Drug eluting stents in the infrainguinal circulation

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.

Limitations of Percutaneous Transluminal Angioplasty and Stenting for the Treatment of Disease of the Superficial Femoral and Popliteal Arteries

The long-term primary patency rates for percutaneous transluminal angioplasty (PTA) and stenting in treatment of disease of the superficial femoral and popliteal arteries have been disappointing. Three-year primary patency rates of ∼50% have been reported for PTA and first-generation stents. Early results with newer nitinol stents appear promising; however, long-term data are lacking. One- and 2-year primary patency rates of 76% to 97% and 60% to 84%, respectively, have been reported with nitinol stents. An emerging concern with nitinol stents is the frequency of stent fracture (≥25%) after interventions for long-segment disease. A recent study has shown that stent fractures are associated with in-stent restenosis and with significantly lower primary patency at 1 year.

The therapeutic success of PTA and stenting correlates with the complexity of the underlying disease. The best results are achieved when treating focal stenoses in patients with good distal runoff. Because endovascular interventions are preferred by patients, can be repeated, and preserve the option of bypass surgery, PTA and stenting are increasingly employed for diffuse and complex SFA disease. Clarifying the role of PTA and stenting in the treatment of complex SFA disease will require future studies that stratify results by both lesion anatomy and treatment indication.

Pilot safety study of perivascular injection of tissue-engineered allogeneic aortic endothelial cells in patients undergoing minimally invasive peripheral revascularization

OBJECTIVE

Restenosis is a limitation of endovascular interventions performed in the superficial femoral artery (SFA). Preclinical studies have demonstrated that the perivascular delivery of tissue-engineered allogeneic aortic endothelial cells (PVS-10200) reduced stenosis in porcine models of SFA revascularization. The purpose of this study was to investigate the safety and feasibility of percutaneous PVS-10200 delivery after angioplasty and stenting in the SFA of patients with peripheral artery disease.

METHODS

In this phase I open-label trial, 21 patients (average lesion length of 10.10 ± 2.36 cm and ≥70% stenosis) were treated with PVS-10200: 11 in a low-dose cohort (cohort A) and 10 in a high-dose cohort (cohort B). The primary objective was to demonstrate the safety (incidence of major adverse events) of PVS-10200 within 4 weeks after surgery. Secondary end points included assessments of resting ankle-brachial index (ABI) in the treated leg, Fontaine class, and time to target lesion revascularization (TLR).

RESULTS

No patient had a major adverse event within 4 weeks. One patient required a limb amputation at 30 weeks. At 48 weeks, cohort A and cohort B patients maintained a 37% and 62% increase in ABI compared with baseline, respectively; 70% of cohort A and 78% of cohort B improved by ≥1 Fontaine classification stage, and the TLR rate was 39% for cohort A and 20% for cohort B.

CONCLUSIONS

Percutaneous local delivery of PVS-10200 is a well-tolerated and novel therapeutic approach that may be a suitable treatment for patients after endovascular intervention of the SFA. Larger randomized trials are needed to determine if PVS-10200 can improve ABI and reduce TLR rates.

Is there an alternative to systemic anticoagulation, as related to interventional biomedical devices?

To reduce the toxic effects, related clinical problems and complications such as bleeding disorders associated with systemic anticoagulation, it has been hypothesized that by coating the surfaces of medical devices, such as stents, bypass grafts, extracorporeal circuits, guide wires and catheters, there will be a significant reduction in the requirement for systemic anticoagulation or, ideally, it will no longer be necessary. However, current coating processes, even covalent ones, still result in leaching followed by reduced functionality. Alternative anticoagulants and related antiplatelet agents have been used for improvement in terms of reduced restenosis, intimal hyperphasia and device failure. This review focuses on existing heparinization processes, their application in clinical devices and the updated list of alternatives to heparinization in order to obtain a broad overview, it then highlights, in particular, the future possibilities of using heparin and related moieties to tissue engineer scaffolds.

Endovascular techniques in limb salvage: stents

In patients with critical limb ischemia, the first-line approach for limb salvage has shifted over the past decade from bypass surgery to endovascular intervention. Stenting for the treatment of lower-extremity arterial occlusive disease is an important tool and continues to evolve, with new stent designs and technologies that have been developed to provide superior patency rates and limb salvage. In this article, we discuss the role of peripheral stenting in the treatment of patients with critical limb ischemia, including a review of the relevant current literature and the future directions of such interventions.

Ultrasound-guided percutaneous delivery of tissue-engineered endothelial cells to the adventitia of stented arteries controls the response to vascular injury in a porcine model

OBJECTIVE

High restenosis rates are a limitation of peripheral vascular interventions. Previous studies have shown that surgical implantation of a tissue-engineered endothelium onto the adventitia surface of injured vessels regulates vascular repair. In the present study, we developed a particulate formulation of tissue-engineered endothelium and a method to deliver the formulation perivascular to injured blood vessels using a percutaneous, minimally invasive technique.

METHODS

Stainless steel stents were implanted in 18 balloon-injured femoral arteries of nine domestic swine, followed by ultrasound-guided percutaneous perivascular injection of gelatin particles containing cultured allogeneic porcine aortic endothelial cells (PAE). Controls received injections of empty particles (matrix) or no perivascular injection (sham) after stent deployment. Animals were sacrificed after 90 days.

RESULTS

Angiographic analysis revealed a significantly greater lumen diameter in the stented segments of arteries treated with PAE/matrix (4.72 ± 0.12 mm) compared with matrix (4.01 ± 0.20 mm) or sham (4.03 ± 0.16 mm) controls (P < .05). Similarly, histologic analysis revealed that PAE/matrix-treated arteries had the greatest lumen area (20.4 ± 0.7 mm(2); P < .05) compared with controls (16.1 ± 0.9 mm(2) and 17.1 ± 1.0 mm(2) for sham and matrix controls, respectively) and the smallest intimal area (3.3 ± 0.4 mm(2); P < .05) compared with controls (6.2 ± 0.5 mm(2) and 4.4 ± 0.5 mm(2) for sham and matrix controls, respectively). Overall, PAE-treated arteries had a 33% to 50% decrease in percent occlusion (P < .05) compared with controls. Histopathological analysis revealed fewer leukocytes present in the intima in the PAE/matrix group compared with control groups, suggesting that the biological effects were in part due to inhibition of the inflammatory phase of the vascular response to injury.

CONCLUSIONS

Minimally invasive, perivascular delivery of PAE/matrix to stented arteries was performed safely using ultrasound-guided percutaneous injections and significantly decreased stenosis. Application at the time of or subsequent to peripheral interventions may decrease clinical restenosis rates.

Factors that affect mass transport from drug eluting stents into the artery wall

Coronary artery disease can be treated by implanting a stent into the blocked region of an artery, thus enabling blood perfusion to distal vessels. Minimally invasive procedures of this nature often result in damage to the arterial tissue culminating in the re-blocking of the vessel. In an effort to alleviate this phenomenon, known as restenosis, drug eluting stents were developed. They are similar in composition to a bare metal stent but encompass a coating with therapeutic agents designed to reduce the overly aggressive healing response that contributes to restenosis. There are many variables that can influence the effectiveness of these therapeutic drugs being transported from the stent coating to and within the artery wall, many of which have been analysed and documented by researchers. However, the physical deformation of the artery substructure due to stent expansion, and its influence on a drugs ability to diffuse evenly within the artery wall have been lacking in published work to date. The paper highlights previous approaches adopted by researchers and proposes the addition of porous artery wall deformation to increase model accuracy.

Delivery site of perivascular endothelial cell matrices determines control of stenosis in a porcine femoral stent model

PURPOSE

Endothelial cells, grown within gelatin matrices and implanted onto the adventitia of injured vessels, inhibit stenosis in experimental models. To determine if this technology could be adapted for minimally invasive procedures, the authors compared the effects of cells in an implantable sponge to that of an injectable formulation and investigated the importance of delivery site in a stent model.

MATERIALS AND METHODS

Stents were implanted in the femoral arteries of 30 pigs. This was followed by perivascular implantation of sponges or injection of particles containing allogeneic endothelial cells. Controls received acellular matrices or nothing. The effects of delivery site were assessed by injecting cellular matrices into or adjacent to the perivascular tissue or into the neighboring muscle. Animals were sacrificed after 28 days. Pre-sacrifice angiograms and tissue sections were evaluated for stenosis.

RESULTS

Arteries treated with cellular matrices had a 55%-63% decrease in angiographic stenosis (P < .05) and a 38%-43% reduction in histologic stenoses (P < .05) compared to controls. Intimal area was greatest when cellular matrices were delivered into the muscle (6.35 mm(2) +/- 0.95) rather than into or adjacent to the perivascular tissue (4.05 mm(2) +/- 0.56 and 4.73 mm(2) +/- 0.53, respectively; P < .05).

CONCLUSIONS

Perivascular endothelial cell matrices reduced stenosis after stent-induced injury. The effects were not dependent on the formulation but appeared to be dependent on delivery site. Minimally invasive injections of endothelial cell matrices to the adventitia of arteries following peripheral interventions may decrease restenosis rates.

Primary nitinol stenting for femoropopliteal disease

The 1- to 2-year primary patency rates associated with self-expanding nitinol stents for the treatment of symptomatic femoropopliteal disease are superior to those for percutaneous transluminal angioplasty (PTA) and the first-generation stainless steel balloon-expandable stents. The advantages of nitinol stents include improved radial strength and flexibility, the ability to recover from being crushed, reduced foreshortening, and (importantly) deployability without balloon dilation of the stent edge (which may decrease the incidence of the edge stenosis, or "candy-wrap" effect, often observed with balloon-expandable stents). The technical success rate associated with primary deployment of nitinol stents is very high, and acute to 6-month patency results are predictably excellent. Prior to the introduction of nitinol stents, the original guidelines (2000) of the multidisciplinary TransAtlantic Inter-Society Consensus (TASC I) recommended only an adjunctive role for femoropopliteal stents following suboptimal PTA. The abbreviated 2007 TASC II report essentially extended this recommendation to nitinol stents. Here, current trials of nitinol stenting in the femoropopliteal segment are discussed, with emphasis on the advantages of primary (and often direct) deployment in selected circumstances dependent on factors including lesion length, lesion location, indication for treatment (critical limb ischemia or claudication, in-stent restenosis, stent-graft restenosis), and the relative appropriateness of other modalities (e.g., covered stents). Technical considerations in primary nitinol stenting are briefly reviewed. Open questions regarding the factors involved in nitinol stent fracture and the possible association of fracture and restenosis are examined in the context of current clinical trials. A new generation of femoropopliteal nitinol stents combining superior durability and flexibility is expected soon. Development and implementation of uniform reporting and surveillance standards is important for optimizing current and future research.

Sirolimus-Loaded Polyurethane Graft for Hemodialysis Access in Sheep

Intimal hyperplasia is the most common final pathway for hemoaccess occlusion in dialysis patients. Drug eluting stents have been shown to decrease intimal hyperplasia in coronary arteries and possibly in peripheral arteries. We evaluated the use of a sirolimus loaded polyurethane graft as prophylaxis in hemodialysis access. Grafts were loaded with sirolimus and elution curves were determined for the polyurethane material. The arteriovenous grafts were then placed in the neck of 20 sheep. A non-loaded graft was placed in the contralateral neck. Patency rates, ultrasound evaluation, angiography and histomorphometry were determined for each graft. At 30, 60 and 90 days the drug loaded graft had improved patency rates compared to the control, with a 25% improvement noted at 3 months. Life table analysis showed the drug loaded graft consistently better patency than the control (p = .136). The control graft had greater neointimal stenosis (14.5% vs 9.17%) over the course of the study (p = .157). Although none of these findings was statistically significant in this pilot study, the sirolimus coated graft out-performed the control in every measured parameter at each time point evaluated. Further work to asses the validity of drug coated materials to prevent intimal hyperplasia in hemodialysis access is warranted.

Randomized, multicenter study comparing expanded polytetrafluoroethylene-covered endoprosthesis placement with percutaneous transluminal angioplasty in the treatment of superficial femoral artery occlusive disease

PURPOSE

To compare the safety and effectiveness of the Viabahn endoprosthesis with that of percutaneous transluminal angioplasty (PTA) alone in the treatment of symptomatic peripheral arterial disease (PAD) affecting the superficial femoral artery (SFA).

MATERIALS AND METHODS

From 1998 to 1999, patients with symptomatic SFA PAD were enrolled in a prospective, multicenter randomized study and underwent either PTA alone (n = 100) or PTA followed by stent-graft placement (expanded polytetrafluoroethylene/nitinol self-expanding stent-graft) (n = 97) for stenoses or occlusions of the SFA that were 13 cm long or shorter. At baseline, there were no significant differences between the PTA and stent-graft treatment groups, including chronic limb ischemia status and treated lesion length.

RESULTS

The stent-graft group had a significantly higher technical success rate (95% vs 66%, P < .0001) and 1-year primary vessel patency rate at duplex ultrasonography (65% vs 40%, P = .0003). A patency benefit was seen for lesions at least 3 cm long. At 12 months, chronic limb ischemia status was 15% further improved for the stent-graft group (P = .003). There were no significant differences between treatment groups with regard to the occurrence of early or late major adverse events.

CONCLUSIONS

In this multicenter study, the patency, technical success, and clinical status results obtained with stent-grafts were superior to those obtained with PTA alone.

A HUVEC line with a stable expression of the VEGF121 gene to achieve complete endothelialization of blood conduits

The purpose of this investigation was to establish monoclonal cell lines of HUVEC with the stable expression of the VEGF(121) gene. Such cells are likely to better adhere to the luminal surface of stents or grafts and to promote a complete endothelialization. The eukaryotic expression vector PCD(2)-VEGF(121) was transfected into cell lines of HUVEC mediated by lipofect AMINE. The positive clones were obtained by the screening of G(418). The transcription and expression of the VEGF gene were investigated by RT-PCR and immunocytochemistry, respectively. The experiment of Miles was applied for the assay of the biological activity of the protein of the VEGF produced by the HUVEC lines with transfected PCD(2)-VEGF(121). The growth curve was made for comparison with that of non-transfected HUVEC line cells. The positive clone cells from which transcripted the mRNA of VEGF(121) gene were obtained by RT-PCR. The positive results of the immunocytochemistry were found and the high biological activity of VEGF in the media was detected in the positive clone cells only. The time to achieve the multiplication of the positive clone cells by a factor of 2 was shorter than that of the non-transfected HUVEC line calculated from the growth curve. The HUVEC line of monoclonal cells with the stable expression of VEGF(121) gene has been established successfully and can be employed on the luminal surfaces of foreign blood conduits.

Thrombogenicity and Related Biological Properties of Heparin Bonded Collagen Coated Polyester and Human Umbilical Vein Prosthetic Vascular Grafts

BACKGROUND

Multiple factors contribute to the process of prosthetic graft failure. Some of them are specifically related to the biological behavior of the used materials. To pursue the ideal substitute for the autologous vein graft, many materials have been taken into consideration. Of these, polyester (Dacron) and human umbilical vein (HUV, Dardik) bypass grafts have gained much attention in vascular surgical practice over the years. This study compares the results of both in vivo and in vitro investigations on graft thrombogenicity and neo-intimal formation in collagen-coated heparin bonded Dacron and in HUV bypass grafts. It is an adjunct to our clinical comparison of graft materials in infrainguinal arterial reconstruction.

METHODS

In 12 adult Beagle dogs, a patch was sewn onto the abdominal aorta (Dacron, n = 6; HUV, n = 6). At defined interval times, thrombocyte aggregation was measured with nuclear imaging of 99mTechnetium labeled platelets. Post-mortem histological analysis of the interface between the native vessel wall and the patch was performed in all animals.

RESULTS

At 4 h (2.67, SD = 0.77) and after 2 weeks (2.21, SD = 0.28) after implantation, significantly higher thrombogenicity was measured in the HUV grafts compared to Dacron grafts (1.98, SD = 0.10 and 1.98, SD = 0.11, P = 0.02 and 0.025, respectively). At 4 weeks, no significant difference could be found (HUV, 2.26; SD = 0.29; Dacron, 2.11; SD = 0.16; P = 0.23). Measurement of 'neo-intimal' thickness after explantation of the patch at 28 days after the initial procedure showed a significant difference: in HUV grafts the mean thickness of the inner lining was 0.76 mm (SD = 0.50), compared to 0.16 mm (SD = 0.10) in the Dacron grafts (P = 0.013).

CONCLUSION

HUV grafts showed a higher thrombogenicity at 4 h and 2 weeks after insertion of the graft compared to Dacron grafts. At 4 weeks this difference is not present. After 28 days the inner ('neo-intimal') lining is significantly more pronounced in HUV grafts than in Dacron grafts.

Limitations of percutaneous transluminal angioplasty and stenting for the treatment of disease of the superficial femoral and popliteal arteries

The long-term primary patency rates for percutaneous transluminal angioplasty (PTA) and stenting in treatment of disease of the superficial femoral and popliteal arteries have been disappointing. Three-year primary patency rates of approximately 50% have been reported for PTA and first-generation stents. Early results with newer nitinol stents appear promising; however, long-term data are lacking. One- and 2-year primary patency rates of 76% to 97% and 60% to 84%, respectively, have been reported with nitinol stents. An emerging concern with nitinol stents is the frequency of stent fracture (> or = 25%) after interventions for long-segment disease. A recent study has shown that stent fractures are associated with in-stent restenosis and with significantly lower primary patency at 1 year. The therapeutic success of PTA and stenting correlates with the complexity of the underlying disease. The best results are achieved when treating focal stenoses in patients with good distal runoff. Because endovascular interventions are preferred by patients, can be repeated, and preserve the option of bypass surgery, PTA and stenting are increasingly employed for diffuse and complex SFA disease. Clarifying the role of PTA and stenting in the treatment of complex SFA disease will require future studies that stratify results by both lesion anatomy and treatment indication.

Transluminal Stenting for Femoropopliteal Occlusive Disease: Analysis of Restenosis by Serial Arteriography

Our objective was to evaluate restenosis after stenting of femoropopliteal occlusions and the impact of percutaneous transluminal angioplasty (PTA) on recurrent stenosis. We used a retrospective analysis of contrast angiograms obtained during follow-up of stented limbs. Subjects included 27 claudicants (34 limbs) who had complete superficial femoral artery occlusion treated with PTA and Wallstents at the Veterans Adminstration Medical Center. During follow-up, 31 PTAs, three thrombolytic treatments, and one additional stenting were performed. Outcome was measured by contrast angiography. Primary patency at 1 and 3 years was 38% and 8% after stenting, and secondary patency (PTA required at least once in 21/34 limbs) was 89% and 55%, respectively. PTA performed during follow-up reduced within-stent restenosis on average from 48.3 +/- 13.6% to 22.8 +/- 18.0%. Recurrent stenosis after PTA measured 14.9 +/- 10.9 months later was 46.8 +/- 16.7%, showing little permanent impact of PTA on stenosis. Severe within-stent stenosis develops commonly after initial stenting of complete femoropopliteal occlusions. Supplemental PTA performed during follow-up provides immediate improvement in lumen diameter, but severe restenosis is still likely to recur.

Treatment for diabetic foot ulcers

People with diabetes develop foot ulcers because of neuropathy (sensory, motor, and autonomic deficits), ischaemia, or both. The initiating injury may be from acute mechanical or thermal trauma or from repetitively or continuously applied mechanical stress. Patients with clinically significant limb ischaemia should be assessed by a vascular surgeon to determine the need for angioplasty, stenting, or femorodistal bypass. When infection complicates a foot ulcer, the combination can be limb or life-threatening. Infection is defined clinically, but wound cultures reveal the causative pathogens. Tissue specimens are strongly preferred to wound swabs for wound cultures. Antimicrobial therapy should be guided by culture results, and should aim to cure the infection, not to heal the wound. Alleviation of the mechanical load on ulcers (off-loading) should always be a part of treatment. Neuropathic ulcers typically heal in 6 weeks with total contact casting, because it effectively relieves pressure at the ulcer site and enforces patient compliance. The success of other approaches to off-loading similarly depends on the patients' adherence to the effectiveness of pressure relief. Surgery to heal ulcers and prevent recurrence can include tenotomy, tendon lengthening, reconstruction, or removal of bony prominences. However, these procedures may result in secondary ulceration and other complications. Ulcer recurrence rates are high, but appropriate education for patients, the provision of posthealing footwear, and regular foot care can reduce rates of re-ulceration.

Interventions in Infrainguinal Bypass Grafts

The interventional radiologist plays an important role in the detection and prevention of infrainguinal bypass failure. Early detection and evaluation of flow-limiting lesions effectively preserve graft (venous bypass and polyester or expanded polytetrafluoroethylene bypass) patency by identifying stenoses before occlusion occurs. Delay in treatment of the at-risk graft may result in graft failure and a reduced chance of successful revascularization. For this reason, surveillance protocols form an important part of follow-up after infrainguinal bypass surgery. As well as having an understanding of the application of imaging techniques including ultrasound, MR angiography, CT angiography and digital subtraction angiography, the interventional radiologist should have detailed knowledge of the minimally invasive therapeutic options. Percutaneous transluminal angioplasty (PTA), or alternatively cutting balloon angioplasty, is the interventional treatment of choice in prevention of graft failure and occlusion. Further alternatives include metallic stent placement, fibrinolysis, and mechanical thrombectomy. Primary assisted patency rates following PTA can be up to 65% at 5 years. When the endovascular approach is unsuccessful, these therapeutic options are complemented by surgical procedures including vein patch revision, jump grafting, or placement of a new graft.