Cardiopulmonary parameters in patients with Tetralogy of Fallot: the reference values for treadmill and cycle ergometer

Background The aim of this study was to establish sex- and age-specific reference values for ramp cycle-ergometer and treadmill cardiopulmonary exercise testing (CPET) in patients with Tetralogy of Fallot (ToF). Despite successful surgical repair, residual pulmonary regurgitation remains common in repaired ToF (rToF), often leading to right or left ventricular dysfunction and reduced exercise capacity. CPET is a reliable tool for evaluating cardiopulmonary function. Although both treadmill and cycle ergometer protocols are used interchangeably, reference value ranges for each method in this population remain unclear. Method CPET data were collected from asymptomatic rToF patients who had undergone cardiac magnetic resonance imaging (CMR) and performed CPET on a treadmill or cycle ergometer between 2020 and 2024. Physical activity was assessed using the International Physical Activity Questionnaire (IPAQ). Results Among 290 patients, median age at CPET was 21.6 years (15.9–29.3), and median BMI was 22.5 kg/m 2 (20.0–24.9). Nearly all participants (99%) were in NYHA class I. Physical activity was classified as sedentary in 29%, moderate in 61%, and high in 9%. Median VO₂ peak was 26.4 mL/min/kg (23.0–31.5), corresponding to 72.9% predicted (62.4–83.2). Median oxygen pulse at peak was 9.9 mL/beat (8.2–12.0), with 76.9% predicted (68.0–87.5). Median VE/VCO₂ slope at the respiratory compensation point was 29.0 (26.0–32.6), and median oxygen uptake efficiency slope (OUES) was 1,792.5 mL/min/log(L/min) (1,535.0–2,181.5). VO₂ peak and percent-predicted VO₂ were significantly higher with treadmill testing in both sexes ( p < 0.05); oxygen pulse was higher only in females. VE/VCO₂ slope and OUES were unaffected by modality. When stratified by age (<18 vs. ≥18 years), treadmill-related differences in VO₂ peak and percent-predicted VO₂ remained significant in both sexes ≥18 years, and in females <18 years. Oxygen pulse was significantly higher with treadmill only in females ≥18 years. VE/VCO₂ slope and OUES remained unchanged across modalities and age groups Conclusion This study provides CPET values stratified by modality and sex in a large cohort of asymptomatic rToF patients, offering valuable reference data for clinical assessment. Future studies should validate pediatric normative CPET values through prospective, inclusive, statistically powered cohorts using standardized protocols and cross-center comparability.