In vivo MR angiographic quantification of axial and twisting deformations of the superficial femoral artery resulting from maximum hip and knee flexion

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.

Fatigue strength and life prediction of lower limb venous stents under three-stage loading conditions

After the implantation of lower limb artery stents, the complex loading conditions imposed on the limb can lead to fatigue failure, which may induce inflammation and restenosis. To investigate the effect of multi-axial loading conditions on the fatigue performance of stents, five stents, namely APsolute Pro (APbott Vascular, USA), Complete SE (Medtronic, USA), Protégé EverFlex (PE3, USA), Pulsar-35 (Biotronik, Germany), and E-luminexx-B (Bard, USA), were analyzed based on the finite element method (FEM). Besides, their fatigue strength was determined under three levels of loading conditions, including tension-bending-torsion and compression-bending-torsion. Based on that, the fatigue life of these stents was predicted. The results showed that based on the nominal stress method, tension-bending-torsion loading had a more significant impact on the fatigue life of stents than compression-bending-torsion loading. Besides, two different types of initial cracks were analyzed by the fracture mechanics method. The results suggested that both the initial crack and the external load were the main causes of stent fatigue fractures. Compared with the loading nature, the influence of the initial crack on stent fatigue life was more significant. Under the same loading condition, the APsolute Pro stent had the longest fatigue life, while the E-luminexx-B stent had the shortest. Moreover, the mechanism of stent fatigue failure was revealed by exploring the fatigue performance and life prediction of stents under complex loading conditions. These findings have important implications for improving the structural design of stents and their clinical selection.

Evaluation of the arterial kink point during flexion of the hip: A dynamic angiographic study in iliac endofibrosis patients

PURPOSE

The aim of the study was to determine the flexion point's location of the ilio-femoral arterial axis and its angulation.

MATERIALS AND METHODS

Thirty-seven dynamic digital subtraction angiographies were analyzed and were included in the current study. Different lengths were measured, based on specific anatomical landmarks: the origin of the external iliac artery, the inguinal ligament and the bifurcation of the femoral artery. These lengths were measured in extension and during flexion of the hip in order to determine the flexion point of the artery.

RESULTS

In extension, some physiological angulations of the external iliac artery were measured. During flexion of the hip joint, the distance from the kink point to the bifurcation of the common iliac artery was respectively 82 ± 21 mm (range 48-116) on the right side and 95 ± 20 mm (range 59-132) on the left side. The distance from the kink point to the inguinal ligament was respectively 38 ± 40 mm (range 12-138) on the right side and 26 ± 23 mm (range 8-136) on the left side. The distance from the kink point to the bifurcation of the femoral artery was respectively 45 ± 29 mm (range 15-107) on the right side and 27 ± 12 mm (range 10-66) on the left side. During flexion, the angulation of the flexion point of the ilio-femoral axis was 114 ± 18° (range 81-136°).

CONCLUSIONS

The flexion point was located cranially to the inguinal ligament and below the departure of the external iliac artery.

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.

Three-year clinical course after fluoropolymer-based drug-eluting stent implantation for femoropopliteal lesions

BACKGROUND

Although the 1-year clinical outcomes of fluoropolymer-based drug-eluting stents (FP-DES) were favorable for the treatment of real-world femoropopliteal lesions in symptomatic peripheral artery disease (PAD), their performance beyond 1 year remained unknown. The current study determined the 3-year clinical course of FP-DES implantation for real-world femoropopliteal lesions.

METHODS

This multicenter, prospective, observational study evaluated 1204 limbs (chronic limb-threatening ischemia, 34.8%; mean lesion length, 18.6 ± 9.9 cm, chronic total occlusion: 53.2%) of 1097 patients with PAD (age, 75 ± 9 years; diabetes mellitus, 60.8%) undergoing FP-DES implantation for femoropopliteal lesions. The primary outcome measure was 3-year restenosis. The secondary outcome measures included 3-year occlusive restenosis, stent thrombosis, target lesion revascularization (TLR), and aneurysmal degeneration.

RESULTS

The 3-year cumulative occurrence of restenosis was 27.3%, whereas that of occlusive restenosis, stent thrombosis, and TLR was 16.1%, 7.3%, and 19.6%, respectively. The annual occurrence of restenosis decreased by 12.0%, 9.5%, and 5.8% in the first, second, and third year, respectively (p < 0.001). Similarly, the rates of occlusive restenosis and stent thrombosis decreased (p < 0.001 and p = 0.007, respectively), whereas the rate of TLR remained unchanged for 3 years (p = 0.15). The incidence of aneurysmal degeneration at 3 years (15.7%) did not significantly differ from that at 1 and 2 years (p = 0.69 and 0.20, respectively).

CONCLUSIONS

This study highlights the favorable long-term clinical course of FP-DES in real-world practice, emphasizing the importance of monitoring for occlusive restenosis and stent thrombosis while considering the potential onset of aneurysmal degeneration.

Meta-analysis of outcomes from drug-eluting stent implantation in femoropopliteal arteries

OBJECTIVE

In recent years, studies of drug-eluting stent (DES) for femoropopliteal artery diseases (FPADs) have been gradually published. To explore whether this type of stent is superior to the traditional bare metal stent (BMS), we performed this study.

METHODS

A systematic search for randomized controlled trials (RCTs) in Excerpta Medica Database (Embase), PubMed, Web of Science (WOS), and Cochrane Library was performed on November 29, 2022. We innovatively adopted the hazard ratio (HR), the most appropriate indicator, as a measure of the outcomes that fall under the category of time-to-event data. The HRs was extracted directly or indirectly. Then, the meta-analyses using random effects model were performed. The bias risks of included papers were assessed by the Cochrane Risk of Bias 2.0 tool. This study was registered on the PROSPER platform (CRD42023391944) and not funded.

RESULTS

Seven RCTs involving 1,889 participants were found. After pooled analyses, we obtained results without propensity on each of the following 3 outcomes of interest: in-stent restenosis (ISR) -free survival, primary patency (PP) survival, and target lesion revascularization (TLR) -free survival (P >0.05, respectively). Because the results of pooled analyses of the other two outcomes of interest (all-cause death free survival and clinical benefit survival) had high heterogeneity both, they were not accepted by us.

CONCLUSION

For FPADs, the DES has not yet demonstrated superiority or inferiority to BMS, in the ability to maintain PP, avoid ISR and TLR.

The effects of axial twisting and material non-symmetry on arterial bent buckling

Artery buckling occurs due to hypertensive lumen pressure or reduced axial tension and other pathological conditions. Since arteries in vivo often experience axial twisting and the collagen fiber alignment in the arterial wall may become nonsymmetric, it is imperative to know how axial twisting and nonsymmetric collagen alignment would affect the buckling behavior of arteries. To this end, the objective of this study was to determine the effect of axial twisting and nonsymmetric collagen fiber distribution on the critical pressure of arterial bent buckling. The buckling model analysis was generalized to incorporate an axial twist angle and nonsymmetric fiber alignment. The effect of axial twisting on the critical pressure was simulated and experimentally tested in a group of porcine carotid arteries. Our results showed that axial twisting tends to reduce the critical pressure depending on the axial stretch ratio and twist angle. In addition, nonsymmetric fiber alignment reduces the critical pressure. Experimental results confirmed that a twist angle of 90° reduces the critical pressure significantly (p < 0.05). It was concluded that axial twisting and non-axisymmetric collagen fibers distribution could make arteries prone to bent buckling. These results enrich our understanding of artery buckling and vessel tortuosity. The model analysis and results could also be applicable to other fiber reinforced tubes under lumen pressure and axial twisting.

Effects of Tapered-Strut Design on Fatigue Life Enhancement of Peripheral Stents

Peripheral stent could fracture from cyclic loadings as a result of our blood pressures or daily activities. Fatigue performance has therefore become a key issue for peripheral stent design. A simple yet powerful tapered-strut design concept for fatigue life enhancement was investigated. This concept is to move the stress concentration away from the crown and re-distribute the stresses along the strut by narrowing the strut geometry. Finite element analysis was performed to evaluate the stent fatigue performance under various conditions consistent with the current clinical practice. Thirty stent prototypes were manufactured in-house by laser with a series of post-laser treatments, followed by the validation of bench fatigue tests for proof of concept. FEA simulation results show that the fatigue safety factor of the 40% tapered-strut design increased by 4.2 times that of a standard counterpart, which was validated by bench tests with 6.6-times and 5.9-times fatigue enhancement at room temperature and body temperature, respectively. Bench fatigue test results agreed very well with the increasing trend predicted by FEA simulation. The effects of the tapered-strut design were significant and could be considered as an option for fatigue optimization of future stent designs.

DEGRADATION PHENOMENA ON LAST GENERATIONS OF POLYETHYLENE TEREPHTHALATE KNITTED VASCULAR PROSTHESES

Objectives

The aim of this study was to analyze a series of new generations of explanted knitted polyethylene terephthalate (PET) vascular grafts (VGs) presenting nonanastomotic degradations according to preoperative computed tomography angiography (CTA) when available in order to better understand the mechanisms leading to rupture.

Methods

Explanted knitted PET VGs were collected as part of the Geprovas European Collaborative Retrieval Program. VGs implanted after 1990 presenting a nonanastomotic rupture of the fabric were included. Clinical data and pre-explantation CTA data when available were retrieved for each VG. The ruptures were characterized by macroscopic examination and optical microscopy according to a standardized protocol.

Results

Nineteen explants were collected across 11 European centers, 13 were implanted as infrainguinal bypasses, 3 at the aortic level, and 1 as an axillobifemoral bypass. The mean implantation duration was 9.2 years. Pre-explantation CTA data were available for 8 VGs and showed false aneurysms at the adductor canal level on 4 VGs, at the inguinal ligament level on 2 VGs, and in the proximal or middle third thigh level on 3 VGs. Examination revealed longitudinal ruptures on 9 explanted VGs (EVGs), transversal ruptures on 15 EVGs, 45°-oriented ruptures on 5 EVGs, V-shaped ruptures on 7 EVGs, and punctiform ruptures on 2 EVGs. Ruptures involved the remeshing line on 11 EVGs, the guideline on 10 EVGs, and the crimping valley on 15 EVGs.At the microscopic level, two main degradation phenomena could be identified: a decrease in the density of the meshing and local ruptures of the PET fibers. Fourteen EVGs presented a loosening of the remeshing line and 17 EVGs an attenuation of the crimping.

Conclusions

New-generation PET VG degradation seems to result from both anatomic constraints and intrinsic textile structure phenomena.

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 Treatment and Outcomes for Femoropopliteal In-Stent Restenosis: Insights from the XLPAD Registry

Background

There is limited "real-world" evidence examining treatment modalities and outcomes in patients with symptomatic peripheral arterial disease undergoing endovascular treatment of femoropopliteal (FP) in-stent restenosis (ISR).

Materials and Methods

We compared outcomes in 2,895 patients from the XLPAD registry (NCT01904851) between 2006 and 2019 treated for FP ISR (n = 347) and non-ISR (n = 2,548) lesions. Primary endpoint included major adverse limb events (MALE) at 1 year, a composite of all-cause death, target limb repeat revascularization, or major amputation.

Results

ISR patients were more frequently on antiplatelet (94.5% vs 89.4%, p=0.007) and statin (68.9% vs 60.3%, p=0.003) therapies. Lesion length was similar (ISR: 145 ± 99 mm vs. non-ISR: 142 ± 99 mm, p=0.55). Fewer treated ISR lesions were chronic total occlusions (47.3% vs. 53.7%, p=0.02) and severely calcified (22.4% vs. 44.7%, p < 0.001). Atherectomy (63.5% vs. 45.0%, p < 0.001) and drug-coated balloons (DCB; 4.7% vs. 1.7%, p < 0.001) were more frequently used in ISR lesions. The distal embolization rate was higher in ISR lesions (2.4% vs. 0.9%, p=0.02). Repeat revascularization (21.5% vs. 16.7%, p=0.04; Figure) was higher and freedom from MALE at 1 year was significantly lower (87% vs. 92.5%, p < 0.001) in the ISR group.

Conclusion

Atherectomy and DCB are more frequently used to treat FP ISR lesions. Patients with FP ISR have more intraprocedural distal embolization, higher repeat revascularization procedures, and lower freedom from MALE at 1 year.

Numerical simulations of the nonsymmetric growth and remodeling of arteries under axial twisting

Blood vessels are often subjected to axial twisting during body movement or surgery. Sustained twisting may lead to blood vessel growth and remodeling, however, it remains unclear how the extracellular matrix in the blood vessels remodel under sustained axial twisting. This study aimed to develop a computational model to simulate stress-induced growth and remodeling (G&R) of thin-walled blood vessels under axial twisting. Cylindrical vessels were subjected to a step increase in axial torque while the axial stretch and lumen pressure remained constant. The vessel walls were modeled based on the constrained mixture theory given as microstructure-based discrete fiber families with isotropic matrix structure models. Simulation results demonstrated that in response to a constant twist angle loading, arterial wall thickness, mass, and twisting torque gradually increase towards a new steady state. However, the stress and mass decrease in one diagonal fiber family while increasing in the other diagonal fiber family before reaching plateaus. A novel finding was that the two helical collagen fiber families showed different growth rates and patterns during remodeling, driven by the different fiber stresses generated by the twisting, and led to non-symmetric material properties. This study sheds new light on arterial wall remodeling under axial twisting.

TORSIONAL BEHAVIOR OF STENTS: THE ROLE OF LINKER AND STENT TAPERING INVESTIGATED WITH NUMERICAL SIMULATION

The torsional performance is a major mechanical property of stent. A stent with good torsional performance is easy to deform along blood vessels without damaging the vascular wall to avoid in-stent restenosis (ISR). Therefore, this study aimed to study the effect of stent parameters on torsional performance. The effect of stent parameters on torsional performance was studied via finite element method (FEM). The twist metric (TM) and stress distribution of various stents were compared. The TM values of stents with I-, S-, M-, C-, and V-shaped linkers were 0.0190, 0.0191, 0.0184, 0.0141, and 0.0201[Formula: see text][Formula: see text], respectively. In addition, the TM value of the stent increased by 35.85 times when the number of linkers was increased from 2 to 8 and the stent was twisted at the same angular displacement in clockwise direction. The TM value of the stent with 1.13∘ tapering was 0.010 [Formula: see text], which was lower by 47.64% compared with that of cylindrical stent. Compared with the shape of the linker, the number of linkers had a more remarkable effect on torsional performance. Torsional performance was observably enhanced with the decrease in the number of linkers. Among the five stents with different linker shapes, the torsional performance of the stent with C-shaped linker was the best. Besides, the torsional performance of the tapered stent was better than that of the cylindrical stent. Moreover, the torsional performance increased by increasing the stent tapering. This work might provide insights into better stent design and clinical decisions.

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.

SUPERA Stenting in the Common Femoral Artery: Early Experience and Practical Considerations

Purpose

Endovascular therapy in the management of de novo common femoral disease remains controversial. Considerable interest has been generated in recent years due to recent technological advancement in the design of vascular stents. In particular, SUPERA (Abbot Vascular Inc, Santa Clara USA) stents are designed to offer increased flexibility and less adverse interactions with the arterial wall, thus making it potentially better suited for common femoral lesions. However, despite such theoretical advantages, there is lack of data in its use in clinical practice. This study provides illustrative examples of SUPERA stents in different clinical settings and contributes to important clinical data for the overall efficacy and safety profile of endovascular interventions in common femoral artery (CFA) disease.

Materials and Methods

Retrospective analysis of all endovascular CFA procedures between January 1, 2011, and December 31, 2019, was conducted. Data collected included demographics, clinical symptoms, medical comorbidities, procedural characteristics, and immediate and short-term complications. Detailed analysis was performed on the stenting cohort.

Results

During our study period, a total of 69 patients underwent endovascular interventions involving the CFA at our institution, of which 16 patients had stenting procedures for a total of 18 stent deployments. Technical success was achieved in all stenting procedures. A total of 15 SUPERA stents were placed in 13 patients. No stent fractures were observed. Overall primary patency rate of SUPERA stents at the time of 12-month follow-up was 100% in patients who had a follow-up assessment (n = 12 stents).

Conclusion

Endovascular intervention of the CFA is an evolving topic in the interventional radiology and vascular surgery community. Recent development of newer generation of devices such as SUPERA peripheral stents offers significant potential benefits given their inherent design. Despite the theoretically promising design of the SUPERA, there is a lack of data to support its use. This study contributes important patient-level data for SUPERA stent deployments.

Creating a Natural Vascular Scaffold by Photochemical Treatment of the Extracellular Matrix for Vascular Applications

The development of bioscaffolds for cardiovascular medical applications, such as peripheral artery disease (PAD), remains to be a challenge for tissue engineering. PAD is an increasingly common and serious cardiovascular illness characterized by progressive atherosclerotic stenosis, resulting in decreased blood perfusion to the lower extremities. Percutaneous transluminal angioplasty and stent placement are routinely performed on these patients with suboptimal outcomes. Natural Vascular Scaffolding (NVS) is a novel treatment in the development for PAD, which offers an alternative to stenting by building on the natural structural constituents in the extracellular matrix (ECM) of the blood vessel wall. During NVS treatment, blood vessels are exposed to a photoactivatable small molecule (10-8-10 Dimer) delivered locally to the vessel wall via an angioplasty balloon. When activated with 450 nm wavelength light, this therapy induces the formation of covalent protein–protein crosslinks of the ECM proteins by a photochemical mechanism, creating a natural scaffold. This therapy has the potential to reduce the need for stent placement by maintaining a larger diameter post-angioplasty and minimizing elastic recoil. Experiments were conducted to elucidate the mechanism of action of NVS, including the molecular mechanism of light activation and the impact of NVS on the ECM.

Nitinol Type Alloys General Characteristics and Applications in Endodontics

A very extensive literature review presents the possibilities and needs of using, in endodontics, the alloys commonly known as nitinol. Nitinol, as the most modern group of engineering materials used to develop root canals, is equilibrium nickel and titanium alloys in terms of the elements’ atomic concentration, or very similar. The main audience of this paper is engineers, tool designers and manufacturers, PhD students, and students of materials and manufacturing engineering but this article can also certainly be used by dentists. The paper aims to present a full material science characterization of the structure and properties of nitinol alloys and to discuss all structural phenomena that determine the performance properties of these alloys, including those applied to manufacture the endodontic tools. The paper presents the selection of these alloys’ chemical composition and processing conditions and their importance in the endodontic treatment of teeth. The results of laboratory studies on the analysis of changes during the sterilization of endodontic instruments made of nitinol alloys are also included. The summary of all the literature analyses is an SWOT analysis of strengths, weaknesses, opportunities, and threats, and is a forecast of the development strategy of this material in a specific application such as endodontics.

Kneeling-induced calf ischemia: a pilot study in apparently healthy European young subjects

PURPOSE

Many tasks, sports or leisure activities require maximal knee flexion. We hypothesized that this position could result in reduced calf perfusion, in young European subjects.

METHODS

We quantified calf ischemia resulting from the knee flexion with transcutaneous oxygen pressure (TcpO2) sensors by assessing the decrease from rest of TcpO2 (DROP) defined as limb changes minus chest changes. A minimal DROP (DROPm) <-15 mmHg defines the presence of ischemia. From the crawling position, participants kneeled for 3 min while bending as in prostration/prayer position (P). Thirty-five participants repeated this maneuver a second time, while 7 participants were also required to sit on their heels with the torso in the vertical position to attain knee flexion without significant groin flexion (S).

RESULT

In 41 healthy young volunteers (30 males), 25 [20-31] years old, 37 patients showed a DROPm < -15 mmHg from "R" to "P" in one (n = 4) or both (n = 33) calves (90.2%; 95% CI 76.9-97.3). After backward regression of the DROPm, there was no significant association with side, body weight of systolic blood pressure. However, age was strongly associated with DROPm (OR 5.34 [2.45-8.69]) so that DROPm was significantly higher in older, with a correlation ρ = 0.31 (p = 0.003).

CONCLUSION

Kneeling dramatically reduces calf perfusion, likely through popliteal artery kinking, possibly through muscle crushing. Eastern lifestyle includes routine flexed position since childhood. Whether or not such a chronic training reduces the risk of kneeling-induced ischemia in adults is unknown to date.

Integration of substrate- and flow-derived stresses in endothelial cell mechanobiology

Endothelial cells (ECs) lining all blood vessels are subjected to large mechanical stresses that regulate their structure and function in health and disease. Here, we review EC responses to substrate-derived biophysical cues, namely topography, curvature, and stiffness, as well as to flow-derived stresses, notably shear stress, pressure, and tensile stresses. Because these mechanical cues in vivo are coupled and are exerted simultaneously on ECs, we also review the effects of multiple cues and describe burgeoning in vitro approaches for elucidating how ECs integrate and interpret various mechanical stimuli. We conclude by highlighting key open questions and upcoming challenges in the field of EC mechanobiology.

Vascular Response of a Polymer-Free Paclitaxel-Coated Stent (Zilver PTX) versus a Polymer-Coated Paclitaxel-Eluting Stent (Eluvia) in Healthy Swine Femoropopliteal Arteries

PURPOSE

To compare the long-term vascular healing responses of healthy swine iliofemoral arteries treated with a polymer-free paclitaxel-eluting stent (Z-PES, Zilver PTX) or a fluoropolymer-based paclitaxel-eluting stent (FP-PES, Eluvia).

MATERIALS AND METHODS

Bilateral iliofemoral arteries in 20 swine were treated with a Z-PES (n = 16) or a FP-PES (n = 24) and were examined histologically at 1, 3, 6, and 12 months.

RESULTS

Morphometric analysis revealed larger external and internal elastic lamina, stent expansion, and lumen area in the FP-PES than in the Z-PES at all timepoints. Luminal narrowing was similar in the 2 groups at 1 month; however, greater stenosis was observed in the Z-PES group at 3 months, with significant regression thereafter, resulting in equivalent stenosis at 6 and 12 months. Greater drug effect and less complete vessel healing were found in the FP-PES group at all timepoints, including greater numbers of malapposed struts with excessive fibrin deposition at 1 and 3 months, than in the Z-PES group. Three of 12 FP-PESs from the 6- and 12-month cohorts also showed circumferential medial disruption with peri-strut inflammation, whereas no abnormal findings were observed in contralateral Z-PESs.

CONCLUSIONS

Prolonged paclitaxel release with the presence of a permanent polymer may contribute to the differential vascular responses seen for the Z-PES and FP-PES groups, including medial layer disruption and aneurysmal vessel degeneration that was sometimes observed in the FP-PES group. These distinct features should be confirmed by pathology and in vivo imaging of human superficial femoral arteries to determine their clinical significance.

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.

Stability Analysis of Arteries Under Torsion

Vascular tortuosity may impede blood flow, occlude the lumen, and ultimately lead to ischemia or even infarction. Mechanical loads like blood pressure, axial force, and also torsion are key factors participating in this complex mechanobiological process. The available studies on arterial torsion instability followed computational or experimental approaches, yet single available theoretical study had modeled the artery as isotropic linear elastic. This paper aim is to validate a theoretical model of arterial torsion instability against experimental data. The artery is modeled as a single-layered, nonlinear, hyperelastic, anisotropic solid, with parameters calibrated from experiment. Linear bifurcation analysis is then performed to predict experimentally measured stability margins. Uncertainties in geometrical parameters and in measured mechanical response were considered. Also, the type of rate (incremental) boundary conditions (RBCs) impact on the results was examined (e.g., dead load, fluid pressure). The predicted critical torque and twist angle followed the experimentally measured trends. The closest prediction errors in the critical torque and twist rate were 22% and 67%, respectively. Using the different RBCs incurred differences of up to 50% difference within the model predictions. The present results suggest that the model may require further improvements. However, it offers an approach that can be used to predict allowable twist levels in surgical procedures (like anastomosis and grafting) and in the design of stents for arteries subjected to high torsion levels (like the femoropopliteal arteries). It may also be instructive in understanding biomechanical processes like arterial tortuosity, kinking, and coiling.

Stent Design Affects Femoropopliteal Artery Deformation

BACKGROUND

Poor durability of femoropopliteal artery (FPA) stenting is multifactorial, and severe FPA deformations occurring with limb flexion are likely involved. Different stent designs result in dissimilar stent-artery interactions, but the degree of these effects in the FPA is insufficiently understood.

OBJECTIVES

To determine how different stent designs affect limb flexion-induced FPA deformations.

METHODS

Retrievable markers were deployed into n = 28 FPAs of lightly embalmed human cadavers. Bodies were perfused and CT images were acquired with limbs in the standing, walking, sitting, and gardening postures. Image analysis allowed measurement of baseline FPA foreshortening, bending, and twisting associated with each posture. Markers were retrieved and 7 different stents were deployed across the adductor hiatus in the same limbs. Markers were then redeployed in the stented FPAs, and limbs were reimaged. Baseline and stented FPA deformations were compared to determine the influence of each stent design.

RESULTS

Proximal to the stent, Innova, Supera, and SmartFlex exacerbated foreshortening, SmartFlex exacerbated twisting, and SmartControl restricted bending of the FPA. Within the stent, all devices except Viabahn restricted foreshortening; Supera, SmartControl, and AbsolutePro restricted twisting; SmartFlex and Innova exacerbated twisting; and Supera and Viabahn restricted bending. Distal to the stents, all devices except AbsolutePro and Innova exacerbated foreshortening, and Viabahn, Supera, Zilver, and SmartControl exacerbated twisting. All stents except Supera were pinched in flexed limb postures.

CONCLUSIONS

Peripheral self-expanding stents significantly affect limb flexion-induced FPA deformations, but in different ways. Although certain designs seem to accommodate some deformation modes, no device was able to match all FPA deformations.

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.

Length Redundancy and Twist Improve the Biomechanical Properties of Polytetrafluoroethylene Bypass Grafts

BACKGROUND

The iliofemoropopliteal artery significantly changes path length during normal hip and knee flexion. Prosthetic bypass grafts, such as polytetrafluoroethylene (PTFE) grafts, are relatively stiff and thus can subject graft anastomoses to high tension when the path length increases. The aim of this study was to examine the influence of length redundancy and twist on the biomechanical properties of PTFE bypass grafts.

METHODS

Unreinforced and ring-reinforced PTFE grafts were loaded in an axial mechanical testing machine to measure the tensile and compressive axial forces with varying levels of length redundancy and axial twist.

RESULTS

Adding 5-15% length redundancy to a graft decreases the force to cause 5% extension by > 90% without substantially increasing shortening forces. Adding 4.5°/cm of axial twist imparts a corkscrew shape to the graft without increasing extension or shortening forces in the presence of length redundancy. Ring-reinforced PTFE grafts require more length redundancy to experience these reductions in forces especially in the presence of axial twist.

CONCLUSIONS

A modest amount of length redundancy and twist (i.e., a cork-screw condition) confers improved biomechanical properties in a PTFE graft, especially in ring-reinforced grafts. This should be taken into consideration when fashioning an arterial bypass graft in the iliofemoropopliteal segment.

Computer-aided analysis of middle cerebral artery tortuosity: association with aneurysm development

OBJECTIVE

Blood vessel tortuosity may play an important role in the development of vessel abnormalities such as aneurysms. Currently, however, there are no studies analyzing the impact of brain blood vessel tortuosity on the risk of aneurysm formation. Therefore, the authors performed a computer-aided analysis of middle cerebral artery (MCA) tortuosity, especially among patients diagnosed with MCA aneurysms.

METHODS

Anatomy of the MCAs of 54 patients with unruptured MCA aneurysms was retrospectively analyzed, as was that of 54 sex-, age-, and vessel side-matched control patients without MCA aneurysms. From medical records, the authors obtained each patient's medical history including previous and current diseases and medications. For each patient, they calculated the following tortuosity descriptors: relative length (RL), sum of angle metrics (SOAM), triangular index (TI), product of angle distance (PAD), and inflection count metric (ICM).

RESULTS

Patients with an MCA aneurysm had significantly lower RLs (0.75 ± 0.09 vs 0.83 ± 0.08, p < 0.01), SOAMs (0.45 ± 0.10 vs 0.60 ± 0.17, p < 0.01), and PADs (0.34 ± 0.09 vs 0.50 ± 0.17, p < 0.01). They also had significantly higher TIs (0.87 ± 0.04 vs 0.81 ± 0.07, p < 0.01) and ICMs (3.07 ± 1.58 vs 2.26 ± 1.12, p < 0.01). Female patients had significantly higher RLs (0.76 ± 0.11 vs 0.80 ± 0.09, p = 0.03) than male patients.

CONCLUSIONS

Middle cerebral artery aneurysm formation is strongly associated with blood vessel tortuosity parameters, which can potentially be used to screen for patients at risk for MCA aneurysm formation.

An Animal Model of Human Peripheral Arterial Bending and Deformation

BACKGROUND

Designing peripheral arterial stents has proved challenging, as implanted devices will repetitively and unpredictably deform and fatigue during movement. Preclinical testing is often inadequate, given the lack of relevant animal models. The purpose of this study was to test the hypothesis that deformation of the human peripheral vasculature could be qualitatively and quantitatively modeled using an experimental animal.

METHODS

Anteroposterior contrast angiography was performed in domestic Landrace-Yorkshire farm pigs. Images were obtained with the hind limbs naturally extended then repeated, (1) flexed approximately 90° at the hip and knee, (2) overflexed in a nonphysiological fashion. Quantitative vascular angiographic analysis was utilized to measure arterial diameter, length, and deformation. Percent axial arterial compression and bending were assessed.

RESULTS

Eight iliofemoral arteries in four animals were imaged. Mean luminal diameters of the iliac and femoral segments in the neutral position were 5.4 ± 0.5 mm and 4.6 ± 0.5 mm. Hind limb physiologic flexion induced profound arterial compression, 17 ± 8% and 29 ± 6% and bending, 36°±10° and 76° ± 13° within the iliac and femoral segments, respectively. With extreme flexion, the femoral artery could be reliably bent >90°. The observed findings exceeded the deformation observed historically within the human superficial femoral (∼5% compression and 10° bending) and popliteal artery (∼10% compression and 70° bending).

CONCLUSIONS

Significant nonradial deformation of the porcine iliofemoral arteries was observed during manual hind limb flexion and exceeded that typically observed in humans. This model constitutes a "worst case" scenario for testing deformation and fatigue of intravascular devices indicated for the human peripheral vasculature.

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.

Validating Fatigue Safety Factor Calculation Methods for Cardiovascular Stents

Evaluating risk of fatigue fractures in cardiovascular implants via nonclinical testing is essential to provide an indication of their durability. This is generally accomplished by experimental accelerated durability testing and often complemented with computational simulations to calculate fatigue safety factors (FSFs). While many methods exist to calculate FSFs, none have been validated against experimental data. The current study presents three methods for calculating FSFs and compares them to experimental fracture outcomes under axial fatigue loading, using cobalt-chromium test specimens designed to represent cardiovascular stents. FSFs were generated by calculating mean and alternating stresses using a simple scalar method, a tensor method which determines principal values based on averages and differences of the stress tensors, and a modified tensor method which accounts for stress rotations. The results indicate that the tensor method and the modified tensor method consistently predicted fracture or survival to 107 cycles for specimens subjected to experimental axial fatigue. In contrast, for one axial deformation condition, the scalar method incorrectly predicted survival even though fractures were observed in experiments. These results demonstrate limitations of the scalar method and potential inaccuracies. A separate computational analysis of torsional fatigue was also completed to illustrate differences between the tensor method and the modified tensor method. Because of its ability to account for changes in principal directions across the fatigue cycle, the modified tensor method offers a general computational method that can be applied for improved predictions for fatigue safety regardless of loading conditions.

Primary Stenting of the Superficial Femoral Artery in Patients with Intermittent Claudication Has Durable Effects on Health-Related Quality of Life at 24 Months: Results of a Randomized Controlled Trial

BACKGROUND

Intermittent claudication (IC) is commonly caused by lesions in the superficial femoral artery (SFA), yet invasive treatment is still controversial and longer term patient-reported outcomes are lacking. This prospective randomized trial assessed the 24-month impact of primary stenting with nitinol self-expanding stents compared to best medical treatment (BMT) alone in patients with stable IC due to SFA disease on health-related quality of life (HRQoL).

METHODS

One hundred patients with stable IC due to SFA disease treated with BMT were randomized to either stent (n = 48) or control (n = 52) group. HRQoL assessed by Short Form 36 Health Survey (SF-36) and EuroQoL 5-dimensions (EQ5D) 24 months after treatment were primary outcome measures. Walking Impairment Questionnaire, ankle-brachial index (ABI), and walking distance were secondary outcomes.

RESULTS

Significantly better SF-36 Physical Component Summary (P = 0.024) and physical domain scores such as Physical Function (P = 0.012), Bodily Pain (P = 0.002), General Health (P = 0.037), and EQ5D (P = 0.010) were reported in intergroup comparison between the stent and the control group. Both ABI (from 0.58 ± 0.11 to 0.85 ± 0.18; P < 0.001 in the stent group and from 0.63 ± 0.17 to 0.69 ± 0.18; P = 0.036 in the control group) and walking distance (from 170 ± 90 m to 616 ± 375 m; P < 0.001 in the stent group and from 209 ± 111 m to 331 ± 304 m; P = 0.006 in the control group) improved significantly in intragroup comparisons.

CONCLUSIONS

In patients with IC caused by lesions in the SFA, primary stenting compared to BMT alone was associated with significant improvements in HRQoL, ABI, and walking distance durable up to 24 months of follow-up. Clinical Trial Registration http://www.clinicaltrials.gov . Unique Identifier: NCT01230229.

Remote Endarterectomy and Lamina Vastoadductoria Dissection Improves Superficial Femoral Artery Biomechanical Behavior during Limb Flexion

BACKGROUND

Superficial femoral artery (SFA) remote endarterectomy offers the advantage of preserving anatomy and geometry of the native artery, but the risk of restenosis still exists. The particular role of the adductor canal (AC) in mechanical constraints has been highlighted. The aim of this study was to assess if a surgical protocol associating remote SFA endarterectomy and AC freeing would modify the SFA geometrical changes during physiological limb flexion.

METHODS

From January 2015 to March 2015, 10 patients (Rutherford 3-5) with unilateral SFA occlusion were included. Functional postoperative assessments were performed through duplex ultrasound (DUS) examinations with flow velocity measurements in both straight and flexed positions and anatomical measurements through 3-dimensional computed tomography angiography (CTA) reconstructions with arterial angulations examination. Functional results were compared with similar findings in healthy volunteers, and anatomical results were compared with contralateral limb findings.

RESULTS

Mean occlusion length was 243.0 ± 17.7 mm. Technical success was achieved in all cases. No difference of peak flow velocities was noticed between operated patients and volunteers. CTA results showed that limb flexion induced SFA shortening in all segments, with a maximal value for the popliteal artery (PA) (10.4 ± 4.4%). Comparisons between the operated and contralateral limbs showed that angles were less sharp during bending in the operated limb.

CONCLUSIONS

This preliminary study demonstrates that freeing the AC modifies the biomechanical properties of the SFA. These results could potentially help in proposing future hybrid techniques that could improve technical performances for SFA occlusive disease treatment.

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.

Waves and fluid-solid interaction in stented blood vessels

This paper focuses on the modelling of fluid–structure interaction and wave propagation problems in a stented artery. Reflection of waves in blood vessels is well documented in the literature, but it has always been linked to a strong variation in geometry, such as the branching of vessels. The aim of this work is to detect the possibility of wave reflection in a stented artery due to the repetitive pattern of the stents. The investigation of wave propagation and possible blockages under time-harmonic conditions is complemented with numerical simulations in the transient regime.

Limb flexion-induced axial compression and bending in human femoropopliteal artery segments

BACKGROUND

High failure rates of femoropopliteal artery (FPA) interventions are often attributed in part to severe mechanical deformations that occur with limb movement. Axial compression and bending of the FPA likely play significant roles in FPA disease development and reconstruction failure, but these deformations are poorly characterized. The goal of this study was to quantify axial compression and bending of human FPAs that are placed in positions commonly assumed during the normal course of daily activities.

METHODS

Retrievable nitinol markers were deployed using a custom-made catheter system into 28 in situ FPAs of 14 human cadavers. Contrast-enhanced, thin-section computed tomography images were acquired with each limb in the standing (180 degrees), walking (110 degrees), sitting (90 degrees), and gardening (60 degrees) postures. Image segmentation and analysis allowed relative comparison of spatial locations of each intra-arterial marker to determine axial compression and bending using the arterial centerlines.

RESULTS

Axial compression in the popliteal artery (PA) was greater than in the proximal superficial femoral artery (SFA) or the adductor hiatus (AH) segments in all postures (P = .02). Average compression in the SFA, AH, and PA ranged from 9% to 15%, 11% to 19%, and 13% to 25%, respectively. The FPA experienced significantly more acute bending in the AH and PA segments compared with the proximal SFA (P < .05) in all postures. In the walking, sitting, and gardening postures, average sphere radii in the SFA, AH, and PA ranged from 21 to 27 mm, 10 to 18 mm, and 8 to 19 mm, whereas bending angles ranged from 150 to 157 degrees, 136 to 147 degrees, and 137 to 148 degrees, respectively.

CONCLUSIONS

The FPA experiences significant axial compression and bending during limb flexion that occur at even modest limb angles. Moreover, different segments of the FPA appear to undergo significantly different degrees of deformation. Understanding the effects of limb flexion on axial compression and bending might assist with reconstructive device selection for patients requiring peripheral arterial disease intervention and may also help guide the development of devices with improved characteristics that can better adapt to the dynamic environment of the lower extremity vasculature.

Limb flexion-induced twist and associated intramural stresses in the human femoropopliteal artery

High failure rates of femoropopliteal artery (FPA) interventions are often attributed to severe mechanical deformations that occur with limb movement. Torsion of the FPA likely plays a significant role, but is poorly characterized and the associated intramural stresses are currently unknown. FPA torsion in the walking, sitting and gardening postures was characterized in n = 28 in situ FPAs using intra-arterial markers. Principal mechanical stresses and strains were quantified in the superficial femoral artery (SFA), adductor hiatus segment (AH) and the popliteal artery (PA) using analytical modelling. The FPA experienced significant torsion during limb flexion that was most severe in the gardening posture. The associated mechanical stresses were non-uniformly distributed along the length of the artery, increasing distally and achieving maximum values in the PA. Maximum twist in the SFA ranged 10-13° cm^-1, at the AH 8-16° cm^-1, and in the PA 14-26° cm^-1 in the walking, sitting and gardening postures. Maximum principal stresses were 30-35 kPa in the SFA, 27-37 kPa at the AH and 39-43 kPa in the PA. Understanding torsional deformations and intramural stresses in the FPA can assist with device selection for peripheral arterial disease interventions and may help guide the development of devices with improved characteristics.

Effect of aging on mechanical stresses, deformations, and hemodynamics in human femoropopliteal artery due to limb flexion

Femoropopliteal artery (FPA) reconstructions are notorious for poor clinical outcomes. Mechanical and flow conditions that occur in the FPA with limb flexion are thought to play a significant role, but are poorly characterized. FPA deformations due to acute limb flexion were quantified using a human cadaver model and used to build a finite element model that simulated surrounding tissue forces associated with limb flexion-induced deformations. Strains and intramural principal mechanical stresses were determined for seven age groups. Computational fluid dynamics analysis was performed to assess hemodynamic variables. FPA shape, stresses, and hemodynamics significantly changed with age. Younger arteries assumed straighter positions in the flexed limb with less pronounced bends and more uniform stress distribution along the length of the artery. Even in the flexed limb posture, FPAs younger than 50 years of age experienced tension, while older FPAs experienced compression. Aging resulted in localization of principal mechanical stresses to the adductor hiatus and popliteal artery below the knee that are typically prone to developing vascular pathology. Maximum principal stresses in these areas increased threefold to fivefold with age with largest increase observed at the adductor hiatus. Atheroprotective wall shear stress reduced after 35 years of age, and atheroprone and oscillatory shear stresses increased after the age of 50. These data can help better understand FPA pathophysiology and can inform the design of targeted materials and devices for peripheral arterial disease treatments.

Arterial wall remodeling under sustained axial twisting in rats

Blood vessels often experience torsion along their axes and it is essential to understand their biological responses and wall remodeling under torsion. To this end, a rat model was developed to investigate the arterial wall remodeling under sustained axial twisting in vivo. Rat carotid arteries were twisted at 180° along the longitudinal axis through a surgical procedure and maintained for different durations up to 4weeks. The wall remodeling in these twisted arteries was examined using histology, immunohistochemistry and fluorescent microscopy. Our data showed that arteries remodeled under twisting in a time-dependent manner during the 4weeks post-surgery. Cell proliferation, MMP-2 and MMP-9 expressions, medial wall thickness and lumen diameter increased while collagen to elastin ratio decreased. The size and number of internal elastic lamina fenestrae increased with elongated shapes, while the endothelial cells elongated and aligned towards the blood flow direction gradually. These results demonstrated that sustained axial twisting results in artery remodeling in vivo. The rat carotid artery twisting model is an effective in vivo model for studying arterial wall remodeling under long-term torsion. These results enrich our understanding of vascular biology and arterial wall remodeling under mechanical stresses.

Diagnosis, classification, and treatment of femoropopliteal artery in-stent restenosis

In-stent restenosis is a pervasive challenge to the durability of stenting for the treatment of lower extremity ischemia. There is considerable controversy about the criteria for diagnosis, indications for treatment, and preferred algorithm for addressing in-stent restenosis. This evidence summary seeks to review existing information on strategies for the treatment of this difficult problem.

A single-center retrospective analysis of patency rates of intraluminal versus subintimal endovascular revascularization of long femoropopliteal occlusions

OBJECTIVE

The evaluation of patency rates of intraluminal versus subintimal endovascular revascularization of long femoropopliteal (FP) lesions.

BACKGROUND

Chronic total occlusions (CTO) of the FP artery in peripheral interventions are crossed either with a support catheter-guidewire based technique or subintimal dissection and re-entry device assisted approach. Both techniques have a high procedural success rate, but their long term patency is not well studied. There is also lack of comparative data addressing the patency of long non-CTO vs. CTO occlusions.

METHODS

We performed a single center retrospective analysis, studying the patency rates in 215 patients (254 limbs) with TASC C and D FP lesions treated with stents. There were 3 patient groups: without CTO (non-CTO); CTO crossed using support catheter and guide-wire (CTO-SW) and CTO crossed with a re-entry device (CTO-RE).

RESULTS

There were 155 limbs in CTO-SW group; 50 in CTO-RE group and 49 in non-CTO. Lesion length (mean±SD) was 251.81±7.48mm in CTO-SW group; 280±13.18mm in CTO-RE group and 248.77±13.31 in non-CTO group (p=non-significant). In-stent restenosis (ISR) at a mean follow-up of 19.26±16.14months did not differ between groups occurring in 23 (47%) limbs in non-CTO; 66 (42%) in CTO-SW; and 24 (48%) in CTO-RE. Smoking and stent fracture were predictors of ISR by multivariate analysis.

CONCLUSION

In patients with long FP lesions, ISR rates were similar between patients with and without CTO. In the CTO group mid-term vessel patency was not affected by the crossing technique utilized.

In Vivo Quantification of the Deformations of the Femoropopliteal Segment: Percutaneous Transluminal Angioplasty vs Nitinol Stent Placement

PURPOSE

To quantify the deformations of the femoropopliteal (FP) segment in patients undergoing endovascular revascularization and to compare the posttreatment deformations caused by primary nitinol stent implantation to those produced by percutaneous transluminal angioplasty (PTA).

METHODS

Thirty-five patients (mean age 69±10 years; 20 men) scheduled for endovascular therapy were recruited for the study. During endovascular interventions, angiographic images were acquired with the legs straight and with a hip/knee flexion of 20°/70°. Image acquisition was performed before PTA for all patients, after PTA in 17 patients receiving this treatment only, and after primary stent implantation in the remaining 18 patients. A semiautomatic approach was used to reconstruct the 3-dimensional patient-specific artery models from 2-dimensional radiographs. Axial shortening and curvature changes in the arteries in vivo were calculated for the calcified, dilated, and stented regions, as well as the regions that were distal and proximal to the diseased and treated segments.

RESULTS

Leg flexion resulted in shortening of the artery in all investigated FP segments. The dilated arteries exhibited greater shortening compared with their stented counterparts (post-PTA 7.6%±4.9%, poststent 3.2%±2.9%; p=0.004). Leg flexion also led to an increase in the curvatures of all the sections of the FP segment. While stented arteries had significantly higher curvature values than PTA within the regions proximal to the treated sections, the choice of the treatment method did not affect the curvature of the other segments. Despite this, 40% of the stented arteries exhibited kinking during leg flexion.

CONCLUSION

The choice of the treatment method affects the postinterventional axial deformations of the FP segment but does not influence the curvature behavior. While PTA results in a more flexible artery, stents restrict the arteries' shortening capabilities. Depending on the anatomical position of the stents, this axial stiffening of the arteries may lead to chronic kinking, which may cause occlusions and, consequently, affect the long-term success of the procedure.