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We describe a 75-year-old woman who underwent right axillary artery cannulation in preparation for reconstruction of the aortic arch and the proximal descending aorta for athesosclerotic aortic aneurysm via a 'clamshell' incision. As soon as cardiopulmonary bypass was established, the ascending aorta and the aortic arch was dissected. The innominate artery was dissected including one-third of its circumferance anteriorly. Arterial perfusion was stopped immediately and the left femoral artery was cannulated to resume CPB. We proceeded with replacement of the ascending aorta, the aortic arch and the proximal descending thoracic aorta with a Dacron branched aortic graft. The patient recovered uneventfully. Arterial blood pressure was equal bilaterally.

Objective: To investigate the alterations of structure and mechanical properties of the aortic wall, resulting from impairment of vasa vasorum flow., Methods: Eight healthy Landrace pigs were subjected to interruption of vasa vasorum flow to the upper segment of their descending thoracic aorta. Under sterile conditions, the periaortic tissue was excised and the contiguous intercostal arteries were ligated. Ten sham-operated pigs were used as controls. Fifteen days postoperatively, the animals were sacrificed and their upper descending thoracic aortas were removed. Histology, and collagen and elastin content determination by image analysis technique were performed. Mechanical analysis of aortic strips was carried out with a uniaxial tension device and stress-strain curves were obtained., Results: In contrast to normal aortic walls of the control group, histology of the avascular aortas revealed severe ischemic necrosis of the outer media along with abnormal straightening of the elastin and collagen fibers, without significant collagen and elastin content changes. The borderline between the outer ischemic and inner 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, the ischemic aorta was significantly stiffer at both low (P=0.03) and high strains (P=0. 003)., Conclusions: Impairment of blood supply to the thoracic 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 flow, reportedly occurring in arterial hypertension, may increase the stiffness of the outer media of the thoracic aorta and produce interlaminar shear stresses, contributing to the development of aortic dissection.