Bicuspid Ascending Aortic Aneurysms Exhibit Increased Dissection Resistance: An Ex Vivo Analysis

In light of the longstanding assumption that ascending thoracic aortic aneurysms (ATAAs) associated with bicuspid aortic valves (BAVs) exhibit greater biomechanical vulnerability than those associated with tricuspid aortic valves (TAVs), we characterized and compared the delamination resistance of BAV- and TAV-ATAAs.

Whole ATAAs were intraoperatively harvested from patients undergoing elective repair. Specimens were sectioned into circumferential and longitudinal strips from all quadrants. Delamination testing, simulating clinical aortic dissection, was performed within the outer media, followed by tensile testing of the resulting strips. Histological analysis assessed the surface roughness of the inner and outer layers along the delamination plane.

A total of 405 specimens from 25 BAV- and 399 from 25 TAV-ATAA patients underwent biomechanical analysis. When comparing the entire cohort plus subgroups matched for age, sex, ATAA diameter, and tissue sampling location, BAV-ATAAs exhibited significantly greater delamination strength across all quadrants than TAV-ATAAs, indicating stronger interlaminar adhesive forces. Histological analysis revealed a rougher peeling surface in BAV-ATAAs, although in only a few quadrants. The left lateral quadrant showed increased resistance, particularly in TAV-ATAAs, suggesting an intrinsic regional feature possibly related to aortic curvature and contributing to the typical localization of dissection. Among BAV subtypes, Sievers type 1 right-left exhibited lower delamination strength than type 1 right-noncoronary, but higher than type 0.

BAV-ATAAs demonstrated greater resistance to dissection propagation than TAV-ATAAs in ex vivo testing. These findings challenge the assumption of intrinsic structural fragility in BAV aortopathy and are consistent with emerging clinical observations.