Stent Design Affects Femoropopliteal Artery Deformation

An in vitro feasibility study of 355 nm laser atherectomy for the treatment of peripheral atherosclerotic lesions

In this study, we utilized a novel 355 nm laser to ablate porcine aortas in the presence of physiological saline and contrast agent. Subsequently, we investigated the shape and depth of the resulting injuries. After ablating bovine tendons and aortas with the laser, we analyzed the size and quantity of particles postablation. Finally, we conducted ablation experiments using human ex vivo plaques. The analysis revealed minimal damage to porcine aortas within 2 s of exposure to the 355 nm laser. The degree of injury in the presence of contrast agent was higher than that in the presence of physiological saline but significantly lower than the damage caused by 308 nm laser. Regardless of whether it was bovine tendon or porcine aorta tissue, the proportion of particles <25 μm postlaser ablation exceeded 99%. Lastly, the 355 nm laser successfully opened three types of plaques: chronically occluded, stent restenosis, and stale thrombosis.

Shape-Setting of Self-Expanding Nickel-Titanium Laser-Cut and Wire-Braided Stents to Introduce a Helical Ridge

PURPOSE

Altered hemodynamics caused by the presence of an endovascular device may undermine the success of peripheral stenting procedures. Flow-enhanced stent designs are under investigation to recover physiological blood flow patterns in the treated artery and reduce long-term complications. However, flow-enhanced designs require the development of customised manufacturing processes that consider the complex behaviour of Nickel-Titanium (Ni-Ti). While the manufacturing routes of traditional self-expanding Ni-Ti stents are well-established, the process to introduce alternative stent designs is rarely reported in the literature, with much of this information (especially related to shape-setting step) being commercially sensitive and not reaching the public domain, as yet.

METHODS

A reliable manufacturing method was developed and improved to induce a helical ridge onto laser-cut and wire-braided Nickel-Titanium self-expanding stents. The process consisted of fastening the stent into a custom-built fixture that provided the helical shape, which was followed by a shape-setting in air furnace and rapid quenching in cold water. The parameters employed for the shape-setting in air furnace were thoroughly explored, and their effects assessed in terms of the mechanical performance of the device, material transformation temperatures and surface finishing.

RESULTS

Both stents were successfully imparted with a helical ridge and the optimal heat treatment parameters combination was found. The settings of 500 °C/30 min provided mechanical properties comparable with the original design, and transformation temperatures suitable for stenting applications (Af = 23.5 °C). Microscopy analysis confirmed that the manufacturing process did not alter the surface finishing. Deliverability testing showed the helical device could be loaded onto a catheter delivery system and deployed with full recovery of the expanded helical configuration.

CONCLUSION

This demonstrates the feasibility of an additional heat treatment regime to allow for helical shape-setting of laser-cut and wire-braided devices that may be applied to further designs.

Navigating complexity: The Supera's triumph in femoropopliteal lesions

INTRODUCTION

The femoropopliteal sector endovascular treatment is particularly challenging due to its high tortuosity and torsional forces. Better results are still needed to ensure the long-term patency of stenting in this area. The Supera stent appears to change this paradigm.

METHODS

This single-center retrospective cohort study aims to evaluate the efficacy and safety of femoropopliteal stenting with Supera in a real-world population. Seventy-nine patients were treated between January 2015 and December 2020, and the results are reported with a median follow-up of 28 months.

RESULTS

Indications for revascularization were chronic limb-threatening ischemia with tissue loss (73.6%) or ischemic rest pain (17.7%) and claudication (7.6%). Thirty-six patients (45.6%) were classified as GLASS stage III according to the Global Limb Anatomic Staging System, with 65.8% and 30.4% in grades 3 and 4 of femoropopliteal and infrapopliteal sectors, respectively. The 36-month primary, primary-assisted, and secondary patency rates were 68.6%, 72.0%, and 79.0%, respectively, with an amputation-free survival rate of 86.6%. There was no significant difference between primary patency rates in GLASS stages I-II compared with GLASS stage III (36-month primary patency rates of 72% vs 63% respectively, p = 0.342) nor in amputation-free survival (88% vs 84%, p = 0.877). After adjusting for potential confounders, only the stent conformation significantly affected the primary patency rates, with a higher hazard of reintervention for the elongated (HR = 3.179; p = 0.36; CI 1.081-9.347) and the compressed (HR = 3.014; p = 0.42; CI 1.039-8.746) forms.

CONCLUSIONS

The 36-month patency of the Supera stents in our real-world cohort was similar to other reported series. The GLASS stage did not interfere with the stent patency, proving it is a good choice even in the most adverse anatomy patients. Only the non-nominal stent conformation affected the primary patency rates in our patients.

Structural and Mechanical Properties of Human Superficial Femoral and Popliteal Arteries

The femoropopliteal artery (FPA) is the main artery in the lower limb. It supplies blood to the leg muscles and undergoes complex deformations during limb flexion. Atherosclerotic disease of the FPA (peripheral arterial disease, PAD) is a major public health burden, and despite advances in surgical and interventional therapies, the clinical outcomes of PAD repairs continue to be suboptimal, particularly in challenging calcified lesions and biomechanically active locations. A better understanding of human FPA mechanical and structural characteristics in relation to age, risk factors, and the severity of vascular disease can help develop more effective and longer-lasting treatments through computational modeling and device optimization. This review aims to summarize recent research on the main biomechanical and structural properties of human superficial femoral and popliteal arteries that comprise the FPA and describe their anatomy, composition, and mechanical behavior under different conditions.

A viscoelastic constitutive model for human femoropopliteal arteries

High failure rates present challenges for surgical and interventional therapies for peripheral artery disease of the femoropopliteal artery (FPA). The FPA's demanding biomechanical environment necessitates complex interactions with repair devices and materials. While a comprehensive understanding of the FPA's mechanical characteristics could improve medical treatments, the viscoelastic properties of these muscular arteries remain poorly understood, and the constitutive model describing their time-dependent behavior is absent. We introduce a new viscoelastic constitutive model for the human FPA grounded in its microstructural composition. The model is capable of detailing the contributions of each intramural component to the overall viscoelastic response. Our model was developed utilizing fractional viscoelasticity and tested using biaxial experimental data with hysteresis and relaxation collected from 10 healthy human subjects aged 57 to 65 and further optimized for high throughput and automation. The model accurately described the experimental data, capturing significant nonlinearity and hysteresis that were particularly pronounced circumferentially, and tracked the contribution of passive smooth muscle cells to viscoelasticity that was twice that of the collagen fibers. The high-throughput parameter estimation procedure we developed included a specialized objective function and modifications to enhance convergence for the common exponential-type fiber laws, facilitating computational implementation. Our new model delineates the time-dependent behavior of human FPAs, which will improve the fidelity of computational simulations investigating device-artery interactions and contribute to their greater physical accuracy. Moreover, it serves as a useful tool to investigate the contribution of arterial constituents to overall tissue viscoelasticity, thereby expanding our knowledge of arterial mechanophysiology. STATEMENT OF SIGNIFICANCE: The demanding biomechanical environment of the femoropopliteal artery (FPA) necessitates complex interactions with repair devices and materials, but the viscoelastic properties of these muscular arteries remain poorly understood with the constitutive model describing their time-dependent behavior being absent. We hereby introduce the first viscoelastic constitutive model for the human FPA grounded in its microstructures. This model was tested using biaxial mechanical data collected from 10 healthy human subjects between the ages of 57 to 65. It can detail the contributions of each intramural component to the overall viscoelastic response, showing that the contribution of passive smooth muscle cells to viscoelasticity is twice that of collagen fibers. The usefulness of this model as tool to better understand arterial mechanophysiology was demonstrated.

Self-expanding interwoven nitinol stent in severe femoropopliteal arterial disease. Real life results of the Supera Peripheral Stent System®

PURPOSE

The excellent performance of the Supera Peripheral Stent System® by Abbott Vascular in femoropopliteal interventions has already been proven through several trials. This retrospective study aims to evaluate the durability and long-term patency of the Supera stent for the treatment of severe femoropopliteal lesions in a real-world population.

METHODS

A retrospective analysis was conducted of 136 consecutive limbs from 128 patients with atherosclerotic disease in the femoropopliteal region, treated with Supera stents between September 2010 and September 2017. As primary endpoints patency rates and freedom from target lesion revascularization (TLR) were calculated and presented using Kaplan-Meier analysis.

RESULTS

Fifty-five percent were treated for claudication (IC), 45% for chronical limb threatening ischemia (CLTI). The mean treated lesion length was 143 mm (±77.8). The majority of lesions (63%) were Trans-Atlantic Inter-Society Consensus Criteria II (TASC II) C/D lesions. The overall primary patency rates at 12 and 24 months of follow-up were 72.6% and 60.8% respectively. The primary patency at 12 and 24 months for TASC II A/B lesions was respectively 86% and 75.4%. For TASC II C/D lesions primary patency at 12 and 24 months was 64% and 51.1% respectively (p = 0.001). Overall freedom from TLR after 12 and 24 months was 73.8% and 62.8% respectively. No significant patency differences were observed based on calcification rate.

CONCLUSION

Endovascular treatment of femoropopliteal disease with Supera Stent is safe, even in extensive, highly calcified lesions. Patency rates and freedom from TLR are acceptable in a real-life population.

Off-label use of interwoven carotid stent in common femoral artery occlusion after surgery

Open surgery is the gold standard for treating common and deep femoral arterial lesions. Nevertheless, significant data have emerged in recent years supporting an endovascular strategy for this peculiar anatomic region, despite certain disadvantages, including the requirement for strong compression resistance and excellent flexibility and conformability when stents are implanted. We present a case of critical limb ischemia due to total common and deep femoral arteries occlusion after endarterectomy that resulted in a very tapered lesion. It was successfully treated with percutaneous angioplasty and off-label application of an interwoven nitinol Roadsaver carotid artery stent, which demonstrated good adaptability.

Stenting performs better than drug-coated balloon angioplasty in popliteal lesions

BACKGROUND

Peripheral arterial disease (PAD) is a common and highly morbid disease. Although there have been recent advancements in the endovascular modalities to treat PAD, comparisons of these strategies, especially in the popliteal region, remain underinvestigated. The objective of this study was to compare midterm outcomes in patients with PAD undergoing treatment with both novel and SS compared with drug-coated balloon (DCB) angioplasty.

METHODS

All patients at a multi-institution health system treated for PAD in the popliteal region from 2011 to 2019 were identified. Presenting features, operative details, and outcomes were included in the analysis. Patients who underwent popliteal revascularization with stents were compared with DCB. SS were compared separately with novel dedicated stents. Two-year primary patency was the primary outcome.

RESULTS

We included 408 patients (72.7 ± 11.8 years old; 57.1% men) in the analysis. There were 221 (54.7%) patients who underwent popliteal stenting and 187 (45.3%) who underwent popliteal DCB. There were high rates of tissue loss in both groups (57.9% vs 50.8%; P = .14). Stented patients had longer lesions (112.4 ± 3.2 vs 100.2 ± 5.8 mm; P = .03) and higher rates of concomitant superficial femoral artery treatment (88.2% vs 39.6%; P < .01). Chronic total occlusions accounted for the majority of lesions treated (stent 62.4%, DCB 64.2%). Perioperative complications were similar between groups. Primary patency for the stented group was higher at two years than the DCB group (61.0% vs 46.1%; P = .03). When evaluating stented patients only, SS had higher 2-year patency than novel stents in the popliteal segment (69.6% vs 51.4%; P = .04). On multivariable analysis, stenosis, as opposed to chronic total occlusion, was associated with improved patency (hazard ratio, 0.49; 95% confidence interval, 0.25-0.96; P = .04), whereas novel stents were associated with worse primary patency (hazard ratio, 2.01; 95% confidence interval, 1.09-3.73; P = .03).

CONCLUSIONS

In a population of patients with severe vascular disease, stents do not have inferior patency and limb salvage rates compared with DCB angioplasty when treating the popliteal region. For patients with advanced vascular disease, and especially tissue loss, stents and DCB are both beneficial when treating popliteal lesions.

Common Femoral Artery Curvature During Hip Flexion

PURPOSE

To assess the conformational changes of the common femoral artery (CFA) during hip joint flexion in patients without atherosclerosis.

METHODS

Patients who underwent digital subtraction angiography for suspicion of arterial endofibrosis between 2007 and 2011 were retrospectively searched. Angiographic images were analyzed by two independent readers. The CFA was divided into four segments of equal length, and the segment containing the folding point was noted. Segments 1 and 2 were located in the proximal half of the CFA and segments 3 and 4 in the distal half. Readers assessed the CFA angulation, located the arterial folding point, and classified the CFA curvature as harmonious, or as a moderate or severe plication.

RESULTS

Forty patients were included. The Lin concordance correlation coefficients, used to evaluate inter-observer variability, were 0.90 (95% CI [0.83; 0.96]), 0.96 (95% CI [0.93; 0.98]) and 0.96 (95% CI [0.94; 0.98]) for the measures of the CFA angle during flexion, of the length between the superficial circumflex iliac artery and the folding point, and of the length between the folding point and the femoral bifurcation, respectively. The CFA curvature was described as harmonious in 12 patients, moderate plication in 14 patients, and severe plication in 14 patients. The CFA folding point was located on segment 1, 2 and 3 in 6, 26 and 8 patients, respectively; no folding point was located on segment 4.

CONCLUSION

In these patients with non-atheromatous disease, hip flexion yielded most frequently a harmonious curvature or a moderate plication of the CFA.

Heterogeneous vascular response after implantation of bare nitinol self-expanding stents in the swine femoropopliteal artery

BACKGROUND

Mechanism of femoropopliteal in-stent restenosis has been underappreciated.

AIM

The aim of this animal study was to elucidate vascular response after femoropopliteal bare nitinol self-expanding stents (SESs) implantation.

METHODS

Misago, Smart Flex, or Innova stent was randomly implanted in 36 swine femoropopliteal arteries. At week 4, quantitative vessel analysis (QVA) was performed on 36 legs, of which 18 underwent histological evaluation after angiography. The remaining 18 legs underwent QVA and histological evaluation at week 13.

RESULTS

Fibrin deposition was excessive at week 4. Internal elastic lamina (IEL) progressively enlarged over time, and vessel injury developed from mild level at week 4 to moderate level at week 13. Vessel inflammatory reaction was mild to moderate at week 4, and was moderate to severe at week 13. Increased fibrin deposition was an early-acting, IEL enlargement and increased vessel inflammation were long-acting, and increased vessel injury and giant cells infiltration were late-acting contributors to neointimal hyperplasia (NIH). Stent type altered time-dependent process of vessel injury, vessel inflammation, eosinophils and giant cells infiltration. Misago had less fibrin deposition and vessel enlargement, and less progressive vessel injury, vessel inflammation, and eosinophils and giant cells infiltration. Net lumen as assessed by percent diameter stenosis or minimum lumen diameter was preserved with Misago, but was not preserved with the other stents.

CONCLUSIONS

In the context of bare nitinol SES platform with less progressive mechanical stress and inflammatory reaction, the advantage of less NIH outweighed the disadvantage of less vessel enlargement, leading to net lumen preservation.

Treatment of Long Femoropopliteal Lesions With Self-Expanding Interwoven Nitinol Stent: 24 Month Outcomes of the STELLA-SUPERA Trial

PURPOSE

The performance of self-expanding interwoven nitinol stent (Supera) in femoropopliteal interventions has been proven through trials with short lesions and with relatively low proportion of occlusions. There is limited evidence of Supera stent in long lesions. The aim of this study was to assess the clinical safety and efficiency of the Supera stent in the treatment of long femoropopliteal lesions (Trans-Atlantic Inter-Society Consensus [TASC] C/D) in patients with symptomatic peripheral arterial disease (PAD).

METHODS

The STELLA SUPERA (STEnting Long de L'Artère fémorale superficielle par le stent métallique Supera) is a prospective, 2-center, single-arm study. Patients with symptomatic (Rutherford stages 2-6) de novo and TASC C/D lesions of the femoropopliteal segment were treated with Supera stent. The primary endpoint was the primary sustained clinical improvement at 12 months. Follow-up included clinical examination, duplex scan, and biplane X-ray up to 24 months.

RESULTS

Between December 2016 and October 2018, 48 symptomatic patients with 49 femoropopliteal lesions (TASC D = 32, 65%) were treated. The mean lesion length was 234 ± 123 mm, and 78% were total occlusion. The mean stented lesion length was 273 ± 127 mm. At 12 and 24 months, the primary sustained clinical improvement rate was 87.2% and 79.7%, respectively. The Rutherford category assessment was significantly improved at 24 months compared with baseline (p=0.02). At 24 months, the primary patency and freedom from target lesion revascularization (TLR) rates were 77.9% and 86.9%, respectively. The ankle-brachial pressure index increased from 0.62 ± 0.15 at baseline to 0.93 ± 0.15 at 24 months (p<0.0001). There were no stent fractures at 24 months.

CONCLUSION

The use of Supera stent in long lesions (TASC C/D) is a safe and effective endovascular alternative. These results reinforce the need for randomized clinical trials to assess the value of interwoven stents for long femoropopliteal lesions.

Effect of balloon pre-dilation on performance of self-expandable nitinol stent in femoropopliteal artery

Balloon pre-dilation is usually performed before implantation of a nitinol stent in a femoropopliteal artery in a case of severe blockage or calcified plaque. However, its effect on performance of the nitinol stent in a diseased femoropopliteal artery has not been studied yet. This study compares the outcomes of stenting with pre-dilation and without it by modelling the entire processes of stent deployment. Fatigue deformation of the implanted stent is also modelled under diastolic-systolic blood pressure, repetitive bending, torsion, axial compression and their combination. Reduced level of stress in the stent occurs after stenting with pre-dilation, but causing the increased damage in the media layer, i.e. the middle layer of the arterial wall. Generally, pre-dilation increases the risk of nitinol stent's fatigue failure. Additionally, the development of in-stent restenosis is predicted based on the stenting-induced tissue damage in the media layer, and no severe mechanical irritation is induced to the media layer by pre-dilation, stent deployment or fatigue loading.

A method of assessing peripheral stent abrasiveness under cyclic deformations experienced during limb movement

Poor outcomes of peripheral arterial disease stenting are often attributed to the inability of stents to accommodate the complex biomechanics of the flexed lower limb. Abrasion damage caused by rubbing of the stent against the artery wall during limb movement plays a significant role in reconstruction failure but has not been characterized. Our goals were to develop a method of assessing the abrasiveness of peripheral nitinol stents and apply it to several commercial devices. Misago, AbsolutePro, Innova, Zilver, SmartControl, SmartFlex, and Supera stents were deployed inside electrospun nanofibrillar tubes with femoropopliteal artery-mimicking mechanical properties and subjected to cyclic axial compression (25%), bending (90°), and torsion (26°/cm) equivalent to five life-years of severe limb flexions. Abrasion was assessed using an abrasion damage score (ADS, range 1-7) for each deformation mode. Misago produced the least abrasion and no stent fractures (ADS 3). Innova caused small abrasion under compression and torsion but large damage under bending (ADS 7). Supera performed well under bending and compression but caused damage under torsion (ADS 8). AbsolutePro produced significant abrasion under bending and compression but less damage under torsion (ADS 12). Zilver fractured under all three deformations and severely abraded the tube under bending and compression (ADS 15). SmartControl and SmartFlex fractured under all three deformations and produced significant abrasion due to strut penetration (ADS 20 and 21). ADS strongly correlated with clinical 12-month primary patency and target lesion revascularization rates, and the described method of assessing peripheral stent abrasiveness can guide device selection and development. STATEMENT OF SIGNIFICANCE: Poor outcomes of peripheral arterial disease stenting are related to the inability of stents to accommodate the complex biomechanics of the flexed lower limb. Abrasion damage caused by rubbing of the stent against the artery wall during limb movement plays a significant role in reconstruction failure but has not been characterized. Our study presents the first attempt at assessing peripheral stent abrasiveness, and the proposed method is applied to compare the abrasion damage caused by Misago, AbsolutePro, Innova, Zilver, SmartControl, SmartFlex, and Supera peripheral stents using artery-mimicking synthetic tubes and cyclic deformations equivalent to five life-years of severe limb flexions. The abrasion damage caused by stents strongly correlates with their clinical 12-month primary patency and target lesion revascularization rates, and the described methodology can be used as a cost-effective and controlled way of assessing stent performance, which can guide device selection and development.

Endovascular retrieval of an elongated Supera stent

Stenting is used to achieve artery patency, and the Supera stent, a self-expanding interwoven nitinol stent, has produced good clinical outcomes. A 70-year-old woman with peripheral artery disease had experienced intermittent claudication (Fontaine stage IIb). Endovascular treatment was performed for a chronic total occlusion TransAtlantic InterSociety Consensus class II type B lesion. A Supera stent (Abbott Vascular, Santa Clara, CA) was used. However, it had become severely elongated to the proximal end in the superficial femoral artery and was removed using a balloon inserted from the side and trapped to the guide sheath with the distal end of the stent outside the sheath. After this bailout, an alternate stent could be placed through an antegrade approach to the contralateral common femoral artery.

Laser Additive Manufacturing of Anti-Tetrachiral Endovascular Stents with Negative Poisson’s Ratio and Favorable Cytocompatibility

Laser additive manufacturing (LAM) of complex-shaped metallic components offers great potential for fabricating customized endovascular stents. In this study, anti-tetrachiral auxetic stents with negative Poisson ratios (NPR) were designed and fabricated via LAM. Poisson’s ratios of models with different diameters of circular node (DCN) were calculated using finite element analysis (FEA). The experimental method was conducted with the LAM-fabricated anti-tetrachiral stents to validate their NPR effect and the simulation results. The results show that, with the increase in DCN from 0.6 to 1.5 mm, the Poisson ratios of anti-tetrachiral stents varied from −1.03 to −1.12, which is in line with the simulation results. The interrelationship between structural parameters of anti-tetrachiral stents, their mechanical properties and biocompatibility was demonstrated. The anti-tetrachiral stents with a DCN of 0.9 mm showed the highest absolute value of negative Poisson’s ratio, combined with good cytocompatibility. The cytocompatibility tests indicate the envisaged cell viability and adhesion of the vascular endothelial cell on the LAM-fabricated anti-tetrachiral auxetic stents. The manufactured stents exhibit great superiority in the application of endovascular stent implantation due to their high flexibility for easy maneuverability during deployment and enough strength for arterial support.

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.

A systematic review and meta-analysis of Supera interwoven nitinol stents for the treatment of infrainguinal peripheral arterial disease

INTRODUCTION

Stenting of infrainguinal lesions can be rather challenging due to the mechanical stress applied on the arteries during motion. We assessed the short-term and mid-term safety and efficacy of Supera interwoven nitinol stent for the treatment of infrainguinal arterial disease.

EVIDENCE ACQUISITION

We conducted a systematic review for articles published from December 2011 up to May 2021 regarding studies assessing the safety and efficacy of Supera interwoven nitinol stents for the treatment of infra-inguinal peripheral arterial disease. Studies that involved synchronous application of the Supera stent and drug delivering devices, or any alternative endoprosthesis were excluded. Pooled Kaplan-Meier survival curves and smoothed hazard estimates were generated. Data were meta-analyzed using a random effects model. Primary endpoints included primary patency and freedom from clinically driven target lesion revascularization (TRL). Secondary endpoints included technical success and major amputation at 1 year post intervention.

EVIDENCE SYNTHESIS

Seventeen studies with 2015 patients (65.3% males) and a mean lesion length of 137.2 mm were included. Of the total treated lesions, 44.9% involved femoropopliteal artery and 37.4% the popliteal artery. Chronic total occlusions made up 49% of the treated lesions. There were no stent fractures reported. The pooled technical success rate is 99.84% (95% CI: 99.26-100). Pooled major amputation rate at 1 year is 1.48% (95% CI: 0.47-2.87). Pooled primary patency and freedom from TLR rates at 1 year are 83.5% (95% CI: 80.24-86.54) and 90.32% (95% CI: 88.75-91.79), respectively. Pooling of individual patient data produced primary patency and freedom from TLR rates of 84.48% (95% CI: 82.66-86.11) and 90.81% (95% CI: 88.64-92.58) respectively. According to the smoothed hazard ratio estimate the risk for losing primary patency peaked between 4 and 5 months while the risk for TLR peaked between 7 and 8 months after the intervention.

CONCLUSIONS

This review and meta-analysis indicated the safety and efficacy of Supera stents for the treatment of challenging infrainguinal lesions in the short-term and mid-term periods, with acceptable primary patency and freedom from TLR rates. Clinicians should be aware that between 4 and 5 months patients face a higher risk for event occurrence.

Delayed stenosis regression after drug-coated balloon angioplasty for femoropopliteal artery lesions

Paclitaxel has the potential for inducing lumen enlargement by vessel enlargement, healing of dissection, and plaque regression. This study was carried out to determine the possibility of and the relevant factors of delayed stenosis regression after drug-coated balloon (DCB) angioplasty for femoropopliteal (FP) artery lesions. A total 105 de novo FP lesions were finalized with DCB angioplasty in our institute between May 2018 and June 2020. Among them, cases in which residual stenosis was detected by duplex ultrasonography (DUS) after the procedure were included in this study. Significant stenosis was defined as peak systolic velocity ratio ≥ 2.4 by DUS. Follow-up DUS was routinely performed 6 months after the procedure, and we defined cases without stenosis as cases of delayed stenosis regression according to the follow-up DUS. DUS showed that 26 (25.5%) of 102 lesions had residual stenosis after DCB angioplasty, and delayed stenosis regression was observed in 12 (57.1%) of 21 lesions 6 months after the procedure. The percentage of lesions containing calcified plaque as detected by intravascular ultrasound analysis was significantly higher in the non-regression group than in the regression group (18.2% vs. 77.8%, p = 0.02). Vessel remodeling and dissection patterns were not associated with delayed stenosis regression. The results of our analyses indicate that delayed stenosis regression may occur after DCB angioplasty for FP lesions in more than half of cases with residual stenosis. Delayed stenosis regression may be difficult in cases of calcified lesions.

First experiences of local pulse wave velocity measurements in 4D-MRI in focally stented femoropopliteal arteries

Background: In peripheral arterial disease (PAD) the femoropopliteal (FP) artery is the most frequently recanalized lower limb artery. Stent-based interventions change the biomechanical properties of FP arteries. However, no clinical tool for functional imaging is established for quantitative measurements in vivo. Four-dimensional-flow magnetic resonance imaging enables a detailed evaluation of the hemodynamics of the central and - more challenging - the peripheral arteries. The present study aimed to determine the feasibility of assessing pulse wave velocities (PWV) as a marker of vessel stiffness in PAD patients with multiple spot stents and to compare the values with age-matched subjects and young-adult healthy subjects. Patients and methods: Contrast-free 4D-flow MRI was performed in seven PAD patients with focally stented FP arteries, five age-matched subjects after exclusion of PAD, and five young, healthy adults. PWV values were calculated from flow curves by using the foot-to-foot method. Results: Four-D-flow MRI sequences offering high spatial and temporal resolution enables quantification of flow velocity measurements and estimation of PWVs. Assessment of segmental PWV as a surrogate of vascular stiffness in focally stented femoral arteries is feasible. PWV values across all groups were 15.6±5.2 m/s, 13.3±4.1 m/s, and 9.9±2.2 m/s in PAD patients, senior-aged volunteers, and young-adult volunteers respectively. PWV values in PAD patients were similar with those in the senior-aged volunteers group (15.6±5.2 vs. 13.3 ±4.1 years, p=0.43). However, when compared to the young-adult volunteers, PAD patients had a statistically significantly higher mean local PWV (15.6±5.2 m/s vs. 9.9±2.2 m/s, p<0.05). Conclusions: Calculating segmental PWV in the femoral arteries is feasible in PAD patients with focally stented FP arteries. PWV values in PAD patients were similar to those in senior-aged volunteers, both of which were higher than in young-adult volunteers.

A computational study of fatigue resistance of nitinol stents subjected to walk-induced femoropopliteal artery motion

Fatigue resistance of nitinol stents implanted in femoropopliteal arteries is a critical issue because of their harsh biomechanical environment. Limb flexions due to daily walk expose the femoropopliteal arteries and, subsequently, the implanted stents to large cyclic deformations, which may lead to fatigue failure of the smart self-expandable stents. For the first time, this paper utilised the up-to-date measurements of walk-induced motion of a human femoropopliteal artery to investigate the fatigue behaviour of nitinol stent after implantation. The study was carried out by modelling the processes of angioplasty, stent crimping, self-expansion and deformation under diastolic-systolic blood pressure, repetitive bending, torsion and axial compression as well as their combination. The highest risk of fatigue failure of the nitinol stent occurs under a combined loading condition, with the bending contributing the most, followed by compression and torsion. The pulsatile blood pressure alone hardly causes any fatigue failure of the stent. The work is significant for understanding and improving the fatigue performance of nitinol stents through innovative design and procedural optimisation.

Comparison of morphometric, structural, mechanical, and physiologic characteristics of human superficial femoral and popliteal arteries

Peripheral arterial disease differentially affects the superficial femoral (SFA) and the popliteal (PA) arteries, but their morphometric, structural, mechanical, and physiologic differences are poorly understood. SFAs and PAs from 125 human subjects (age 13-92, average 52±17 years) were compared in terms of radii, wall thickness, and opening angles. Structure and vascular disease were quantified using histology, mechanical properties were determined with planar biaxial extension, and constitutive modeling was used to calculate the physiologic stress-stretch state, elastic energy, and the circumferential physiologic stiffness. SFAs had larger radii than PAs, and both segments widened with age. Young SFAs were 5% thicker, but in old subjects the PAs were thicker. Circumferential (SFA: 96→193°, PA: 105→139°) and longitudinal (SFA: 139→306°, PA: 133→320°) opening angles increased with age in both segments. PAs were more diseased than SFAs and had 11% thicker intima. With age, intimal thickness increased 8.5-fold, but medial thickness remained unchanged (620μm) in both arteries. SFAs had 30% more elastin than the PAs, and its density decreased ~50% with age. SFAs were more compliant than PAs circumferentially, but there was no difference longitudinally. Physiologic circumferential stress and stiffness were 21% and 11% higher in the SFA than in the PA across all ages. The stored elastic energy decreased with age (SFA: 1.4→0.4kPa, PA: 2.5→0.3kPa). While the SFA and PA demonstrate appreciable differences, most of them are due to vascular disease. When pathology is the same, so are the mechanical properties, but not the physiologic characteristics that remain distinct due to geometrical differences.

Efficacy and Safety of a Novel Helical Self-Expanding Nitinol Stent for Femoropopliteal Artery Obliterans Disease

BACKGROUND

The aim of this study was to evaluate the efficacy and safety of a novel self-expanding nitinol stent (Smartflex stent) in femoropopliteal artery obliterans disease.

METHODS

From June 2016 to May 2019, patients with atherosclerotic occlusion disease of the superficial femoral and popliteal arteries using the Smartflex stents were retrospectively analyzed in our institution. Patients were monitored at 1, 3, 6, and 12 months and annually thereafter. The main characteristics of the diseased vessels, perioperative and follow-up outcome were evaluated. Kaplan-Meier method was used to assess patency rate and the rate of freedom from clinically driven target lesion revascularization (CD-TLR).

RESULTS

A total of 50 limbs from 48 patients (mean age 69.4 ± 8.95 years; 38 men) were included. Eighty-eight Smartflex stents (1.76 stents per limb) were deployed successfully. Of the study patients, 82% had claudication (Rutherford III), 10% had rest pain (Rutherford IV), and 8% had tissue loss (Rutherford V). Trans-Atlantic Inter-Society Consensus II C and D lesions were 26% and 42%, respectively. The mean lesion length was 18.2 ± 8.5 cm and the mean stented length was 22.3 ± 9.9 cm. The average follow-up time was 16.4 ± 8.2 months. Of these lesions, 42 (94%) were chronic total occlusions and 16 (32%) were severely calcified. The primary patency rate at 1 year per Kaplan-Meier estimating, the rate of freedom from CD-TLR at 1 year, and the second patency rate was 83.3%, 88.1%, and 94%, respectively. Among them, 90% patients had improved ankle-brachial indexes (0.47 ± 0.13 before and 0.84 ± 0.16 after). No stent fractures and kinking were identified.

CONCLUSIONS

Stenting of the femoropopliteal artery diseases using the Smartflex stent appeared to be safe and effective. It performed well in long-segment and above knee joint lesions.

DESIGN AND ANALYSIS OF NEW STENT PATTERNS FOR ENHANCED PERFORMANCE

Deploying a stent to restore blood flow in the coronary artery is very complicated, as its internal diameter is smaller than 3[Formula: see text]mm. It has already been proven that mechanical stresses induced on stent and artery during deployment make the placement of stent very difficult, besides the development of complications due to artery damage. Various stent designs have already been developed, especially in the metallic category. Still, there are possibilities for developing new stent designs and patterns to overcome the complexities of the existing models. Also, the technology of metallic stents can be carried forward towards the development of bioresorbable polymeric stents. In this work, three new stent cell designs (curvature, diamond, and oval) have been proposed to obtain better performance and life. The finite element method is utilized to explore the mechanical behavior of stent expansion and determine the biomechanical stresses imposed on the stent and artery during the stenting procedure. The results obtained have been compared with the available literature and found that the curvature cell design develops lower stresses and, hence, be suitable for better performance and life.

Lesion Revascularisation Subsequent to Femoropopliteal Spot Stenting Using the Multi-LOC Stent Delivery System

BACKGROUND/AIM

Restenosis and stent fractures are well-characterised treatment failures following femoropopliteal (FP) stent-based interventions. We aimed to determine patterns of restenosis and fracture rates following focal stenting of FP arteries.

PATIENTS AND METHODS

This retrospective study investigated angiographic patterns of restenosis and the occurrence of stent fractures following focal FP stenting with the multiple stent delivery system VascuFlex® Multi-LOC.

RESULTS

We identified 10 patients with 10 (of 129) FP lesions (mean length 11.7±4.6 cm) and a total of 51 (of 646) Multi-LOC stents that underwent clinically driven target lesion revascularizations (TLR) after 11.5±9.2 months, due to symptomatic recurrence of stenosis. None of the Multi-LOC stents had fractured. No isolated in-stent restenosis (>50%) was observed. Median diameter lumen loss was significantly more pronounced at the inter-stent segments (27.0%) compared to in-stent segments (7.8%, p=0.023).

CONCLUSION

No evidence of fracture or susceptibility to stent-related restenosis using Multi-LOC stents was observed. Focal FP stenting may be more effective when combined with strategies known to reduce restenosis in non-stented artery segments.

Endovascular Removal of a Detached Supera Stent Delivery Catheter Tip in a Patient with Heavily Calcified Vessels Associated with Peripheral Artery Disease

A 62-year-old man was admitted with nonhealing wounds on his right toes. Computed tomography and angiography showed heavily calcified arteries in both lower extremities and steno-occlusive lesions of the right femoropopliteal artery. During Supera stenting, the catheter tip detached after adhering to the heavily calcified vessel wall. Endovascular removal of the detached tip was performed using ipsilateral peroneal access with a 5F angiographic catheter and a through-and-through wire. Contrast-enhanced computed tomography and angiography after 16 months showed patent Supera stents. Our report suggests that detachment of the Supera stent delivery catheter tip could occur, especially in patients with heavily calcified vessels associated with peripheral artery disease, and demonstrates the possibility for endovascular retrieval of the detached tip.

Long-term performance and biocompatibility of a novel bioresorbable scaffold for peripheral arteries: A three-year pilot study in Yucatan miniswine

AIMS

Peripheral arteries are constantly exposed to deformation (elongation, twisting, shortening, compression) making bioresorbable scaffolds (BRS) a potentially attractive therapeutic alternative to metallic stents. We conducted a long-term pilot preclinical study of a novel sirolimus-eluting BRS in peripheral arteries.

METHODS AND RESULTS

Fourteen BRS were deployed in iliofemoral arteries of seven healthy Yucatan miniswine and examined with imaging, pharmacokinetic, histopathologic, and polymer degradation techniques at 0, 30, 90, 180 days, 1, 2, and 3.3 years. Angiographic late luminal loss remained unchanged at 30 and 180 days but significantly decreased from 1 to 3.3 years. optical coherence tomography (OCT) showed late increase in lumen area (1 year: 14.70 ± 3.58 mm² , 2 years 22.04 ± 3.81 mm² , and 3.3 years 23.45 ± 7.07 mm² ; p < .05) primarily due to scaffold area enlargement between 1 and 3.3 years, while there was no difference in the percent area stenosis at all time points. Histologic evidence of scaffold degradation was observed starting at 2 years, with minimal inflammatory reaction. At 3.3 years, BRS struts were rarely discernible by OCT, confirmed by a nearly complete polymer degradation by molecular weight analysis.

CONCLUSIONS

In this pilot study, novel sirolimus-eluting BRS showed promising acute and chronic performance in the iliofemoral arteries of Yucatan miniswine.

Cross-sectional pinching in human femoropopliteal arteries due to limb flexion, and stent design optimization for maximum cross-sectional opening and minimum intramural stresses

High failure rates of femoropopliteal artery (FPA) interventions are often attributed to severe mechanical deformations that occur with limb flexion. One of these deformations, cross-sectional pinching, has a direct effect on blood flow, but is poorly characterized. Intra-arterial markers were deployed into n = 50 in situ cadaveric FPAs (80 ± 12 years old, 14F/11M), and limbs were imaged in standing, walking, sitting and gardening postures. Image analysis was used to measure marker openings and calculate FPA pinching. Parametric finite element analysis on a stent section was used to determine the optimal combination of stent strut amplitude, thickness and the number of struts per section to maximize cross-sectional opening and minimize intramural mechanical stress and low wall shear stress. Pinching was higher distally and increased with increasing limb flexion. In the walking, sitting and gardening postures, it was 1.16-1.24, 1.17-1.26 and 1.19-1.35, respectively. Stent strut amplitude and thickness had strong effects on both intramural stresses and pinching. Stents with a strut amplitude of 3 mm, thickness of 175 µm and 20 struts per section produced pinching and intramural stresses typical for a non-stented FPA, while also minimizing low wall shear stress areas, and ensuring a stent lifespan of at least 10⁷ cycles. These results can help guide the development of improved devices and materials to treat peripheral arterial disease.

PTA and Stenting of Femoropopliteal Trunk With Cordis Smartflex Stent System: A Single-Center Experience

Introduction:

The aim of this study is to describe our experience in the treatment of femoropopliteal occlusive disease with percutaneous transluminal angioplasty (PTA) followed by stenting with S.M.A.R.T. Flex vascular stent system.

Materials and Methods:

From June 2014 to October 2018, 80 patients were treated at our Institution for intermittent claudication, critical, or acute limb ischemia due to total occlusion or long diffused lesions of the femoropopliteal segment. Main study end points are primary patency, target lesion revascularization, and stent fractures; secondary end points are major amputation rate, procedure-related bleeding, incidence of intrastent restenosis, and primary assisted patency after reintervention.

Results:

Mean follow-up time was 21 months (range 2-48 months). Primary patency rate was 80% (64 patients of 80), with mean covered lesion length of 8.2 cm. The deployment of a single stent was obtained for 57 (89%) patients, with a mean stent length of 9.86 cm. Of 80 patients, 2 (2.5%) had early stent occlusion within first 48 hours after the procedure, while 4 (5%) of 80 patients experienced stent occlusion within first 6 months. Of 80 patients, 6 (7.5%) had an intrastent restenosis detected at duplex ultrasound with a primary-assisted patency after simple re-PTA procedures of 83.3% at 12 months.

Discussion:

In the literature, primary patency after PTA and stenting of the femoropopliteal trunk seems to be related to several variables, such as number of stents used, specific stent length, diameters, type and length of lesions, type of pathology (if acute or chronic), and number of preoperatory patent below-the-knee vessels. In this study, we try to analyze each single factor in order to understand their role in predisposing specific stent restenosis.

Conclusions:

S.M.A.R.T. Flex vascular stent system has shown good results in terms of primary patency in the treatment of calcified lesions both at SFA and at popliteal level. However, in our experience, stent patency seems to be significantly poorer in patients presenting with acute limb ischemia associated with chronic atherosclerotic disease as well as for lesions located in the mid-distal part of the popliteal artery and both when number of stents increases or number of runoff vessel decreases.

In Vivo Morphological Changes of the Femoropopliteal Arteries due to Knee Flexion After Endovascular Treatment of Popliteal Aneurysm

Purpose: To evaluate morphological changes of the femoropopliteal (FP) arteries due to limb flexion in patients undergoing endovascular treatment of popliteal artery aneurysms (PAAs). Materials and Methods: Seven male patients (mean age 68 years) underwent endovascular treatment of PAA with a Viabahn stent-graft between January 2013 and December 2017. During follow-up, one contrast-enhanced computed tomography angiography (CTA) scan of the lower limbs was acquired for each recruited patient. A standardized CTA protocol for acquisitions in both straight-leg and bent-leg positions was used to visualize changes in artery shape due to limb flexion. Three-dimensional reconstruction of the FP segment was performed to compute mean diameter and eccentricity of the vascular lumen and to measure length, tortuosity, and curvature of the vessel centerline in 3 arterial zones: (A) between the origin of the superficial femoral artery and the proximal end of the stent-graft, (B) within the stent-graft, and (C) from the distal end of the stent-graft to the origin of the anterior tibial artery. Results: After limb flexion, all zones of the FP segment foreshortened: 6% in zone A (p=0.001), 4% in zone B (p=0.001), and 8% in zone C (p=0.07), which was the shortest (mean 4.5±3.6 cm compared with 23.8±5.7 cm in zone A and 23.6±7.4 cm in zone B). Tortuosity increased in zone A (mean 0.03 to 0.05, p=0.03), in zone B (0.06 to 0.15, p=0.005), and in zone C (0.027 to 0.031, p=0.1). Mean curvature increased 15% (p=0.05) in zone A, 27% (p=0.005) in zone B, and 95% (p=0.06) in zone C. In all zones, the mean artery diameter and eccentricity were not significantly affected by limb flexion. Conclusion: Limb flexion induces vessel foreshortening and increases mean curvature and tortuosity of the FP segment both within and outside the area of the stent-graft.

Prediction of restenosis based on hemodynamical markers in revascularized femoro-popliteal arteries during leg flexion

Endovascular therapy in patients suffering from peripheral arterial disease shows high rates of restenosis. The poor clinical outcomes are commonly explained by the demanding mechanical environment due to leg movements, but the mechanisms responsible for restenosis remain unknown. In this study, we hypothesized that restenosis following revascularization is associated with hemodynamical markers derived from blood flow during leg flexion. Therefore, we performed personalized computational fluid dynamics (CFD) analyses of 20 patients, who underwent routine endovascular femoro-popliteal interventions. The CFD analyses were conducted using 3D models of the arterial geometry in straight and flexed positions, which were reconstructed from 2D angiographic images. Based on restenosis rates reported at 6-month follow-up, logistic regression analyses were performed to predict restenosis from hemodynamical parameters. Results showed that severe arterial deformations, such as kinking, induced by leg flexion in stented arteries led to adverse hemodynamic conditions that may trigger restenosis. A logistic regression analysis based solely on hemodynamical markers had an accuracy of 75%, which showed that flow parameters are sufficient to predict restenosis (p = 0.031). However, better predictions were achieved by adding the treatment method in the model. This suggests that a more accurate image acquisition technique is required to capture the localized modifications of blood flow following intervention, especially around the stented artery. This approach, based on the immediate postoperative configuration of the artery, has the potential to identify patients at increased risk of restenosis. Based on this information, clinicians could take preventive measures and more closely follow these patients to avoid complications.

Mechanical damage characterization in human femoropopliteal arteries of different ages

Endovascular treatment of Peripheral Arterial Disease (PAD) is notorious for high failure rates, and interaction between the arterial wall and the repair devices plays a significant role. Computational modeling can help improve clinical outcomes of these interventions, but it requires accurate inputs of elastic and damage characteristics of the femoropopliteal artery (FPA) which are currently not available. Fresh human FPAs from n = 104 tissue donors 14-80 years old were tested using planar biaxial extension to capture elastic and damage characteristics. Damage initiation stretches and stresses were determined for both longitudinal and circumferential directions, and their correlations with age and risk factors were assessed. Two and four-fiber-family invariant-based constitutive models augmented with damage functions were used to describe stress softening with accumulating damage. In FPAs younger than 50 years, damage began accumulating after 1.51 ± 0.13 and 1.49 ± 0.11 stretch, or 196 ± 110 kPa and 239 ± 79 kPa Cauchy stress in the longitudinal and circumferential directions, respectively. In FPAs older than 50 years, damage initiation stretches and stresses decreased to 1.27 ± 0.09 (106 ± 52 kPa) and 1.26 ± 0.09 (104 ± 59 kPa), respectively. Damage manifested primarily as tears at the internal and external elastic laminae and within the tunica media layer. Higher body mass index and presence of diabetes were associated with lower damage initiation stretches and higher stresses. The selected constitutive models were able to accurately portray the FPA behavior in both elastic and inelastic domains, and properties were derived for six age groups. Presented data can help improve fidelity of computational models simulating endovascular PAD repairs that involve arterial damage. STATEMENT OF SIGNIFICANCE: This manuscript describes inelastic, i.e. damage, behavior of human femoropopliteal arteries, and provides values for three constitutive models simulating this behavior computationally. Using a set of 104 human FPAs 14-80 years old, we have investigated stress and stretch levels corresponding to damage initiation, and have studied how these damage characteristics change across different age groups. Presented inelastic arterial characteristics are important for computational simulations modeling balloon angioplasty and stenting of peripheral arterial disease lesions.

Demystifying the Use of Self-Expandable Interwoven Nitinol Stents in Femoropopliteal Peripheral Arterial Disease

Femoropopliteal atherosclerosis affects a significant percentage of the world population, leading to intermittent claudication and critical limb ischemia. The femoropopliteal segment has a unique set of biomechanical challenges that must be considered and overcome for treatment. The use of stents is a reality and a necessity in peripheral interventions. The success of first-generation femoropopliteal stents was limited by their rigidity and deformability. The standard nitinol stents overcame certain biomechanical challenges because of their superelasticity and thermal shape memory, although stent fracture is still an issue. Therefore, interwoven nitinol stents with helical structure have been developed, borrowing the concept from biliary stents, aiming to provide good flexibility while still maintaining a uniform cell size and significant radial strength. This unique interwoven structure gains it advantage in the femoropopliteal region. The purpose of this review article is to investigate the current published evidence of the use of self-expandable interwoven nitinol stents in femoropopliteal arterial disease and compare them with other endovascular treatment options.

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.