Axial stent strut angle influences wall shear stress after stent implantation: analysis using 3D computational fluid dynamics models of stent foreshortening

Abstract

Introduction: The success of vascular stents in the restoration of blood flow is limited by restenosis. Recent data generated from computational fluid dynamics (CFD) models suggest that the vascular geometry created by an implanted stent causes local alterations in wall shear stress (WSS) that are associated with neointimal hyperplasia (NH). Foreshortening is a potential limitation of stent design that may affect stent performance and the rate of restenosis. The angle created between axially aligned stent struts and the principal direction of blood flow varies with the degree to which the stent foreshortens after implantation.

Methods: In the current investigation, we tested the hypothesis that stent foreshortening adversely influences the distribution of WSS and WSS gradients using time-dependent 3D CFD simulations of normal arteries based on canine coronary artery measurements of diameter and blood flow. WSS and WSS gradients were calculated using conventional techniques in ideal (16 mm) and progressively foreshortened (14 and 12 mm) stented computational vessels.

Results: Stent foreshortening increased the intrastrut area of the luminal surface exposed to low WSS and elevated spatial WSS gradients. Progressive degrees of stent foreshortening were also associated with strut misalignment relative to the direction of blood flow as indicated by analysis of near-wall velocity vectors.

Conclusion: The current results suggest that foreshortening may predispose the stented vessel to a higher risk of neointimal hyperplasia.

Figure 1

Computational vessels implanted with 12, 14 or 16 mm stents consisting of 8 axial and circumferential repeating strut sections that were deployed using a stent-to-artery diameter convention of 1.2 to 1. The diameter of the native vessel for all simulations was 2.74 mm. The computational vessel implanted with the 16 mm stent was designated as the ideal stent length after implantation and the 14 and 12 mm stents represent progressive degrees of foreshortening.

Figure 2

Schematic illustration demonstrating measurement of the stent strut angle with respect to the primary direction of blood flow.

Figure 3

Blood flow velocity waveform measured in the proximal portion of a canine left anterior descending coronary artery and used for the time-dependent simulations conducted in the current investigation.

Figure 4

Value-weighted near-wall velocity vectors in the proximal, middle and distal portions of the stent resulting from the unique strut orientation angles corresponding to ideal (16 mm) and progressively foreshortened stents (14 and 12 mm).

Figure 5

Time-dependent alterations in spatial wall shear stress throughout the cardiac cycle in ideal stents (16 mm) and those with progressive degrees of foreshortening (14 and 12 mm).