Schiavone Nicole K, Elkins Christopher J, McElhinney Doff B, Eaton John K, Marsden Alison L
Mechanical Engineering, Stanford University, Stanford, CA, USA.
Cardiothoracic Surgery, Stanford University, Stanford, CA, USA.
Cardiovasc Eng Technol. 2021 Apr;12(2):215-231. doi: 10.1007/s13239-020-00507-6. Epub 2021 Jan 15.
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.
在美国，先天性心脏缺陷法洛四联症（ToF）每年影响每2500名新生儿中的1名，通常需要在生命早期对右心室流出道（RVOT）进行手术修复，手术技术的差异导致患者之间RVOT解剖结构存在很大差异。随后，通常在青春期或成年早期，患者通常需要手术植入异种移植或同种异体移植肺动脉瓣假体。瓣膜寿命差异很大，原因尚不清楚。
这项工作旨在使用两种3D打印几何结构在体外评估生物人工肺动脉瓣的性能：一种基于11至13岁健康受试者的理想化病例，另一种是瓣膜下游血管直径扩张150%的患病病例。每种几何结构都研究了两种瓣膜方向：一种瓣膜小叶开口向后，这是天然肺动脉瓣的位置，另一种瓣膜小叶开口向前。
使用4D流动MRI在生理模型中获得了完整的三维、三分量、相位平均速度场。RVOT几何结构和瓣膜方向之间的流动特征，特别是涡流形成和逆流区域，存在显著差异。在所有情况下，流向速度都存在明显的不对称，而患病几何结构在径向流中产生了额外的不对称。定量积分指标表明，患病几何结构在旋转方向上二次流强度和再循环增加。
本研究中阐述的几何结构和方向对生物人工瓣膜血流动力学的复合影响可能对瓣膜的长期性能产生关键影响。
