Computational modelling of abdominal aortic aneurysms: Effect of suprarenal vs infrarenal positions

Abdominal aortic aneurysms (AAA) are seen in both suprarenal and infrarenal positions though infrarenal is more common. Initiation and development of thrombosis and atherosclerosis in abdominal aneurysms and renal arteries have previously been correlated to areas of adverse haemodynamic conditions such as flow recirculation, low shear stress and high temporal oscillation in shear. However, it is still unknown if the haemodynamic perturbations arisen from different types of aneurysms, suprarenal vs infrarenal, contribute to the formation of atherosclerosis within the renal branches. In this work, virtual models of symmetric and asymmetric AAAs located above and below renal branches were simulated under resting and exercise conditions to determine the influence of location of the aneurysm on important haemodynamic parameters. The results showed that the size of the recirculation zones and vortices inside the renal branches and aneurysm region is considerably smaller in the infrarenal AAAs than the suprarenal models. Furthermore, our data demonstrated that occurrence of the aneurysm below the renal level augments the magnitude of shear stress and reduces the oscillations in shear in renal branches. These results confirm that the suprarenal AAA promotes thrombosis initiation within the aneurysm and increases the risk of endothelial dysfunction and the development of atherosclerosis in renal arteries. The findings also showed that under exercise conditions the haemodynamic differences between the suprarenal and infrarenal AAAs become less important and the local unfavourable haemodynamic conditions are improved to some extent.