The Study Of QT Interval Dispersion (QTd) And Heart Rate Variability (HRV) In Children With Vasovagal Syncope (VVS)

Objective To explore the changes of QT interval dispersion (QTd) and hart rate variability (HRV) in children with vasovagal syncope (VVS) .Methods Children was collected from pediatrics of emergency, out-patient and ward department of 1st affiliated hospital of Dalian Medical University,including 49 cases with VVS as case group aged from 7 to 14 years old (mean age is 10.38±2.23 years) and 28 healthy children as control group aged from 6 to 14 years old (mean age is 10.56±2.11 years). 12 - lead simultaneous body surface electrocardiogram (12ECG) were taken for two groups.19 children in case group did head-up tilt test(HUTT) (including basic tilt test and drug provocation test) . Basic tilt test required patients prostration for 20-45min before test,fast at least for 3hours,stop taking vasoactive agents for at least 5 half lives.The children were requested to stand at a 60°tilt board and observed whether the positive reactions appeared within 45min. Drug provocation test was done with HUTT provocated by taking nitroglycerol.The method was as follows:The patient taking nitroglycerol when the basic tilt test was negative.Maintain orthostatic body position for 20min or the children appeared syncope or threatened syncope. The HR ,QT were tested by hand during three clear cardiac cycles in 12ECG. QTd was calculated.There QT internals were measured in each lead,at least 9 leads totally.Mean value was calculated. QTcd was gained according to Bazell formula.All children experienced 24 hour dynamic electrocardiogram (Holter) and Holter recordings were analyzed in the computer. Holter recordings were used to analyze time domain and frequency domain indexes such as SDNN,SADNN,RMDNN. SPSS 11.0 software was used for the statistical analysis of these datas. Results (1)HUTT was positive in 10 children from 19 children from syncope group,the positive rate is 52.63%.(2)there were no differences in HR,QTmin ( P > 0.05) between syncope group and control group.But there were significant differences in QTmax,QTcd and QTd ( P < 0.05 or P < 0.01) between two groups,there were no differences in QTd between HUTT positive group and HUTT negative groups.(3) SDNN and RMDNN were significant lower in syncope group( P < 0.05). Compared with the control group,there were no differences in HRV between HUTT positive group and HUTT negative group.Conclusions (1) The change of HUTT,QTd,HRV signified that the occurrence mechanism of VVS was related to regulatory dysfunction of of sympathetic nerve and parasympathetic nerve Compared with the control The occurrence mechanism of VVS was related to regulatory dysfunction of of sympathetic nerve and parasympathetic nerve.(2)The positive rate of HUTT was 52.63%. HUTT was the gold standard for VVS diagnosis,but the negative of HUTT couldn't refuse VVS. There were no differences in QTd and HRV between HUTT positive group and HUTT negative groups.(3) QTmax,QTcd and QTd were significant longer and SDNN and RMDNN were significant lower in syncope group.With the lengthen of QTc,the incidence rate of myocardial ischemia and cardiac arrhythmia increased. QTd may be helpful to predict the occurrence of sever cardiovascular ,but the value of it only can be certifid by followed study.