Electrocardiographic Screening of One-Month-Old Infants for Long QT Syndrome in Japan

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Introduction: Electrocardiographic and molecular studies have clarified an association between sudden infant death syndrome and long QT syndrome (LQTS). A prospective study to screen infants with LQTS was performed at one month medical check. Methods: Resting ECGs were recorded and the QT intervals of three consecutive beats were measured. A formula to minimize the effect of heart rate for infants was used: QTc=QT/RR0.43. A provisional criterion of a QTc => 0.440.43 was used. To assess the validity of the criterion, all infants with a QTc => 0.43 were followed. Results: Of 4,319 infants who participated, six infants had a QTc value of => 0.440.43. From the follow-up ECGs, four infants were diagnosed as LQTS clinically. Two infants showed progress prolongation of the QT intervals; propranolol and mexiletine were administered when their QTc values exceeded => 0.500.43. Genetic testing revealed a KCNH2 mutation (3065 delT, L1021fs+34X) in one of these two infants. Ten infants with the QTc values between 0.43 and 0.44 showed decline in their QTc values during follow-up. The study screened another infant with left ventricular non-compaction with decreased ejection fraction. Conclusion: The incidence of LQTS infants who are clinically diagnosed may be close to 1:1,000. Electrocardiographic screening for infants will be successful to prevent deterioration of infants with risk.