Abstract

BACKGROUND: Physiological changes in the QT interval caused by sleep areimportant in the evaluation of the normal QT interval. Traditionally, Bazett's formula is used for correctingthe QT interval for heart rate in childhood. We set out to establish the QT-RR relationship in infantsduring sleep and concurrently test the performance of four QT correction formulae to determine theircomparability and clinical utility. MATERIAL/METHODS: 130 healthy term born infants undergoing routine8-hour polysomnography were enrolled. Continuous EKG limb lead II recording, saturation monitoring, andelectroencephalography were conducted. QT intervals and heart rate were measured manually digitally on-screenat hourly intervals. The QT-RR relationship was plotted and QTc calculated using the Bazett, Hodges,Fridericia and Framingham formulae. QTc values for each formula were plotted against age and RR interval.Analysis of variance and regression analysis were used to compare the four formulae and the QT-RR relationship.RESULTS: Mean age was 17.7 weeks (range 4-72) and mean weight 6.3 kg (range 2.68-12.7). The QT-RR relationshipduring sleep is curvilinear and appears to be slightly shifted. With increasing heart rate and youngerage the Bazett and Hodges formulae overcorrect the QTc whereas the Fridericia and Framingham formulaeundercorrect. The Hodges formula correlated best with the RR interval. CONCLUSIONS: These formulae arestrongly dependent on heart rate. In the setting of a borderline QTc Bazett prolongation, Hodges formulamay be a useful adjunct. Normal infants may have a slightly longer QTc Bazett during sleep.

Keywords: Algorithms, Analysis of Variance, Arrhythmia, Body Weight, Child, Preschool, Comparative Study, Electrocardiography, Heart Rate, Reference Values, Regression Analysis, Sleep Disorders, Time Factors