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.