Abstract
Reduced heart rate (HR) variability in preterm infants compared with full-term infants suggests that autonomic cardiac control is developmentally delayed. However, the association between developmental changes in myocardial repolarization and gestational age remains unknown. This study investigated the association between the myocardial repolarization lability index, namely the QT variability index (QTVI) = log10 [(QTv/QTm2)/(HRv/HRm2)], and the perinatal profile of healthy 1-month-old infants. We included 209 infants (143 boys and 87 girls; mean gestational weeks at birth, 38.6 ± 1.7) who were born in university hospitals between 2014 and 2015 without apparent cardiac disease. We compared the ECG variability indices in 28 infants born before 37 gestational weeks (mean gestational weeks at birth, 35.6 ± 1.1 as preterm) and 181 infants born at the average number of gestational weeks (mean gestational weeks at birth, 38.8 ± 1.1 as controls). There was a negative correlation between the QTVI and gestational weeks (r = − 0.460, p = 0.035). QTVI values in preterm infants were larger than those in the controls (0.01 ± 0.50 vs. −0.26 ± 0.48, p = 0.023). In conclusion, the QTVI is negatively correlated with gestational age. The QTVI can serve as an index of the maturity of the cardiac autonomic nervous system and myocardial depolarization.
Highlights
Japan is currently the country with the lowest neonatal mortality rate in the world [1, 2]
The QT variability index (QTVI), which is used as an index of the variable ratio of the RR and QT intervals, is calculated from a single lead using a well-defined algorithm
We found that the QTVI was impaired in preterm infants and it was inversely related to gestational age (GA)
Summary
Japan is currently the country with the lowest neonatal mortality rate in the world [1, 2]. In the fiscal year of 2015, 96 infants in Japan died because of sudden infant death syndrome (SIDS), for which there were no warning signs or past history. The pathophysiology of SIDS is still under investigation, dysfunction of the autonomic nervous system, including the respiratory and cardiovascular systems, may be involved [4, 5]. The QT variability index (QTVI), which is used as an index of the variable ratio of the RR and QT intervals, is calculated from a single lead using a well-defined algorithm. The QTVI is practically applicable if the ECG record has a stable baseline [13]
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