By Anna Maria Ierardi and Gianpaolo Carrafielo
Endovascular treatment for atherosclerotic obstructions in femoropopliteal arteries is widely used for patients with intermittent claudication and critical limb ischaemia, although the optimal treatment of superficial femoral artery disease in these patients is a matter of continuing debate.
The femoropopliteal arterial segment is known to be exposed to special mechanical influences. The superficial course of the artery with crossing of flexion points as well as interaction with the surrounding musculature, potentially exposes the artery to relevant external forces, including compression, torsion, and elongation. This may have a negative impact on vessel patency after both angioplasty and stenting. In fact, stent compression has been identified as one of the principal causes of restenosis, particularly after implantation of balloon-expandable stents.
The use of percutaneous transluminal angioplasty to revascularise the superficial femoral artery can result in initial technical success rates of more than 95%, with a low risk of complications. However, at one year, the rates of restenosis exceed 70% for lesions longer than 100mm.
Endovascular stenting avoids the problems of early elastic recoil, residual stenosis, and flow-limiting dissection after balloon angioplasty and can thus be used for the treatment of long and complex lesions, even in heavily calcified arteries.
The problem of external stent compression was thought to be overcome with the introduction of self-expanding stents and particularly with the clinical use of the new generation of nitinol stents.
A recent study (J Endovasc Ther. 2010;17:767–776) compared seven different superficial femoral artery nitinol stents during mechanical bending, compression, and torsion testing showing differences in the incidence of high strain zones, which indicates a potential for stent fracture.
The Zilver PTX drug-eluting stent is a self-expanding nitinol stent with a polymer-free paclitaxel coating; in the literature there is only a single-arm clinical study with a follow up of one year in which the results are promising but not definitive. The fracture percentage may be considered in accordance with other nitinol stents.
A second generation stent designed to improve the long-term superficial femoral artery outcomes is the Easy Flype stent (CID). Two features of this nitinol stent (Fig 1) make it unique. The mirror-like finishing of the stent surface, with rounded edge, and the integral coating with iCarbofilm improve the metal surface compatibility with blood and arterial wall.
The iCarbofilm is a high density carbon coating with turbostratic structure characterised by high adhesion to the substrate, chemical inertness, ion impermeability and very low thickness.
The compatibility of this carbon coating has been extensively evaluated, and it has been demonstrated (Appl Biomater 2009; 90B:338-349) that in contact with blood it strongly inhibits the activation of the coagulative cascade, release of pro-thrombotic and pro-inflammatory factors promoting a complete surface endothelialisation already at seven days as observed in animal model (Fig 2).
In superficial femoral artery implants, the nitinol stents have negative outcomes related to the tissue response under the cyclic stimulation to the vessel wall. In this circumstances Easy Flype, thanks to its mechanical performance and biocompatible surfaces, minimises thrombotic risk and neointimal growth as observed in-vivo preclinical investigations (% area stenosis and neointimal thickness at 180 days respectively 25.1±15.1% and 0.27±0.25mm).
Clinical evidence so far collected includes the Casper study with a total of 60 patients with 70 lesions have been treated (98.6% de novo, 1.4% restenotic), most of them eccentric and calcified with a mean length of 25.6±12.3mm. In 70 % of lesions the stent was implanted using the direct stenting technique. Post-dilatation was necessary in 94.3% of the Flype/HiFlype Carbostent stent implants in order to obtain a satisfactory final angiographic result. All lesions were successfully treated, in all cases obtaining a residual vessel stenosis minor than 20%. In terms of procedural performance, no complications or acute thrombosis phenomena were observed during the delivery phase.
The follow-up clinical assessments did not reveal any sub-acute or delayed clinical events and patients’ status improved in 89.3% and 94.2% of the cases respectively at 30 days and at 180 days. An important aspect of the Easy Flype/HiFlype Carbostent, is related with its cell’s elements’ structure: stresses induced by the main stent loading conditions occur in different areas thus avoiding elastic distortion and stress concentration on the vessel wall which, otherwise, can stimulate abnormal tissue response. In vitro, no yet published experiences, demonstrated fatigue resistance tests.
However, randomised controlled trials are warranted to confirm these results because the effects of confounding factors cannot be ruled out with certainty in a retrospective study.
Gianpaolo Carrafiello and Anna Maria Ierardi are with the Interventional Radiology Department, Unisubria, Varese, Italy. They declared no conflict of interest.