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The congenital heart defect Tetralogy of Fallot (ToF) affects 1 in 2500 newborns annually in the US and typically requires surgical repair of the right ventricular outflow tract (RVOT) early in life, with variations in surgical technique leading to large disparities in RVOT anatomy among patients. Subsequently, often in adolescence or early adulthood, patients usually require surgical placement of a xenograft or allograft pulmonary valve prosthesis. Valve longevity is highly variable for reasons that remain poorly understood. This work aims to assess the performance of bioprosthetic pulmonary valves in vitro using two 3D printed geometries: an idealized case based on healthy subjects aged 11 to 13 years and a diseased case with a 150% dilation in vessel diameter downstream of the valve. Each geometry was studied with two valve orientations: one with a valve leaflet opening posterior, which is the native pulmonary valve position, and one with a valve leaflet opening anterior. Full three-dimensional, three-component, phase-averaged velocity fields were obtained in the physiological models using 4D flow MRI. Flow features, particularly vortex formation and reversed flow regions, differed significantly between the RVOT geometries and valve orientations. Pronounced asymmetry in streamwise velocity was present in all cases, while the diseased geometry produced additional asymmetry in radial flows. Quantitative integral metrics demonstrated increased secondary flow strength and recirculation in the rotated orientation for the diseased geometry. The compound effects of geometry and orientation on bioprosthetic valve hemodynamics illustrated in this study could have a crucial impact on long-term valve performance.

Introduction: Aortic dilation and aneurysm formation is common in patients with a bicuspid aortic valve. Hemodynamics and genetics are both believed to cause dilation, but the relative contributions remain controversial. Further, retrospective studies assess hemodynamics when dilation has already set in. We simulate flows through a tricuspid and three bicuspid aortic valves and study their hemodynamics from a baseline non-dilated aorta. Hypothesis: We hypothesize that the bicuspid phenotype determines flow in the ascending aortic, and high velocity jets will correlate with known regions of dilation in patients with bicuspid valves. Methods: Using methods we recently developed, we constructed a tricuspid valve and bicuspid valves with left/right (LR), right/non (RN) and non/left (NL) coronary cusp fusion. To isolate the effect of leaflet fusion phenotype, we use one healthy, patient-specific aortic geometry throughout. Fluid-structure interaction simulations were performed. Results: Dramatic differences in flow occur between all cases. The tricuspid case shows a relatively uniform flow profile, velocities of ~200cm/s, normalized streamwise momentum 300cm/s, normalized streamwise momentum >2.0, normalized tangential flow strength >1.0, >50% transient reverse flow and sustained pressure gradients >18 mmHg. With LR fusion, the jet hugs the outer curvature of the aorta from the sinotubular junction through the ascending aorta. With RN fusion, the jet moves from the inner to outer curvature of the aorta. Conclusions: With LR and RN cusp fusion, high flow rate jets occur at regions that generally correlate with dilation in prior studies, suggesting that hemodynamic factors alone may be sufficient to cause aortic dilation. This hypothesis should be tested in an animal model.

Introduction: Tetralogy of Fallot (ToF) typically requires surgical repair of the right ventricular outflow tract (RVOT) and subsequent placement of an artificial pulmonary valve. Bioprosthetic valve longevity is highly variable and there is currently little understanding of what hemodynamic factors may lead to early valve dysfunction. Hypothesis: We hypothesize that cardiac output and valve orientation impact the performance of bioprosthetic valves by affecting blood flow patterns in the RVOT. Methods: We analyzed hemodynamics in a 3D printed ToF anatomy model in a physiological flow loop. A 25mm surgical valve was implanted in the model at two orientations: native and rotated 180 degrees. Full 3D, three-component, phase-averaged velocity fields were obtained over the cardiac cycle using 4D flow MRI at cardiac outputs of 2, 3.5, and 5 L/min. We acquired images of valve leaflet motion at 1500Hz. The 4D flow MRI and high-speed camera experiments were run identically, allowing us to examine the relationship between flow fields and leaflet motion. Results: The full velocity fields from the MRI scans revealed key differences among cases in flow features including location of reverse flow regions, systolic jet shape, and asymmetry local to the valve. At 2 L/min, the forward flow through the jet was more asymmetric compared to the other cases and a strong vortex formed, indicating a region of recirculation. With the rotated valve orientation, the 2 L/min case also produced a unique pattern as flow was washed from the RVOT inner curve back toward the center of the valve (Fig 1). Leaflet behavior during systole varied with cardiac output as well, as higher frequency flutter was observed at 5 L/min and the effective valve orifice area was decreased by 8.5% at 2 L/min compared to 5 L/min. Conclusions: We observed key differences in flow patterns and leaflet motion due to cardiac output and valve orientation that could impact leaflet loading and fatigue and long-term valve function.