Clinical significance and technical assessment of stent cell geometry in carotid artery stenting

Abstract

Carotid artery stenting has gained popularity due to its minimally invasive approach. However, several design concerns preclude the successful use of carotid stents. Technical issues, such as open versus closed cells, scaffolding, trackability, foreshortening, and changes in local geometry and hemodynamics, affect stent performance. Previous clinical and experimental studies have evaluated current stent models while proposing and testing novel stent designs. This review focuses on the technical aspects of carotid stent design and the clinical significance of key design parameters identified via computational and experimental modeling.

Figure 1

Cross section of a specimen demonstrating a balloon-expandable stent with excellent apposition and plaque scaffolding.

Figure 2

(A) A significant stenotic lesion with major ulceration in the right ICA (B) effectively managed with a stent precisely positioned at the ostium.

Figure 3

First-generation Palmaz-Schatz stent demonstrating the bridge that allowed increased length with flexibility.

Figure 4

Closed-cell design with a detailed view of the bridge (arrows) demonstrating flexibility and conformability after expansion.

Figure 5

(A) Closed-cell stent demonstrating the diamond configuration with radial segments and bridge connection (arrow); (B) open-cell stent with removal of a bridge connection illustrated.

Figure 6

(A) Fully supported closed-cell stent, demonstrating comparable flexibility to the (B) unsupported open-cell stent.

Figure 7

(A) Larger open-cell design stents may not provide adequate scaffolding in a complex bend, but do provide conformability. (B) Open-cell design at the concave surface of the stent showing scaling. (C) Post-procedure angiogram demonstrating the open-cell struts extending beyond the intima, with focal contrast extravasation to the adventitia.

Figure 8

Strut fracture in a nitinol carotid stent as seen on a 3-dimensional reconstructed angiogram.

Figure 9

Stent configurations in a carotid glass model with variations in conformability: (from left to right) NexStent, Wallstent, and Precise stents.

Figure 10

(A) Cross section of the carotid artery. CCA: common carotid artery, ICA: internal carotid artery, ECA: external carotid artery. (B) The CCA-ICA angle of the vessel, which reflects ICA tortuosity. (C) The segmented nitinol stent models S_ori and S_mod. Reproduced with permission from Journal of Biomechanics. Copyright 2007 Elsevier.

Figure 11

Design parameters for a generic stent showing the 3 parameters identified by the optimization algorithm: strut spacing (h), radius of curvature (ρ), and axial amplitude (f). Reproduced with permission from Medical and Biological Engineering and Computing. Copyright 2007 Springer.

Figure 12

(A) Virtual histology images at 3 sites in a carotid artery demonstrating lesion characteristics that are best suited for endarterectomy rather than stenting. Note the absence of any fibrous cap and the exposure to the necrotic core at the intimal surface. (B) Pre-occlusive ICA lesion with complex ulceration and angulation. (C) Virtual histology of the lesion demonstrating significant necrotic core and dystrophic calcification at the intimal surface. These lesion characteristics are best suited for endarterectomy.

Figure 13

(A) A high-grade stenotic lesion with ulcerative changes best suited for a closed-cell stent; (B) post-procedure angiogram showing flow pathway restored.