Physiological QT Interval Changes in Early Infancy Using Post-Menstrual and Post-Natal Age Calculation for Electrocardiogram Long QT Interval Screening in Taiwan.

Background: Prolongation of the QT interval is associated with the risk of sudden infant death syndrome. QT interval differs depending on age at the time of screening. Screening protocols have yet to be established for Taiwanese patients.

Objectives: To construct QT interval reference values during early infancy, to investigate whether QT interval change differs according to age calculation methods, and to identify an optimal QT correction method and associated infant factors.

Methods: Electrocardiographic readings and QT intervals were recorded cross-sectionally in 595 healthy infants and screened prospectively for long QT interval. Corrected QT intervals with Bazett's (QTc-B) and Fridericia's (QTc-F) formulas were compared by post-natal and post-menstrual screening age, sex, body mass index (BMI), heart rate (HR), birth and family history.

Results: QTc-B and QTc-F decreased in the second month (31-60 days), and peaked in the third month (61-90 days). QT interval length was similar between post-menstrual and post-natal ages for QTc-B. Simple linear regression showed that post-menstrual age, post-natal age, HR and BMI were associated with QTc-F, while only sex and HR were associated with QTc-B. Although both QTc-B and QTc-F were significantly associated with HR, QTc-B was less affected by HR than QTc-F (β = -0.1, p < 0.05 for QTc-B vs. β = -0.3, p < 0.001 for QTc-F). Female infants tended to have slightly longer QTc intervals.

Conclusions: QT interval in early infancy changed physiologically, peaking in the third month. The rate of QT change was not affected by different age correction methods. QTc-B was less affected by age, BMI and HR, although differences in sex should be noted.