Regional Failure Properties of Ex-Vivo Ascending Thoracic Aortic Aneurysms

Abstract

Acute type A aortic dissection is a life-threatening event that often occurs in the setting of ascending thoracic aortic aneurysms (aTAA). Though diameter is the standard criterion for elective aTAA repair, it is far from optimal. Biomechanical testing of aTAA failure properties can be used to elucidate factors contributing to dissection. We performed uniaxial failure testing on 32 surgical aTAA specimens from patients who underwent elective repair from 2014 to 2021. Regional and layer-specific wall failure stresses were calculated for each aTAA specimen. We compared failure stress between wall layers where specimens were divided into adventitial-medial and intimal-medial layers, as well as circumferential vs longitudinal directions using the Mann-Whitney U test. Differences across anatomical regions were evaluated with the Kruskal-Wallis test. Full thickness aTAA wall was stronger in the circumferential than longitudinal direction (546 kPa vs 317 kPa, p = 0.003). Adventitial-medial layers were stronger than intimal-medial layers in circumferential (734 kPa vs 476 kPa, p = 0.008) and longitudinal directions (562 kPa vs 225 kPa, p = 3.22e-08). Controlling by layer, the posterior region of intimal-medial layers was strongest circumferentially (1,126 kPa, p=0.038). In the adventitial-medial layer, the lateral (outer curvature) region was strongest longitudinally (979 kPa, p=0.002). Longitudinal direction full-thickness failure stress varied across regions, with the strongest segments located laterally (382 kPa, 0.007). Our findings highlight that aTAAs are weaker in the longitudinal direction, partially explaining why intimal tears begin transversely. Regional patterns of layer-specific wall failure could help identify aTAA regions with intrinsic vulnerability to dissection.