Exercise assessment in infants after cardiac transplantation

Background Few data describe exercise performance after cardiac transplantation during infancy. The aim of this study was to compare the cardiorespiratory response to exercise in healthy subjects with that of subjects who had undergone heart transplantation during infancy to treat hypoplastic left heart syndrome. Methods Subjects (24 heart transplant recipients and 25 healthy controls) exercised on a treadmill using pediatric ramp protocols. We measured heart rate (HR), blood pressure, and metabolic data. Median age at transplantation was 20 days (range, 4 to 97 days). Age of recipients at exercise testing was 9.7 ± 2.3 years and in healthy subjects was 10.5 ± 1.4 years (p = not significant [NS]). Results Exercise duration was similar in both groups (10.3 ± 2.0 minutes in recipients vs 11.1 ± 1.5 minutes in healthy subjects, (p = NS). Heart rate at rest was greater in recipients (94 ± 15 beats per minute [bpm] vs 85 ± 11 bpm, p = 0.02). Peak HR also was less in the recipient group (158 ± 15 bpm vs 189 ± 12 bpm, p < 0.001). Peak oxygen consumption was 14% less in the recipients (32.3 ± 5.6 ml/kg/min vs 36.8 ± 5.5 ml/kg/min, p < 0.01). Ventilatory anaerobic threshold was decreased in recipients, 27.6 ± 9.6 vs 32.8 ± 6.0, p < 0.05. Respiratory exchange ratio at peak exercise was equal in both groups (1.06 ± 0.06 vs 1.06 ± 0.08). Oxygen pulse index did not differ significantly, 5.5 ± 1.1 ml/beat/m² in recipients and 6.1 ± 1.7 ml/beat/m² in healthy subjects (p = NS). Conclusions Overall, children who undergo cardiac transplantation in infancy have exercise capacities within the normal range. These recipients have a decreased heart rate reserve that may account for the differences in peak oxygen consumption when compared with healthy subjects.