Functional Capacity Assessment in Adults After Fontan Palliation: A Cardiopulmonary Exercise Test-Invasive Exercise Hemodynamics Correlation Study

Although cardiopulmonary exercise testing (CPET) parameters have known prognostic value in adults after Fontan palliation, there are limited data correlating treadmill CPET with invasive exercise hemodynamics. Furthermore, the invasive hemodynamic underpinnings of exercise limitations have not been thoroughly investigated. This is a retrospective analysis of 55 adults (age ≥18 years) with prior Fontan palliation who underwent treadmill CPET before invasive exercise hemodynamic testing using a supine cycle protocol between November 2018 and April 2023. The median age was 32.2 (IQR 24.1; 37.2) years. The peak heart rate (HR) was 139.7 ± 28.1 beats per minute and the peak oxygen consumption (VO₂) was 19.1 ± 5.7 ml/kg/min (47.4 ± 13.5% predicted). VO₂/HR was directly related to exercise stroke volume index (r = 0.50, p = 0.0002), whereas no association was seen with exercise arterio-mixed venous O₂ content difference (r = 0.14, p = 0.32). Peak HR was inversely related to exercise pulmonary artery (PA) pressures (r = -0.61, p <0.0001) and PA wedge pressures (PAWP) (r = -0.61, p <0.0001). Moreover, %predicted VO₂ was inversely related to exercise PA pressures (r = -0.50, p <0.0001) and PAWP (r = -0.55, p <0.0001). Peak VO₂ ≤19.1 ml/kg/min had a sensitivity of 81% and a specificity of 76% (area under the curve 0.82) for predicting a ΔPAWP/ΔQs ratio >2 mmHg/L/min and/or a ΔPA/ΔQp >3 mmHg/L/min, whereas a predicted peak VO₂ ≤48% had a sensitivity of 74% and a specificity of 81% (area under the curve 0.79) for the same parameters. In summary, lower peak HR and peak VO₂ were associated with higher exercise PAWP and PA pressure. Peak VO₂ ≤48% predicted provided the optimal cutoff for predicting increased indexed exercise PAWP or PA pressures; therefore, low peak VO₂ should alert clinicians of abnormal underlying hemodynamics.