Cardiopulmonary exercise testing in Fontan patients: unmasking the secret of Super-Fontans

Abstract Background Exercise capacity is usually reduced in Fontan patients, however there is a subset of patients who have normal exercise capacity and better outcomes, the “Super-Fontans”. The aim of this study was to characterize a cohort of Fontan patients undergoing cardiopulmonary exercise testing (CPET) and identify predictors of better functional capacity. Methods Single center retrospective analysis of consecutive Fontan patients aged >10 years old who underwent CPET, between March 2018 and May 2021. Peak respiratory exchange ratio1.05 defined maximal CPET. Peak VO2 (pVO2) as a percentage of its predicted value was used as reference value to stratify patients in tertiles. Patients in 3rd tertile, with a percentage predicted pVO2 superior to 75%, were considered good-performers. Blood tests and transthoracic echocardiogram (TTE) were performed on the same day. Additional data were collected from electronic charts. Results In total, 49 patients were included (mean age 19±7 years old, 67% male) with intra or extracardiac conduit implanted in mean 12±7 years prior to the CPET. The most common primary diagnoses were tricuspid/pulmonary atresia (43%), followed by unbalanced complete AV septal defect (14%) and double inlet left ventricle (14%). 12 patients had a systemic right ventricle. All, except 5 patients, had preserved systolic ventricular function and 37% had moderate to severe AV regurgitation. The majority had normal hemoglobin levels (median 15.6 g/dL), hepatic enzymes (median total bilirubin 0.8 mg/dL), renal function (median creatinine 0.8 mg/dL) and low NT-proBNP (median 122 pg/mL). All patients had maximal CPET, median %VO2 at VT1 was 57% of peak and mean pVO2 was 66±14% of the predicted. Most patients (69%) showed exercise limitation due to cardiovascular cause, followed by O2 desaturation, present in 22% of CPETs. The age of Fontan completion was not associated with functional capacity (p=0.6). The good-performer group comprised 13 patients (27%), all in sinus rhythm, of which 10 were physically active. Compared with the remainder, this group had higher VO2 at VT1 (18.7 vs. 14.6, p=0.01) and VO2 at VT2 (25.9 vs. 22.1, p=0.02), both in mL/kg/min. Also, peak heart rate (% predicted) (90 vs. 81, p=0.03) was higher in this subgroup – fig.1. Conversely, differences on TTE parameters (GLS and AV valve regurgitation) and blood biomarkers were not statistically significant. On multivariable analysis, no single variable predicted better functional capacity. Conclusion In our Fontan cohort, most patients had reduced exercise capacity, largely due to cardiovascular dysfunction. However, “Super-Fontans” stood out as they had a higher anaerobic threshold illustrating their better physical condition. These findings highlight the role of regular physical activity in Fontan patients as a cornerstone for better functional capacity. Funding Acknowledgement Type of funding sources: None.