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

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.