Sukin Natarajan

Purpose: To investigate the theoretical forces involved in and the nature of fixation between the modular components of a variety of aortic stent-grafts. Methods: An in vitro study of 6 aortic stent-grafts was performed using a tensometer. The modular stent-graft components were distracted until the iliac limb was completely separated from the main body. Tests were repeated at least 6 times for each stent-graft. Results: The maximum pullout force was 36.0 N using the Fortron stent-graft, which resulted in stent-graft disintegration. The maximum median forces of the other stent-grafts were 23.7 N (19.9–31.2) for the Aorfix, 7.3 N (6.9–7.6) for the AneuRx, 7.0 N (6.8–7.1) for the Zenith BiFab, 5.4 N (5.0–6.5) for the Talent, and 2.4 N (2.2–2.4) for the Vanguard II Conclusion: The results of this in vitro study suggest that current forms of iliac limb fixation in modular aortic stent-grafts are adequate provided the components are deployed with sufficient overlap. However, for many of the stent-grafts tested, the safety margin was small.

The investigation presented in this paper has attempted to study, from a fluid dynamics point of view, the consequences of the presence of a stent on the flow of blood. The method adopted is mainly by numerical simulation using a finite element technique, but visualization experiments and an analytical study have also been carried out. The flow of blood is treated as being transient, laminar and Newtonian within a rigid section of the stented vessel. The flow is driven by an imposed pressure gradient in the form of a physiological waveform. A periodic boundary condition has been applied. Particle trajectories, fluid shear rate contours and wall shear stress maps, together with the use of a simplified form of particle image velocimetry in the experimental work, have been used to interpret the results. It was found that the vessel wall experienced oscillating levels of wall shear stress, in particular extensive exposure to low shear stress. Regions of flow recirculation, points of flow separation and reattachment constantly move in regions of low shear stress. Vortices form and then are destroyed rapidly by reversing flow. Their potential physiological significance to stented arteries is discussed.