Objective To explore the cause of secondary QT interval shortening. Method The data of a child with vasovagal syncope and cardiac depression in whom shortened QT interval was induced in head-up tilt test (HUTT) was analyzed retrospectively, and the related literatures were reviewed. Result A 12-year-old boy visited for fainting when brushing his teeth in the morning. ECG showed sinus bradycardia, heart rate at 55 times /min and normal QT and QTc interval. Dynamic electrocardiogram showed sinus rhythm, mean heart rate at 70 times/min, atrial anterior contraction 3 times, normal mean QT and mean QTc. UCG showed approximately normal heart structure and the left ventricular systolic function. There was no abnormality in EEG and cranial CT. His fasting blood glucose was 5.2 mmol/L. The basal tilt test was positive with vasovagal syncope and cardiac depression. During the tilt table test, Holter monitoring showed that sinus arrest occurred in the child when upright tilt for16 min, and then fainted. Time of sinus arrest was 2.9 s and 11.4 s, respectively, and artificial chest compressions were performed. The QT interval was shortened (QT=330 ms), and so was QTc interval (QTc=320 ms). The ratio of QT/QTp was 78% (the lower limit of normal QT interval was 88% of QTp) before sinus arrest occurred. Conclusion Increased vagal tone may induce QT interval shortening.%目的 探讨继发性QT间期缩短的原因.方法 回顾分析1例血管迷走性晕厥心脏抑制型患儿在直立倾斜试验中诱发QT间期缩短,同时复习相关文献.结果 患儿,男,12岁,晨起刷牙时晕厥1次就诊.心电图示窦性心动过缓,心率55次/min,QT及QTc间期正常.动态心电图示窦性心律,平均心率70次/min,房性期前收缩3次,QT及QTc均值正常.彩色超声心动图示心脏内结构大致正常,左心室收缩功能正常.脑电图无异常.头颅CT无异常.空腹血糖5.2 mmol/L.基础直立倾斜试验为阳性,血管迷走性晕厥-心脏抑制型.直立倾斜试验过程中,动态心电图同步监测显示,患儿在直立倾斜16 min时出现窦性停搏,随即晕厥,窦性停搏分别为2.9 s和11.4 s,并行人工胸外按压.在出现窦性停搏之前可见QT间期缩短(QT=330 ms),QTc间期(按心率校正的QT间期=QT/RR)缩短(QTc=320 ms),QT/QTp=78%[QTp:QT间期预测值=656/(1+心率/100),正常QT间期的下限为QTp的88%].结论 迷走神经张力增高可诱发QT间期缩短.
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