Chronotropic Response and Pulmonary Function are Associated with Exercise Performance in Children and Adolescents with Repaired Tetralogy of Fallot Independent of Cardiac Function

Objective: The determinants of exercise capacity in repaired tetralogy of Fallot (rTOF) are multifactorial and remain incompletely understood. This study sought to evaluate the association of chronotropic response with exercise parametersand investigate the determinants of heart rate reserve (HRR) in a cohort of children and adolescents with rTOF. Design: We retrospectively analyzed patients with rTOF, age 8–18 years, who underwent cardiac magnetic resonance (CMR) and cardiopulmonary exercise test (CPET) for research purposes. Linear regression models were performed to test associations among clinical, CMR and CPET parameters. Outcomes included percent-predicted maximum VO₂ (%mVO₂) and HRR. Results: A total of 148 patients were included (mean age 12.3 ± 3.1 years). The majority of patients had TOF with pulmonary stenosis (80%) and underwent transannular patch TOF repair (78%). Median age at surgical repair was 4.2 months(IQR 1.2, 8.4). There was preserved RV ejection fraction (60.4 ± 8.3%) and moderate pulmonary insufficiency (regurgitant fraction 35.2 ± 16.6 %). On CPET, %mVO₂ was overall diminished (76.5 ± 17.9 %), and % predicted forced vital capacity (FVC) was diminished on spirometry. HRR, FVC and ability to reach maximum effort were independently associated with greater %mVO₂. FVC, net forward flow in the main pulmonary artery/m², and reaching maximum effort were associated with greater HRR, independently of RV volume, degree of PI and RV ejection fraction. Conclusions: In patients with rTOF, HRR and pulmonary function(FVC) are more important contributors to exercise performance than right ventricular function. Interventions to improve chronotropic health and pulmonary function should be explored.