Exercise assessment in children after cardiac transplant in infancy: effect of chronotropic incompetence

Abstract Limited data are available on exercise performance after infant cardiac transplantation (CTX). Purpose: The aim of this study was to compare the cardiorespiratory response to exercise in children who had undergone CTX for hypoplastic left heart syndrome in infancy with normal (NML) subjects. Procedure: Subjects (24 CTX; 25 NML) were exercised on a treadmill using pediatric ramp protocols. Heart rate (HR), blood pressure (BP), oxygen consumption (VO2), CO2 production and ventilatory anaerobic threshold (VAT) were measured. Mean age at CTX was 32±26 days. Age of CTX subjects at time of exercise was 9.7±2.3 years and 10.5±1.4 years in NML subjects (p=NS). All subjects in both groups were NYHA Class I. Results: Exercise duration was similar (p=NS) in both groups (10.3±2.0 minutes(CTX) versus 11.1±1.5 minutes (NML). HR at rest was greater in CTX patients (94±15 BPM versus 85±11 BPM (p=0.02). Peak HR was also less in the CTX group (158 BPM±15 BPM versus 189 BPM±12 BPM (p Conclusions: 1) Overall, children receiving cardiac transplantation in infancy have an exercise capacity within the normal range. 2) Subjects undergoing cardiac transplantation in early infancy have decreased heart rate reserve that may account for the differences in peak oxygen consumption compared to normal subjects.