Effect of impaired vasa vasorum flow on the structure and mechanics of thethoracic aorta: implications for the pathogenesis of aortic dissection

Objective: To investigate the alterations of structure and mechanical prope rties of the aortic wall, resulting from impairment of vasa vasorum Row. Me thods: Eight healthy Landrace pigs were subjected to interruption of vasa v asorum how to the upper segment of their descending thoracic aorta. Under s terile conditions, the periaortic tissue was excised and the contiguous int ercostal arteries were ligated. Ten sham-operated pigs were used as control s. Fifteen days postoperatively, the animals were sacrificed and their uppe r descending thoracic aortas were removed. Histology, and collagen and elas tin content determination by image analysis technique were performed. Mecha nical analysis of aortic strips was carried out with a uniaxial tension dev ice and stress-strain curves were obtained. Results: In contrast to normal aortic walls of the control group, histology of the avascular aortas reveal ed severe ischemic necrosis of the outer media along with abnormal straight ening of the elastin and collagen fibers, without significant collagen and elastin content changes. The borderline between the outer ischemic and inne r non-ischemic media was sharp, and an outset of dissection was observed at this point. Mechanical analysis showed that at the same level of strain, t he ischemic aorta was significantly stiffer at both low (P = 0.03) and high strains (P = 0.003). Conclusions: Impairment of blood supply to the thorac ic aorta leads to abnormal morphology of elastin and collagen fibers of the outer media, resulting in increased aortic stiffness under a wide range of stresses. In the clinical setting, decreased vasa vasorum flew, reportedly occurring in arterial hypertension, may increase the stiffness of the oute r media of the thoracic aorta and produce interlaminar shear stresses, cont ributing to the development of aortic dissection. (C) 2000 Elsevier Science B.V. All rights reserved.