The exercise capacity of children after arterial switch for transposition of the great arteries (TGA) is known to be at the lower limit of normal. We aimed to ascertain whether this results from compromised hemodynamics or deconditioning. A total of 17 children with TGA (12 male and 5 female children; age 12.1 ± 2.0 years) treated with the arterial switch operation were compared with 20 age-matched controls (13 male and 7 female children; age 12.8 ± 2.4 years) regarding their peak exercise capacity, peak workload, and peak heart rate, as assessed by cycle ergometry. The children’s physical activity level was monitored for a 7-day period using a pedometer and diary, and a questionnaire was used to assess physical activity participation and overprotection. The results demonstrated that TGA children showed a significantly reduced peak exercise capacity (47.4 ± 6.4 vs 41.1 ± 6.6 ml/kg/min; p <0.05), maximal workload (3.7 ± 0.5 vs 3.1 ± 0.6 W/kg; p <0.01), and maximal heart rate (189 ± 9 vs 180 ± 14 beats/min; p <0.05) compared to the controls. No significant differences were found in the physical activity pattern or overprotection. In conclusion, given the comparable physical activity level, but reduced exercise capacity in the TGA children, these children most likely fall short in their exercise performance because of restrictive hemodynamics rather than deconditioning from reduced daily life activity.
Previous studies have shown that the exercise capacity of children after arterial switch for transposition of the great arteries (TGA) is, in general, slightly lower than that of their healthy peers. Although previous research focused on either exercise capacity or activity pattern (24-hour heart rate monitoring survey ), the present study has uniquely addressed both physical fitness and the physical activity pattern of children with TGA treated by the arterial switch operation (ASO).
Moreover, the physical activity pattern was studied comprehensively in our participants using 7-day activity monitoring (pedometer and diary) and a questionnaire on physical activity and participation. We combined the approach of exercise testing and activity monitoring in an attempt to determine whether (1) the aerobic capacity is indeed reduced in children with TGA compared to that of healthy peers, and (2), if true, whether this resulted from reduced physical activity or cardiac restriction. The results of the present study might aid in the preparation of specific recommendations regarding participation in daily physical activity functioning, sports, and therapy for children with TGA that could improve their quality of life.
Methods
Children eligible for participation in the present study were selected from a database of the Department of Pediatric Cardiology that includes patients with TGA who underwent surgery from 1990 to 1999 at the Radboud University Nijmegen Medical Centre (Nijmegen, The Netherlands). Patients with metabolic, neurologic, muscular, or orthopedic anomalies were excluded. Also, syndromes with congenital heart defects as one of the features, heart failure (New York Heart Association class ≥I), cyanosis at rest (oxygen saturation <90%), and severe cardiac arrhythmia were considered exclusion criteria. A total of 35 children were contacted by letter and invited to participate in the study. The siblings of these children were asked to participate in the control group. Of the 35 children, 5 could not be traced because of invalid address data. In total, 17 children with TGA aged 10 to 17 years and 20 gender-matched control subjects were included in the present study. The local ethical committee of the Radboud University Nijmegen approved the study, and the children and their parents provided written informed consent.
Anthropometric measurements were taken and included height, weight, abdominal girth, and skin fold thickness. For each participant, body mass index was calculated. The abdominal girth was assessed to estimate the amount of abdominal fat and was measured 1 cm above the level of the iliac crest. A 4-site (biceps, triceps, subscapular, and suprailiac) skin fold thickness measurement of the nondominant body site was performed (Ponderal, Zoetermeer, The Netherlands). The sum of the 4 skin folds was used to determine the age- and gender-adjusted body fat percentage. Using the tables provided by Deurenberg et al and this information, the lean body mass was calculated. The blood pressure at rest was measured with a manual sphygmomanometer (Welch Allyn Max-Stabil 3, Jungingen, Germany).
To measure cardiovascular fitness and exercise capacity, all children performed an incremental exercise test on a half-supine, electronically braked, cycle ergometer (Sensormedics BV, Bilthoven, The Netherlands) adhering to a standardized ramp protocol. During cycling, the workload was gradually increased by 10, 15, or 20 W/min (depending on the subject’s weight, age, gender, and exercise habits), and the cycling speed was maintained at approximately 65 rpm. The exercise was terminated at the subjects’ request, because of electrocardiographic changes associated with myocardial ischemia, physical exhaustion, dyspnea, or calf/thigh pain. To prevent decreases in systolic blood pressure from venous pooling after test termination, the subjects were instructed to continue cycling for 3 additional minutes at 30 rpm against a workload of 20 W. A 12-lead electrocardiogram was obtained during each minute of exercise and recovery. The heart rate and rhythm were monitored continuously (GEMS IT Cardiosoft V4.2, Freiburg, Germany), and blood pressure was measured with 2-minute intervals. Gas exchange parameters were obtained throughout the exercise test and during the first 2 minutes of recovery on a breath-by-breath basis using a metabolic cart (Vmax Spectra 29, SensorMedics, Yorba Linda, California). The oxygen consumption and respiratory quotient were measured every 20 seconds. The peak oxygen uptake (VO 2peak ) was defined as the mean of the last 40 seconds of the ergometer test. The exercise test results were considered valid when the following criteria were met: (1) observed exhaustion of the child, (2) VO 2peak leveling off, and (3) respiratory quotient >1.00. The subjects were asked to repeat the cycle ergometer test 1 week later if the respiratory quotient had remained <1.00. Only data meeting these criteria were analyzed.
The daily physical activity level was assessed using an electronic pedometer (Yamax SW-200 DigiWalkers, Yamax, Japan) and an activity diary for 7 days, including 2 weekend days. The pedometer was clipped to the waistline at the right side according to the manufacturer’s instructions. The activity diary consisted of 7 timelines, 1 for each day. Each day was divided into 48 U, with 1 U representing 30 minutes. The activities were indicated using numbers drawn from a previously devised legend. Arrows were used to indicate the child’s waking hours. The activities were computed to the metabolic equivalent (MET) values (1 MET = 1 kcal/kg/hr) using the Compendium of Physical Activities, a coding scheme that classifies specific physical activity by the rate of energy expenditure.
To obtain a questionnaire concerning physical fitness and participation in sports for children with coronary heart disease (CHD), the Haemophilia and Physical Fitness Questionnaire (Department of Paediatric Physical Therapy, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands) was modified to suit our study purposes. This CHD and physical fitness questionnaire was used to acquire information on co-morbidities, the number of hours of sports participation at school and during leisure time, recreational exercise, other leisure activities, type of transport to and from school, self-rated fitness and health and physical activity, and overprotection.
The results are expressed as the mean ± SD, with the range. For comparison of the anthropometric measurements, exercise testing parameters, pedometer and activity measurements, unpaired Student’s t tests were applied. For comparison of frequencies, chi-square tests were administered. For intergroup comparison of ordinal variables, the nonparametric Mann-Whitney U test was used. Descriptive statistics were used for questions concerning overprotection. For all tests, a level of significance of p <0.05 was used. All statistical analyses were performed with Statistical Package for Social Sciences for Windows, version 16.0 (SPSS, Chicago, Illinois).
Results
Two subjects in the TGA group could not perform the cycle test because of practical problems. One child had a cold and difficulties breathing through the mask and one was too small and could not reach the pedals properly. The remaining children (n = 15) met the criteria for a valid exercise test, and physical exhaustion was the reason for test termination. Because the predicted VO 2peak values were greater for the male children than for the female children, the exercise test results of the 15 TGA subjects who were able to complete the test were compared with the results of 15 gender- and age-matched control subjects. The pedometer, diary, and questionnaire results of the entire TGA group were compared with the results of 17 age- and gender-matched subjects. The data from 20 control subjects were used. No significant differences were found in age, weight, length, body mass index, lean body mass, or blood pressure between the TGA and control groups ( Table 1 ).
| Variable | Control Group (n = 20) | TGA Group (n = 17) |
|---|---|---|
| Gender | ||
| Male | 13 | 12 |
| female | 7 | 5 |
| Age (years) | 12.8 ± 2.4 (10–17) | 12.1 ± 2.0 (10–17) |
| Weight (kg) | 49.5 ± 10.6 (33.1–70.7) | 47.3 ± 14.1 (28.5–76.8) |
| Length (cm) | 159.9 ± 12.2 (141–186) | 156.2 ± 14.6 (138–186) |
| Body mass index (kg/m 2 ) | 19.2 ± 2.3 (16.4–23.8) | 19.1 ± 2.4 (14.8–23.5) |
| Lean body mass (kg) | 40.9 ± 9.4 (26.4–59.8) | 38.5 ± 11.5 (23.3–65.4) |
| Systolic blood pressure (mm Hg) | 110 ± 11 (85–132) | 119 ± 13 (90–154) |
| Diastolic blood pressure (mm Hg) | 76 ± 8 (60–114) | 72 ± 9 (60–90) |
The mean age at surgery was 7.6 ± 10.8 days. Of the 17 subjects with TGA, 15 underwent ASO during the first 2 months of life, with closure of an atrial septal defect and/or ventricular septal defect, if necessary. One subject with partial anomalous pulmonary venous return and left atrial isomerism underwent an ASO with correction of the partial anomalous pulmonary venous return. At 11 years of age, an atrial inhibited rate modulated pacemaker was implanted with a lower rate of 70 beats/min and an upper center rate of 180 beats/min because of an abnormal chronotropic response to exercise. One patient had TGA with a large subaortic ventricular septal defect and pulmonary stenosis. For this patient, a Blalock-Taussig shunt was placed as a palliative procedure 3 days after birth, followed by a Rastelli procedure 2 years later. Four patients required cardiac catheterization with balloon dilation to treat stenosis at the site at which the pulmonary artery was reconnected during the ASO. One subject underwent repeat surgery to close the remainder of an atrial septal defect at 6 and 8 years of age. The residual postoperative cardiac co-morbidities are listed in Table 2 .
| Deficiency | Patients (n) |
|---|---|
| Complete right bundle branch block | 1 |
| Incomplete right bundle branch block | 5 |
| First-degree atrioventricular block | 1 |
| Homograft stenosis | 1 |
| Pulmonary stenosis | 13 |
| Pulmonary insufficiency | 1 |
| Neoaortic insufficiency | 5 |
| Aortic valve stenosis | 1 |
| Pulmonary valve stenosis | 1 |
| Tricuspid valve insufficiency | 1 |
| Mitral valve insufficiency | 1 |
| Narrowing of left ventricular outflow tract | 1 |
| Enlarged neoaortic root diameter | 2 |
The VO 2peak (ml/kg/min) and the adjusted per kilogram lean body mass were significantly lower in the TGA group than in the controls ( Figure 1 , Table 3 ). In addition, the peak workload ( Figure 2 ) and peak heart rate ( Figure 3 ) were significantly lower in the TGA subjects than in the controls ( Table 3 ).
| Variable | Control Group (n = 15) | TGA Group (n = 15) | p Value |
|---|---|---|---|
| VO 2peak (ml/kg/min) | 47.4 ± 6.4 (39.3–58.4) | 41.1 ± 6.6 ⁎ (32.1–55.5) | 0.013 |
| VO 2peak lean body mass (ml/kg/min) | 58.2 ± 10.0 (46.1–85.4) | 50.5 ± 7.1 ⁎ (32.1–55.5) | 0.021 |
| VO 2peak (% of predicted) | 94.6 ± 12.1 (75.6–111.5) | 81.4 ± 10.9 ⁎ (63.0–103.8) | 0.004 |
| Respiratory quotient | 1.04 ± 0.03 (0.98–1.09) | 1.03 ± 0.04 (0.98–1.12) | 0.46 |
| Peak workload (W) | 179.3 ± 60.5 (96–320) | 154.1 ± 61.6 (80–312) | 0.27 |
| Peak workload (W/kg) | 3.7 ± 0.5 (2.7–4.7) | 3.1 ± 0.6 ⁎ (2.5–4.2) | 0.005 |
| Peak heart rate (beats/minute) | 189 ± 9 (168–200) | 180 ± 14 (155–202) | 0.045 |
| Heart rate after 1 min (beats/minute) | 153 ± 17 (113–178) | 149 ± 16 (126–179) | 0.40 |
| Heart rate after 3 min (beats/minute) | 120 ± 16 (83–146) | 118 ± 14 (89–146) | 0.80 |
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