Palmaz-Schatz Stent Research Articles

Optimization of Coronary Stent Design Using Response Surface Modeling

AbstractCardiovascular diseases (CVDs) are the leading cause of premature death and can partially be treated using coronary stents. During stent placement in the artery, vascular wall injuries occur due to the nonuniform expansion of the stent. The radial displacement at the distal end of the stent becomes greater than the radial displacement at the middle of the stent. This phenomenon is known as the dogboning effect. This paper presents a possible solution to counteract this effect by optimizing the design parameters of polymeric bioresorbable Palmaz-Schatz stent. SolidWorks 2019 (Dassault Systèmes) is used to design the coronary stent. The finite element method (Abaqus standard) is used to investigate the expansion behavior of the stents. The optimization method uses forty initial samples to approximate the functional relationship between design parameters and the objective function. Optimization methods based on response surface methodology (RSM) using a regression model are proposed to decrease the dogboning effect. The optimization technique using RSM resulted in a 78.67% reduction in the dogboning rate from the average dogboning rate of initial samples and an 87.7% reduction in comparison with the original stent. This research offers valuable insights into mitigating the dogboning effect, thereby advancing the development of more efficient stent designs for treating CVDs.

PERFORMANCE ANALYSIS OF HEXAGONAL UNIT CELL STENT DESIGN AND SINGLE-LAYERED MANUFACTURABILITY WITH FDM

İlaç salınımlı stentlerden sonra geliştirilen biyobozunur polimer esaslı stentler için yapılan ön klinik çalışmalardan elde edilen sonuçlara göre polimer stentlerin kullanılabilirliği sorgulanmaktadır. Polimer stentlerde strat kalınlığının yüksek olması ve mekanik özelliklerin zayıflığı nedeniyle tasarım ve malzeme iyileştirmesine gidilerek yeni modellerin ortaya çıkarılması üzerine araştırmalara devam edilmektedir. Balonla genişleyen stentlerde oluşan uç açılması arter içerisinde intimal ve medial katmanlara zarar vermektedir. Bu zarar, erken dönemde neointimal hiperplazi ve restenoza sebep olmaktadır. Metalik stent geometrilerinden biri olan Palmaz-Schatz birim hücre modelinde balonla genişleme esnasında uç açılması ve kısalma oranı meydana gelmektedir. Bu çalışmada, Palmaz-Schatz stent geometrisinin genişlemesiyle oluşturduğu geometri dikkate alınarak PLLA malzemeden altıgen birim stent geometrisinde yeni tasarım gerçekleştirilmiştir. Sonlu elemanlar simülasyonuyla, ince strat kalınlığında tasarlanan altıgen stendin genişlemesinde oluşan uç açılması ve kısalma oranı belirlenmiştir. Ayrıca, stent genişlemesinde üç katmanlı arter ve kalsifik plak yapısında meydana gelen doku hasarı ölçülmüştür. Altıgen geometrideki stentte oluşan uç açılması ve kısalma oranı Palmaz-Schatz modeline göre azaltılmıştır. Bununla birlikte, PLA/PHA karışımı malzemeden eriyik yığma modelleme ile altıgen stent geometrisinin 3B plaka baskısı tek katmanlı olarak üretilmesi sonrası ısıtıcı bir tubular tabla üzerinde sarılarak stent formuna getirilmiştir

In Silico Evaluation of Bilinear Elastoplastic Coronary Artery Stents

Mechanical responses of the endovascular stent determine the arterial homeostasis and vulnerability of the atherosclerotic plaque. Given the various plaque components when the stent is deployed, the stent may apply excessive stress to the lesion and cause plaque rupture. Herein, using the interaction between the Palmaz–Schatz stent with two stent biomaterials, stainless steel, and magnesium alloy, and three different types of plaque, namely hypocellular, hypercellular, and calcified, are studied. An implicit finite element method is used to simulate and analyze the stress and strain acting on the stents, artery, and plaques. The Mooney–Rivlin hyperelastic material model is considered to study the responses of each component. The results reveal that stainless‐steel stents applied a higher level of stress to the plaques and vessel wall, which may lead to vascular damage and plaque rupture. However, a magnesium alloy stent with the similar design and geometrical parameters generates less stress on the plaque and artery. Interestingly, a minor improvement in magnesium alloy stents, increasing the strut thickness, can enhance the stent performance and lower the applied stresses to the vasculature and plaque, making them an ideal choice of material for stenting applications.

Design optimization of biomedical stent under the influence of the radial pressure using FEM

Atherosclerosis problem is treated using stenting a percutaneous transluminal angioplasty method. During the process, a stent is deployed into the artery by using a balloon as an expander. The balloon is removed after deflation but the stent remains expanded to act as a scaffold and keeping the blood vessel open. In this paper, the non-uniform deformation of the stent and for shortening effect is simulated using Finite Element Simulation using COMSOL. The dog boning and foreshortening effects are simulated to change the geometry parameters for optimum performance of the study. The Palmaz Schatz stent model is used for this simulation. The stress evaluation is calculated using the FEM. The stent is expanded from an original diameter of 0.74 mm to a diameter of 2 mm in the middle section. The average displacement of the stent's inner radius is determined and a global equation is used to compute the corresponding applied pressure load. The longitudinal recoils are about −0.9%, the distal radial recoil is about 0.4% and the central radial recoil is about 0.7%.

Is modeling stents still an important issue?

Numerical models of cardiovascular devices have always appeared in literature studies few years after their use in clinical practice. As example, FDA approval of Palmaz-Schatz stent was in 1994, while the first numerical studies on a similar stent model appeared after 1999. The same temporal delay can be observed for degradable stents, transcatheter valves or more recently for devices like the stent retrievers. This observation does not necessarily mean that numerical modeling had not been used in the design of the stents or cardiovascular devices. Companies might have used numerical tools but not published the results. Was the publication activity committed mainly to the academic world? Or was the numerical modeling an exclusive academic activity until a few years ago? Modeling has intrinsic errors, while prototyping looks immune, as it is the natural design process for a company. The real world has always attracted more attention than the virtual world. Models are useful and the gap between the industrial production and numerical tools in the designing of devices is being reduced recently. Nowadays advances in medical images and augmentation of computer power allow to think of building real-time simulations as well as patient-specific models to be used to predict the device behavior; this is a plus that numerical modeling has over the traditional design process of cardiovascular devices. Furthermore, as in the past, the identification of new unknown problems/failures will always make the usage of numerical modeling a useful tool to explain the reasons of failure. The future in modeling stents is envisioned in their use for in silico trials and in the link between biology, engineering, and science.

Shape and functional optimization of biodegradable magnesium stents for manufacturing by ultrasonic-microcasting technique

In this study, a well-known stent model, Palmaz–Schatz, and a new geometry, NG, are optimized, in agreement with a set of optimization variables and limiting values of the design parameters, imposed by a new manufacturing process—ultrasonic-microcasting—, which allows to surpass some difficulties presented by other manufacturing technologies. The optimized designs shown that significantly lower values of the considered performance parameters can be obtained, namely in terms of required expansion pressure, which was reduced 30.31% for Palmaz–Schatz stent and 55% for NG stent. Dogboning and foreshortening were minimized and a reduction of 97.30 and 86.64%, respectively, was achieved for Palmaz–Schatz model, while for NG model such values were 13.64 and 50.00%. Despite the greater values of thickness comparing to the stainless-steel devices (0.30 vs 0.10 mm), the optimized stents studied present a similar or even better performance than those. Furthermore, results suggest that the adopted optimization methodology can effectively optimize the stent’s design and their functionality for devices to be manufacturing by the ultrasonic-microcasting processing. The presented optimization methodology allows the interaction between the requirements imposed by the patient’s condition, i.e. the initial and expanded diameter of the stent and its length, and the constraints imposed by the manufacturing process, having as result the optimal geometry regarding the defined objectives.

A numerical study on the effect of geometrical parameters and loading profile on the expansion of stent.

Stenting has been proposed as an effective treatment to restore blood flow in obstructed arteries by plaques. Although several modified designs for stents have been suggested, most designs have the risk of disturbing blood flow. The main objective is to propose a stent design to attain a uniform lumen section after stent deployment. Mechanical response of five different designs of J & J Palmaz-Schatz stent with the presence of plaque and artery are investigated; four stents have variable strut thickness of different magnitudes and the rest one is a uniform-strut-thickness stent. Nonlinear finite element is employed to simulate the expansion procedure of the intended designs using ABAQUS explicit. The stent design whose first cell thickness linearly increases by 35 percent, exhibits the best performance, that is it has the lowest recoiling and stress induced in the intima for a given lumen gain. It also enjoys the minimal discrepancy between the final at the distal and proximal ends. A uniform widened artery can be achieved by using the stent design with 35 percent increase in its first cell, which provides the possibility to prevent from disturbing blood flow and consequently post-operation complications.

Analysis of the stent expansion in a stenosed artery using finite element method: application to stent versus stent study.

In this article, finite element method is used to investigate the mechanical behavior of a stent and to determine the biomechanical interaction between the stent and the artery in a stenting procedure. The main objective of this study is to reach to a model close to a real condition of coronary stent placement. Unlike most of the models proposed in the literature, all the steps of the deployment of a stent in the stenotic vessel (i.e. pressure increasing, constant load pressure and pressure decreasing) are simulated in this article to show the behavior of the stent in different stages of implantation. The results indicate that the first step of deployment, that is, pressure increasing, plays a main role in the success of stent implantation. So that, in order to compare the behavior of different types of stents, it is sufficient to compare their behavior at the end of pressure increasing step. In order to show the application of the findings in stent versus stent studies, three commercially available stents (the Palmaz-Schatz, Multi-Link and NIR stents) are modeled and their behavior is compared at the end of pressure increasing step. The effect of stent design on the restenosis rate is investigated. According to the findings, the possibility of restenosis is lower for Multi-Link and NIR stents in comparison with Palmaz-Schatz stent which is in good agreement with clinical results. Therefore, the testing methodology outlined here is proposed as a simple and economical alternative for "stent versus stent" complicated clinical trials.

The coronary stent story

The objective of this article is to narrate the story of stent development as witnessed by the author who was present from the very beginning. By the end of eighties, coronary angioplasty (PTCA) had clearly shown its limitations such as abrupt vessel occlusion, dissection and restenosis rate of up to 35%. The Medinvent Company developed a self-expanding-stent that was implanted in a first series of patients by Ulrich Sigwart in Lausanne, Switzerland in 1986. However, the multicenter study in 1989 had disastrous results, with 25% of stent occlusion rate and restenosis of >20% in remained patients. The Palmaz-Schatz stent was first bare-metal stent (BMS) largely used in the world since 1990. The heavy anticoagulation treatment was abolished by A. Colombo in 1993. By 1997, about 17 new models existed, still the abrupt stent occlusion, subacute stent thrombosis (2-4%), and restenosis (25-30%), were major problems. Drug-eluting stents (DES) were developed to specifically address the problems of restenosis encountered with BMS. The sirolimus eluting stents used since 2002 have shown better clinical results than paclitaxel eluting stents arriving in 2004, but newcomers using zotaralimus, everolimus and biolimus elusions have arrived showing even better results. Currently, the last generation of stent need only 3 months of dual antiplatelet treatment, bioapsorbale coating is only on ab-luminal side of stent, struts are thin and metallic cage is laser cut hypotube. The case of chronic total coronary occlusion is discussed, as this indication benefited most from the stent development. Bioresorbable vascular scaffolds (BVS) are intended to overcome most drawbacks of stents: the presence of a metallic cage, positive remodelling, and normal vasomotor vessel function, but long-term results are still unknown.

Neoatherosclerosis 16 years following bare-metal stent implantation: Different tissue components in different underlying lesions observed with optical coherence tomography

A 61 years old male with a history of multiple treatments ofpercutaneous coronary intervention (PCI) with bare-metal stents (BMS)was admitted for the treatment of acute coronary syndrome (ACS).Sixteen years prior to this admission when he was 45 years old, heexperienced inferior ST-elevation myocardial infarction. He receivedone Palmaz-Schatz Stent (PS) for the treatment of lesion in distal rightcoronary artery (RCA). During the hospitalization, he received one PSfor the treatment of stable lesion in proximal left anterior descendingartery (LAD) (Fig. 1). Routine 3-year follow up angiography revealed norestenosis. The controls of other coronary risk factors were good exceptforobesity(BMI=36).SixteenyearsafterPSimplantation,hefeltsuddenchest pain suggestive of ACS, although there was no signi ficant ST-Tchange in electrocardiography at rest. The angiography revealed focalsevere stenoses in both the PS at the RCA and LAD. Optical coherencetomography(OCT)wasperformedtodecidewhichlesionwastheculprit.OCT findings within both lesion demonstrated intimal hyperplasia overthe BMSs. OCT in the RCA demonstrated diffusely thickened neointimathat exhibited low signal intensity with attenuation, partially coveredwith layered tissue pattern. Disrupted thin fibrous cap with intraluminalthrombus was observed at the culprit lesion ( Fig. 2,PanelA1,A2),whichpresumably caused plaque rupture responsible for ACS. In contrast, OCTin the LAD showed neointima accompanied with homogeneousconcentric high backscatte r structure with calcification in all of thestent area. Within the stable neointima, microvessels with tubularstructures differentiated from any side branches were observed ( Fig. 2,Panel B1, B2). In this LAD lesion, thin cap fibroatheroma was notobserved, which is compatible with a stable plaque. PCI was performedfor in-stent neoatherosclerotic lesions in both distal RCA and proximalLAD with zotarolimus-eluting stents.Inthepresentcase,OCTrevealedtypicalunstableplaquemorphologyin the RCA in-stent lesion, which was the culprit of acute myocardialinfarction treated 16 years prior to the event. Also, OCT found stableplaque morphology in the LAD in-stent segment whose underlyingsegment was the stable lesion. Theref ore, the types of neoatherosclerosiswere different according to the unde rlying plaque, although the BMSimplantation was performed 16years ago.PCI with stenting is the most widely performed procedure for thetreatmentofischemicheartdisease,andthisdeviceimprovedtheclinicalperformance as well [1]. In addition to in-stent restenosis (ISR) and latestent thrombosis, neoatherosclerosis within the stent has been recentlybrought into focus [2,3]. Traditionally, intimal hyperplasia after BMSimplantation has been considered stable, with an early peak between6 months and 1 year at late quiescent period thereafter [4].However,Kimura et al. demonstrated that lat e luminal re-narrowing was commonbeyond 4years following BMS implantation [5]. Hasegawa et al. reportedthat atherosclerotic progression occurred in the in-stent intima of BMSmore than 5years after stent deployment based on pathological analysis[6]. OCT has demonstrated its potential capacity to accurately char-acterize or evaluate the responses after stent deployment. Habara et al.reported that the qualitative OCT findings of BMS restenosis tissuebetween very-late-ISR and early-ISR are signi ficantly different [6].Basedon their OCT analysis, the restenosis lesions N5years after BMSimplantation were found with a high incidence (90.7%) accompaniedwith heterogeneous OCT appearance with low-density area, whereaslesions b1 year after BMS implantation showed extremely lowerincidence (17.9%) of neoatherosclerosis [7]. Nakazawa et al. reportedthat an underlying unstable lesion, which included ruptured plaque andthin-cap fibroatheroma, is an independent risk factor for neo-atheroscrelosis [3]. It has been reported that the quality of underlyingplaque has influenced the incidence of neatherosclerosis after stenting[3], however, it is not known whether the quality of the underlyingplaque affects neoatherosclerotic process. In the present case, based onOCT analysis, the observed neointima demonstrated very similar

Numerical fatigue life assessment of cardiovascular stents: A two-scale plasticity-damage model

Cardiovascular disease has become a major global health care problem in the last decades. To tackle this problem, the use of cardiovascular stents has been considered a promising and effective approach. Numerical simulations to evaluate the in vivo behavior of stents are becoming more and more important to assess potential failures. As the material failure of a stent device has been often associated with fatigue issues, numerical approaches for fatigue life assessment of stents have gained special interest in the engineering community. Numerical fatigue life predictions can be used to modify the design and prevent failure without making and testing numerous physical devices, thus preventing from undesired fatigue failures. We present a numerical fatigue life model for the analysis of cardiovascular balloon-expandable stainless steel stents that can hopefully provide useful information either to be used for product improvement or for clinicians to make life-saving decisions. This model incorporates a two-scale continuum damage mechanics model and the so-called Soderberg fatigue failure criterion. We provide numerical results for both Palmaz-Schatz and Cypher stent designs and demonstrate that a good agreement is found between the numerical and the available experimental results.

Dosimetric aspects of 103Pd radioactive stent source

Abstract This study aims to determine AAPM TG-60 dosimetric quantities in regions surrounding the 103Pd stent wall by MCNP5 Monte Carlo code. The Palmaz-Schatz stent was modeled by a hollow cylinder of 17.89mm length (2mm diameter) with net surface very similar to real stent. The Dose deposited per photon (Gy), relative dose, Anisotropy function, F(r,θ), and radial dose function, gL(r), were described at AAPM TG-60 protocol were generated from these values and listed in tabular format. For benchmarking, the relative dose values were verified with TG-43 and EGS4 code results at identical conditions, relative to the radial distances from surface of the stent. There were noticeable results. These physical dosimetric parameters can be used in future treatment planning systems for IVBT.

ARTERIAL WALL MECHANICS AND CLINICAL IMPLICATIONS AFTER CORONARY STENTING: COMPARISONS OF THREE STENT DESIGNS

The goal of this work is to quantitatively assess the relationship between the reported restenosis rates and stent induced arterial stress or strain parameters through finite element method. The impact of three stent designs (Palmaz–Schatz stent, Express stent, and Multilink Vision stent) on the arterial stress distributions were characterized. The influences of initial stent deployment location, stent-tissue friction, and plaque properties on the arterial stresses were also investigated. Higher arterial stresses were observed at the proximal end of the plaque. The Multilink–Vision stent induced lesser stress concentrations due to the high stiffness of the Cobalt Chromium material and thinner strut thickness. The stent-induced arterial stress concentrations were positively correlated with the reported in-stent restenosis rates, with a correlation coefficient of 0.992. Stent deployment initiated at the center of the lumen led to less arterial stress variation, while deployment closer to the thinner edge of the plaque causes higher arterial stresses. The friction between the stent and tissue was found to contribute to larger stress alternations for the plaque only. Increased plaque stiffness resulted in a reduced arterial stress concentration and clinical restenosis rate. Results presented herein suggested that arterial stresses serve as a comprehensive index factor to predict the occurrence of in-stent restenosis, which will facilitate the new stent design and surgical planning.

Comparison of drug-eluting versus bare-metal stents after rotational atherectomy for the treatment of calcified coronary lesions

Calcified coronary lesions are a well-known risk factor for short and long-term failure after both bare metal stent (BMS) [ 1 Tan K. Sulke N. Taub N. Sowton E. Clinical and lesion morphologic determinants of coronary angioplasty success and complications: current experience. J Am Coll Cardiol. 1995; 25: 855-865 Google Scholar , 2 Hoffmann R. Mintz G.S. Popma J.J. et al. Treatment of calcified coronary lesions with Palmaz–Schatz stents. An intravascular ultrasound study. Eur Heart J. 1998; 19: 1224-1231 Google Scholar ] and drug eluting stent (DES) implantation [ 3 Moussa I. Ellis S.G. Jones M. et al. Impact of coronary culprit lesion calcium in patients undergoing paclitaxel-eluting stent implantation (a TAXUS-IV sub study). Am J Cardiol. 2005; 96: 1242-1247 Google Scholar , 4 Berenguer A. Mainar V. Bordes P. Valencia J. Gomez S. Lozano T. Incidence and predictors of restenosis after sirolimus-eluting stent implantation in high-risk patients. Am Heart J. 2005; 150: 536-542 Google Scholar , 5 Migliorini A. Shehu M. Carrabba N. et al. Predictors of outcome after sirolimus-eluting stent implantation for complex in-stent restenosis. Am J Cardiol. 2005; 96: 1110-1112 Google Scholar ]. Rotational atherectomy facilitates the delivery of stents in severely calcified coronary lesions by modifying plaque anatomy and smoothing inner vascular lumen. Recent reports suggest that the use of rotational atherectomy in combination with DES implantation for the treatment of severely calcified lesions might result in high procedural success and acceptable restenosis rate [ 6 Clavijo L.C. Steinberg D.H. Torguson R. et al. Sirolimus-eluting stents and calcified coronary lesions: clinical outcomes of patients treated with and without rotational atherectomy. Catheter Cardiovasc Interv. 2006; 68: 873-878 Google Scholar , 7 Garcia de Lara J. Pinar E. Ramon Gimeno J. et al. Percutaneous coronary intervention in heavily calcified lesions using rotational atherectomy and paclitaxel-eluting stents: outcomes at one year. Rev Esp Cardiol. 2010; 63: 107-110 Google Scholar , 8 Furuichi S. Sangiorgi G.M. Godino C. et al. Rotational atherectomy followed by drug-eluting stent implantation in calcified coronary lesions. EuroIntervention. 2009; 5: 370-374 Google Scholar , 9 Mezilis N. Dardas P. Ninios V. Tsikaderis D. Rotablation in the drug eluting era: immediate and long-term results from a single center experience. J Interv Cardiol. 2010; 23: 249-253 Google Scholar , 10 Benezet J. de la Llera LS Diaz Cubero J.M. Villa M. Fernandez-Quero M. Sanchez-Gonzalez A. Drug-eluting stents following rotational atherectomy for heavily calcified coronary lesions: long-term clinical outcomes. J Invasive Cardiol. 2011; 23: 28-32 Google Scholar ]. However, the long-term efficacy and safety of DES compared to BMS, in combination with rotational atherectomy in patients with calcified coronary lesions is limited.

Novel dose calculation and characterization of 32P intravascular brachytherapy stent source

Abstract Derived from AAPM task group No. 60/149 protocol, applicable in treatment planning In this study, the two-dimensional dose distributions in water for a 32P intravascular brachytherapy stent have been calculated. The pure beta emitter source 32P which has been coated on Palmaz-Schatz stent is discussed. The dosimetric parameters required by the AAPM TG-60/149 formalism are discussed and calculated. Version 5 of the (MCNP) Monte Carlo radiation transport code was used to calculate the dosimetry parameters around the source. The Monte Carlo calculated dose rate at the reference point is found to be 2.8 Gy/μCi. Also in this study, the geometry function, G(r,θ), radial dose function, g(r), and the anisotropy function, F(r,θ), have been calculated at distances from 1.8 to 9 mm. The results of these calculations have been compared with other published calculated and measured values for an actual same source. High dose variants were visible near the 32P stent surface, but these values decreased with depth in water rapidly. There is an acceptable agreement between the calculated data in this study and other published data for the same source, which validate our simulations method.

Sirolimus and its Analogs and its Effects on Vascular Diseases

Sirolimus (rapamycin), a macrolide antibiotic approved for use as an immunosuppressive agent in the prevention of organ rejection, is a cell proliferation inhibitor and regulator of the immune response which acts through inhibition of TOR (target of rapamycin), a kinase essential to cell cycle progression. Recent studies suggest that the TOR pathway is critical to overall cell function, and at a basic mechanistic level, may be a regulator and potential therapeutic target involved in many of the major (and minor) disorders seen in man today. Cardiovascular diseases including restenosis following percutaneous coronary intervention as well as the more widespread condition of atherosclerosis, share this common involvement of TOR. The present report addresses the current state of intervention in cardiovascular disorders with Sirolimus and similar inhibitors of TOR, including the rationale for this approach and the successes observed to date. Success of the first drug-eluting stent to locally treat restenosis in the clinic is discussed, as are preclinical studies addressing a role in overall atherosclerosis in animal models. In addition, due to the known toxicities when given systemically, an approach for targeted delivery to local areas of vascular disease is discussed.

Very Long-Term (15 to 20 Years) Clinical and Angiographic Outcome After Coronary Bare Metal Stent Implantation

We previously reported that the long-term luminal response after coronary bare metal stenting is triphasic, with an early restenosis phase spanning the 6 months after the index procedure, an intermediate-term regression phase from 6 months to 3 years, and a late renarrowing phase beyond 4 years. However, the clinical significance of late luminal renarrowing remains unknown. Angiographic and clinical follow-up of the same cohort of 405 patients with successful Palmaz-Schatz stent placement was extended beyond 15 years. Clinical follow-up was completed in 98% of patients at 5 years and in 81% at 15 years. The incidence of death and cardiac death at 15 years was 45.4% and 20.6%, respectively. Paired long-term (4 to 10 years) and very long-term (>10 years) angiographic studies without intercurrent target lesion revascularization were performed in 55 lesions, and minimal luminal diameter further decreased from 1.88±0.50 mm to 1.60±0.73 mm (P=0.002). Late target lesion revascularization after initial stabilization of the stented segments occurred rarely within 4 years. Beyond 4 years, however, the incidence of late target lesion revascularization increased steadily from 3.3% at 4 years to 24.7% at 15 years. The incidence of definite very late stent thrombosis was low (1.5% at 15 years). Luminal renarrowing of the stented segment beyond 4 years was a progressive process extending beyond 10 years. The angiographic observation of late in-stent restenosis was clinically relevant because a corresponding progressive increase in the incidence of late target lesion revascularization was observed beyond 4 years and up to 15 to 20 years after bare metal stent implantation.

The Relation Between the Arterial Stress and Restenosis Rate After Coronary Stenting

Two commercially available stents (the Palmaz–Schatz (PS) and S670 stents) with reported high and low restenosis rates, respectively, have been investigated in this paper. Finite element models simulating the stent, plaque, and artery interactions in 3 mm stenosed right coronary arteries were developed. These models were used to determine the stress field in artery walls after stent implantation. The material properties of porcine arteries were measured and implemented in the numerical models. The stress concentration induced in the artery by the PS stent was found to be more than double that of the S670 stent. It demonstrated a good correlation with the reported restenosis rate. The effects of stent structures, compliance mismatch, plaque geometry, and level of stenosis were studied. Results suggested that stent designs and tissue properties cause alterations in vascular anatomy that adversely affect arterial stress distributions within the wall, which impact vessel responses such as restenosis. Appropriate modeling of stent, plaque, and artery interactions provided insights for evaluating alterations to the arterial mechanical environment, as well as biomechanical factors leading to restenosis.

The use of a handmade balloon-expandable covered stent for native coarctation of the aorta in an adult patient: A report of a first case in Japan

In western countries, the use of a balloon-expandable covered stent is recommended for the treatment of native coarctation of the aorta (CoA) in adult patients because endovascular bare stents cannot completely prevent complications such as aneurysms or aortic rupture. However, such a product that is appropriate and officially approved is not available in Japan. We developed and used a handmade balloon-expandable covered stent in a 32-year-old patient with native CoA and achieved a good outcome. A Palmaz-Schatz stent (XL 10-series 4010; Johnson & Johnson, Warren, NJ, USA) was covered with an Ube woven-graft (WST series; 18 mm across; Ube Junken Medical, Tokyo, Japan). Because the stent shortens when dilated, one end of the graft was firmly sutured to one end of the stent, whereas the other end of the graft was stitched loosely to the other end of the stent so that it could slide along the struts of the stent to accommodate foreshortening. After meticulous in vitro simulations, the covered stent was implanted with right ventricular overdrive pacing. No complications were observed, and the pressure gradient disappeared. These results indicate that angioplasty using a balloon-expandable covered stent is highly safe and effective for correcting native CoA in adult patients and hopefully in children.

Effects of Material on the Deployment of Coronary Stents

Coronary stents have been more and more widely used in clinic over the past decade. There have been a large number of stents made of different biocompatible materials available commercially in the market. It is however unclear which is more suitable to specific patients. This raises a major concern whether the choice of stents could be assessed before a delivery surgery. This paper aims to provide a computational approach for evaluating the effect of stent materials on biomechanical outcomes of the deployments of stents in different patient. It will review the typical biomaterials being used for coronary stents, seeking to qualitatively assess them for use as coronary stents. Non-linear explicit finite element (FE) procedure is carried out using the Palmaz-Schatz stent geometry to quantitatively predict the effect of mechanical properties of these biomaterials on stent and coronary artery behavior during stent deployment. A quantitative comparison is made for exploring the effect of different materials on the deployment of stents. The study is considered significant in understanding the role how stent materials affect biomechanical responses to the coronary stenting. It provides a new methodology to promote a patient-specific assessment before surgery.