The area-preserving 12-mm Y-graft is a promising modification of the Fontan procedure that should be clinically evaluated. Further work is needed to correlate our performance metrics with clinical outcomes, including exercise intolerance, incidence of protein-losing enteropathy, and thrombus formation.

Background: Not all Fontan patients are “equal” despite similar hemodynamics using current diagnostic modalities. Recent advances in imaging and computational fluid dynamics simulations (CFDS) enable the evaluation of both previously unmeasurable parameters (e.g. efficiency (either at rest or with exercise)) and in patient-specific scenarios. We hypothesize CFDS at rest and simulated exercise will demonstrate large differences in pressure and efficiency among Fontan patients. Methods: Using MRI-obtained anatomy and flow, time-dependent, 3-D simulations were performed using a custom finite element solver in 4 patient-specific Fontan models. Flow features, pressure, and energy efficiency were analyzed at rest and with increasing flow to simulate light, moderate and heavy exercise. Resistance boundary conditions enabled simulation at physiologic pressures and vasodilation with “exercise.” Results: Large variations in geometry, efficiency (96 – 87% at rest, 90–75% with exercise) and mean SVC pressure were seen (figure ). Efficiency did not correlate with Fontan pressures and did not decrease linearly with increased exercise. The most efficient among these four particular patients was a traditional t-junction connection though it had one of the highest SVC pressures. Conclusions: Geometries, efficiency and pressure levels vary dramatically among Fontan patients. Patients may have similar hemodynamic performance at rest, but large differences in both efficiency and pressure can be demonstrated during simulated exercise. CFDS and determination of patient specific efficiency may provide an additional tool for risk stratification among patients.

Hypoplastic left heart syndrome is a congenital heart defect that occurs in 20 per 100,000 live births. Patients are born with severe underdevelopment of the left side of the heart which, if left untreated, is uniformly fatal. A series of operations is performed, including a cavopulmonary (Glenn) shunt and total cavopulmonary connection (Fontan procedure), which connect the superior (SVC) and inferior vena cavae (IVC) respectively in an end-to-side fashion to the left (LPA) and right pulmonary arteries (RPA), resulting in a T-shaped junction. This bypasses the heart on the venous side as blood flows from the IVC and SVC directly into the pulmonary arteries. Early survival rates following the Fontan are as high as 90%. However, these figures drop to 60% survival after 10 years [1], and most patients exhibit diminished exercise capacity.