Comparison of second-generation stents for application in the superficial femoral artery: an in vitro evaluation focusing on stent design

Systematic Review of Femoral Artery Stent Fractures

Objective

Primary stenting for long femoropopliteal (FP) lesions remains controversial because of the high risk of stent fracture (SF). This study aimed to summarise current knowledge on SF from randomised control trials about FP stenting.

Methods

A systematic review of the Medline database was performed by a combined strategy of MeSH terms: femoral artery, popliteal artery, stenting, and stent fracture. SF was classified according to a standard classification: 1 = single strut fracture; 2 = ≥ two struts fracture; 3 = type 2 with deformation; 4 = multiple struts fracture with acquired transection; 5, type 4 with gap in the stent body.

Results

The literature search identified 25 publications including covered stents (CSs; n = 3), drug eluting stents (DESs; n = 8), bare metal stents (BMS; n = 17), and bioabsorbable stents (n = 1). Data were extracted from 4 047 patients; mean age ± standard deviation was 68.9 ± 3.0 years and 69% were male. The median lesion length was 87.6 mm (interquartile range [IQR] 70.0, 149) with a median chronic total occlusion proportion of 36.8% (IQR 29.0, 56.5). In 208 patients treated with CS, SF rates ranged from none to 2.6% at 36 months with no clinical correlation. In 1 106 patients treated with DES, SF rates were relatively low in large cohorts, ranging from 0% at 12 months to 1.9% at 60 months. In smaller cohorts (under 100 patients per group), they ranged from 12.5% at six months to 46.7% at 12 months, with no clinical repercussion. In 1 610 patients treated with BMS, SF rates ranged from 2% to 32.7% at 12 months and from 2.9% to 48.9% at 24 months, with no clinical repercussion.

Conclusion

SF rates in large cohorts were low in CF and DES, and quite common in BMS, although none of them had clinical consequences. However, longer follow up and detailed, accurate reports are needed to assess eventual real clinical outcomes.

Relevant Choices Affecting the Fatigue Analysis of Ni-Ti Endovascular Devices

Ni-Ti alloys are widely used for biomedical applications due to their superelastic properties, which are especially convenient for endovascular devices that require minimally invasive insertion and durable effects, such as peripheral/carotid stents and valve frames. After crimping and deployment, stents undergo millions of cyclic loads imposed by heart/neck/leg movements, causing fatigue failure and device fracture that can lead to possibly severe consequences for the patient. Standard regulations require experimental testing for the preclinical assessment of such devices, which can be coupled with numerical modeling to reduce the time and costs of such campaigns and to obtain more information regarding the local state of stress and strain in the device. In this frame, this review aimed to enlighten the relevant choices that can affect the outcome of the fatigue analysis of Ni-Ti devices, both from experimental and numerical perspectives.

A review on femoropopliteal arterial deformation during daily lives and nickel-titanium stent properties

The increasing number of studies on the behaviour of stent placement in recent decades provides a clear understanding of peripheral artery disease (PAD). The severe mechanical loads (axial tension and compression, bending, radial compression and torsion) deformation of the femoropopliteal artery (FPA) is responsible for the highest failure rate of permanent nickel-titanium (Nitinol) stents. Therefore, the purpose of this article is to review research papers that examined the deformation of the natural load environment of FPA, the properties of Nitinol and mechanical considerations. In conclusion, a better understanding of mechanical behaviour for FPA Nitinol stents contributes to increased mechanical performance and fatigue-life.

Three-Year Efficacy and Safety of the Misago Peripheral Stent for Superficial Femoral Artery Disease: Final Results from the OSPREY Trial

PURPOSE

This study evaluated the long-term outcomes of the Misago peripheral stent trial (Terumo) for atherosclerotic lesions in the superficial femoral artery (SFA) in patients with claudication.

MATERIALS AND METHODS

This was a prospective multicenter, single-arm, clinical trial of primary stent placement for de novo cases of SFA disease conducted in the United States and Asia. The primary endpoint was freedom from clinically driven target lesion revascularization (CD-TLR) at 36 months. Secondary outcomes were ankle-brachial index (ABI), Rutherford score, Walking Impairment Questionnaire (WIQ), a quality of life survey, and rate of device fracture.

RESULTS

A total of 276 patients (64.4% male; mean age, 69.3 ± 10.1 years) were enrolled. Freedom from CD-TLR was 78.5% (95% confidence interval [CI], 73.0%-83.0%) at 24 months and 75.4% (95% CI, 69.6%-80.2%) at 36 months. Baseline ABI was 0.7 ± 0.1 and 0.98 ± 0.20 (P < .001) at 30 days after the procedure. Baseline Rutherford score was 3.6 ± 0.6 and 1.6 ± 1.0 30 at 30 days after the procedure (P < .001). Mean (and changed) ABI and Rutherford score at 36 months compared to day 30 after the procedure were, respectively, 0.91 (-0.1 ± 0.2) and 1.5 (-0.2 ± 1.1). WIQ score at baseline was 21.49 ± 26.30 and 50.51 ± 38.49 at 30 days after the procedure ( P < .001). The mean WIQ score at 2 years was 46.65 ± 37.31 (P = .12). Stent fracture rate at 36 months was 2.0% (4 of 202 patients).

CONCLUSIONS

OSPREY (Occlusive-Stenotic Peripheral Artery Revascularization Study) 36-month data demonstrated persistent freedom from CD-TLR and sustained improvement in ABI and Rutherford score with primary stent placement for SFA lesions.

Biomechanical interpretation of observed fatigue fractures of peripheral Nitinol stents in the superficial femoral arteries through in silico modelling

PURPOSE

To suggest an in silico modelling approach to estimate the fatigue failure on peripheral Nitinol stents implanted in the superficial femoral artery (SFA) and interpret the clinically observed stent fractures of a retrospective series of patients.

MATERIALS AND METHODS

Preoperative data of 27 patients who underwent SFA Nitinol stenting were retrospectively analyzed. Data about preoperative features of the SFA and the lesion were collected. Follow-up data were also collected about the occurrence of restenosis/occlusion and stent fracture.

RESULTS

After a lengthening of the entire vessel, the occluded region was slightly stretched due to its high stiffness, whereas the healthy regions accommodated the artery length variation. The stent fatigue was predicted to be higher in the regions of low stiffness and higher shortening. In 7 out of 27 patients a stent fracture was clinically recorded. The model resulted to be accurate in 90% of the cases.

CONCLUSIONS

The clinical outcomes in terms of biomechanical fatigue behavior of peripheral Nitinol stents of the SFA could be interpreted by our new approach.

Mechanical and physio-biological properties of peptide-coated stent for re-endothelialization

Background

The aim of this study was to characterize the mechanical and physio-biological properties of peptide-coated stent (PCS) compared to commercialized drug-eluting stents (DESs).

Methods

WKYMVm (Trp-Lys-Tyr-Met-Val-D-Met), a stimulating peptide for homing endothelial colony-forming cell was specially synthesized and coated to bare metal stent (BMS) by dopamine-derived coordinated bond. Biological effects of PCS were investigated by endothelial cell proliferation assay and pre-clinical animal study. And mechanical properties were examined by various experiment.

Results

The peptide was well-coated to BMS and was maintained and delivered to 21 and 7 days in vitro and in vivo, respectively. Moreover, the proliferation of endothelial cell in PCS group was increased (approximately 36.4 ± 5.77%) in PCS group at 7 day of culture compare to BMS. Although, the radial force of PCS was moderated among study group. The flexibility of PCS was (0.49 ± 0.082 N) was greatest among study group. PCS did not show the outstanding performance in recoil and foreshortening test (3.1 ± 0.22% and 2.1 ± 0.06%, respectively), which was the reasonable result under the guide line of FDA (less than 7.0%). The nominal pressure (3.0 mm in a diameter) of PCS established by compliance analysis was 9 atm. The changing of PCS diameter by expansion was similar to other DESs, which is less than 10 atm of pressure for the nominal pressure.

Conclusions

These results suggest that the PCS is not inferior to commercialized DES. In addition, since the PCS was fabricated as polymer–free process, secondary coating with polymer-based immunosuppressive drugs such as –limus derivatives may possible.

Nitinol Self-Expanding Stents for the Treatment of Obstructive Superficial Femoral Artery Disease: Three-Year Results of the RELIABLE Japanese Multicenter Study

Objective: To assess the use of a nitinol stent to treat symptomatic stenoses or occlusions of the native superficial femoral artery (SFA).

Materials and Methods: Seventy-four patients were treated at 12 Japanese sites. The primary endpoint, freedom from target-limb failure (TLF), was a composite of device- or procedure-related death, target-limb amputation, target-vessel revascularization (TVR), or restenosis compared to an objective performance goal (OPG) at 12 months. Secondary endpoints, including primary patency, freedom from TVR/target-lesion revascularization (TLR), improvements in clinical parameters, and major adverse events (MAEs) were evaluated through 36 months.

Results: The mean overall lesion length was 80.7±38.9 mm (mean stented length: 98.8±46.1 mm). Freedom from TLF was 81.2% (p<0.001 compared to OPG) with a Kaplan–Meier estimate of 84.2% [95% confidence interval (95%CI) 73.3%, 90.9%] at 12 months. Primary patency was 71.0% at 12 months and 67.8% at 36 months. A total of 94.7% of patients improved by at least one Rutherford category and 70.2% of patients improved ankle–brachial indices ≧0.10 from baseline to 36 months. Freedom from TVR/TLR (Kaplan–Meier) was 90% at 12 months and 79.5% at 36 months. Four MAEs were reported; none were found to be device or procedure related.

Conclusion: A self-expanding stent was used safely to treat stenotic and occlusive lesions of the SFA in a Japanese patient population. The composite endpoint, freedom from TLF, was superior to an historical control at one year, with low rates of revascularization and good functional and clinical outcomes through three years.

Nitinol Stents in the Femoropopliteal Artery: A Mechanical Perspective on Material, Design, and Performance

Endovascular stenting has matured into a commonly used treatment for peripheral arterial disease (PAD) due to its minimally invasive nature and associated reductions in short-term morbidity and mortality. The mechanical properties of the superelastic Nitinol alloy have played a major role in the explosion of peripheral artery stenting, with modern stents demonstrating reasonable resilience and durability. Yet in the superficial femoral and popliteal arteries, even the newest generation Nitinol stents continue to demonstrate clinical outcomes that leave significant room for improvement. Restenosis and progression of native arterial disease often lead to recurrence of symptoms and reinterventions that increase morbidity and health care expenditures. One of the main factors thought to be associated with stent failure in the femoropopliteal artery (FPA) is the unique and highly dynamic mechanical environment of the lower limb. Clinical and experimental data demonstrate that the FPA undergoes significant deformations with limb flexion. It is hypothesized that the inability of many existing stent designs to conform to these deformations likely plays a role in reconstruction failure, as repetitive movements of the leg and thigh combine with mechanical mismatch between the artery and the stent and result in mechanical damage to both the artery and the stent. In this review we will identify challenges and provide a mechanical perspective of FPA stenting, and then discuss current research directions with promise to provide a better understanding of Nitinol, specific features of stent design, and improved characterization of the biomechanical environment of the FPA to facilitate development of better stents for patients with PAD.

Evolution of patency rates of self-expandable bare metal stents for endovascular treatment of femoro-popliteal arterial occlusive disease: Does stent design matter?

OBJECTIVE

To analyse the patency rates of femoro-popliteal stenting with different self-expandable Nitinol stent-designs.

METHODS

Two hundred and twenty-two patients (142 (64%) male; age 72.4 ± 11.6 years) with symptomatic femoro-popliteal peripheral arterial occlusive disease (PAOD) underwent percutaneous transluminal angioplasty (PTA) and stenting with three different Nitinol stents (interwoven IW: n = 70; closed-cell CC: n = 85; open-cell OC: n = 67). One-year post-procedural target lesion revascularization (TLR_12M) rates were investigated with regard to co-morbidities: diabetes (DBM), hyperlipidaemia (HLP), hypertension (RR), coronary artery disease (CAD) and degree of calcification.

RESULTS

Twelve-month follow-up data were available for 60, 69 and 50 patients in the IW, OC and CC groups (179 patients in total). The cumulative patency (IW: 52 (86.7%); OC: 50 (72.5%); CC: 23 (46.0%); P < 0.001) and the TLR_12M rates (IW: 8 (13.3%); OC: 19 (27.5%); CC: 27 (54.0%); P < 0.001) differed significantly, as did the subgroup analyses (DBM: P = 0.05; RR: P = 0.003; HLP: P = 0.005; CAD: P = 0.02; localization: P < 0.001; calcification: P < 0.001), with the best patency for the IW stent and the highest TLR_12M for the CC stent.

CONCLUSION

The interwoven stent-design was superior to the standard open- and closed-cell stent-designs in endovascular treatment of femoro-popliteal PAOD in a follow-up period of 12 months.

KEY POINTS

• Results of femoro-popliteal stenting are still unsatisfactory. • Comparative studies for currently available different Nitinol stent-designs are lacking. • This is a first comparative study on long-term patency of different Nitinol stent-designs. • Interwoven stent-design leads to improved long-term patency. • Interwoven stent-design leads to lower TLR than other stent-designs.

STUDY ON THE IMPACT OF STRAIGHT STENTS ON ARTERIES WITH DIFFERENT CURVATURES

Different stent structures lead to different deformations of blood vessels, such as different cross-sectional shapes, which further influence the blood flow patterns. In this paper, six non-commercial stents with different link structures called I-, C-, S-, U-, N- and W-types were considered. Their influences on arteries with five different curvatures (i.e., 0[Formula: see text], 15[Formula: see text], 30[Formula: see text], 45[Formula: see text] and 60[Formula: see text]) were studied using finite element method. Four indices including the maximum plastic strain of stents, the rate of expansion, the maximum von Mises stress and the ellipticity of arteries, were compared for all cases. The results showed that the S-type or U-type stents, with larger plastic strain and lower von Mises stress on the arteries, provided the optimal outcome. As the link structures became complex, the arterial expansion increased monotonically, while the ellipticity of arteries showed a decreasing tendency in the vessel models. The present study could be useful for the commercial design and clinic selection of a stent with different link structures for different curved arteries.

Fatigue of Metallic Stents: From Clinical Evidence to Computational Analysis

The great success of stents in treating cardiovascular disease is actually undermined by their long-term fatigue failure. The high variability of stent failure incidence suggests that it is due to several correlated aspects, such as loading conditions, material properties, component design, surgical procedure, and patient functional anatomy. Numerical and experimental non-clinical assessments are included in the recommendations and requirements of several regulatory bodies and they are thus exploited in the analysis of stent fatigue performance. Optimization-based simulation methodologies have been developed as well, to improve the fatigue endurance of novel designs. This paper presents a review on the fatigue issue in metallic stents, starting from a description of clinical evidence about stent fracture up to the analysis of computational approaches available from the literature. The reported discussion on both the experimental and numerical framework aims at providing a general insight into stent lifetime prediction as well as at understanding the factors which affect stent fatigue performance for the design of novel components.

Fatigue and in vivo validation of a peritoneum-lined self-expanding nitinol stent-graft

PURPOSE

To assess the fatigue and in vivo performance of a new stent-graft incorporating bovine peritoneum lining that is designed for application in peripheral vascular occlusive disease.

METHODS

Bovine peritoneum-lined stent-grafts were subjected to accelerated in vitro pulsatile fatigue and axial/torsional fatigue testing designed to simulate 10 years of physiological strain on the devices. At specified times the devices were evaluated for stent fracture, suture failure, or tissue tearing. Seven dogs underwent bilateral common iliac artery (CIA) balloon angioplasty injury with unilateral placement of the peritoneum-lined stent-graft. Angiography and intravascular ultrasound were performed prior to treatment, after treatment, and prior to sacrifice at 30 days. Vessels were perfusion fixed and histologically evaluated at 5 regions: above stent, proximal stent, mid stent, distal stent, and below stent.

RESULTS

No evidence of stent, suture, or tissue failure was present during or after pulsatile and axial/torsional fatigue testing. At 30±0.3 days after implantation, all vessels were patent. The average lumen area at explantation across stented vessels was 25.45 mm(2). Lumen areas tended to be reduced above (23.57 mm(2)) and below (24.17 mm(2)) the stent. Lumen areas were consistent across stented regions at explantation (proximal stent 27.80 mm(2), mid stent 25.88 mm(2), and distal stent 25.81 mm(2)). The mean neointimal area in peritoneum-lined stents was 2.02±1.52 mm(2), with a neointima:media ratio of 1.03±0.50. These values were significantly lower in the above and below stent areas than in the stented regions, but there was no difference in either measure within the proximal, mid, or distal stent.

CONCLUSION

The custom-designed peritoneum-lined stent-graft is promising for clinical peripheral applications due to its ability to resist relevant long-term physiological stresses and outstanding short-term patency rates in canine implantations.

Efficacy of two different self-expanding nitinol stents for atherosclerotic femoropopliteal arterial disease (SENS-FP trial): study protocol for a randomized controlled trial

Background

There have been few randomized control trials comparing the incidence of stent fracture and primary patency among different self-expanding nitinol stents to date. The SMART™ CONTROL stent (Cordis Corp, Miami Lakes, Florida, United States) has a peak-to-valley bridge and inline interconnection, whereas the COMPLETE™-SE stent (Medtronic Vascular, Santa Rosa, California, United States) crowns have been configured to minimize crown-to-crown interaction, increasing the stent's flexibility without compromising radial strength. Further, the 2011 ESC (European society of cardiology) guidelines recommend that dual antiplatelet therapy with aspirin and a thienopyridine such as clopidogrel should be administered for at least one month after infrainguinal bare metal stent implantation. Cilostazol has been reported to reduce intimal hyperplasia and subsequent repeat revascularization. To date, there has been no randomized study comparing the safety and efficacy of two different antiplatelet regimens, clopidogrel and cilostazol, following successful femoropopliteal stenting.

Methods/Design

The primary purpose of our study is to examine the incidence of stent fracture and primary patency between two different major representative self-expanding nitinol stents (SMART™ CONTROL versus COMPLETE™-SE) in stenotic or occlusive femoropopliteal arterial lesion. The secondary purpose is to examine whether there is any difference in efficacy and safety between aspirin plus clopidogrel versus aspirin plus cilostazol for one month following stent implantation in femoropopliteal lesions. This is a prospective, randomized, multicenter trial to assess the efficacy of the COMPLETE™-SE versus SMART™ CONTROL stent for provisional stenting after balloon angioplasty in femoropopliteal arterial lesions. The study design is a 2x2 randomization design and a total of 346 patients will be enrolled. The primary endpoint of this study is the rate of binary restenosis in the treated segment at 12 months after intervention as determined by catheter angiography or duplex ultrasound.

Discussion

This trial will provide powerful insight into whether the design of the COMPLETE™-SE stent is more fracture-resistant or effective in preventing restenosis compared with the SMART™ CONTROL stent. Also, it will determine the efficacy and safety of aspirin plus clopidogrel versus aspirin plus cilostazol in patients undergoing stent implantation in femoropopliteal lesions.

Trial registration

Registered on 2 April 2012 with the National Institutes of Health Clinical Trials Registry (ClinicalTrials.gov identifier# NCT01570803).

Fatigue behaviour of Nitinol peripheral stents: the role of plaque shape studied with computational structural analyses

Fatigue resistance of Nitinol stents implanted into femoro-popliteal arteries is a critical issue for the particular biomechanical environment of this district. Hip and knee joint movements due to the cyclic daily activity expose the superficial femoral artery (SFA), and therefore the implanted stents, to quite large and cyclic deformations influencing stent fatigue resistance. Objective of this work is to provide a tool based on finite element analysis able to evaluate the biomechanical effect of SFA on stent fatigue resistance. Computer simulations of the treatment of stenotic vessel by angioplasty and stenting and of the subsequent in vivo loading conditions (axial compression and bending) were carried out. Three different stenotic vessel models were defined, by keeping a constant stenosis rate and changing the plaque sharpness and number of stenoses. The fatigue behaviour was analysed comparing the amplitude and mean value distribution of the first principal strain in the whole stent for the different simulated conditions. Results showed that the maximum mean strain is similar in all the models, while the alternating strain is related to both plaque shape and loading conditions. In conclusion, this study confirms the requisite of replicating in vivo loading conditions. It also reveals the importance of taking into account the thickness variation of the vessel in the stenotic zone in the assessment of the stent fatigue resistance.

Effects of knee flexion on the femoropopliteal artery: a computational study

During knee flexion, the muscles of the upper leg impose various loads on the underlying femoropopliteal artery resulting in radial compression, bending, torsion, axial extension and axial compression. Measuring the dynamic force environment of the femoropopliteal artery and quantifying its resulting deformation characteristics is an essential input to peripheral device design. The goal of this study was to create an anatomically accurate, three dimensional finite element model capable of capturing the loading conditions and deformation characteristics of the femoropopliteal artery during knee flexion. Three dimensional geometries of the muscle, bone, arterial and soft tissues of the leg were constructed from CT scan data and meshed for finite element analysis. Knee flexion was simulated and deformation characteristics of length change (axial compression), curvature, radial compression and axial twist were quantified and compared to previous experimental studies. The model predicts 8.23% shortening and an average curvature of 0.294±0.26 cm(-1) in the vessel after knee flexion, with maximum stresses of 61.17 kPa and maximum strains of 0.16%. The model created replicates known in vivo deformation characteristics seen previously in angiographic images and for the first time associates femoropopliteal artery deformation characteristics with stress and strain levels within the arterial tissue.

Stent Placement Versus Balloon Angioplasty for the Treatment of Obstructive Lesions of the Popliteal Artery

Background—

Stenting has been shown to improve patency after femoral artery revascularization compared with balloon angioplasty. Limited data are available evaluating endovascular treatment for obstructive lesions of the popliteal artery.

Methods and Results—

This prospective, randomized, multicenter trial compared primary nitinol stent placement to percutaneous transluminal balloon angioplasty in patients with peripheral artery disease Rutherford-Becker class 2 to 5 who had a de novo lesion in the popliteal artery. The primary study end point was 1-year primary patency, defined as freedom from target-lesion restenosis (luminal narrowing of ≥50%) as detected by duplex ultrasound. Secondary end points included target-lesion revascularization rate and changes in Rutherford-Becker class. Provisional stent placement was considered target-lesion revascularization and loss of primary patency. Two hundred forty-six patients were included in this trial. The mean target-lesion length was 42.3 mm. One hundred ninety-seven patients were available for the1-year follow-up. The 1-year primary patency rate was significantly higher in the group with primary nitinol stent placement (67.4%) than in the percutaneous transluminal balloon angioplasty group (44.9%, P =0.002). Target-lesion revascularization rates were 14.7% and 44.1%, respectively ( P =0.0001); however, when provisional nitinol stent placement was not considered target-lesion revascularization and loss in patency, no significant differences prevailed between the study groups (67.4% versus 65.7%, P =0.92 for primary patency). Approximately 73% of patients in the percutaneous transluminal balloon angioplasty group and 77% in the nitinol stent group showed an improvement of ≥1 Rutherford-Becker class ( P =0.31).

Conclusions—

Primary nitinol stent placement for obstructive lesions of the popliteal artery achieves superior acute technical success and higher 1-year primary patency only if provisional stenting is considered target-lesion revascularization. Provisional stenting as part of a percutaneous transluminal balloon angioplasty strategy has equivalent 1-year patency and should be preferred over primary stenting.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00712309.