Circumferential and longitudinal cyclic strain of the human thoracic aorta: Age-related changes

Objective: We developed a novel method using anatomic markers along the thoracic aorta to accurately quantify longitudinal and circumferential cyclic strain in nondiseased thoracic aortas during the cardiac cycle and to compute age-related changes of the human thoracic aorta. Methods: Changes in thoracic aorta cyclic strains were quantified using cardiac-gated computed tomography image data of 14 patients (aged 35 to 80 years) with no visible aortic pathology (aneurysms or dissection). We measured the diameter and circumferential cyclic strain in the arch and descending thoracic aorta (DTA), the longitudinal cyclic strain along the DTA, and changes in arch length and motion of the ascending aorta relative to the DTA. Diameters were computed distal to the left coronary artery, proximal and distal to the brachiocephalic trunk, and distal to the left common carotid, left subclavian, and the first and seventh intercostal arteries. Cyclic strains were computed using the Green-Lagrange strain tensor. Arch length was defined along the vessel centerline from the left coronary artery to the first intercostal artery. The length of the DTA was defined along the vessel centerline from the first to seventh intercostal artery. Longitudinal cyclic strain was quantified as the difference between the systolic and diastolic DTA lengths divided by the diastolic DTA length. Comparisons were made between seven younger (age, 41 7 years; 5 men) and seven older (age, 68 6 years; 5 men) patients. Results: The average increase of diameters of the thoracic aorta was 14% with age from the younger to the older (mean age, 41 vs 68 years) group. The average circumferential cyclic strain of the thoracic aorta decreased by 55% with age from the younger to the older group. The longitudinal cyclic strain decreased with age by 50% from the younger to older group (2.0% +/- 0.4% vs 1.0% +/- 1%, P = .03). The arch length increased by 14% with age from the younger to the older group (134 +/- 17 mm vs 152 +/- 10 mm, P = .03). Conclusions: The thoracic aorta enlarges circumferentially and axially and deforms significantly less in the circumferential and longitudinal directions with increasing age. To our knowledge, this is the first quantitative description of in vivo longitudinal cyclic strain and length changes for the human thoracic aorta, creating a foundation for standards in reporting data related to in vivo deformation and may have significant implications in endoaortic device design, testing, and stability. (J Vase Surg 2009;49:1029-36.) Clinical Relevance: Aortic aneurysms remain the 13th leading cause of death in Western countries, with all incidence of 12.7 cases per 100,000 for thoracic aortic aneurysms (TAA). The ascending aorta is the most common location for TAA formation, followed by the descending thoracic aorta and the arch. In contrast to the considerable data that have been obtained on the biomechanical environment of the abdominal aorta, relatively little is known about the thoracic aorta, healthy or diseased. Wall motion and force data are lacking, which affects the design and testing of stent grafts that are used to treat TAA.