Oversizing of self-expanding stents: influence on the development of neointimal hyperplasia of the carotid artery in a canine model

Abstract

Background and purpose: In carotid artery stent placement, marked oversizing of the stent relative to the internal carotid artery lumen is common. This study was performed to determine the influence of using oversized self-expanding nitinol stents on neointimal hyperplasia.

Methods: In six greyhound dogs, 24 self-expanding nitinol stents (eight SMART stents, eight Easy Wallstents, eight Sinus-Flex stents) were inserted into both common carotid arteries (CCAs). In each CCA, two stents were deployed; a stent of the appropriate diameter was implanted distally and an oversized stent proximally. After 4 months, transverse sections of each stent were examined histologically and at computerized image analysis. Neointimal hyperplasia was determined as the proportion of the residual diameter of the patent vessel lumen compared with the stent lumen.

Results: The amount of neointimal hyperplasia did not differ between the normal-sized and oversized stents. The mean preserved luminal diameter (+/-SEM) with normal- and oversized stents, respectively, were as follows: Easy Wallstent, 94% +/- 1.0 and 96% +/- 1.5; SMART stent, 92% +/- 1.6 and 93% +/- 1.8; and Sinus-Flex stent, 93% +/- 2.7 and 93% +/- 2.6. The mean preserved patent lumen with the 12 normal-sized stents (93% +/-1.0) was not significantly different from that of the 12 oversized stents (94% +/- 1.1, P =.502).

Conclusion: Under experimental conditions, use of self-expanding stents oversized by 30-40% appeared to result in neointimal hyperplasia comparable to that caused by normal-sized stents. All three stent types appeared to have similarly low neointimal responses.

Fig 1.

Unsubtracted (left) and subtracted (right) digital angiograms show the stents in the right CCA after implantation. A, The normal-sized stent (6 mm) is implanted in the distal position (arrows); the oversized stent (10 mm), in the proximal position (arrowheads). B, Control angiograms of a distally implanted stent obtained after 4 months show no obvious luminal narrowing (arrows). Note the partially depicted proximal stent (arrowheads) in these magnified views.

Fig 2.

Light microscopic image of a representative transverse section (thickness, approximately 50 μm) through a stent shows a smooth and asymmetric, developed neointima in this CCA segment (arrowheads). Note that the stent wires were left in place (hematoxylin-eosin, original magnification ×10).

Fig 3.

Graph shows the amounts of neointimal hyperplasia with normal-sized (distal position; size, 6–7 mm) and oversized (proximal position; size, 10 mm) stents in the CCA. N indicates the number of sections.

Fig 4.

Graph shows the mean neointimal thickness with the 24 stents, when normal-sized (distal position; size, 6–7 mm) and oversized (proximal position; size 10 mm) stents are compared. Data are a summary of that of all stent types studied. N indicates number of sections.