Gross J M, Shu M C, Dai F F, Ellis J, Yoganathan A P
Medtronic Heart Valves, Inc., Irvine, CA 92614, USA.
J Heart Valve Dis. 1996 Nov;5(6):581-90.
During recent clinical trials, the Medtronic Parallel bileaflet heart valve was found to have an unacceptable thrombosis complication rate. As patient- and material-related factors proved negative causes for this outcome, it was hypothesized that the flow fields within the valve's hinge pocket contributed to the thrombus formation.
A microstructural flow analysis within the hinge pocket is presented which uses the techniques of flow visualization, computational fluid dynamics (CFD), and laser Doppler velocimetry (LDV). The application of these techniques towards solving this problem has become possible through (i) the ability to manufacture dimensionally correct 1-X transparent heart valve housings, (ii) advances in CFD technology, and (iii) advances in LDV measurement techniques.
This analysis showed that a vortex was present at the hinge pocket's inflow channel during forward flow and degenerated to a disturbed three-dimensional structure during reverse flow with zones of turbulent shear stress large enough to cause blood cell damage. In addition, multiple zones of flow stagnation and disturbed flow existed along the leaflet's pivot throughout the entire cardiac cycle. It was felt that these complex fluid structures created conditions which resulted in the formation of thrombus within the hinges of the Medtronic Parallel valve. These findings were supported by limited clinical explant data which illustrated early thrombus formation within the Parallel valve's hinge pocket at sites predicted by the analysis.
This study provides, for the first time, an understanding of the detailed flow structures within the hinges of a mechanical heart valve and demonstrates an analysis technique by which future mechanical heart valve designs may be assessed for the potential of thrombus formation within the valve's hinge regions.
在近期的临床试验中，美敦力双叶平行式心脏瓣膜被发现存在不可接受的血栓形成并发症发生率。由于患者和材料相关因素被证明并非导致这一结果的负面原因，因此推测瓣膜铰链腔内的流场促成了血栓形成。
本文介绍了一种针对铰链腔的微观结构流动分析，该分析采用了流动可视化、计算流体动力学（CFD）和激光多普勒测速技术（LDV）。通过以下几点，这些技术得以应用于解决该问题：（i）制造尺寸正确的1-X透明心脏瓣膜外壳的能力；（ii）CFD技术的进步；（iii）LDV测量技术的进步。
该分析表明，正向流动时，在铰链腔的流入通道处存在一个涡流，反向流动时该涡流退化为一个紊乱的三维结构，其湍流剪切应力区域大到足以导致血细胞损伤。此外，在整个心动周期中，沿着瓣叶枢轴存在多个流动停滞和紊乱流动区域。据认为，这些复杂的流体结构创造了导致美敦力双叶平行式瓣膜铰链内形成血栓的条件。有限的临床瓣膜取出数据支持了这些发现，这些数据表明在分析预测的部位，双叶平行式瓣膜的铰链腔内早期形成了血栓。
本研究首次对机械心脏瓣膜铰链内的详细流动结构有了认识，并展示了一种分析技术，通过该技术可评估未来机械心脏瓣膜设计在瓣膜铰链区域形成血栓的可能性。
