Histopathological and biomechanical properties of the aortic wall in 2 patients with chronic type A aortic dissection.

Type A aortic dissection is an acute condition that requires urgent surgical intervention. However, in a subset of patients, aortic dissections go undiagnosed and become chronic, thereby allowing the dissected wall to undergo a distinct remodeling process from that of the surrounding intact wall. Here, we observe the biomechanical and histological changes in the aortic wall of two patients with chronic Type A aortic dissection. Partial or complete disruption of the elastic structure of the medial layer was observed in the dissected wall of both patients; however, aortic stiffness in the region of dissection covaried with a change in collagen content. A ~50% increase in viscous energy loss was observed in the region of dissection of both patients which suggests an impaired elastic recoil and Windkessel function of the proximal aorta. MMP expression (2 and 9) differed between the dissected and intact wall and was distinct between the two patients. Our observations suggest that an active remodeling process occurs in the dissected aortic wall resulting in a vastly different biomechanical behavior.