Biomechanics and clinical implications of Fontan upsizing

The Fontan operation, a palliative procedure for single ventricle patients, has evolved to improve outcomes and reduce complications. While extracardiac conduit (ECC) is favored for its simplicity and potential hemodynamic benefits, concerns arise about conduit size adequacy over time. Undersized ECC conduits may cause hemodynamic inefficiencies and long-term complications, while oversizing can lead to flow disturbances, stagnation, and thrombosis, necessitating surgical revision or upsizing to optimize hemodynamics.

The study aimed to predict the impact of upsizing by developing a patient-specific workflow using cardiac magnetic resonance-based imaging and computational fluid dynamics to assess Fontan hemodynamic changes and determine the most optimal conduit size.

We simulated upsizing in patient-specific models, computing reduction in power loss (PL), and analyzed pressure gradients, wall shear stress (WSS), and other local flow dynamic parameters such as vorticity and viscous dissipation that influence PL in a Fontan. Additionally, we quantified the impact of upsizing on hepatic flow distribution (HFD).

Across the patient cohort, upsizing resulted in a PL reduction of 16 %-63 %, with the greatest reduction observed in patients with the smallest pre-existing conduit sizes (14 mm). The optimal conduit size for minimizing PL was highly patient-specific. For instance, a 20 mm conduit reduced PL by 63 % in one patient, while another patient showed 16 % reduction with upsizing. Pressure gradients decreased by 15 %-35 %, correlating with the reduction in PL, while WSS decreased consistently with upsizing. Vorticity and viscous dissipation exhibited more variability but followed the overall trend of reduced PL. HFD changes were modest with a maximum variation of 30 %.

Our findings underscore the importance of individualized approaches in Fontan conduit upsizing. CFD-based quantitative evaluations of PL, pressure gradients, HFD, and WSS can guide optimal conduit sizing, improving long-term outcomes for patients.