In vitro evaluation of endovascular stents to assess suitability for endovascular graft fixation

Abstract

A nitinol stent may be suitable for aortic graft fixation, has characteristics similar to the Palmaz stent and has shape memory effect which may overcome the difficulties of introduction of wider diameter stents through narrow arteries.

A mathematical model to predict the in vivo pulsatile drag forces acting on bifurcated stent grafts used in endovascular treatment of abdominal aortic aneurysms (AAA)

“…However, their results can be used as an initial guide to assess the possibility of stent migration. For example, smooth stents are shown to have distraction loads of between 2 and 4 N (Andrews et al, 1995;Lambert et al, 1999;Malina et al, 1998), loads that are significantly lower than most of the calculated drag forces. Stents with weak hooks and barbs have distraction loads of between 7 and 10 N, and stents with strong hooks and no barbs have a mean distraction load of 12 N (Malina et al, 1998).…”

“…To assess the possibility of stent graft migration, these drag forces can be compared to the longitudinal loads required to cause stent graft migration. Numerous investigators have conducted experimental procedures by applying longitudinal loads on commercially available stents until movement occurred (Andrews et al, 1995;Lambert et al, 1999;Malina et al, 1998;Resch et al, 2000a, b). These procedures are limited with most studies directed at defining the static longitudinal loads required for migration.…”

“…The experimental procedures applied longitudinal loads until movement occurred to various stent types. The results found that for smooth stents a longitudinal load of between 2 and 4 N was needed, and for stents with hooks and barbs a load of between 8 and 22 N was needed to cause stent graft migration (Andrews et al, 1995;Lambert et al, 1999;Malina et al, 1998;Resch et al, 2000a, b). This type of measurement is sufficient for ranking stent types and parameters.…”

Increasing angulation decreases measured aortic stent graft pullout forces

“…Whereas it is impractical to study long-term SG migration in a laboratory setting, experimental studies have been performed to establish threshold forces required to displace various SGs. [3][4][5][6][7] These in vitro force measurements, referred to as pullout forces, serve as estimates of the forces required in vivo to induce SG migration. These studies, which have focused on comparisons between different types of devices 3,5-7 and different fixation lengths, 4,6 are used as benchmarks against which comparisons can be made.…”

Endovascular Repositioning of a Pipeline Embolization Device Dislocated from the Vertebral into the Basilar Artery Using a Stent-in-Stent Technique

“…While uniaxial tension has been used before to record pull-out forces to test proximal fixation strength of aortic endografts [22,23], it is of importance to realize that the tensile forces reported in the manuscript cannot be directly transferred to the in vivo situation, in which due to the tortuosity of the vessels and friction of the catheters the pulling force cannot be measured. In fact, the finding that the larger inner PeD gets thinner and reaches almost the size of the first PED before dislodgement is of importance, as one may expect a similar behaviour in vivo.…”