Design and Comparison of Large Vessel Stents: Balloon Expandable and Self-Expanding Peripheral Arterial Stents

Investigation of mechanical behaviors and improved design of V-shaped braid stents

V-shaped braid stents (VBSs), as highly retrievable and flexible nitinol stents, are extensively applied in endovascular diseases. They also cause less damage to vessel wall compared to tube-cutting stents. However, poor performance of VBS or suboptimal operation can give rise to unwanted clinical situations such as thrombosis and intimal hyperplasia. Therefore, research on designing factors affecting the performance of these devices is of great significance. Furthermore, simulation of stenting process can help designers understand the interactions of stents and vessel wall to reduce time to market. Thus, finite element analysis (FEA) and bench test are performed taking into account both designing factors and stenting process of VBS, including development of parametric modeling tool, research on the relationships among structural parameters and radial force, exploration of the interactions of VBS and vessel wall and pulsating load effect. This research was performed using a commercial solver Abaqus/standard with a user material subroutine (UMAT/nitinol). Structural parameters of VBS, unit-cell height and wire diameter have significant impacts on radial force, unit-cell number has slight influence on radial force, and arc diameter has almost negligible impact on radial force. Without pulsatile load, maximum stress and strain always occur in arc position; however, in pulsatile load, maximum stress and strain are gradually transformed to strut position. The stress created near vessel wall and VBS interface is higher than interaction stress due to pulsating load. The obtained result provided valuable information on the structural design of stents as well as the effects of stent on vessel wall and that vessel wall on stent deformation.Graphical abstract[Formula: see text].

First in man study of a new semi-open cell design Zephyr cobalt-chromium stent in large vessels and conduits

OBJECTIVES

We present a first-in-man clinical use of a new hybrid design stent in stenosed large vessels. Its unique C and S polylinks prevent foreshortening without compromising its strength. Its thin profile permits use of smaller introducer sheaths.

BACKGROUND

Stent angioplasty is widely employed in large vessel and conduit stenosis. These procedures are associated with difficulties due to large stent profiles, stent fractures, foreshortening and recoil. Cobalt chromium stents have high tensile strengths compared to stainless steel stents.

METHODS

A retrospective analysis of feasibility and safety of a new Cobalt chromium stent in large vessels namely aorta, pulmonary arteries and outflow conduits was done from two institutions. Demographic patient details, procedural results, complications and medium term follow-up were analyzed. Stent recoil, foreshortening, fractures were assessed.

RESULTS

Twenty patients including three with aortic coarctations, seven with stenosed conduits and 10 with pulmonary artery stenosis underwent stent angioplasty using 23 stents. Three stents were deployed to expand further a previously implanted stent. Procedure was successful in all patients, lumen increased by 150-300%, gradients reduced in all patients. There was no stent recoil, foreshortening or fractures. There were no complications. At a follow up of 3-27 months, there were no stent related complications and the gradients remained stable.

CONCLUSIONS

The new Zephyr stent was useful in a wide variety of stenotic lesions involving large vessels including those that were previously stented. Lack of stent recoil and foreshortening seems to be an advantage for this new stent that needs validation in larger multicenter studies.