Weltert Luca, De Paulis Ruggero, Scaffa Raffaele, Maselli Daniele, Bellisario Alessandro, D'Alessandro Stefano
Cardiac Surgery Department, European Hospital, Rome, Italy.
J Thorac Cardiovasc Surg. 2009 May;137(5):1082-7. doi: 10.1016/j.jtcvs.2008.10.013. Epub 2009 Jan 26.
The Bentall procedure is routinely performed using a straight Dacron graft coupled with a mechanical or a biologic valve. Creation of coronary ostia buttons significantly reduces tension on the coronary anastomoses and consequently the incidence of pseudoaneurysm formation. We sought to evaluate if the use of a specifically designed graft with a sinuslike root portion that bulges out upon pressurization can reduce stress on coronary anastomoses. A finite element computer-assisted stress analysis was used to simulate these 2 different anatomic conditions and to analyze tension in computed tomographic scans obtained from patients operated on with either a straight or a "sinus" graft.
Theoretical models of the procedures with finite element computer-aided design technique were created and tested with the Abaqus Standard Suite, verifying the pattern of stress and strain when a uniform pressure of 200 mm Hg was applied to the model. Next, using SimpleWare SCanIP technology, computed tomographic scans of patients having both procedures were used to obtain finite element mesh models. A uniform pressure of 200 mm Hg was then applied, and the distribution of stress and strain was analyzed.
Von Mises Charts are color-coded, computational, 3-dimensional stress-pattern graphics that show that stress around the coronary ostia in a standard straight graft model is nearly double compared with the model with sinuses (peak stress of 0.4 Mpa for the sinus model and 0.7 Mpa for the traditional straight model). In computed tomographic scan reconstructions, the stress contour is uniformly distributed in the graft with sinuses, and it is highly concentrated around the ostia in the straight graft. Accordingly, higher-peak stress values are registered in the straight configuration (1.8 MPa for the sinus graft and 2.5 MPa for standard graft).
Even though finite elements technique is necessarily a simplification of a real biologic environment, all tests seem to indicate that a standard tubular graft gives a higher stress to coronary sutures. Relieving the stress on the coronary anastomoses by using a graft with preformed sinuses of Valsalva may decrease the incidence of postoperative complications such as bleeding and late pseudoaneurysm formation.
Bentall手术通常使用直的涤纶移植物结合机械瓣膜或生物瓣膜进行。制作冠状动脉开口纽扣可显著降低冠状动脉吻合口的张力，从而降低假性动脉瘤形成的发生率。我们试图评估使用一种专门设计的、在加压时根部呈窦状膨出的移植物是否能减轻冠状动脉吻合口的应力。采用有限元计算机辅助应力分析来模拟这两种不同的解剖条件，并分析从接受直形或“窦状”移植物手术的患者获得的计算机断层扫描中的张力。
使用有限元计算机辅助设计技术创建手术的理论模型，并用Abaqus标准套件进行测试，在模型上施加200 mmHg的均匀压力时验证应力和应变模式。接下来，使用SimpleWare SCanIP技术，对接受这两种手术的患者的计算机断层扫描进行处理，以获得有限元网格模型。然后施加200 mmHg的均匀压力，并分析应力和应变的分布。
冯·米塞斯图表是彩色编码的、计算性的三维应力模式图形，显示标准直形移植物模型中冠状动脉开口周围的应力与有窦状结构的模型相比几乎翻倍（窦状模型的峰值应力为0.4 Mpa，传统直形模型为0.7 Mpa）。在计算机断层扫描重建中，应力轮廓在有窦状结构的移植物中均匀分布，而在直形移植物中则高度集中在开口周围。因此，直形结构中的峰值应力值更高（窦状移植物为1.8 MPa，标准移植物为2.5 MPa）。
尽管有限元技术必然是对真实生物环境的简化，但所有测试似乎都表明，标准管状移植物会给冠状动脉缝合处带来更高的应力。使用带有预成型主动脉窦的移植物减轻冠状动脉吻合口的应力，可能会降低术后并发症如出血和晚期假性动脉瘤形成的发生率。
