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J Thorac Cardiovasc Surg 2009;137:101-109
© 2009 The American Association for Thoracic Surgery

Acquired Cardiovascular Disease

Ascending thoracic aortic aneurysms are associated with compositional remodeling and vessel stiffening but not weakening in age-matched subjects

^a Laboratory of Experimental Surgery and Surgical Research, School of Medicine, University of Athens, Athens, Greece
^d Department of Forensic Medicine and Toxicology, School of Medicine, University of Athens, Athens, Greece
^b Department of Cardiothoracic Surgery, Athens Medical Center, Athens, Greece
^c Laboratory of Biomechanics, Foundation of Biomedical Research, Academy of Athens, Athens, Greece

Received for publication March 24, 2008; revisions received May 13, 2008; accepted for publication July 5, 2008.

^_* Address for reprints: Dimitrios P. Sokolis, PhD, 35 Lefkados St, Athens 15354, Greece. (Email: DimitrisSokolis{at}ath.forthnet.gr).

Objective: We sought to examine in age-matched subjects the biomechanical and compositional remodeling associated with ascending thoracic aortic aneurysms according to region and direction.

Methods: Whole, fresh, degenerative ascending thoracic aortic aneurysms were taken from 26 patients (age, 69 ± 2 years; maximum aortic diameter, 5.9 ± 0.3 cm) during elective surgical intervention, and 15 nonaneurysmal ascending thoracic aortas were obtained during autopsies (age, 66 ± 3 years; maximum aortic diameter, 3.3 ± 0.2 cm). These were cut into anterior, right lateral, posterior, and left lateral regions, and circumferentially and longitudinally oriented specimens were prepared. The aortic specimens were submitted to histomorphometric and biomechanical studies, including measurement of failure strain (ie, extensibility), failure stress (ie, strength), and peak elastic modulus (ie, stiffness).

Results: Wall elastin, but not collagen content, decreased in aneurysmal specimens, displaying lower wall thickness and failure strain, higher peak elastic modulus, and equal failure stress than control specimens in the majority of regions and directions. Similar differences were noted in pooled data from all regions. Regional variations in mechanical parameters were mostly found in longitudinally oriented tissue. Circumferential specimens showed higher failure stress and peak elastic modulus but equal failure strain than longitudinal specimens.

Conclusions: Our findings contradict previous studies on ascending thoracic and abdominal aortic aneurysms, suggesting that the former might not cause weakening but rather only stiffening and reduction in tissue extensibility and elastin content. Marked heterogeneity was evident in healthy and aneurysmal aortas. The present data offer insight into the pathogenesis of aneurysm dissection. Information on directional and regional variations is pertinent because dissections develop circumferentially and bulging preferentially occurs in the anterior region.