Fontan conduit cross-sectional area and relationship to exercise performance

The synthetic extracardiac (EC) Fontan conduit may become inadequate as patients grow, potentially limiting cardiovascular capacity.

To evaluate the relationship between EC-Fontan conduit cross-sectional area (CSA), indexed to body surface area (BSA), and exercise performance.

A cross-sectional analysis of data from the Fontan Outcomes Registry using Clinical Examinations (FORCE) registry was performed. Patients with EC-Fontan anatomy who underwent cardiovascular magnetic resonance imaging (CMR) and cardiopulmonary exercise testing (CPET) within 1 year of each other were analyzed. Median length-averaged and minimum Fontan CSAs were measured using three-dimensional (3D) segmentation and indexed to BSA. The primary outcome was percent predicted peak VO₂ (ppVO₂) on maximal effort CPET. Multivariable linear regression models assessed associations between Fontan CSA/BSA and ppVO₂, adjusting for known predictors of ppVO₂ in Fontan patients.

Of the 493 patients with an EC Fontan and with time-matched CMR and EST, 324 had technically adequate 3D imaging for Fontan conduit measurements and an appropriately documented maximal effort excercise stress test (EST). CMRs occurred at median age of 15 years old and median time of 11 years after Fontan surgery. The median length-averaged and minimum Fontan CSA were 268 mm² (IQR 227-309mm²) and 229 mm² (IQR 194-273mm²), respectively. After adjusting for known predictors of ppVO2 in Fontan patients, both minimum and length-averaged Fontan CSA/BSA were positively associated with ppVO2, such that each mm²/m² increase in minimum CSA/BSA was associated with a 0.08% increase in ppVO2 (p<0.001) or each mm²/m² increase length-averaged CSA/BSA was associated with a 0.07% increase in ppVO2 (p<0.001). Fontan CSA/BSA was not significantly associated with cardiac function measures at rest, including ejection fraction and cardiac output.

Smaller EC-Fontan CSA/BSA is independently associated with reduced exercise capacity after controlling for other known predictors of exercise performance.