Oversizing and Restenosis with Self-Expanding Stents in Iliofemoral Arteries

Abstract

Purpose Uncoated self-expanding nitinol stents (NS) are commonly oversized in peripheral arteries. In current practice, 1-mm oversizing is recommended. Yet, oversizing of NS may be associated with increased restenosis. To provide further evidence, NS were implanted in porcine iliofemoral arteries with a stent-to-artery-ratio between 1.0 and 2.3. Besides conventional uncoated NS, a novel selfexpanding NS with an antiproliferative titanium-nitrideoxide (TiNOX) coating was tested for safety and efficacy. Methods Ten uncoated NS and six TiNOX-coated NS (5-6 mm) were implanted randomly in the iliofemoral artery of six mini-pigs. After implantation, quantitative angiography (QA) was performed for calculation of artery and minimal luminal diameter. Follow-up was performed by QA and histomorphometry after 5 months. Results Stent migration, stent fracture, or thrombus formation were not observed. All stents were patent at followup. Based on the location of the stent (iliac/femoral) and the stent-to-artery-ratio, stent segments were divided into ''normal-sized'' (stent-to-artery-ratio \ 1.4, n = 12) and ''oversized'' (stent-to-artery-ratio C 1.4, n = 9). All stent segments expanded to their near nominal diameter during follow-up. Normal-sized stent segments increased their diameter by 6% and oversized segments by 29%. A significant correlation between oversizing and restenosis by both angiography and histomorphometry was observed. Restenosis rates were similar for uncoated NS and TiNOXcoated NS. Conclusions TiNOX-coated NS are as safe and effective as uncoated NS in the porcine iliofemoral artery. All stents further expand to near their nominal diameter during follow-up. Oversizing is linearly and positively correlated with neointimal proliferation and restenosis, which may not be reduced by TiNOX-coating.

Numerical Modeling of Nitinol Stent Oversizing in Arteries with Clinically Relevant Levels of Peripheral Arterial Disease: The Influence of Plaque Type on the Outcomes of Endovascular Therapy

“…38,47 The procedure can occur either on purpose, by selecting a stent diameter that is larger than the healthy lumen diameter, or inadvertently, by implanting a single long stent over a considerably long lesion (>300 mm), which results in a mismatch between the constant stent diameter and the narrowing lumen. 7,25 Currently, stent manufacturers provide a stent-specific value as the recommended oversizing ratio.…”

“…More recently, animal studies and numerical analyses have been conducted to define an ideal oversizing ratio for the peripheral arteries. 38,47 However, they were limited by the use of healthy arteries, whose morphologies are considerably different than diseased arteries. Thus, to understand the real-world implications of Nitinol stent oversizing, these studies should primarily be conducted on diseased arteries.…”

“…18,33 In the case of the latter, choosing the correct stent size is crucial to simultaneously counteract arterial recoil and prevent extensive damage to the arterial tissues. 38,47 However, due to a lack of established guidelines, the current clinical practice consists of the qualitative selection of the proper stent size based solely on recommendations provided by the stent manufacturers. As a result, Nitinol stent oversizing is frequently performed to maintain full wall apposition and prevent stent migration.…”

“…As a result, Nitinol stent oversizing is frequently performed to maintain full wall apposition and prevent stent migration. 25,36,38,47 Despite these perceived advantages, the large stresses inflicted onto the arteries due to oversizing might lead to arterial damage and, ultimately, to restenosis. 8,20,37,45 The number of studies on Nitinol stent oversizing in the peripheral vasculatory system are scarce.…”

“…To date, there have only been two animal investigations that have studied the implications of coated and non-coated Nitinol stent oversizing in Yucatan swine and minipigs. 38,47 Both studies have defined over-sized arteries as having a stent-to-artery ratio, i.e. the ratio of nominal stent diameter to lumen diameter of the artery, above 1.4 and suggested that while all the arteries have shown neointimal proliferation, only the oversized arteries (stent-to-artery ratio > 1.4) were damaged enough to exhibit restenosis.…”