Wisneski Andrew D, Mookhoek Aart, Chitsaz Sam, Hope Michael D, Guccione Julius M, Ge Liang, Tseng Elaine E
J Heart Valve Dis. 2014 Nov;23(6):765-72.
Rupture/dissection of ascending thoracic aortic aneurysm (aTAA) is a cardiovascular emergency. Elective surgical repair is primarily based on maximum diameter, but complications have occurred under the size limits for surgical intervention. aTAA wall stress may be a better predictor of patient-specific rupture risk, but cannot be directly measured in vivo. The study aim was to develop an aTAA computational model associated with tricuspid aortic valve (TAV) to determine patient-specific wall stresses.
A TAV-associated aTAA was excised intact during surgery. Zero-pressure geometry was generated from microcomputed tomography, and an opening angle was used to calculate residual stress. Material properties determined from stress-strain data were incorporated into an Ogden hyperelastic model. Wall stress distribution and magnitudes at systemic pressure were determined using finite element analyses (FEA) in LS-DYNA.
Regional material property differences were noted: the left aTAA region had a higher stiffness compared to the right, and anterior/posterior walls. During systole, the mean principal wall stresses were 172.0 kPa (circumferential) and 71.9 kPa (longitudinal), while peak wall stresses were 545.1 kPa (circumferential) and 430.1 kPa (longitudinal). Elevated wall stress pockets were seen in anatomic left and right aTAA regions.
A validated computational approach was demonstrated to determine aTAA wall stresses in a patient-specific fashion, taking into account the required zero-stress geometry, wall thickness, material properties and residual stress. Regions of maximal wall stress may indicate the sites most prone to rupture. The creation of a patient-specific aTAA model based on a surgical specimen is necessary to serve as the 'gold standard' for comparing models based on in-vivo data alone. Validated data using the surgical specimen are essential for establishing wall stress and rupture-risk relationships.
升主动脉瘤（aTAA）破裂/夹层是一种心血管急症。择期手术修复主要基于最大直径，但在手术干预的尺寸限制下仍有并发症发生。aTAA壁应力可能是预测个体破裂风险的更好指标，但无法在体内直接测量。本研究的目的是建立一个与三尖瓣主动脉瓣（TAV）相关的aTAA计算模型，以确定个体的壁应力。
手术中完整切除一个与TAV相关的aTAA。通过微型计算机断层扫描生成零压力几何形状，并使用开口角度计算残余应力。根据应力-应变数据确定的材料特性被纳入Ogden超弹性模型。使用LS-DYNA中的有限元分析（FEA）确定系统压力下的壁应力分布和大小。
注意到区域材料特性存在差异：左aTAA区域比右区域以及前/后壁具有更高的刚度。在收缩期，平均主壁应力为172.0 kPa（周向）和71.9 kPa（纵向），而峰值壁应力为545.1 kPa（周向）和430.1 kPa（纵向）。在解剖学上的左、右aTAA区域可见壁应力升高区。
已证明一种经过验证的计算方法能够以个体特异性方式确定aTAA壁应力，同时考虑到所需的零应力几何形状、壁厚、材料特性和残余应力。最大壁应力区域可能指示最易破裂的部位。基于手术标本创建个体特异性aTAA模型对于作为仅基于体内数据的模型的“金标准”至关重要。使用手术标本的验证数据对于建立壁应力与破裂风险关系至关重要。
