Department of Cardiothoracic Surgery, Hygeia Medical Center, Athens, Greece.
Laboratory of Biomechanics, Center of Clinical, Experimental Surgery, and Translational Research, Biomedical Research Foundation of the Academy of Athens, Athens, Greece.
Ann Thorac Surg. 2018 Dec;106(6):1692-1701. doi: 10.1016/j.athoracsur.2018.05.071. Epub 2018 Jun 30.
Previous studies have not examined the participation of intimal, medial, and adventitial layers in providing mechanical strength to the ascending thoracic aortic aneurysm (ATAA) wall compared with the nonaneurysmal aorta. In this study we compared the mechanical properties of intact wall and its layers among ATAAs and nonaneurysmal aortas, with explicit consideration of the effects of valve morphology; that is, bicuspid aortic valve (BAV) versus tricuspid aortic valve (TAV), and aortic quadrant.
Whole ATAAs were taken from patients undergoing elective repair and nonaneurysmal aortas from age-matched autopsy subjects. These were cut into 2 circumferential and longitudinal tissue strips for the intact wall and its layers per quadrant, permitting examination of the aortic wall as a multilayered structure. Tissue underwent tensile testing for determination of failure properties.
Intact wall and layer-specific failure stretches (ie, extensibilities) were significantly greater in nonaneurysmal and BAV-ATAA than in TAV-ATAA, unaccounted for by elastin/collagen content changes. Intact wall failure stress (ie, strength) was significantly greater in BAV-ATAA than in TAV-ATAA, in analogy with medial failure stress. Failure stress and stretch associated negatively with age in most subject groups, layers, and intact wall, but failure stretch correlated positively with residual stretch (ie, structural bonds between layers).
No mechanical vulnerability of BAV-ATAA was found, corroborating current conservative guidelines regarding the management of bicuspid aortopathy. Weakening and added vulnerability was found in patients with valvular deficiency, aortic root aneurysm, hypertension, and hyperlipidemia. Aging led to increased susceptibility to dissection initiation or full rupture, or both, in both patient classes.
既往研究并未比较胸主动脉瘤（ATAA）与非动脉瘤主动脉的内膜、中膜和外膜在提供升主动脉机械强度方面的作用。本研究旨在比较不同主动脉瓣形态（二叶式主动脉瓣[BAV]与三叶式主动脉瓣[TAV]）和主动脉象限条件下，完整主动脉壁及其各层的机械特性，并明确考虑瓣膜形态的影响。
本研究纳入择期行主动脉修复术的 ATAA 患者的全主动脉段和年龄匹配的尸检主动脉段。将主动脉段按象限切取 2 个环向和纵向组织条带，以研究主动脉壁的多层结构。对组织条带进行拉伸试验以测定失效特性。
非动脉瘤和 BAV-ATAA 的完整主动脉壁及其各层的失效延伸率（即延展性）明显大于 TAV-ATAA，这与弹力蛋白/胶原含量变化无关。BAV-ATAA 的完整主动脉壁失效强度（即强度）明显大于 TAV-ATAA，与中膜失效强度相似。失效强度和延伸率与大多数患者群体、各层和完整主动脉壁的年龄呈负相关，但失效延伸率与残余延伸率（即各层之间的结构键）呈正相关。
本研究未发现 BAV-ATAA 的机械脆弱性，这与当前关于二叶式主动脉瓣病变处理的保守指南一致。瓣叶发育不全、主动脉根部瘤、高血压和高脂血症患者的主动脉壁存在弱化和易损性增加。衰老导致两患者群体均更易发生夹层起始或完全破裂，或两者皆有。
