Longitudinal Changes in Heart Rate Recovery After Maximal Exercise in Pediatric Heart Transplant Recipients: Evidence of Autonomic Re-innervation?

Chronotropic Response to Exercise is Decreased in Patients With Congenital Heart Disease Compared to Cardiomyopathy Following Pediatric Heart Transplantation

BACKGROUND

Two common indications for pediatric heart transplantation are congenital heart disease and cardiomyopathy. Prior studies suggest differences in chronotropy on cardiopulmonary exercise testing outcomes depending on indication for heart transplantation. We aimed to determine whether the number of pretransplant sternotomies is associated with differences in heart rate response during exercise testing.

METHODS

A retrospective analysis of our institutional pediatric heart transplant data between 2004 and 2022 was performed. Patients were categorized by indication for transplantation into a cardiomyopathy (CM) group if they had a congenital or acquired cardiomyopathy or a congenital heart disease (CHD) group including all other forms of congenital cardiac anatomic abnormalities.

RESULTS

CHD patients (n = 40) differed from CM patients (n = 53) by mean number of sternotomies prior to transplant (2.4 ± 1.8 vs. 0.5 ± 0.9, p < 0.001). There were no significant differences in echocardiographic function or catheterization hemodynamics. In cardiopulmonary exercise testing performance, the congenital heart disease group had a significantly higher resting heart rate (91.8 ± 11.2 vs. 86.4 ± 10.2 bpm, p = 0.019), lower percent predicted age-predicted maximal heart rate achieved (78.3 ± 8.5% vs. 83.2 ± 11.4%, p = 0.032), and lower heart rate reserve (68.6 ± 19.8 vs. 84.4 ± 24.0 bpm, p = 0.001) despite a similar age and average time from transplantation. Regression analysis confirmed number of pretransplant sternotomies as a main predictor of heart rate metrics.

CONCLUSIONS

There is greater chronotropic incompetence in patients who underwent transplantation due to congenital heart disease compared to cardiomyopathy. The groups differ significantly by number of sternotomies, potentially supporting the hypothesis that prior surgical disruption of cardiac innervation may cause decreased chronotropic response to exercise following transplantation.

Indication for Pediatric Heart Transplant Affects Longitudinal Chronotropy on Cardiopulmonary Exercise Testing

Studies have suggested that pediatric patients with heart transplants (HT) due to congenital heart disease (CHD) perform differently on cardiopulmonary exercise testing compared to pediatric patients with HT due to cardiomyopathy (CM). However, it is not known if this relationship changes over time. The aim of this study was to examine the differences in cardiopulmonary exercise test (CPET) parameters over time between patients with HT due to CHD versus CM. A large single-institution CPET database was used for this study. We conducted a retrospective cohort study of 250 total CPETs from 93 unique patients, examining how patients with HT due to CHD (109 CPETs, 40 unique patients) differed in CPET performance from patients with HT due to CM (141 CPETs, 53 unique patients) from < 2 years post-HT, 2 to < 6 years post-HT, and ≥ 6 years post-HT. There were no differences between patients with HT due to CHD compared to CM in CPETs performed < 2 years post-HT. In CPETs performed 2 to < 6 years post-HT, the CM group had higher maximal HR and percentage of age-predicted maximal heart rate (APMHR) achieved. At ≥ 6 years post-HT, the CM group continued to have higher maximal HR and percentage of APMHR achieved, but also improved HR recovery at one minute. Initial indication for transplant may affect performance on CPETs post-transplant. Patients with HT due to CM have improved chronotropic measures compared to patients with HT due to CHD and these differences are more pronounced with increased time post-HT.

Development of a Pediatric Cardiology Cardiopulmonary Exercise Testing Database

Cardiopulmonary exercise testing (CPET) provides clinicians with information vital to the management of pediatric cardiology patients. CPET can also be used to measure cardiorespiratory fitness (CRF) in these patients. CRF is a robust marker of overall health in children. However, a complete understanding of CRF in pediatric cardiology patients is limited by lack of large, standardized CPET databases. Our purpose was to develop a standardized CPET database, describe available data at our institution, and discuss challenges and opportunities associated with this project. CPETs performed from 1993 to present in an urban pediatric hospital were collected and compiled into a research database. Historical data included demographic and clinical variables and CPET outcomes, and additional variables were calculated and coded to facilitate analyses in these cohorts. Patient diagnoses were coded to facilitate sub-analyses of specific cohorts. Quality assurance protocols were established to ensure future database contributions and promote inter-institutional collaborations. This database includes 10,319 CPETs (56.1% male), predominantly using the Bruce Protocol. Patients ranging from ages 6 to 18 years comprise 86.8% of available CPETs. Diagnosis classification scheme includes patients with structurally normal hearts (n = 3,454), congenital heart disease (n = 3,614), electrophysiological abnormalities (n = 2,082), heart transplant or cardiomyopathy (n = 833), and other diagnoses (n = 336). Historically, clinicians were provided with suboptimal interpretive resources for CPET, often generalizing inferences from these resources to non-representative clinical populations. This database supports representative CRF comparisons and establishes a framework for future CRF-based registries in pediatric patients referred for CPET, ultimately improving clinical decision-making regarding fitness in these populations.

Effect of body mass index on exercise capacity following pediatric heart transplantation

BACKGROUND

Obesity and impaired exercise tolerance following heart transplantation increase the risk of post-transplant morbidity and mortality. The aim of this study was to evaluate the effect of body mass index on markers of exercise capacity in pediatric heart transplant recipients and compare this effect with a healthy pediatric cohort.

METHODS

A retrospective analysis of cardiopulmonary exercise test data between 2004 and 2022 was performed. All patients exercised on a treadmill using the Bruce protocol. Inclusion criteria included patients aged 6-21 years, history of heart transplantation (transplant cohort) or no cardiac diagnosis (control cohort) at the time of testing, and a maximal effort test. Patients were further stratified within these two cohorts as underweight, normal, overweight, and obese based on body mass index groups. Two-way analyses of variance were performed with diagnosis and body mass index category as the independent variables.

RESULTS

A total of 250 exercise tests following heart transplant and 1963 exercise tests of healthy patients were included. Heart transplant patients across all body mass index groups had higher resting heart rate and lower maximal heart rate, heart rate recovery at 1 min, exercise duration, and peak aerobic capacity (VO2peak). Heart transplant patients in the normal and overweight body mass index categories had higher VO2peak and exercise duration when compared to underweight and obese patients.

CONCLUSION

Underweight status and obesity are strongly associated with lower VO2peak and exercise duration in heart transplant patients. Normal and overweight heart transplant patients had the best markers of exercise capacity.

Age-specific determinants of reduced exercise capacity in youth after heart transplant: A longitudinal cohort study

Background

Although prior studies show that children have impaired exercise capacity after heart transplant, the age-specific determinants of this phenomenon are not well understood. We examine exercise capacity and its associations in school-age and adolescent youth post-heart transplant.

Methods

This retrospective cohort study of heart transplant patients who completed a cardiopulmonary exercise test between 1999 and 2018 includes 332 tests on 104 patients younger than 18 years. Tests were stratified into those by school-aged children (5-11 years old) and adolescents (12-17). The primary outcome was peak oxygen consumption; secondary outcomes were anaerobic threshold and peak power production. Potential determinants included age at transplant, diagnosis, and laboratory and invasive hemodynamic measurements.

Results

All exercise capacity outcomes for patients post-transplant regardless of age were significantly reduced compared to the predicted performance of age and sex-matched controls. Percent predicted median peak oxygen consumption (62.63, 95% confidence interval (CI) 59.18, 66.07), anaerobic threshold (66.52, 95%CI 62.24, 70.81), and peak power production (54.00, 95%CI 50.56, 57.44) were reduced. Younger age at transplant and a higher peak heart rate were independently associated with increased peak oxygen consumption across age groups. Elevated wedge pressure and brain natriuretic peptide predicted decreased exercise capacity in adolescents.

Conclusions

Youth after heart transplant have significantly reduced exercise capacity. Younger age at transplant and higher peak heart rate predict increased exercise capacity throughout childhood. Indicators of congestion predict decreased exercise capacity in adolescents. These findings should encourage deeper attention to the relationship between exercise physiology and the social context of children after transplant.

Evaluating a Telemedicine Video Game-Linked High-Intensity Interval Training Exercise Programme in Paediatric Heart Transplant Recipients

Paediatric heart transplant recipients (HTRs) have reduced exercise capacity, physical activity (PA), health-related quality of life (HRQoL), and self-efficacy towards PA. Exercise interventions have demonstrated improvements in exercise capacity and functional status in adult HTRs, with a specific emerging interest in the role of high-intensity interval training (HIIT). Studies of exercise interventions in paediatric HTRs have been limited and nonrandomized to date. HIIT has not yet been evaluated in paediatric HTRs. We thus seek to evaluate the safety and feasibility of a randomized crossover trial of a 12-week, home-based, video game-linked HIIT intervention using a cycle ergometer with telemedicine and remote physiological monitoring capabilities (MedBIKE) in paediatric HTRs. The secondary objective is to evaluate the impact of the intervention on (1) exercise capacity, (2) PA, (3) HRQoL and self-efficacy towards PA, and (4) sustained changes in secondary outcomes at 6 and 12 months after intervention. After a baseline assessment of the secondary outcomes, participants will be randomized to receive the MedBIKE intervention (12 weeks, 36 sessions) or usual care. After the intervention and a repeated assessment, all participants will cross over. Follow-up assessments will be administered at 6 and 12 months after the MedBIKE intervention. We anticipate that the MedBIKE intervention will be feasible and safely yield sustained improvements in exercise capacity, PA, HRQoL, and self-efficacy towards PA in paediatric HTRs. This study will serve as the foundation for a larger, multicentre randomized crossover trial and will help inform exercise rehabilitation programmes for paediatric HTRs.

Enhancing a Rehabilitation Pathway for Pediatric Heart Transplant Recipients: An Improvement Project to Increase Adherence, Satisfaction, and Outcomes

AIMS

To refine a cardiac rehabilitation pathway for pediatric heart transplant recipients; assess clinician knowledge and adherence to the program; and evaluate patient outcomes.

METHODS

The center has utilized a rehabilitation pathway for pediatric heart transplant recipients. Challenges in practice include access to centers, lack of data tracing, and adherence to the pathway. The quality initiative focused on program refinements: implementation of text templates to improve data collection, collection of the Pediatric Cardiac Quality of Life Inventory (PCQLI), Functional Independence Measure (WeeFIM) and Child Occupational Self-Assessment (COSA), development of an outreach program, and creation of an educational program for therapists to increase content knowledge and improve clinician satisfaction.

RESULTS

In the evaluation of rehabilitation follow-up post-transplant, there was no statistical significance between the pre- and post-implementation groups. After the implementation of the refined pathway, there was an increase in the completion of the six-minute walk test post-transplant (p = 0.048). Clinicians' responses post educational session noted familiarity with the pathway (88%), documentation (78.8%), and outcome measures (97%). Results of outcomes noted improvement in six-minute walk distances and a decrease in the rate of perceived exertion post-transplant. To ensure future pathway adherence, clinical support should be implemented, and key players identified to maintain sustainability.

Heart rate kinetics during standard cardiopulmonary exercise testing in heart transplant recipients: a longitudinal study

AIMS

Heart transplantation (HTx) results in complete autonomic denervation of the donor heart, causing resting tachycardia and abnormal heart rate (HR) responses to exercise. We determined the time course of suggestive cardiac reinnervation post HTx and investigated its clinical significance.

METHODS AND RESULTS

Heart rate kinetics during standard cardiopulmonary exercise testing at 2.5-5 years after HTx was assessed in 58 patients. According to their HR increase 30 s after exercise onset, HTx recipients were classified as denervated (slow responders: <5 beats per minute [b.p.m.]) or potentially reinnervated (fast responders: ≥5 b.p.m.). Additionally, in 30 patients, longitudinal changes of maximal oxygen consumption and HR kinetics were assessed during the first 15 post-operative years. At 2.5-5 years post HTx, 38% of our study population was potentially reinnervated. Fast responders were significantly younger (41 ± 15 years) than slow responders (53 ± 13 years, P = 0.003) but did not differ with regard to donor age, immunosuppressive regime, cardiovascular risk factors, endomyocardial biopsy, or vasculopathy parameters. While HR reserve (56 ± 20 vs. 39 ± 15 b.p.m., P = 0.002) and HR recovery after 60 s (15 ± 11 vs. 5 ± 6 b.p.m., P < 0.001) were greater in fast responders, resting HR, peak HR of predicted, and peak oxygen consumption of predicted were comparable.

CONCLUSIONS

Signs of reinnervation occurred mainly in younger patients. Maximal oxygen consumption was independent of HR kinetics.

Chronotropic incompetence in paediatric heart transplant recipients with prior congenital heart disease

BACKGROUND

Cardiopulmonary exercise testing has been used to measure functional capacity in children who have undergone a heart transplant. Cardiopulmonary exercise testing results have not been compared between children transplanted for a primary diagnosis of CHD and those with a primary diagnosis of cardiomyopathy despite differences in outcomes. This study is aimed to compare cardiopulmonary exercise testing performance between these two groups.

METHODS

Patients who underwent heart transplant with subsequent cardiopulmonary exercise testing at least 6 months after transplant at our institution were identified. They were then divided into two groups based on primary cardiac diagnosis: CHD or cardiomyopathy. Patient characteristics, echocardiograms, cardiac catheterisations, outcomes, and cardiopulmonary exercise test results were compared between the two groups.

RESULTS

From the total of 35 patients, 15 (43%) had CHD and 20 (57%) had cardiomyopathy. Age at transplant, kidney disease, lung disease, previous rejection, coronary vasculopathy, catheterisation, and echocardiographic data were similar between the groups. Mean time from transplant to cardiopulmonary exercise testing, exercise duration, and maximum oxygen consumption were similar in both groups. There was a difference in heart rate response with CHD heart rate response of 63 beats per minute compared to cardiomyopathy group of 78 (p = 0.028). Patients with CHD had more chronotropic incompetence than those with cardiomyopathy (p = 0.036).

CONCLUSION

Primary diagnosis of CHD is associated with abnormal heart rate response and more chronotropic incompetence compared to those transplanted for cardiomyopathy.

Exercise capacity following pediatric heart transplantation: A systematic review

Pediatric HTs account for 13% of all HTs with >60% of recipients surviving at least 10 years post-HT. The purpose of this systematic review is to synthesize the literature on exercise capacity of pediatric HT recipients to improve understanding of the mechanisms that may explain the decreased exercise capacity. Six databases were searched for studies that compared the exercise capacity of HT recipients ≤21 years old with a control group or normative data. Sixteen studies were included. Pediatric HT recipients, as compared to controls or normative data, exhibit significantly higher resting HR, and at peak exercise exhibit significantly decreased HR, VO₂ , power, work, minute ventilation, and exercise duration. Peak VO₂ appears to improve within the first 2.5 years post-HT; peak work remains constant; and there is inconclusive evidence that peak HR, HR recovery, and HR reserve improve with time since HT. These results are discussed in the context of the mechanisms that may explain the impaired exercise capacity of pediatric HT recipients, including chronotropic incompetence, graft dysfunction, side effects of immunosuppression therapy, and deconditioning. In addition, the limited literature on rehabilitation after pediatric HT is summarized.

Heart rate recovery is impaired after maximal exercise testing in children with sickle cell anemia

OBJECTIVE

To examine heart rate recovery (HRR) as an indicator of autonomic nervous system dysfunction after maximal exercise testing in children and young adults with sickle cell anemia (SCA).

STUDY DESIGN

Recovery phase heart rate (HR) in the first 5 minutes after maximal exercise testing in 60 subjects with SCA and 30 matched controls without SCA was assessed. The difference between peak HR and HR at both 1-minute (ΔHR1min) and 2-minutes recovery was our primary outcome.

RESULTS

Compared with controls, subjects with SCA demonstrated significantly smaller mean ΔHR1min (23 beats per minute [bpm], 95% CI 20-26 vs 32 bpm, 95% CI 26-37, P = .006) and the difference between maximal HR and HR at 2 minutes (39 bpm, 95% CI 36-43 vs 48 bpm, 95% CI 42-53, P = .011). Subjects with SCA also showed smaller mean changes in HR from peak HR to 1 minute, from 1 minute to 2 minutes, and from 2 through 5 minutes of recovery by repeated-measures testing. In a multivariable regression model, older age was independently associated with smaller ΔHR1min in subjects with SCA. Cardiopulmonary fitness and hydroxyurea use, however, were not independent predictors of ΔHR1min.

CONCLUSIONS

Children with SCA demonstrate impaired HRR after maximal exercise. Reduced postexercise HRR in SCA suggests impaired parasympathetic function, which may become progressively worse with age, in this population.

Exercise limitation following transplantation

Organ transplantation is one of the medical miracles or the 20th century. It has the capacity to substantially improve exercise performance and quality of life in patients who are severely limited with chronic organ failure. We focus on the most commonly performed solid-organ transplants and describe peak exercise performance following recovery from transplantation. Across all of the common transplants, evaluated significant reduction in VO2peak is seen (typically renal and liver 65%-80% with heart and/or lung 50%-60% of predicted). Those with the lowest VO2peak pretransplant have the lowest VO2peak posttransplant. Overall very few patients have a VO2peak in the normal range. Investigation of the cause of the reduction of VO2peak has identified many factors pre- and posttransplant that may contribute. These include organ-specific factors in the otherwise well-functioning allograft (e.g., chronotropic incompetence in heart transplantation) as well as allograft dysfunction itself (e.g., chronic lung allograft dysfunction). However, looking across all transplants, a pattern emerges. A low muscle mass with qualitative change in large exercising skeletal muscle groups is seen pretransplant. Many factor posttransplant aggravate these changes or prevent them recovering, especially calcineurin antagonist drugs which are key immunosuppressing agents. This results in the reduction of VO2peak despite restoration of near normal function of the initially failing organ system. As such organ transplantation has provided an experiment of nature that has focused our attention on an important confounder of chronic organ failure-skeletal muscle dysfunction.

The correlates of body composition with heart rate recovery after step test: an exploratory study of Malaysian adolescents

BACKGROUND

In adults, heart rate recovery is a predictor of mortality, while in adolescents it is associated with cardio-metabolic risk factors. The aim of this study was to examine the relationship between body composition measures and heart rate recovery (HRR) after step test in Malaysian secondary school students.

METHODS

In the Malaysian Health and Adolescents Longitudinal Research Team (MyHEART) study, 1071 healthy secondary school students, aged 13 years old, participated in the step test. Parameters for body composition measures were body mass index z-score, body fat percentage, waist circumference, and waist height ratio. The step test was conducted by using a modified Harvard step test. Heart rate recovery of 1 minute (HRR1min) and heart rate recovery of 2 minutes (HRR2min) were calculated by the difference between the peak pulse rate during exercise and the resting pulse rate at 1 and 2 minutes, respectively. Analysis was done separately based on gender. Pearson correlation analysis was used to determine the association between the HRR parameters with body composition measures, while multiple regression analysis was used to determine which body composition measures was the strongest predictor for HRR.

RESULTS

For both gender groups, all body composition measures were inversely correlated with HRR1min. In girls, all body composition measures were inversely correlated with HRR2min, while in boys all body composition measures, except BMI z-score, were associated with HRR2min. In multiple regression, only waist circumference was inversely associated with HRR2min (p=0.024) in boys, while in girls it was body fat percentage for HRR2min (p=0.008).

CONCLUSION

There was an inverse association between body composition measurements and HRR among apparently healthy adolescents. Therefore, it is important to identify cardio-metabolic risk factors in adolescent as an early prevention of consequent adulthood morbidity. This reiterates the importance of healthy living which should start from young.

Impairment of heart rate recovery after peak exercise predicts poor outcome after pediatric heart transplantation

BACKGROUND

A blunted heart rate recovery (HRR) from peak exercise is associated with adverse outcome in adults with ischemic heart disease. We assessed HRR after pediatric heart transplantation (HTx) and its prognostic use.

METHODS AND RESULTS

Between 2004 and 2010 we performed 360 maximal exercise tests (median, 2 tests/patient; range, 1-7) in 128 children (66 men; age at test, 14 ± 3 years) who received HTx (age, 8.5 ± 5.1 years) because of cardiomyopathy (66%) or congenital heart defects (34%). The change in heart rate from peak exercise to 1 minute of recovery was measured as HRR and was expressed as Z score calculated from reference data obtained in 160 healthy children. HRR was impaired soon after HTx (average in first 2 years Z=-1.9 ± 3.5) but improved afterward (Z=+0.52/y), such that HRR Z score normalized in most patients by 6 years after HTx (average, 0.6 ± 1.8). A subsequent decline in HRR Z score was noted from 6 years after HTx (rate of Z=-0.11/y). After 27 ± 15 months from the most recent exercise test, 19 patients died or were re-heart transplantation. For the follow-up after 6 years, HRR Z score was the only predictor of death/re-heart transplantation (P=0.003). Patients in the lowest quartile of HRR Z score had a much higher 5-year event rate (event-free rate, 29% versus 84%; hazard ratio, 7.0; P=0.0013).

CONCLUSIONS

HRR is blunted soon after HTx but normalizes at ≈ 6 years, potentially as a result of parasympathetic reinnervation of the graft, but then declines. This late decline in HRR Z score is associated with worse outcome.

Enhanced exercise performance and survival associated with evidence of autonomic reinnervation in pediatric heart transplant recipients

Following heart transplantation (HTx), loss of autonomic input to the allograft results in elevated resting heart rate (HR) and decreased chronotropic reserve. As enhanced exercise capacity and HR recovery post exercise are suggestive of reinnervation in pediatric cohorts, we used heart rate variability (HRV) analysis to assess autonomic reinnervation in pediatric HTx recipients. Pediatric patients transplanted between 1996 and 2010 and with serial 24-hour Holter recordings post-HTx were analyzed for HRV using time and frequency domain measures. Of 112 patients, 68 (57%) showed evidence of autonomic reinnervation that was not associated with age at HTx. Evidence of reinnervation was associated with a significant increase in low-frequency power spectrum (p<0.001), suggesting sympathetic reinnervation. Patients with evidence of reinnervation showed higher percent-predicted maxVO(2) on performing an exercise test (+10.2 ± 3.6%, p = 0.006) and improved HR recovery at 3 minutes (-11.4 ± 3.9 bpm, p = 0.004), but no difference in percent-predicted maximal HR. Cox hazards modeling using presumed sinus reinnervation criteria at last Holter recording as a time-dependent covariate was associated with decreased hazard of mortality and/or retransplantation (HR: 0.2, 95% CI 0.04-1.0, p = 0.05). In conclusion, a majority of pediatric HTx recipients demonstrate evidence of reinnervation that is associated with functional outcomes. Studies to assess graft reinnervation as a marker of long-term prognosis are warranted.

Serial measurements of exercise performance in pediatric heart transplant patients using stress echocardiography

Heart transplantation is an increasingly acceptable therapeutic option for children with end-stage and complex congenital heart disease. With advances in surgery, immunosuppression, and follow-up care, functional outcomes need to be evaluated. We report the results of serial exercise testing performed using stress echocardiography in a cohort of pediatric HTP. HTP (n = 7) exercised on a semi-recumbent ergometer to volitional fatigue. Echocardiography-Doppler measurements, HR, and blood pressure were taken at rest and during staged exercise. Results were compared with healthy CON (n = 12). HTP did significantly less work during exercise (940 vs. 1218 J/kg, p < 0.03). Their SVI (33 vs. 49 mL/m(2), p < 0.003), CI (5.16 vs. 9.25 L/min/m(2), p < 0.0005), and HR (162 vs. 185 bpm, p < 0.02) were lower at peak exercise. HTP had a lower SF at peak exercise (48% vs. 52%, p < 0.03) and an abnormal relationship between the MVCFc and σPS. During follow-up, hemodynamics and left ventricular function remained relatively constant in HTP. HTP are able to exercise safely; however, their exercise tolerance is reduced, and hemodynamics and contractility are diminished. Over time, their hemodynamics and left ventricular function have remained relatively constant.

Most commonly asked questions from parents of pediatric transplant recipients

Pediatric solid-organ transplant (SOT) recipients and their parents are often challenged to cope with new transplant regimens as well as common situations in the context of organ transplantation. Health care professionals will receive questions from parents and children regarding clinical transplant care as well as general pediatric concerns that seem unfamiliar to families now that their child has a transplant. The literature is limited in some areas of pediatric care after SOT, and there is little guidance for the health care practitioner. To help address gaps in the literature and provide guidance for health care professionals, this article reviews some of the most commonly asked questions regarding general care after SOT, parenting the child with a chronic illness, and growth and development. The answers provided stem from the literature in part but also the combined clinical experiences of transplant centers that over time have moved toward decreased limitations and full social integration.

Determinants of exercise capacity after arterial switch operation for transposition of the great arteries

Patients who undergo the arterial switch operation for transposition of the great arteries (TGA) are at risk of reduced exercise capacity, with most reports focusing on chronotropic incompetence as the cause. Residual right ventricular outflow tract (RVOT) obstruction is relatively common after the arterial switch operation, but its effect on exercise capacity is unknown. We studied 60 patients (44 males, age 13.3 +/- 3.4 years) who had undergone a neonatal arterial switch operation using the cardiopulmonary exercise test and transthoracic echocardiography. The peak exercise oxygen uptake (VO(2)), and heart rate were recorded and are expressed as the percentage of predicted values. The greatest velocity detected by echocardiography across the pulmonary valve, pulmonary trunk, or pulmonary branches was used in the analysis as an index of RVOT obstruction. The peak VO(2)% was 84 +/- 15%, and the peak heart rate percentage was 97 +/- 8%. Of the 60 patients, 29 had an abnormal peak VO(2)% (< or =84%) and 3 (5%) had an abnormal peak heart rate percentage (< or =85%). The maximal RVOT velocity was 2.3 +/- 0.6 m/s, and it correlated with the peak VO(2)% (r = -0.392, p = 0.004). On multivariate analysis, the presence of residual RVOT obstruction (p = 0.0007) was the only variable associated with a reduced peak VO(2)%. Patients with a RVOT maximal velocity > or =2.5 m/s had a lower peak VO(2)% than those with lower velocities (p <0.0001). No relation was found between age at testing and the peak VO(2)%. In conclusion, a reduced exercise capacity is relatively common in children and young adults who have undergone an arterial switch operation, but it does not decrease with age. The presence of residual RVOT obstruction seems to have an effect on exercise capacity.