Local Hemodynamic Differences Between Commercially Available Y-Grafts and Traditional Fontan Baffles Under Simulated Exercise Conditions: Implications for Exercise Tolerance.

Fontan completion, resulting in a total cavopulmonary connection (TCPC), is accomplished using a lateral tunnel (LT), extracardiac conduit (ECC), or recently a bifurcated Y-graft. The local energetic differences between these graft types have not been substantially analyzed under exercise conditions. The present study evaluates the energetic performance of Y-grafts under simulated exercise conditions, compares their performance to the previous LT/ECC Fontan options, and discusses implications for exercise tolerance and hemodynamic predictability. Twenty Y-graft and 20 LT/ECC patients were analyzed. TCPC anatomies and flow waveforms were reconstructed using patient-specific cardiac magnetic resonance (CMR) images and phase-contrast CMR. Computational fluid dynamics simulations were performed to quantify indexed power loss (iPL) under both resting and simulated exercise conditions. Comparisons between graft types were investigated. iPL was significantly higher (p < 0.01) for Y-grafts at all activity levels. No significant interaction effects were observed between graft type and activity level. iPL at rest was strongly correlated (r  = 0.97, p < 0.001) with iPL at moderate exercise for Y-grafts, but less so for the LT/ECC cohort (r  = 0.66, p < 0.001). Similar results were seen for intense exercise, with a strong correlation for Y-grafts (r  = 0.94, p < 0.001) and a moderate correlation for LT/ECC (r  = 0.52, p < 0.001). Commercially available Y-grafts were found to have significantly higher iPL at all activity levels, suggesting worse exercise tolerance than the LT/ECC alternatives. Y-grafts offered impressive hemodynamic predictability which was not seen in the LT/ECC cohort. Our results encourage the further evaluation of an area-preserving Y-graft design to offer both improved energetic performance and hemodynamic predictability. Commercial Y-grafts show worse energetics, but more predictable responses than traditional Fontan connections under simulated exercise conditions. During simulated exercise conditions, commercially available Y-grafts show predictable but inferior energetic performance compared to lateral tunnel and extracardiac conduit Fontan connections, suggesting poorer exercise capacity. If Y-graft use is continued, these results encourage further evaluation of a cross sectional area-preserving Y-graft design as a additional alternative for Fontan completion.