The role of porosity and 3D cross-stent configuration of multiple overlapping uncovered stents in the management of complex aortic aneurysms – insights from haemodynamics
Background: Multiple overlapping uncovered stents (MOUS) have been introduced to manage complex aortic aneurysms with vital branches involvement. It has been shown that the porosity is a key determinant of the treatment outcome. However, the role of 3D cross-stent configuration remains unclear.
Methods: One patient with a complex aortic aneurysm judged not suitable for open surgery nor endovascular repair was invited to participate this study. In total, four bare metal stents were deployed. 3D lesion geometry was reconstructed based on pre- and post-operative CTA, and the zero-pressure configuration was recovered using an inverse procedure. Local haemodynamic parameters, including wall shear stress (WSS), oscillatory shear index (OSI), and particle relative resident time (RRT), as well as the vessel structural stress (VSS), were quantified using one-way fluid-structure interaction (FSI) analysis. In comparison to MOUS, a corresponding compact model was reconstructed by projecting inner layer stents to the most outer layer to form a single layer to eliminate the 3D cross-stent configuration and one-way FSI analysis was performed.
Results: Results obtained showed that the porosity decreased linearly with the number of stents. When the 1st stent was deployed, the mean velocity decreased 36.4% and further reduction of 49.3%, 59.8%, and 62.8% were observed when the 2nd, 3rd and 4th stents were deployed. WSS also decreased with the number of stents deployed, and both OSI and RRT increased, but the increase was very minor with the 4th stent. MOUS deployment induced high VSS concentration in the landing zone while the VSS and pressure in the sac remained nearly unchanged. The compact model yielded a small difference in the value of flow-related parameters and 10%-20% reduction in VSS.
Conclusion: Compared with porosity, the 3D cross-stent of MOUS configuration plays a minor role in the modulation of local haemodynamics. A compact model does not reduce high VSS concentration in the diseased region significantly.