Background
A chronic imbalance of the autonomic nervous system(ANS) may contribute to long term complications in different congenital heart diseases. The purpose of this study was to determine whether the ANS plays a role in the long-term outcome of patients with Transposition of great arteries(TGA) after arterial switch operation(ASO) as its contribution is as yet not clear.
Methods
The ANS activity was evaluated non-invasively in 26 TGA patients and 52 age-appropriate healthy subjects combining impedance cardiography and electrocardiography. Heart rate, pre-ejection period(sympathetic activity parameter) and respiratory sinus arrhythmia and the root of the mean square of successive normal-to-normal interval differences(parasympathetic activity parameter) were measured during 5 different daily activities(sleep, sitting, active sitting, light and moderate/vigorous physical activity). Whether the ANS activity was related to ventricular function, exercise test performance or clinical outcome in the patient group was also analyzed.
Results
Compared to healthy subjects: heart rate was significantly lower in TGA patients at rest and during quiet and active sitting; sympathetic activity was significantly reduced in patients during physical activity; and the parasympathetic activity was higher in TGA patients while quiet and active sitting. In the patient group a significant positive correlation between 4-chamber longitudinal strain and parasympathetic activity during 3 different daily activities was found.
Conclusions
The sympathetic nervous system response to physical activity is reduced in TGA patients after ASO. Additionally, we observed a positive correlation between better left ventricular function and higher parasympathetic activity that could be in line with the known protective effect of a higher vagal activity.

Large individual differences exist in aerobic fitness in childhood and adolescence, but the relative contribution of genetic factors to this variation remains to be established. In a sample of adolescent twins and siblings (n = 479), heart rate (HR) and maximal oxygen uptake (V̇o2max) were recorded during the climax of a graded maximal exercise test. In addition, V̇o2max was predicted in two graded submaximal exercise tests on the cycle ergometer and the treadmill, using extrapolation of the HR/V̇o2 curve to the predicted HRmax. Heritability estimates for measured V̇o2max were 60% in ml/min and 55% for V̇o2max in ml·min−1·kg−1. Phenotypic correlations between measured V̇o2max and predicted V̇o2max from either submaximal treadmill or cycle ergometer tests were modest (0.57 < r < 0.70), in part because of the poor agreement between predicted and actual HRmax. The majority of this correlation was explained by genetic factors; therefore, the submaximal exercise tests still led to very comparable estimates of heritability of V̇o2max. To arrive at a robust estimate for the heritability of V̇o2max in children to young adults, a sample size weighted meta-analysis was performed on all extant twin and sibling studies in this age range. Eight studies, including the current study, were meta-analyzed and resulted in a weighted heritability estimate of 59% (ml/min) and 72% (ml·min−1·kg−1) for V̇o2max. Taken together, the twin-sibling study and meta-analyses showed that from childhood to early adulthood genetic factors determine more than half of the individual differences in V̇o2max.

The prognostic power of heart rate recovery (HRR) after exercise has been well established but the exact origin of individual differences in HRR remains unclear. This study aims to estimate the heritability of HRR and vagal rebound after maximal exercise in adolescents. Furthermore, the role of voluntary regular exercise behavior (EB) in HRR and vagal rebound is tested.

Background
Coarctation of the aorta (CoA) is one of the most common congenital heart defects. Most patients live into adulthood as a result of improved surgical techniques; however, late complications, including hypertension, recoarctation, and arrhythmias, are common. The autonomic nervous system (ANS) might play a role in the pathology. This study evaluated cardiac ANS activity and cardiac function in children after CoA repair and investigated the relationship between the two.
Methods
The study participants were 31 children after CoA repair and 62 healthy controls aged between 8 and 18 years. Ambulatory impedance cardiography was used to measure cardiac ANS activity and cardiac output for 24 hours. Transthoracic echocardiography and cardiac magnetic resonance imaging were used to measure cardiac function.
Results
No group differences were found in ambulatory cardiac ANS activity. However, ambulatory cardiac output and left ventricular function were significantly decreased in patients compared with controls.
Conclusions
Left ventricular function and ambulatory cardiac output are impaired in patients after CoA repair, despite unchanged cardiac ANS activity in this group. These results underscore the importance of clinical follow-up, even in patients without residual stenosis.

Introduction
Stroke volume (SV) and cardiac output are important measures in the clinical evaluation of cardiac patients and are also frequently used in research applications. This study was aimed to improve SV scoring derived from spot-electrode based impedance cardiography (ICG) in a pediatric population of healthy volunteers and patients with a corrected congenital heart defect.
Methods
128 healthy volunteers and 66 patients participated. First, scoring methods for ambiguous ICG signals were optimized to improve agreement of B- and X-points with aortic valve opening/closure in simultaneously recorded transthoracic echocardiography (TTE). Building on the improved scoring of B- and X-points, the Kubicek equation for SV estimation was optimized by testing the agreement with the simultaneously recorded SV by TTE. Both steps were initially done in a subset of the sample of healthy children and then validated in the remaining subset of healthy children and in a sample of patients.
Results
SV assessment by ICG in healthy children strongly improved (intra class correlation increased from 0.26 to 0.72) after replacing baseline thorax impedance (Z0) in the Kubicek equation by an equation (7.337–6.208∗dZ/dtmax), where dZ/dtmax is the amplitude of the ICG signal at the C-point. Reliable SV assessment remained more difficult in patients compared to healthy controls.
Conclusions
After proper adjustment of the Kubicek equation, SV assessed by the use of spot-electrode based ICG is comparable to that obtained from TTE. This approach is highly feasible in a pediatric population and can be used in an ambulatory setting.

Background

Despite the increasing interest in cardiac autonomic nervous activity, the normal development is not fully understood. The main aim was to determine the maturation of different cardiac sympathetic‐(SNS) and parasympathetic nervous system (PNS) activity parameters in healthy patients aged 0.5 to 20 years. A second aim was to determine potential sex differences.

Methods and Results

Five studies covering the 0.5‐ to 20‐year age range provided impedance‐ and electrocardiography recordings from which heart rate, different PNS‐parameters (eg, respiratory sinus arrhythmia) and an SNS‐parameter (pre‐ejection period) were collected. Age trends were computed in the mean values across 12 age‐bins and in the age‐specific variances. Age was associated with changes in mean and variance of all parameters. PNS‐activity followed a cubic trend, with an exponential increase from infancy, a plateau phase during middle childhood, followed by a decrease to adolescence. SNS‐activity showed a more linear trend, with a gradual decrease from infancy to adolescence. Boys had higher SNS‐activity at ages 11 to 15 years, while PNS‐activity was higher at 5 and 11 to 12 years with the plateau level reached earlier in girls. Interindividual variation was high at all ages. Variance was reasonably stable for SNS‐ and the log‐transformed PNS‐parameters.

Conclusions

Cardiac PNS‐ and SNS‐activity in childhood follows different maturational trajectories. Whereas PNS‐activity shows a cubic trend with a plateau phase during middle childhood, SNS‐activity shows a linear decrease from 0.5 to 20 years. Despite the large samples used, clinical use of the sex‐specific centile and percentile normative values is modest in view of the large individual differences, even within narrow age bands.