Role of aortic root motion in the pathogenesis of aortic dissection

Background - The downward movement of the aortic root during the cardiac cycle may be responsible for producing the circumferential tear observed in aortic dissections. Methods and Results - Contrast injections were investigated in 40 cardiac patients, and a finite element model of the aortic root, arch, and branches of the arch was built to assess the influence of aortic root displacement and pressure on the aortic wall stress. The axial displacement of the aortic root ranged from 0 to 14 mm. It was increased in patients with aortic insufficiency ( 22 +/- 13% of the sino-tubular junction diameter versus 12 +/- 9%) and reduced in patients with hypokinesis of the left ventricle ( 10 +/- 9% of sino-tubular junction versus 17 +/- 12%). The largest stress increase due to aortic root displacement was found approximately 2 cm above the sino- tubular junction, where the longitudinal stress increased by 50% to 0.32 Nmm(-2) when 8.9-mm axial displacement was applied in addition to 120-mm Hg luminal pressure. A similar result was observed when the pressure load was increased to 180 mm Hg without axial displacement. Conclusions - Both aortic root displacement and hypertension significantly increase the longitudinal stress in the ascending aorta. For patients with hypertension who are at risk of dissection, aortic root movement may be monitored as an important risk factor.