Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway.
Haukeland University Hospital, Department of Heart Disease, Bergen, Norway; Institute of Clinical Science, University of Bergen, Bergen, Norway.
Acta Biomater. 2023 Jul 1;164:269-281. doi: 10.1016/j.actbio.2023.03.029. Epub 2023 Mar 31.
Degenerative mitral valve disease is the main cause of primary mitral regurgitation with two phenotypes: fibroelastic deficiency (FED) often with localized myxomatous degeneration and diffuse myxomatous degeneration or Barlow's disease. Myxomatous degeneration disrupts the microstructure of the mitral valve leaflets, particularly the collagen fibers, which affects the mechanical behavior of the leaflets. The present study uses biaxial mechanical tests and second harmonic generation microscopy to examine the mechanical behavior of Barlow and FED tissue. Three tissue samples were harvested from a FED patient and one sample is from a Barlow patient. Then we use an appropriate constitutive model by excluding the collagen fibers under compression. Finally, we built an FE model based on the echocardiography of patients diagnosed with FED and Barlow and the characterized material model and collagen fiber orientation. The Barlow sample and the FED sample from the most affected segment showed different mechanical behavior and collagen structure compared to the other two FED samples. The FE model showed very good agreement with echocardiography with 2.02±1.8 mm and 1.05±0.79 mm point-to-mesh distance errors for Barlow and FED patients, respectively. It has also been shown that the exclusion of collagen fibers under compression provides versatility for the material model; it behaves stiff in the belly region, preventing excessive bulging, while it behaves very softly in the commissures to facilitate folding. STATEMENT OF SIGNIFICANCE: This study quantifies for the first time the collagen microstructure and mechanical behavior of degenerative mitral valve (DMV) leaflets. These data will then be used for the first disease-specific finite element (FE) model of DMV. While current surgical repair of DMV is based on surgical experience, FE modeling has the potential to support decision-making and make outcomes predictable. We adopt a constitutive model to exclude collagen fiber under compressions, an important consideration when modeling the mitral valve, where the leaflets are folded to ensure complete closure. The results of this study provide essential data for understanding the relationship between collagen microstructure and degenerative mitral valve mechanics.
退行性二尖瓣病变是原发性二尖瓣反流的主要原因，有两种表型：纤维弹性缺失（FED）常伴有局灶性黏液样变性和弥漫性黏液样变性或巴洛病。黏液样变性破坏了二尖瓣瓣叶的微观结构，特别是胶原纤维，从而影响瓣叶的力学行为。本研究采用双轴力学试验和二次谐波产生显微镜检查巴洛病和 FED 组织的力学行为。从 FED 患者中采集了三个组织样本，从巴洛病患者中采集了一个组织样本。然后，我们通过排除在压缩下的胶原纤维来使用适当的本构模型。最后，我们基于 FED 和巴洛病患者的超声心动图、特征化的材料模型和胶原纤维取向构建了一个有限元模型。与另外两个 FED 样本相比，巴洛病样本和最受影响节段的 FED 样本显示出不同的力学行为和胶原结构。FE 模型与超声心动图非常吻合，巴洛病和 FED 患者的点到网格距离误差分别为 2.02±1.8mm 和 1.05±0.79mm。结果还表明，在压缩下排除胶原纤维为材料模型提供了多功能性；它在腹部区域表现得很坚硬，防止过度膨出，而在连合处则表现得非常柔软，以方便折叠。意义声明：本研究首次定量研究了退行性二尖瓣（DMV）瓣叶的胶原微观结构和力学行为。这些数据将用于首次针对 DMV 的特定疾病的有限元（FE）模型。虽然目前 DMV 的外科修复是基于外科经验，但 FE 建模有可能支持决策并使结果可预测。我们采用本构模型来排除压缩下的胶原纤维，这是在建模二尖瓣时的一个重要考虑因素，在二尖瓣中，瓣叶折叠以确保完全关闭。这项研究的结果为了解胶原微观结构和退行性二尖瓣力学之间的关系提供了重要数据。
