, Hubei Province, and Shanghai of China. All of the patients underwent head-up tilt tests; data were analyzed using SPSS version 10.0 for Windows.Continuous variables were expressed as the mean±standard deviation. Dichotomous variables were compared through a χ2 test. A value of P＜0.05 (two sided) was regarded as statistically significant.Results The age distribution of children with syncope was approximately normal. Head-up tilt tests was positive in 155 children, and the incidence of positive response of the baseline head-up tilt test for diagnosing unexplained syncope was 50.48%. The sensitivity value and diagnostic value of sublingual nitroglycerin head-up tilt test were both 74.52%. The hemodynamic pattern was normal in 53 children. The 155 children, who were positive in head-up tilt tests, showed signs of postural orthostatic tachycardia syndrome (60, 28.8%), the vasoinhibitory pattern (72, 34.6%), the cardioinhibitory pattern (5, 2.4%), and the mixed pattern (18, 8.7%). The gender distribution between the two age groups (age ＜ 12 years vs age ≥ 12 years) was not different (P＞0.05).The distribution of hemodynamic patterns between the children of the two age groups (age ＜ 12 years vs age ≥12 years), and the children with different complaints (dizziness vs syncope) was significantly different (P＜0.05),while the distribution between the children of different sexes and different lasting time of syncope (≤ 5 minutes vs ＞ 5 minutes) was not significantly different (P＞0.05). Different hemodynamic patterns were differentiated by differing syncope inducements,presymptoms, and complicated symptoms during and after syncope.Conclusion The tested girls were more prone when compared with the boys to have unexplained syncope, and the peak age was around twelve years old. The incidence of positive response of head-up tilt tests was also relatively higher for the girls. The distribution of hemodynamic patterns for different ages was different. For children with unexplained syncope,we should use head-up tilttests to distinguish the hemodynamic patterns in order to adopt rational therapeutic measures.