Wisneski Andrew D, Mookhoek Aart, Chitsaz Sam, Hope Michael D, Guccione Julius M, Ge Liang, Tseng Elaine E
Department of Surgery, University of California San Francisco and San Francisco VA Medical Center, San Francisco, CA, USA.
Department of Cardiothoracic Surgery, Erasmus University Medical Center, Rotterdam, Netherlands.
J Heart Valve Dis. 2015 Nov;24(6):714-721.
Elective repair of bicuspid aortic valve (BAV)-associated ascending thoracic aortic aneurysm (aTAA) is recommended at lower size limits than tricuspid aortic valve (TAV)-associated aTAA. Rupture/dissection can occur when wall stress exceeds wall strength. Previously, a validated computational method was developed for determining aTAA wall stress, but to date this method has not applied to a patient-specific BAV aTAA. The study aim was to develop a patient-specific BAV aTAA computational model to determine regional wall stress, using the required zero-pressure geometry, wall thickness, material properties, and residual stress.
A BAV aTAA specimen was excised intact during elective repair, and zero-pressure geometry generated using micro-computed tomography. Residual stress was determined from the aTAA opening angle. aTAA material properties determined using biaxial stretch testing were incorporated into an Ogden hyperelastic model. Finite element analyses (FEAs) were performed in LS-DYNA to determine wall stress distribution and magnitudes at systemic pressure.
The left aTAA region had the highest stiffness, followed by the right, and then anterior/posterior walls, suggesting regional variability in mechanical properties. During systole, the mean principal wall stresses were 108.8 kPa (circumferential) and 59.9 kPa (longitudinal), while peak wall stresses were 789.4 kPa (circumferential) and 618.8 kPa (longitudinal). Elevated wall stress pockets were seen in anatomic left aTAA regions.
To the present authors' knowledge, this was the first patient-specific BAV aTAA model based on surgical specimens to be developed. Surgical specimens serve as the 'gold standard' for determining wall stress to validate models based on in-vivo imaging data alone. Regions of maximal wall stress may indicate sites most prone to rupture, and are crucial for evaluating rupture risk based on the wall stress/strength relationship.
与三尖瓣主动脉瓣（TAV）相关的升主动脉瘤（aTAA）相比，对于二叶式主动脉瓣（BAV）相关的aTAA，建议在较小尺寸界限时进行择期修复。当壁应力超过壁强度时，可能会发生破裂/夹层。此前，已开发出一种经过验证的计算方法来确定aTAA壁应力，但迄今为止，该方法尚未应用于特定患者的BAV aTAA。本研究的目的是开发一种特定患者的BAV aTAA计算模型，以使用所需的零压力几何形状、壁厚、材料特性和残余应力来确定局部壁应力。
在择期修复期间完整切除一个BAV aTAA标本，并使用微型计算机断层扫描生成零压力几何形状。根据aTAA开口角度确定残余应力。将使用双轴拉伸试验确定的aTAA材料特性纳入Ogden超弹性模型。在LS-DYNA中进行有限元分析（FEA），以确定全身压力下的壁应力分布和大小。
左aTAA区域刚度最高，其次是右侧，然后是前/后壁，表明力学性能存在区域差异。在收缩期，平均主壁应力为108.8 kPa（周向）和59.9 kPa（纵向），而壁应力峰值为789.4 kPa（周向）和618.8 kPa（纵向）。在解剖学上的左aTAA区域可见壁应力升高区。
据作者所知，这是首个基于手术标本开发的特定患者BAV aTAA模型。手术标本是确定壁应力的“金标准”，用于仅基于体内成像数据验证模型。最大壁应力区域可能表明最易破裂的部位，对于基于壁应力/强度关系评估破裂风险至关重要。
