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.

Objective:To assess the efficacy and the safety of the radiofrequency catheter ablation (RFCA) for the septal accessory pathway (AP) in children.Methods:From September 2013 to March 2019, 626 patients plan to underwent RFCA for paroxysmal supraventricular tachycardia (PSVT) in Shanghai Children′s Medical Center Affiliated to Shanghai Jiaotong University School of Medicine.Among them, 74 consecutive patients with right or left septal APs were included in the study and their clinical and RFCA data were analyzed.Results:The age of these 74 children (45 males, 29 female) was (7.8±3.5) years, ranging from 10 months to 13 years.The body weight (BW) was (27.7±14.4) kg, with 3 patients BW<15 kg.A discordant ventricular wall motion (DVWM) was found in 5 patients, and the combined congenital heart diseases were discovered in 2 patients.A three dimensional mapping system was applied in 69 ablations, and 3 ablations were performed only with the fluoroscopy monitor of 5 cases.According to the AP location, the number of cases located in the anteroseptal, the midseptal, the mouth of coronary sinus, the left posteroseptal and the right posteroseptal, were 28, 18, 10, 10 and 8, respectively.The ablation operations were applied in 72 patients.The initial acute success reached in 67 (93.1%) patients.The ablation energy was (18.0±1.8) W, the fluoroscopy time during the ablations was (4.7±2.7) minutes, and the procedure duration was (151.5±58.6) minutes.One inadvertent complete atrioventricular block (AVB) was noted as the ablation-related complication.All 5 children with the pre-DVWM were recovered after ablations.During a follow-up of (23.8±10.8) months, 4 patients experienced the recurrence of preexcitation syndrome atrioventricular reentrant tachycardia.Conclusions:With the 3D-mapping system, the RFCA of septal APs can be performed safely and effectively in pediatric patients of paroxysmal supraventri-cular tachycardia.However, as the ablation-related complication, AVB should not be ignored.