Cardiopulmonary Exercise Testing in Children and Adolescents With Dystrophinopathies: A Pilot Study.

PURPOSE: To determine exercise response during cardiopulmonary exercise testing in children and adolescents with dystrophinopathies. METHODS: Exercise response on the cardiopulmonary exercise test (CPET) was compared with a standard care test protocol. RESULTS: Nine boys (aged 10.8 ± 4.7 years) with Becker muscular dystrophy (n = 6) and Duchenne muscular dystrophy (n = 3) were included. The feasibility of the CPET was similar to a standard care test protocol, and no serious adverse events occurred. In 67% of the subjects with normal or only mildly impaired functional capacity, the CPET could be used to detect moderate to severe cardiopulmonary exercise limitations. CONCLUSIONS: The CPET seems to be a promising outcome measure for cardiopulmonary exercise limitations in youth with mild functional limitations. Further research with larger samples is warranted to confirm current findings and investigate the additional value of the CPET to longitudinal follow-up of cardiomyopathy and the development of safe exercise programs for youth with dystrophinopathies.

Exercise capacity in children with isolated congenital complete atrioventricular block: does pacing make a difference?

The management of patients with isolated congenital complete atrioventricular block (CCAVB) has changed during the last decades. The current policy is to pace the majority of patients based on a variety of criteria, among which is limited exercise capacity. Data regarding exercise capacity in this population stems from previous publications reporting small case series of unpaced patients. Therefore, we have investigated the exercise capacity of a group of contemporary children with CCAVB. Sixteen children (mean age 11.5 ± 4; seven boys, nine girls) with CCAVB were tested. In 13 patients, a median number of three pacemakers were implanted, whereas in three patients no pacemaker was given. All patients had an echocardiogram and completed a cardiopulmonary cycle exercise test. Exercise parameters were determined and compared with reference values obtained from healthy Dutch peers. The peak oxygen uptake/body mass was reduced to 34.4 ± 9.5 ml kg(-1) min(-1) (79 ± 24% of predicted) and the ventilatory threshold was reduced to 52 ± 17% of peak oxygen uptake (78 ± 21% of predicted), whereas the peak work load/body mass was 2.8 ± 0.6 W/kg (91 ± 24% of predicted), which was similar to controls. Importantly, 25% of the paced patients showed upper rate restriction by the pacemaker. In conclusion, children with CCAVB show a reduced peak oxygen uptake and ventilatory threshold, whereas they show normal peak work rates. This indicates that they generate more energy during exercise from anaerobic energy sources. Paced children with CCAVB do not perform better than unpaced children.

Midterm Follow-Up After Biventricular Repair of the Hypoplastic Left Heart Complex.

BACKGROUND: In neonates with hypoplastic left heart complex (HLHC), biventricular repair is considered superior to univentricular repair. The Z-scores of the mitral and the aortic valve annulus are primary factors for the choice of repair. Predictive cutoff values for the feasibility and optimal outcome of biventricular repair are unknown. This study assesses the growth of left side heart structures and the midterm outcome after biventricular repair with an interatrial fenestration in our HLHC population. METHODS: Retrospective study of 19 HLHC patients who underwent biventricular repair in a single tertiary referral center between 2004 and 2013. The cardiac dimensions (mitral and aortic valve annulus, left ventricle inlet length, left ventricular internal diastolic dimension) were measured before and at 6, 12, 24, and 48 months after biventricular repair. RESULTS: The follow-up ranged from 2 to 98 months. There was no early mortality, and the midterm survival rate was 95%. One patient died of a noncardiac- and nonintervention-related cause. Seven patients (37%) required a total of 8 reinterventions because of recurring or residual obstructive lesions. After biventricular repair, the left cardiac structures grew significantly. CONCLUSIONS: Neonatal biventricular repair is successful and safe in HLHC patients, even with preoperative mitral and aortic valve annulus Z-scores of -4.5 and -5.5, respectively. Residual or restenosis required reintervention in 37% of our HLHC population, but was not significantly correlated with the magnitude of the preoperative Z-scores. Within the first 6 months of follow-up, the Z-scores almost normalized.

Comparability of Z-score equations of cardiac structures in hypoplastic left heart complex.

BACKGROUND: Hypoplastic left heart complex (HLHC) is characterized by a mitral valve or an aortic valve annular Z score < -2, antegrade flow in the ascending aorta, ductal dependency, coarctation or aortic arch hypoplasia, and absence of significant (sub)valvar stenosis. The Z scores of the mitral and aortic valve annuli are major determinants of HLHC. Therefore, the algorithm for Z-score calculation is essential for diagnosis. However, no single universal method of calculation is in use. In the scientific literature addressing HLHC, various Z-score calculation methods have been applied. The aim of this study was to evaluate Z scores derived from two-dimensional echocardiographic dimensions in patients with HLHC. METHODS: To compare the different published methods using two-dimensional echocardiographic measures for Z-score calculation, a cohort of 18 newborns diagnosed with HLHC was retrospectively evaluated. In addition, the methods to determine body surface area in newborns were evaluated. RESULTS: Three Z-score calculation methods were included and compared. Using the method of Daubeney et al. to calculate Z scores in our cohort illustrated a lack of correlation beyond a Z score < 0, compared with the methods of Zilberman et al. and Pettersen et al. Z scores calculated using Zilberman et al.'s and Pettersen et al.'s methods were fairly consistent. The equations used by Pettersen et al. are based on the largest population of neonates. CONCLUSION: Although the different methods for calculating Z scores for mitral and aortic valve dimensions correspond fairly well in the normal range, Z scores < -2 diverge substantially. A useful scientific comparison of published data and outcomes of patients with HLHC remains elusive. The Z-score calculation algorithms used by Pettersen et al. appear to be the most appropriate for use in an evaluation of HLHC. Because these different methods can yield different values, reporting the method as well as the Z score is essential for an accurate diagnosis. Similarly, the method used to determine body surface area should be reported.

Rewiring the heart: stem cell therapy to restore normal cardiac excitability and conduction.

The regenerative capacity of the mammalian heart is insufficient to recover from myocardial infarction. Stem cells are currently considered as a promising and valuable tool to replace the, often large, loss of contractile tissue. One of the bottlenecks hampering fast clinical application is the large amount of cells required to replace a single damaged region combined with an appropriate strategy to succeed in homogeneous repair. A second class of major cardiac disorders for which stem cell therapy might be fruitful and would require less cells for repair, are chronic rhythm disorders. In this area, most research has been focused on stem-cell based biological pacemakers, but increasing amounts of data on AV nodal repair appear in literature. Both therapies, in principle, could eventually replace current instrumentation with electronic pacemakers. Finally, an emerging field of interest explores transplantation of stem cells expressing specific ion channels aiming at suppression of focal arrhythmias, providing an alternative strategy for surgical and catheter-mediated ablation. Since in this second class of applications the number of transplanted cells required may be relatively low, effective clinical therapy may be within close range. Here, we will review recent achievements in the fields of stem-cell based biological pacemakers, AV nodal repair and biological ablation.

Exercise limitation in patients with Fontan circulation: a review.

The aim of the current literature study was to perform a literature review of the factors contributing to exercise limitation and physiological response to exercise in patients with Fontan circulation. In patients with Fontan circulation, peak oxygen uptake ranged from about 14.4 to 32.3 ml/min/kg, and showed a slowed acceleration in the kinetics of oxygen uptake at the onset of exercise. Peak heart rate during exercise was decreased to an average of 153 +/- 10 bpm and arterial oxygen saturation was also decreased at peak exercise, with an average of 89.5 +/- 1.94%. Cardiac output was subnormal, owing to reduced stroke volume, heart rate response and affected pulmonary venous return. Ventilatory anaerobic threshold was below normal values. Moreover, the ventilatory equivalent for carbon dioxide was found to be higher. Patients with Fontan circulation possess a unique physiological response to exercise. Although there is a wide range in exercise capacity among patients, all patients have reduced tolerance to exercise. Cardiac, pulmonary, and muscular factors might play a role in reduced exercise capacity and this distinct response to exercise.