A three-dimensional computational study of critical pressures of dissection propagation in the aorta.

Aortic dissection is a life-threatening disease with high mortality rates. The degradation of the layers of the aorta wall causes tears, which then propagate further due to high-pressure blood penetrating the vessel wall, creating a false lumen. The intimal flap separating the true and false lumen can either bulge inwards constricting the true lumen's blood flow or bulge outwards leading to catastrophic rupture and internal bleeding. Therefore, to understand the role of critical pressure on tear propagation, a computational study of the initiation and propagation of tears of various sizes and at multiple depths and locations in three-dimensional aortas was conducted. Tears were modelled using the extended finite element method, and the wall of the aortas is an anisotropic hyperelastic material. Blood-pressure-loaded aorta geometries were obtained from the corresponding unloaded geometries using an iterative procedure to match the in vivo geometries. Pressure-driven tear initiation and propagation were studied. Our results show that when the tear surface's normal is perpendicular to the blood flow, the critical pressure required to cause further propagation is higher for the shorter and deeper tears and reduces when the initial tear size increases. When the normal is parallel to the blood flow, the difference in critical pressure with an increase in tear depth is small and is more likely to propagate transversely. Also, the critical pressure decreases with an increase in the diameter of the aorta for all the tear orientations. This study concludes that tear size, depth inside the medial layer and the diameter of the aorta near the tear location are critical parameters in assessing the risk of further propagation.