Mechanical Modeling of Stents Deployed in Tapered Arteries

Abstract

The biomechanical interaction of stents and the arteries into which they are deployed is a potentially important consideration for long-term success. Adverse arterial reactions to excessive stress and the resulting damage have been linked to the development of restenosis. Complex geometric features often encountered in these procedures can confound treatment. In some cases, it is desirable to deploy a stent across a region in which the diameter decreases significantly over the length of the stent. This study aimed to assess the final arterial diameter and circumferential stress in tapered arteries into which two different stents were deployed (one stiff and one less stiff). The artery wall was assumed to be made of a strain stiffening material subjected to large deformations, with a 10% decrease in diameter over the length of the stent. A commercially available finite element code was employed to solve the contact problem between the two elastic bodies. The stiffer stent dominated over arterial taper, resulting in a nearly constant final diameter along the length of the stent, and very high stresses, particularly at the distal end. The less stiff stent followed more closely the tapered contour of the artery, resulting in lower artery wall stresses. More compliant stents should be considered for tapered artery applications, perhaps even to the exclusion of tapered stents.

Wall shear stress in the development of in-stent restenosis revisited. A critical review of clinical data on shear stress after intracoronary stent implantation

“…1 Pa in coronary arteries, while the stretching effect of an implanted coronary stent can generate up to 3 × 10 5 times higher circumferential stress in the vessel wall (Fig. 2) [35].…”

Angiographically confirmed stent over expansion in the internal carotid artery during stenting: incidence, predictors, and outcomes

“…Not only the essential diameter of the ICA but also the elastic modulus of the ICA may play a role in the development of SOE. Timmins et al [16] suggested that neointimal hyperplasia after stent implantation is mediated by stress placed on the arterial wall by the stent. Regions near the stent edge are particularly susceptible to restenosis because the compliance mismatch between the artery and the stent imposes high levels of stress on these areas [17].…”

Anatomic assessment of the left main bifurcation and dynamic bifurcation angles using computed tomography angiography

“…Vessel tapering of a stenotic vessel is an important issue for stenting [30]. Stents have generally tubular shape and are designed to be selected slightly larger in diameter than artery for proper expansion [30].…”

“…Stents have generally tubular shape and are designed to be selected slightly larger in diameter than artery for proper expansion [30]. Stent size selection is generally determined based on a stent-to-artery ratio of 1.0:1 to 1.2:1 [15].…”

“…Nevertheless, particularly in left main [5] and likewise long and bifurcated lesions [20,29], vessel tapering can be an important problem, which may not be adequately solved by conventional tubular stents [30]. Thus, a large diameter mismatch at the distal site of the stent may lead to damage in the arterial wall, increased wall stress, endothelial dysfunction and, as a result, worse clinical outcomes [5,27,30]. Also, in case of pronounced tapering, there is a possibility of underexpansion of distal end of the stent and attempts for obtaining proper expansion with balloon dilatation may further increase the vascular injury.…”