Biomechanics of the Ascending Thoracic Aorta: A Clinical Perspective on Engineering Data

Aneurysms of the ascending thoracic aorta often require prophylactic surgical intervention to resect and replace the aortic wall with a synthetic graft to avoid the risk of dissection or rupture. The main criterion for surgical intervention is the size of the aneurysm, with elective surgery recommended with a maximal aortic diameter of 4.2-5.5 cm depending on valve type and other patient risk factors. Although the risk of dissection and rupture increases with the size of aneurysm, different pathologies, including aortic valve phenotype and connective tissue disorders uniquely influence the mechanical dysfunction of the aortic wall. Dissection and rupture are mechanical modes of failure caused by an inability of the tissue to withstand local tissue stresses. Tensile testing of aortic tissues, therefore, has been used to reveal the mechanical parameters of diseased and healthy tissues to better characterize the mechanical function of aortic tissues in different patient groups. In this review, we highlight the principles and methods of ex vivo tensile analysis as well as the composition and structural properties that contribute to the mechanical behaviour of the ascending aorta. We also present a clinically oriented description of mechanical testing along with insight into the characterization of aneurysm. Finally, we highlight recent advances in echocardiography, computer tomographic angiography, and magnetic resonance angiography that have the potential to measure biomechanical properties noninvasively and therefore help select aortas at risk.