Minor aortic injury may be at risk of progression from uncontrolled shear stress: An in-vitro model demonstrates aortic lesion expansion

Abstract

Background Non-operative management is considered appropriate treatment for minor aortic injury, while blood pressure and anti-impulse therapy are routinely utilized to prevent higher grade aortic injury progression. However, a universal medical regimen for low grade intimal injuries has not been adopted and risks of low-grade injury progression not well described. The purpose of this study is to determine the fracture response of minimally damaged aortic tissue to the various applied forces. Our hypothesis is that internal circumferential shear within the aortic wall is a primary fracture mode. This knowledge may help guide clinical management to minimize risk of injury progression, including instituting standard medical regimens with anti-impulse therapy and β-blockade for such minor injuries. Methods Human ascending aortic tissue was obtained after aneurysm repair or heart transplant, stored at 4°C and tested within 48 hours. Minor injury was modeled with a small radial notch on the luminal aspect of aortic rings, circumferentially expanded under video acquisition and analyzed to determine lesion propagation. Results 15 rings were obtained from 8 aneurysmal and 4 healthy aortas. All specimens demonstrated circumferential crack propagation. Propagation was longer (8.02 ± 5.92 mm vs 2.70 ± 1.23 mm) and initiation of crack propagation earlier in aneurysmal tissue (1.54 ± 0.17 versus 1.90 ± 0.17 times initial diameter). Conclusions Dilation of minimally injured aortic rings is associated with lesion expansion and injury progression in all specimens including healthy and aneurysmal tissue. This propagation illustrates the mechanical response to increased levels of internal shear, compromising structural integrity and increasing risk of aortic rupture in all injured aortas. Shear forces are routinely generated through normal circumferential aortic expansion with each pulsation, the magnitude of these forces determined by pulse and blood pressure. This suggests minor aortic injuries are not trivial and strategies to reduce shear stress be implemented in all such patients without contraindications to β- blockers.