Maturation of the QT Variability Index is Impaired in Preterm Infants.

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.

Relationship between QT and JT peak interval variability in prepubertal children.

BACKGROUND: The QT variability index (QTVI) is a noninvasive index of repolarization lability that has been applied to subjects with cardiovascular disease. QTVI provides a ratio of normalized QT variability to normalized heart rate variability, and therefore includes an assessment of autonomic nervous activity. However, measurement of QT time is particularly difficult in children, who exhibit physiologically high heart rates compared with adults. In this study, we developed a set of standard values of J-point to Tpeak interval (JTp) for infants by age, and assessed the correlation of QTVI with the JTp variability index (JTpVI). METHODS: Subjects included 623 infants and children (0-7 years of age) without heart disease and 57 healthy university students. All subjects were divided into three groups by age. QTVI and JTpVI were calculated based on an electrocardiogram, and age-specific standard values, a gender-specific classification, and a standard growth curve were constructed. RESULTS: JTpVI markedly decreased in infancy and slowly decreased thereafter, reaching adult values by school age. There was also a strong correlation of JTpVI with QTVI (r = .856). CONCLUSIONS: JTp can be used to evaluate the variability of the repolarization time in healthy infants, and may be useful for detection of early repolarization abnormalities.

Electrocardiographic RR and QT Interval Variability in Patients with Atrial Septal Defect and Healthy Children.

Atrial septal defect is a common congenital heart disease. In patients with atrial septal defect, left-to-right shunting increases the right atrial and right ventricular preload. This pathological change affects sinus node automaticity and myocardial depolarization and repolarization, and has the potential to evoke arrhythmogenic substrates. We examined the effect of atrial septal defect on sinus node automaticity and myocardial repolarization by investigating the variability in the repolarization interval, namely the QT variability index (QTVI) and variability ratio (VR). This retrospective study included 38 patients (mean age, 2.2 ± 1.9 years; mean left-to-right shunt ratio, 2.1 ± 0.70) and 40 age-matched healthy control subjects evaluated from 2008 to 2015. QTVI was calculated using the ratio of the repolarization parameter variance to heart rate variance, and VR was calculated as the ratio of the standard deviation (SD) of QT intervals to the SD of RR intervals on electrocardiography. There was a significant difference in the SD of all normal RR intervals, heart rate variance, VR, and QTVI of control subjects or patients with low shunt ratio compared with patients with high shunt ratio (all P < 0.05). Linear regression analysis revealed strong positive correlations between the left-to-right shunt ratio and VR (r = 0.662, P < 0.0001) or QTVI (r = 0.808, P < 0.0001). These repolarization indices provide information on alteration of sinus node autonomic control and the pathophysiology of myocardial repolarization, and could be used as a noninvasive indicator of the shunt ratio in children with atrial septal defect.

Variability of Myocardial Repolarization in Pediatric Patients with a Ventricular Septal Defect.

In patients with a ventricular septal defect, left-to-right shunting increases the left ventricular preload. This pathological change affects myocardial depolarization and repolarization and has the potential to evoke arrhythmogenic substrates. We examined the effect of ventricular septal defects on myocardial repolarization by investigating the variability in the repolarization interval. This retrospective study included 19 patients (mean age, 1.8 ± 2.1 years) who underwent surgical closure (mean left-to-right shunt ratio, 2.60 ± 0.55) and 26 age-matched healthy controls from 2008 to 2015. Using preoperative electrocardiograms, we studied two electrocardiographic parameters (heart rate-corrected repolarization and variability of repolarization) and four repolarization intervals (QT, JT, J point to T peak [JTp], and T peak to T end [Tp-e] intervals). The variability index (VI) was calculated from the logarithm of the ratio of the repolarization parameter variance to heart rate variance. The various measures were compared between the patients and controls, and significant differences were found in the corrected QT, JTp, and Tp-e intervals (p < 0.05). The VI of the four intervals also showed significant differences (patients vs. CONTROLS: QTVI, -0.55 ± 0.61 vs. -1.10 ± 0.53; JTVI, -0.33 ± 0.60 vs. -0.86 ± 0.57; JTpVI, -0.15 ± 0.78 vs. -0.73 ± 0.56; Tp-eVI, 0.75 ± 0.70 vs. 0.11 ± 0.73, respectively; p < 0.05). No correlation was found between the QTVI and corrected QT interval using linear regression analysis. These repolarization characteristics provide not only electrophysiological indices but also a new index with which to assess the pathophysiology of congenital heart disease.

Inflammation aggravates heterogeneity of ventricular repolarization in children with Kawasaki disease.

Kawasaki disease complicates with myocarditis and vasculitis. Even if myocarditis is asymptomatic, heterogeneity of ventricular repolarization may be increased in the acute phase. We evaluated whether the change in repolarization characteristics can be used as a predictor for myocarditis and coronary lesions. Enrolled 34 children who were treated with intravenous immunoglobulin therapy. There were no sequelae in the recovery phase in any subjects, including those who had transient coronary artery lesion. QT and the interval from the Tpeak to Tend (Tp-e) were determined. The Tp-e/QT ratios were compared between the acute and recovery phases and correlations with CRP level and body temperature were evaluated. A retrospective evaluation of Tp-e/QT as predictors of coronary dilation was also performed. Tp-e/QT in the acute phase correlated positively with body temperature and CRP level. In a comparison of patients with and without transient coronary artery lesion, Tp-e/QT was significantly higher in those with dilation. In conclusion, Tp-e/QT was strongly related to transient coronary dilation, in comparison with inflammatory indicators including fever and CRP level.

Isoproterenol stress test during catheterization of patients with coarctation of the aorta.

BACKGROUND: The exercise test is considered useful in selecting high-risk patients with repaired coarctation of the aorta (CoA), but it is difficult to obtain the cooperation of pediatric patients. The present study determines the feasibility of the isoproterenol stress test (IST) among pediatric patients with CoA. METHODS: Thirteen patients with repaired or mild preoperative CoA aged 1-207 (median 13) months underwent 16 IST during cardiac catheterization. Peak-to-peak pressure gradients (PG) over the coarctation site were measured at baseline and at IST. Balloon angioplasty (BAP) was applied to patients with significant stenosis on angiography. RESULTS: The PG between the ascending and the descending aorta was significantly higher at IST than at baseline (20.5 ± 11.5 vs 5.6 ± 3.9 mmHg, P < 0.0001). Heart rate, the systolic blood pressure measured at the ascending aorta, and pulse pressure were all significantly higher at IST than at baseline. The PG at IST decreased >10 mmHg in three of six patients after BAP. CONCLUSIONS: Significant pressure gradients over the coarctation site develop at IST in pediatric patients with repaired CoA or in preoperative patients with mild coarctation.

Beat-to-beat QT interval variability in children: normal and physiologic data.

BACKGROUND: QT interval variability provides information on ventricular vulnerability. However, QT interval variability in children has not been adequately evaluated. METHODS: One hundred seventy-three consecutive nursing infants and children (male-female, 106:67) up to school age with no intrinsic cardiac disease were included in this study, and they were categorized into 6 age-related groups. The QT variability index (QTVI) was calculated based on an electrocardiogram; and age-specific standard values, sex-specific classification, and a standard growth curve covering 0 to 7 years were constructed. RESULTS: The QTVI decreased in an age-dependent manner, reached constant values after school age, and exhibited no sex-specific differences in 6 age-related groups. CONCLUSIONS: Based on the age-dependent standardized QTVI values, it is possible to estimate the instability of ventricular repolarization in pediatric patients with better accuracy.

Ventricular repolarization lability in children with Kawasaki disease.

Kawasaki disease (KD) is an acute febrile disease of unknown etiology that develops in children and is sometimes accompanied by myocardial dysfunction and systemic vasculitis. However, myocardial repolarization lability has not yet been fully investigated. Thus, the objective of this study was to evaluate myocardial repolarization lability (QT variability index-QTVI) based on the body surface electrocardiograms in the acute and recovery phases. The subjects were 25 children with acute KD who were hospitalized for treatment. An equal number of age-matched healthy children were selected as controls. The RR-intervals and QT-intervals were measured based on a body surface electrocardiogram of 120 consecutive heartbeats to calculate the QTVI. The QTVI values were then compared with the acute and recovery phases. The relationships between blood biochemistry data and QTVI values were also examined. QTVI was significantly decreased from the acute phase to the recovery phase (P < 0.05) and then recovered to the same level as that of the control. QTVI in the acute phase showed a significant positive relationship with body temperature and C-reactive protein (P <0.05). QTVI was high in the acute phase and was correlated with an inflammatory reaction and became normalized during the recovery phase.

Outcome of prenatally diagnosed isolated congenital complete atrioventricular block treated with transplacental betamethasone or ritodrine therapy.

The effectiveness of transplacental drug therapy for prenatally diagnosed isolated congenital complete atrioventricular block (CCAVB) is controversial. Nine cases of prenatal isolated CCAVB were treated from 2002 to 2007. Ritodrine was administered transplacentally to all fetuses and betamethasone to those whose mothers tested positive for maternal anti-SSA/Ro antibodies. Six of the nine patients had an anti-SSA/Ro-positive mother and received transplacental betamethasone 4 mg/day at a median gestational age of 28 weeks (range, 24-31 weeks). No patients exhibited an improvement in the degrees of complete heart block, and one patient died in utero. No serious adverse events occurred. After the mean follow-up period of 1.7 +/- 1.3 years, all five patients treated with transplacental betamethasone experienced a good cardiac function, whereas one of the three patients not treated with transplacental betamethasone experienced cardiomyopathy and died at the age of 4 months. Pacemaker implantation was required for seven of the eight live-born infants. Transplacental betamethasone therapy for the patients with isolated CCAVB neither improved the degree of atrioventricular block nor decreased the rate of patients requiring pacemaker implantation, but it probably reduced the risk for the development of myocardial disease.