Screening of 1-Month-Old Infants With Prolonged QT Interval and Its Cutoff Value

Abstract

Background: The prevalence of congenital long QT syndrome (LQTS) (1 : 2,000) is based on genetic testing and ECG data, but the prevalence of electrocardiographically determined prolonged corrected QT interval (pQTc) in infants is unclear.

Methods and Results: Subjects were 10,282 1-month-old infants who participated in 2 prospective ECG screening studies performed in 2010–2011 and 2014–2016. Infants with a QTc ≥0.45 using Bazett’s formula [QTc(B)] at 1-month medical checks were re-examined. pQTc was defined as QTc ≥0.46 on 2 different ECGs in early infancy. Infants with QTc ≥0.50 or progressive prolongation of QTc to 0.50 were defined as at high risk. The prevalence of infants with a pQTc was 11/10,282 (1 : 935; 95% confidence interval, 1 : 588–1 : 2,283). Five infants were diagnosed as at high risk, and all infants had an abrupt increase in QTc(B) values in early infancy, mostly at 6–11 weeks after birth and when medication was started. No infants with a pQTc experienced LQTS-related symptoms. Statistical analysis showed that a cutoff QTc(B) ≥0.45 was optimal for screening infants with a pQTc.

Conclusions: The prevalence of ECG-determined pQTc is approximately 1 : 1,000. An abrupt increase in QTc(B) values occurs in infants at high risk, mostly at 6–11 weeks after birth. A cutoff QTc(B) value ≥0.45 may be appropriate for 1-month-old screening in this population.