Effect of aneurysm on the tensile strength and biomechanical behavior of the ascending thoracic aorta

Background. Rupture of an ascending thoracic aortic aneurysm (ATAA), which is associated with significant mortality, occurs when the mechanical forces acting on the aneurysm exceed the strength of the degenerated aortic wall. The purpose of this study was to evaluate changes in biomechanical properties of the aortic wall related to ATAA formation. Methods. Ascending thoracic aortic aneurysm tissue was obtained from surgery; control (nonaneurysmal) aorta was obtained from autopsy. Tissue strips with longitudinal (LONG) or circumferential (CIRC) orientation were stretched to failure. Maximum tissue stiffness and tensile strength were determined from plots of stress (normalized force) versus strain (normalized deformation). Student's t test was used for all comparisons. Results. Tensile strength of LONG (n(ATAA) = 17, n(control) = 7) and CIRC (n(ATAA) = 23, = 7) ATAA specimens were 29% and 34% less than that of control tissue, respectively (p < 0.05). Maximum tissue stiffness was 72% stiffer for LONG ATAA (P < 0.05) and 44% stiffer for CIRC ATAA (P = 0.06) than for control tissue, respectively. Conclusions. The data suggest that ATAA formation is associated with stiffening and weakening of the aortic wall, which may potentiate aneurysm rupture. (C) 2003 by The Society of Thoracic Surgeons.