DISPERSION OF QT AND QTC INTERVAL IN HEALTHY-CHILDREN, AND EFFECTS OFSINUS ARRHYTHMIA ON QT DISPERSION

Objective-To determine the normal values of QT and QTc dispersion and the effects of sinus arrhythmia on QT dispersion in healthy children. Patients and setting-The study was carried out in a university hospita l on 372 local schoolchildren (200 male, 172 female), aged seven to 18 years. Methods-The QT and preceding RR intervals of at least one sinu s beat were measured manually in a range of nine to 12 leads on standa rd 12 lead surface ECGs. The corrected QT interval was computed by the method of Bazett. Dispersion of QT and QTc were defined as (1) the di fference between the maximum and minimum QT and QTc intervals occurrin g in any of the 12 leads (QTD and QTcD), (2) the standard deviation of the QT and QTc interval in the measurable leads (QT-SD and QTc-SD). R esults-There was no significant difference in QT, QTc, and RR dispersi on between girls and boys. Overall 53% of children had sinus arrhythmi a. Although QTD and QT-SD were not affected by sinus arrhythmia, both QTcD and QTc-SD were significantly greater in children with sinus arrh ythmia than in those without (QTcD: 52.9 (17.4) v 40.9 (13.1); QTc-SD: 17.5 (5.9)v 13,2 (4.0); p < 0.001). Conclusions-As calculation of QTc dispersion is affected by sinus arrhythmia, which is common in childh ood, we suggest that QT dispersion should not be corrected for heart r ate in children.