Heparin-coated balloon-expandable stent reduces intimal hyperplasia in the iliac artery in baboons

Sustained Thromboresistant Bioactivity with Reduced Intimal Hyperplasia of Heparin-Bonded Polytetrafluoroethylene Propaten Graft in a Chronic Canine Femoral Artery Bypass Model

BACKGROUND

Bypass graft thrombosis remains a significant mode of failure in prosthetic graft revascularization. The purpose of this investigation was to evaluate the long-term thromboresistant effect of heparin-bonded expanded polytetrafluoroethylene (ePTFE) graft using Carmeda BioActive Surface technology in a canine model.

METHODS

Bilateral femorofemoral artery bypass grafts with ePTFE grafts were performed in 25 adult grayhound dogs. In each animal, a heparin-bonded ePTFE graft (Propaten, WL Gore) was placed on one side, whereas a control nonheparin graft was placed on the contralateral side. The graft patency was assessed at 1, 6, 12, 18, and 24 months (n = 5 per group) following the bypass. Heparin bioactivity of the graft material was analyzed. The effect of intimal hyperplasia was also assessed.

RESULTS

All bypass grafts were patent at 1 month. Significantly greater patency rates were noted in the Propaten group compared to the control group at 12, 18, and 24 months, which were 84%, 80%, and 80% vs. 55%, 35%, and 20%, respectively (P < 0.02). There was a significant reduction in the anastomotic neointimal area and neointimal cell proliferation in Propaten grafts compared with control grafts at all groups between 6 and 24 months (P < 0.05). Heparin bioactivity as measured by antithrombin binding assay was demonstrated in the Propaten graft between 1 and 24 months. Mean heparin activities on Propaten grafts ranged from 26.3 ± 6.4 pmol/cm² to 18.4 ± 8.7 pmol/cm² between 1 and 24 months, which were significantly greater than the control group (P < 0.001). Differences between mean heparin activities of explanted Propaten graft samples at the various time points were nonsignificant (P > 0.05).

CONCLUSIONS

Heparin-bonded ePTFE graft provides a thromboresistant surface and reduced anastomotic intimal hyperplasia at 2 years. The stable heparin bioactivity of the Propaten graft confers an advantage in long-term graft patency.

Heparin coatings for improving blood compatibility of medical devices

Blood contact with biomaterials triggers activation of multiple reactive mechanisms that can impair the performance of implantable medical devices and potentially cause serious adverse clinical events. This includes thrombosis and thromboembolic complications due to activation of platelets and the coagulation cascade, activation of the complement system, and inflammation. Numerous surface coatings have been developed to improve blood compatibility of biomaterials. For more than thirty years, the anticoagulant drug heparin has been employed as a covalently immobilized surface coating on a variety of medical devices. This review describes the fundamental principles of non-eluting heparin coatings, mechanisms of action, and clinical applications with focus on those technologies which have been commercialized. Because of its extensive publication history, there is emphasis on the CARMEDA^® BioActive Surface (CBAS^® Heparin Surface), a widely used commercialized technology for the covalent bonding of heparin.

Surface modification with dopamine and heparin/poly-L-lysine nanoparticles provides a favorable release behavior for the healing of vascular stent lesions

Surface biofunctional modification of coronary artery stents to prevent thrombosis and restenosis formation, as well as accelerate endothelialization, has become a new hot spot. However, bioactive coatings on implants are not yet sufficiently developed for long-term activity, as they quickly lose efficiency in vivo and finally fail. On the basis of a novel time-ordered concept of biofunctionality for vascular stents, heparin/poly l-lysine nanoparticle (NP) was developed and immobilized on a polydopamine-coated titanium surface, with the aim of regulating and maintaining the intravascular biological response within the normal range after biomaterial implantation. An in vitro dynamic release model was established to mimic the blood flow condition in vivo with three phases: (1) An early phase (1-7 days) with release of predominantly anticoagulant and anti-inflammatory substances and to a minor degree antiproliferative effects against smooth muscle cells (SMCs); (2) this is followed by a phase (7-14 days) of supported endothelial cell (ECs) proliferation and suppressed SMC proliferation with persisting high antithrombogenicity and anti-inflammatory properties of the surface. (3) Finally, a stable stage (14-28 days) with adequate biomolecules on the surface that maintain hemocompatibility and anti inflammation as well as inhibit SMCs proliferation and promote ECs growth. In vivo animal tests further confirmed that the NP-modified surface provides a favorable release behavior to apply a stage-adjusted remedy. We suggested that these observations provide important guidance and potential means for reasonable and suitable platform construction on a stent surface.

Microfabrication and nanotechnology in stent design

Intravascular stents were first introduced in the 1980s as an adjunct to primary angioplasty for management of early complications, including arterial dissection, or treatment of an inadequate technical outcome due to early elastic recoil of the atherosclerotic lesion. Despite the beneficial effects of stenting, persistent high rates of restenosis motivated the design of drug-eluting stents for delivery of agents to limit the proliferative and other inflammatory responses within the vascular wall that contribute to the development of a restenotic lesion. These strategies have yielded a significant reduction in the incidence of restenosis, but challenges remain, including incomplete repair of the endothelium at the site of vascular wall injury that may be associated with a late risk of thrombosis. A failure of vessel wall healing has been attributed primarily to the use of polymeric stent coatings, but the effects of the eluted drug and other material properties or design features of the stent cannot be excluded. Improvements in stent microfabrication, as well as the introduction of alternative materials may help to address those limitations that inhibit stent performance. This review describes the application of novel microfabrication processes and the evolution of new nanotechnologies that hold significant promise in eliminating existing shortcomings of current stent platforms.

Covalent linkage of heparin provides a stable anti-coagulation surface of decellularized porcine arteries

Establishing thrombosis-resistant surface is crucial to develop tissue-engineered small diameter vascular grafts for arterial reconstructive procedures. The objective of this study was to evaluate the stability and anti-coagulation properties of heparin covalently linked to decellularized porcine carotid arteries. Cellular components of porcine carotid arteries were completely removed with chemical and physical means. Heparin was covalently linked to the decellularized vessels by a chemical reaction of the carboxyl end of amino acids with hydroxylamine sulphate salt and heparin-EDC. Bound heparin contents were measured by quantitative colorimetric assay of toluidine blue staining. The average content of heparin in treated vessels was 35.6 +/- 11.6 mg/cm(2) tissue, which represented 6.21 +/- 2.03 UPS heparin/cm(2) tissue. The stability of heparin linkage was tested by incubating the heparin-linked vessels either in PBS at 37 degrees C or in 70% alcohol at room temperature up to 21 days, showing no significant reduction of heparin content. Anti-coagulation property of bound heparin was determined with a clotting time assay using fresh dog blood. Standardized small pieces of non-heparin-bound vessels were clotted in fresh dog blood within 10 min., whereas all heparin-bound vessels did not form clot during 1-hr observation. In vivo platelet deposition of the vessel was determined with a baboon model of the femoral arteriovenous external shunt and (111)Indium labelling of platelets. There were 1.38 +/- 0.07 x 10(9) and 0.64 +/- 0.11 x 10(9) baboon platelets deposited on the control and heparin-linked vessels, respectively, at 60 min. These data demonstrate that covalent linkage of heparin provides an effective and stable anti-coagulation surface of decellularized porcine carotid arteries. This study may suggest a new strategy to develop tissue-engineered biological vascular grafts, which could be used for human coronary or low extremity artery bypasses.

Restenosis after lower extremity interventions: current status and future directions

The incidence of restenosis after percutaneous peripheral interventions (PPI) varies considerably depending upon the vascular bed but appears to be highest in the femoropopliteal and tibioperoneal arteries. The restenosis process in the periphery does not appear to stop at the 6-month mark, as seen with bare metal stents in the coronary arteries, but continues for a longer time, possibly years, after the intervention. This review evaluates the incidence of restenosis following lower extremity arterial interventions and potential drugs or devices that could alter this process, including nonpharmacological (stents, cryoplasty, Cutting Balloon angioplasty, atherectomy, brachytherapy, and photodynamic therapy) and pharmacological (systemic and direct drug delivery) approaches. A global strategy to achieve optimal outcome with PPI is offered: (1) obtain excellent acute angiographic results with less dissection and recoil, (2) protect the distal tibial vascular bed, and (3) reduce smooth muscle cell proliferation with pharmacological intervention.

Atualização sobre endopróteses vasculares (stents): dos estudos experimentais à prática clínica

Atualmente, o tratamento das doenças vasculares periféricas é uma das áreas da medicina de maior expansão. O número de intervenções vasculares aumenta e os resultados das novas técnicas endovasculares estão muito próximos aos das tradicionais cirurgias vasculares. Embora a angioplastia ofereça bons resultados em curto prazo, o implante de stents procura melhorar o sucesso do procedimento e estender o seu uso a um número maior de pacientes com doença vascular periférica. Entretanto, a sua utilização ainda é controversa. O implante de stents no sistema aorto-ilíaco tem bons resultados; porém, a sua indicação para as lesões femoro-poplíteas ainda é discutida. Além disso, o rápido desenvolvimento de stents e sua escolha para uso no sistema vascular periférico têm sido uma difícil tarefa para o cirurgião endovascular. Muitos fatores influenciam a escolha do stent, e um amplo conhecimento desse material é essencial. Tal escolha depende da avaliação pré-operatória, da localização e das características da lesão e também do uso do stent primário ou seletivo. Nesse trabalho, são realizadas revisão do histórico do desenvolvimento dos stents, desde os estudos experimentais até os ensaios clínicos e também discussão sobre a sua aplicação no tratamento das doenças vasculares periféricas.

Human umbilical vein versus heparin-bonded polyester for femoro-popliteal bypass: 5-year results of a prospective randomized multicentre trial

PURPOSE

To compare long-term patency of Heparin-Bonded Dacron (HBD) and Human Umbilical Vein (HUV) vascular prostheses in above-knee femoro-popliteal bypass surgery.

DESIGN

A prospective randomized multi-centre clinical trial.

PATIENTS AND METHODS

Femoro-popliteal bypasses were performed in 129 patients between 1996 and 2001. After randomization 70 patients received an HUV and 59 an HBD prosthesis. Patients were followed up every three months during the first postoperative year and yearly thereafter. The median follow-up was 60 months (range 3-96 months). Graft occlusions were detected by duplex scanning, angiography or surgical exploration.

RESULTS

The cumulative primary patency rates were 79%, 66% and 58% at 1, 3 and 5 years postoperatively. Primary patency rates for HUV were 74%, 64% and 58% at 1, 3 and 5 years and 84%, 68% and 58% for HBD, respectively (log-rank test, p=0.745). Overall secondary patency rates were 82%, 72% and 61% at 1, 3 and 5 years postoperatively. The overall cumulative limb salvage at 5 years follow-up was 89% (CI 80%-91%) and was not dependent on graft type. Smoking (p=0.019), number of patent crural arteries (p=0.030) and previous cerebro-vascular events (p=0.030) were significant predictors of graft occlusion.

CONCLUSION

There was no difference in long-term graft performance between HUV and HBD for above knee infrainguinal bypass.

Use of heparin-coated stents in neurovascular interventional procedures: preliminary experience with 10 patients

OBJECTIVE

Currently, there is minimal published data on the use of heparin-coated stents in the neurovasculature; however, these stents have a proven clinical record in the treatment of coronary disease. This article details our experience with the safety and technical aspects of stent deployment in the first 10 patients who had heparin-coated stents placed in the intracranial and cervical vasculature and the preliminary follow-up in most cases.

METHODS

We retrospectively reviewed the clinical history, intra- and periprocedural data, and imaging for the patients who received heparin-coated stents in the cervical and intracranial vasculature for cerebrovascular disease between October 2002 and October 2003.

RESULTS

Thirteen heparin-coated stents were placed in 10 patients. Seven out of the 10 patients had heparin-coated stents placed in the posterior circulation; the remaining three patients had stents placed in the anterior circulation. Four patients had stents placed intracranially. There was no acute or subacute in-stent thrombosis and no procedure-related complications. Follow-up was performed on most patients, with no clinical symptoms attributable to restenosis in any patient.

CONCLUSION

This small series suggests that heparin-coated stents are safe for use in the treatment of cervical and intracranial atherosclerotic disease. Longer-term follow-up is needed to study the heparin coating effect on in-stent restenosis rates and to assess the long-term durability and clinical efficacy of this stent. The use of drug-coated stents in the cerebrovascular circulation is an area that warrants further investigation.

Transrenal fixation of aortic stent-grafts: current status and future directions

Aortic stent-graft repair has been widely used in clinical practice for more than a decade, achieving satisfactory results compared to open surgical techniques. Transrenal fixation of stent-grafts is designed to obtain secure fixation of the proximal end of the stent-graft to avoid graft migration and to prevent type I endoleak. Unlike infrarenal deployment of stent-grafts, transrenal fixation takes advantage of the relative stability of the suprarenal aorta as a landing zone for the uncovered struts of the proximal stent. These transostial wires have sparked concern about the patency of the renal arteries, interference with renal blood flow, and effects on renal function. Although short to midterm results with suprarenal stent-grafts have not shown significant changes in renal function, long-term effects of this technique are still not fully understood. This review will explore the current status of transrenal fixation of aortic stent-grafts, potential risks of stent struts relative to the renal ostium, alternative methods to preserve blood flow to the renal arteries, and future directions or developments in stent-graft design to prevent myointimal proliferation around the stent struts.

Evaluation of platelet deposition and neointimal hyperplasia of heparin-coated small-caliber ePTFE grafts in a canine femoral artery bypass model

INTRODUCTION

Bypass graft failure due to acute thrombosis and intimal hyperplasia remains a major challenge in small-diameter vascular prosthetic graft reconstruction. Heparin has been shown to prevent thrombus formation and inhibit intimal antithrombotic in animal studies. In this study, we evaluated the effect of small-caliber heparin-coated expanded polytetrafluoroethylene (ePTFE) grafts on platelet deposition and intimal hyperplasia in a canine model of femoral artery bypass grafting.

METHODS

Nine adult greyhound dogs underwent placement of bilateral femorofemoral artery bypass grafts with ePTFE grafts (4 mm diameter and 7 cm long). In each animal, a heparin-coated ePTFE graft was placed on one side while a noncoated graft was placed on the contralateral side which served as the control. Platelet deposition was measured by autologous (111)indium-labeling and scintillation camera imaging analysis in 24 h. The graft patency was assessed at 4 weeks following the bypass. The effect of intimal hyperplasia was assessed with histological and morphometric analysis.

RESULTS

Platelet deposition on the heparin-coated grafts at 24 h was significantly reduced by 72% as compared to controls (P = 0.001). The patency rate was 44% in control grafts and 89% in heparin-coated grafts. There was a significant reduction of graft intimal hyperplasia at both proximal (0.38 +/- 0.21 mm(2)) and distal (0.19 +/- 0.06 mm(2)) anastomoses in the heparin-coated grafts as compared with proximal (1.01 +/- 0.28 mm(2)) and distal (0.42 +/- 0.01 mm(2)) anastomoses in the untreated control grafts, respectively (P < 0.05). Heparin coating significantly reduced graft neointimal hyperplasia at patent graft anastomoses by 55-72% as compared to controls.

CONCLUSIONS

These data demonstrate that heparin coating of ePTFE significantly reduced early platelet deposition and inhibited anastomotic neointimal hyperplasia. Moreover, small-caliber heparin-coated ePTFE graft significantly increased graft patency in a canine femoral artery bypass model. This may represent a promising treatment strategy for improving the clinical performance of small-caliber prosthetic vascular grafts.

Small-caliber heparin-coated ePTFE grafts reduce platelet deposition and neointimal hyperplasia in a baboon model

PURPOSE

Intimal hyperplasia and graft thrombosis are major causes of graft failure. Heparin prolongs graft patency and inhibits neointimal hyperplasia in animal models. The purpose of this study was to evaluate the effect of a heparin-coated expanded polytetrafluoroethylene (ePTFE) graft on platelet deposition and anastomotic neointimal hyperplasia after aortoiliac bypass grafting in a baboon model.

METHODS

Heparin-coated ePTFE grafts (4-mm diameter) were incorporated into exteriorized femoral arteriovenous shunts placed in five baboons. Platelet deposition was analyzed by measuring the accumulation of indium 111-labeled platelets on the grafts, with dynamic scintillation camera imaging. Eight adult male baboons (mean weight, 9.3 kg) underwent bilateral aortoiliac bypass grafting with ePTFE grafts (4-mm internal diameter). In each animal a heparin-coated ePTFE graft was placed in one aortoiliac artery, and an uncoated graft, which served as the control, was placed in the contralateral aortoiliac artery. All grafts were harvested at 4 weeks, and were analyzed quantitatively for neointimal hyperplasia at graft-vessel anastomoses.

RESULTS

Early platelet deposition on heparin-coated grafts after 1 to 4 hours of ex vivo circuitry was significantly reduced. All the harvested aortoiliac grafts were patent at 4 weeks. There was a significant reduction in neointimal area at both proximal (0.26 +/- 0.11 mm(2)) and distal (0.29 +/- 0.14 mm(2)) anastomoses in the heparin-coated grafts, compared with proximal (0.56 +/- 0.18 mm(2)) and distal (0.63 +/- 0.21 mm(2)) anastomoses in the untreated control grafts (P <.05). In addition, neointimal cell proliferation assayed with bromodeoxyuridine (BrdU) incorporation was reduced in the graft neointima (3.47% +/- 0.43%) in heparin-coated grafts compared with the graft neointima (6.21% +/- 0.59%) in untreated control grafts (P <.05).

CONCLUSIONS

Small-caliber heparin-coated ePTFE grafts significantly reduce platelet deposition and anastomotic neointimal hyperplasia and cell proliferation, without measurable side effects, in baboons. Surface coating with heparin in small-caliber ePTFE grafts is useful for improving prosthetic bypass graft patency.

CLINICAL RELEVANCE

An autologous vein graft is the ideal bypass conduit in peripheral arterial reconstruction; however, many patients who undergo bypass grafting do not have adequate or available autologous vein graft. As a result surgeons often must rely on prosthetic grafts as an alternative conduit in arterial bypass procedures. Clinical outcomes with prosthetic grafts in peripheral arterial reconstruction are generally inferior to those with autologous vein bypass grafts, in part because of anastomotic neointimal hyperplasia. This study evaluated the effect of small-caliber heparin-coated expandable polytetrafluoroethylene (ePTFE) grafts in aortoiliac reconstruction in a baboon model. The study found that heparin-coated ePTFE grafts resulted in less intimal hyperplasia and less platelet deposition after implantation, compared with noncoated control ePTFE grafts.