Pham Thuy, Kong Fanwei, Martin Caitlin, Wang Qian, Primiano Charles, McKay Raymond, Elefteriades John, Sun Wei
The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Technology Enterprise Park, Room 206, 387 Technology Circle, Atlanta, GA, 30313-2412, USA.
Cardiology Department of Hartford Hospital, Hartford, CT, USA.
Cardiovasc Eng Technol. 2017 Mar;8(1):3-16. doi: 10.1007/s13239-016-0291-9. Epub 2017 Jan 9.
Functional mitral regurgitation (FMR) is a significant complication of left ventricular dysfunction and strongly associated with a poor prognosis. In this study, we developed a patient-specific finite element (FE) model of the mitral apparatus in a FMR patient which included: both leaflets with thickness, annulus, chordae tendineae, and chordae insertions on the leaflets and origins on the papillary muscles. The FE model incorporated human age- and gender-matched anisotropic hyperelastic material properties, and MV closure at systole was simulated. The model was validated by comparing the FE results from valve closure simulation with the in vivo geometry of the MV at systole. It was found that the FE model could not replicate the in vivo MV geometry without the application of tethering pre-tension force in the chordae at diastole. Upon applying the pre-tension force and performing model optimization by adjusting the chordal length, position, and leaflet length, a good agreement between the FE model and the in vivo model was established. Not only were the chordal forces high at both diastole and systole, but the tethering force on the anterior papillary muscle was higher than that of the posterior papillary muscle, which resulted in an asymmetrical gap with a larger orifice area at the anterolateral commissure resulting in MR. The analyses further show that high peak stress and strain were found at the chordal insertions where large chordal tethering forces were found. This study shows that the pre-tension tethering force plays an important role in accurately simulating the MV dynamics in this FMR patient, particularly in quantifying the degree of leaflet coaptation and stress distribution. Due to the complexity of the disease, the patient-specific computational modeling procedure of FMR patients presented should be further evaluated using a large patient cohort. However, this study provides useful insights into the MV biomechanics of a FMR patient, and could serve as a tool to assist in pre-operative planning for MV repair or replacement surgical or interventional procedures.
功能性二尖瓣反流（FMR）是左心室功能障碍的一种重要并发症，且与不良预后密切相关。在本研究中，我们构建了一名FMR患者二尖瓣装置的个体化有限元（FE）模型，该模型包括：具有厚度的两个瓣叶、瓣环、腱索以及腱索在瓣叶上的附着点和在乳头肌上的起始点。该有限元模型纳入了与人类年龄和性别匹配的各向异性超弹性材料特性，并模拟了收缩期二尖瓣关闭过程。通过将瓣膜关闭模拟的有限元结果与收缩期二尖瓣的体内几何形状进行比较，对模型进行了验证。结果发现，在舒张期不施加腱索预张力的情况下，有限元模型无法复制二尖瓣的体内几何形状。在施加预张力并通过调整腱索长度、位置和瓣叶长度进行模型优化后，有限元模型与体内模型之间建立了良好的一致性。不仅舒张期和收缩期的腱索力都很高，而且前乳头肌上的系留力高于后乳头肌，这导致前外侧连合处出现不对称间隙，孔口面积更大，从而导致二尖瓣反流。分析进一步表明，在发现较大腱索系留力的腱索附着点处存在高峰应力和应变。本研究表明，预张力系留力在准确模拟该FMR患者的二尖瓣动力学方面起着重要作用，特别是在量化瓣叶对合程度和应力分布方面。由于该疾病的复杂性，所提出的FMR患者个体化计算建模程序应使用大量患者队列进行进一步评估。然而，本研究为FMR患者的二尖瓣生物力学提供了有用的见解，并可作为辅助二尖瓣修复或置换手术或介入手术术前规划的工具。
