Relationship between blood flow, thrombus, and neointima in stents

Integrative multiomics analysis of neointima proliferation in human saphenous vein: implications for bypass graft disease

Introduction

Human saphenous veins (SV) are widely used as grafts in coronary artery bypass (CABG) surgery but often fail due to neointima proliferation (NP). NP involves complex interplay between vascular smooth muscle cells (VSMC) and fibroblasts. Little is known, however, regarding the transcriptomic and proteomic dynamics of NP. Here, we performed multi-omics analysis in an ex vivo tissue culture model of NP in human SV procured for CABG surgery.

Methods and results

Histological examination demonstrated significant elastin degradation and NP (indicated by increased neointima area and neointima/media ratio) in SV subjected to tissue culture. Analysis of data from 73 patients suggest that the process of SV adaptation and NP may differ according to sex and body mass index. RNA sequencing confirmed upregulation of pro-inflammatory and proliferation-related genes during NP and identified novel processes, including increased cellular stress and DNA damage responses, which may reflect tissue trauma associated with SV harvesting. Proteomic analysis identified upregulated extracellular matrix-related and coagulation/thrombosis proteins and downregulated metabolic proteins. Spatial transcriptomics detected transdifferentiating VSMC in the intima on the day of harvesting and highlighted dynamic alterations in fibroblast and VSMC phenotype and behavior during NP. Specifically, we identified new cell subpopulations contributing to NP, including SPP1 + , LGALS3 + VSMC and MMP2 + , MMP14 + fibroblasts.

Conclusion

Dynamic alterations of gene and protein expression occur during NP in human SV. Identification of the human-specific molecular and cellular mechanisms may provide novel insight into SV bypass graft disease.

Increase of wall shear stress caused by arteriovenous fistula reduces neointimal hyperplasia after stent implantation in healthy arteries

BACKGROUND AND OBJECTIVES

Wall shear stress plays a critical role in neointimal hyperplasia after stent implantation. It has been found that there is an inverse relation between wall shear stress and neointimal hyperplasia. This study hypothesized that the increase of arterial wall shear stress caused by arteriovenous fistula could reduce neointimal hyperplasia after stents implantation.

METHODS AND RESULTS

Thirty-six male rabbits were randomly divided into three groups: STENT, rabbits received stent implantation into right common carotid artery; STENT/arteriovenous fistula, rabbits received stent implantation into right common carotid artery and carotid-jugular arteriovenous fistula; Control, rabbits received no treatment. After 21 days, stented common carotid artery specimens were harvested for histological staining and protein expression analysis. In STENT group, wall shear stress maintained at a low level from 43.2 to 48.9% of baseline. In STENT/arteriovenous fistula group, wall shear stress gradually increased to 86% over baseline. There was a more significant neointimal hyperplasia in group STENT compared with the STENT/arteriovenous fistula group (neointima area: 0.87 mm² versus 0.19 mm²; neointima-to-media area ratio: 1.13 versus 0.18). Western blot analysis demonstrated that the protein level of endothelial nitric oxide synthase in STENT group was significantly lower than that in STENT/arteriovenous fistula group, but the protein levels of proliferating cell nuclear antigen, vascular cell adhesion molecule 1, phospho-p38 mitogen-activated protein kinase (Pp38), and phospho-c-Jun N-terminal kinase in STENT group were significantly higher than that in the STENT group.

CONCLUSION

High wall shear stress caused by arteriovenous fistula as associated with the induction in neointimal hyperplasia after stent implantation. The underlying mechanisms may be related to modulating the expression and activation of endothelial nitric oxide synthase, vascular cell adhesion molecule 1, p38, and c-Jun N-terminal kinase.

Polyester vascular patches acquire arterial or venous identity depending on their environment

Polyester is commonly used in vascular surgery for patch angioplasty and grafts. We hypothesized that polyester patches heal by infiltration of arterial or venous progenitor cells depending on the site of implantation. Polyester patches were implanted into the Wistar rat aorta or inferior vena cava and explanted on day 7 or 30. Neointima that formed on polyester patches was thicker in the venous environment compared to the amount that formed on patches in the arterial environment. Venous patches had more cell proliferation and greater numbers of VCAM-positive and CD68-positive cells, whereas arterial patches had greater numbers of vimentin-positive and alpha-actin-positive cells. Although there were similar numbers of endothelial progenitor cells in the neointimal endothelium, cells in the arterial patch were Ephrin-B2- and notch-4-positive while those in the venous patch were Eph-B4- and COUP-TFII-positive. Venous patches treated with an arteriovenous fistula had decreased neointimal thickness; neointimal endothelial cells expressed Ephrin-B2 and notch-4 in addition to Eph-B4 and COUP-TFII. Polyester patches in the venous environment acquire venous identity, whereas patches in the arterial environment acquire arterial identity; patches in the fistula environment acquire dual arterial-venous identity. These data suggest that synthetic patches heal by acquisition of identity of their environment. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3422-3431, 2017.

Continuously Grooved Stent Struts for Enhanced Endothelial Cell Seeding

Purpose

Implantation of pre-endothelialized stents could enhance cellular recovery of a damaged vessel wall provided attached cells remain viable, functional and are present in sufficient numbers after deployment. The purpose of this study was to evaluate the feasibility of grooved stainless steel (SS) stents as a primary endothelial cell (EC) carrier with potentially enhanced EC protection upon stent deployment.

Materials and Methods

Attachment and behavior of enzymatically harvested human adult venous ECs seeded onto gelatin-coated vascular stents were evaluated in an in vitro setting. Smooth and grooved SS stents and smooth nitinol stents were studied.

Results

All cells expressed EC markers vWF and CD31. Using rotational seeding for a period of 16–24 h, ECs attached firmly to the stents with sufficient coverage to form a confluent EC monolayer. The grooved SS wire design was found to enable attachment of three times the number of cells compared to smooth wires. This also resulted in an increased number of cells remaining on the stent after deployment and after pulsatile flow of 180 ml/min for 24 h, which did not result in additional EC detachment.

Conclusions

The grooved stent provides a potential percutaneous means to deliver sufficient numbers of viable and functional cells to a vessel segment during vascular intervention. The grooves were found to offer a favorable surface for EC attachment and protection during stent deployment in an in vitro setting.

Electronic supplementary material

The online version of this article (doi:10.1007/s00270-017-1659-4) contains supplementary material, which is available to authorized users.

Pericardial patch venoplasty heals via attraction of venous progenitor cells

Pericardial patches are commonly used during cardiovascular surgery to close blood vessels. In arteries, patches accumulate arterial progenitor cells; we hypothesized that venous patches would accumulate venous progenitor cells, in the absence of arterial pressure. We developed a novel rat inferior vena cava (IVC) venotomy model and repaired it with a pericardial patch. Cells infiltrated the patch to form a thick neointima by day 7; some cells were CD34(+)/VEGFR2(+) and CD31(+)/Eph-B4(+) consistent with development of venous identity in the healing patch. Compared to arterial patches, the venous patches had increased neointimal thickness at day 7 without any pseudoaneurysms. Addition of an arteriovenous fistula (AVF) to increase blood flow on the patch resulted in reduced patch neointimal thickness and proliferation, but neointimal thickness was not reversible with AVF ligation. These results show that rat patch venoplasty is a novel model of aggressive venous neointimal hyperplasia.

Geometrical consequences of kissing stents and the Covered Endovascular Reconstruction of the Aortic Bifurcation configuration in an in vitro model for endovascular reconstruction of aortic bifurcation

OBJECTIVE

Kissing stents (KS) are commonly used to treat aortoiliac occlusive disease, but patency results are often lower than those of isolated stents. The Covered Endovascular Reconstruction of the Aortic Bifurcation (CERAB) technique was recently introduced to reconstruct the aortic bifurcation in a more anatomical and physiological fashion. The aim of this study is to compare the geometrical consequences of various stent configurations in vitro.

METHODS

Anatomic vessel phantoms of the aortoiliac bifurcation were created to accommodate stent configurations. Self-expandable nitinol KS, balloon-expandable covered KS, and two versions of the CERAB configuration were deployed, one with the iliac legs positioned inside the tapered part of the aortic cuff (1) and one with the legs deployed above this level (2). Computed tomography data were obtained to assess the geometry. The conformation ratio (D-ratio) was calculated by use of the ratio of the major and minor axes. The proximal mismatch area, mean mismatch area, and total mismatch volume were calculated.

RESULTS

The highest D-ratios were observed in the nitinol KS and the CERAB configuration, implying an ideal "double-D" shape. The proximal and mean mismatch areas were four- to sixfold lower in the CERAB (1) configuration when compared with nitinol KS and CERAB (2), respectively, whereas the covered KS had the highest mismatch area. Nitinol and covered KS had the largest mismatch volume, whereas the mismatch volume was the lowest in the CERAB (1) configuration.

CONCLUSIONS

Although nitinol self-expandable stents have a high stent conformation, the lowest radial mismatch was found in the CERAB (1) configuration, supporting the hypothesis that the CERAB configuration is the most anatomical and physiological reconstruction of the aortic bifurcation. Within the CERAB configuration, the two limbs are ideally positioned inside the tapering portion of the cuff, minimizing mismatch.

Abdominal aortic aneurysm: Treatment options, image visualizations and follow-up procedures

Abdominal aortic aneurysm is a common vascular disease that affects elderly population. Open surgical repair is regarded as the gold standard technique for treatment of abdominal aortic aneurysm, however, endovascular aneurysm repair has rapidly expanded since its first introduction in 1990s. As a less invasive technique, endovascular aneurysm repair has been confirmed to be an effective alternative to open surgical repair, especially in patients with co-morbid conditions. Computed tomography (CT) angiography is currently the preferred imaging modality for both preoperative planning and post-operative follow-up. 2D CT images are complemented by a number of 3D reconstructions which enhance the diagnostic applications of CT angiography in both planning and follow-up of endovascular repair. CT has the disadvantage of high cummulative radiation dose, of particular concern in younger patients, since patients require regular imaging follow-ups after endovascular repair, thus, exposing patients to repeated radiation exposure for life. There is a trend to change from CT to ultrasound surveillance of endovascular aneurysm repair. Medical image visualizations demonstrate excellent morphological assessment of aneurysm and stent-grafts, but fail to provide hemodynamic changes caused by the complex stent-graft device that is implanted into the aorta. This article reviews the treatment options of abdominal aortic aneurysm, various image visualization tools, and follow-up procedures with use of different modalities including both imaging and computational fluid dynamics methods. Future directions to improve treatment outcomes in the follow-up of endovascular aneurysm repair are outlined.

In vitro and in vivo performance of a dual drug-eluting stent (DDES)

This study reports on a dual drug-eluting stent (DDES) that has an anti-proliferative and an anti-thrombotic in a biodegradable polymer-coated onto a cobalt-chromium stent. The DDES was prepared by spray coating the bare metal stent with a biodegradable polymer loaded with sirolimus and triflusal, to treat against restenosis and thrombosis, respectively. The 2-layered dual-drug coated stent was characterized in vitro for surface properties before and after expansion, as well as for possible delamination by cross-sectioning the stent in vitro. The in vitro anti-platelet behavior of the triflusal-loaded films was investigated by using dynamic platelet adhesion measurements. Additionally, the in vitro degradation and release study of the films and the stents w/single sirolimus and dual sirolimus-triflusal in different formulations were examined. Finally, in vivo studies (in a porcine carotid artery model) were performed for acute thrombosis, inflammation and restenosis at 30 days. The in vitro results show DDES can sustain release both anti-proliferation drug (sirolimus) and anti-thrombosis drug (triflusal), two drugs were controlled in different rates to effectively reduce thrombosis and proliferation at the same time. In vivo results show a significant reduction in restenosis with dual-drug eluting stent compared with the controls (a bare metal stent, a sirolimus coated and a pure polymer-coated stent). The reduction in restenosis with a dual sirolimus-triflusal eluting stent is associated with an inhibition of inflammation, especially thrombus formation, suggesting that such dual-drug eluting stents have a role to play for the treatment of coronary artery disease.

Fenestrated stent graft repair of abdominal aortic aneurysm: hemodynamic analysis of the effect of fenestrated stents on the renal arteries

Objective

We wanted to investigate the hemodynamic effect of fenestrated stents on the renal arteries with using a fluid structure interaction method.

Materials and Methods

Two representative patients who each had abdominal aortic aneurysm that was treated with fenestrated stent grafts were selected for the study. 3D realistic aorta models for the main artery branches and aneurysm were generated based on the multislice CT scans from two patients with different aortic geometries. The simulated fenestrated stents were designed and modelled based on the 3D intraluminal appearance, and these were placed inside the renal artery with an intra-aortic protrusion of 5.0-7.0 mm to reflect the actual patients' treatment. The stent wire thickness was simulated with a diameter of 0.4 mm and hemodynamic analysis was performed at different cardiac cycles.

Results

Our results showed that the effect of the fenestrated stent wires on the renal blood flow was minimal because the flow velocity was not significantly affected when compared to that calculated at pre-stent graft implantation, and this was despite the presence of recirculation patterns at the proximal part of the renal arteries. The wall pressure was found to be significantly decreased after fenestration, yet no significant change of the wall shear stress was noticed at post-fenestration, although the wall shear stress was shown to decrease slightly at the proximal aneurysm necks.

Conclusion

Our analysis demonstrates that the hemodynamic effect of fenestrated renal stents on the renal arteries is insignificant. Further studies are needed to investigate the effect of different lengths of stent protrusion with variable stent thicknesses on the renal blood flow, and this is valuable for understanding the long-term outcomes of fenestrated repair.

The short-term effect on restenosis and thrombosis of a cobalt-chromium stent eluting two drugs in a porcine coronary artery model

The aim of this article was to study the effect of dual drug-eluting stent (DES) on both restenosis and thrombosis in a porcine coronary artery model. This study reports on the use of two drugs coated on the stent to simultaneously minimize both restenosis and thrombosis. The DES was prepared by spray coating a bare metal stent with a biodegradable polymer loaded with sirolimus and triflusal, to treat against restenosis and thrombosis, respectively. The two-layered dual drug-coated stent was characterized in vitro for surface properties before and after expansion, as well as for possible delamination by cross-sectioning the stent in vitro. In vivo animal studies (in a pig model) were then performed for acute thrombosis, inflammation, and restenosis. The results show a significant reduction in restenosis with a stent coated with both drugs compared with the controls (a bare metal stent, a sirolimus-coated, and a pure polymer-coated stent). The reduction in restenosis with a sirolimus/triflusal-eluting stent is associated with an inhibition of inflammation and thrombus formation, suggesting that such dual DES have a role to play for the treatment of coronary artery diseases.

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.

Palliative portal vein stent placement in malignant and symptomatic extrinsic portal vein stenosis or occlusion

This article evaluates the results of portal vein (PV) stent placement in patients with malignant extrinsic lesions stenosing or obstructing the PV and causing symptomatic PV hypertension (PVHT). Fourteen patients with bile duct cancer (n = 7), pancreatic adenocarcinoma (n = 4), or another cancer (n = 3) underwent percutaneous transhepatic portal venous stent placement because of gastroesophageal or jejunal varices (n = 9), ascites (n = 7), and/or thrombocytopenia (n = 2). Concurrent tumoral obstruction of the main bile duct was treated via the transhepatic route in the same session in four patients. Changes in portal venous pressure, complications, stent patency, and survival were evaluated. Mean +/- standard deviation (SD) gradient of portal venous pressure decreased significantly immediately after stent placement from 11.2 mmHg +/- 4.6 to 1.1 mmHg +/- 1.0 (P < 0.00001). Three patients had minor complications, and one developed a liver abscess. During a mean +/- SD follow-up of 134.4 +/- 123.3 days, portal stents remained patent in 11 patients (78.6%); stent occlusion occurred in 3 patients, 2 of whom had undergone previous major hepatectomy. After stent placement, PVHT symptoms were relieved in four (57.1%) of seven patients who died (mean survival, 97 +/- 71.2 days), and relieved in six (85.7%) of seven patients still alive at the end of follow-up (mean follow-up, 171.7 +/- 153.5 days). Stent placement in the PV is feasible and relatively safe. It helped to relieve PVHT symptoms in a single session.

Self-expandable nitinol stent placement in homocysteinemic porcine aorta

PURPOSE

To compare aortic intimal thickening of normal and hyperhomocysteinemic pigs (induced with a methionine-rich diet) following placement of a self-expanding nitinol stent.

METHODS

Eighteen Macau pigs were used. They were older than eight weeks in age and had an average weight of 30 kg. Pigs were randomly divided into two groups. The first, Group C (control), was fed a regular diet, and the second group, Group M, was fed a methionine-rich diet for 30 days to induce hyperhomocysteinemia. The self-expandable nitinol stents were 25mm in length and 8 mm in diameter after expansion. Blood samples were collected to measure total cholesterol, triglycerides, HDL and homocysteine concentrations. All animals were subjected to angiography. Thirty days after the procedure, the animals were sacrificed, and the abdominal aorta was removed for histological and digital morphometry analysis.

RESULTS

Under microscopic evaluation, the intima was significantly thicker in Group C than in Group M. When groups were compared by digital morphometric analysis, intimal thickening of the vessel wall was higher in Group C than in Group M. There was no significant change in total cholesterol, triglycerides or HDL concentrations in either group. In group C the levels of plasma homocysteine ranged from 14,40 to 16,73 micromol/l; in Group M, plasma homocysteine levels ranged from 17.47 to 59.80 micromol/l after 30 days of a methionine-rich diet.

CONCLUSION

Compared to normal pigs, less intimal hyperplasia was observed in the abdominal aortas of hyperhomocysteinemic pigs thirty days after the insertion of a self-expandable nitinol stent.

The efficacy of nanoscale poly[bis(trifluoroethoxy) phosphazene] (PTFEP) coatings in reducing thrombogenicity and late in-stent stenosis in a porcine coronary artery model

OBJECTIVES

Previous experimental studies have demonstrated that poly[bis(trifluoroethoxy)phosphazene] (PTFEP) nanocoated stents have antithrombotic characteristics, reduce in-stent stenosis, prevent wall inflammation, and do not hamper endothelialization. This study was designed to validate these findings in a porcine coronary artery model.

MATERIALS AND METHODS

PTFEP-coated (n = 15) and bare stents (n= 13) were implanted in coronary arteries of 18 mini-pigs (4- and 12-week follow-up). Primary study endpoints were thrombogenicity and in-stent stenosis, secondary study endpoints were inflammatory response and re-endothelialization evaluated by quantitative angiography and light microscopy.

RESULTS

No thrombus deposition occurred on any stent. At 4 weeks follow-up, the bare stents (n = 4) had a significantly smaller neointimal area (1.93 vs. 3.20 mm(2), P = 0.009). At 12 weeks, PTFEP-coated stents (n = 11) had significantly superior results in almost all parameters: neointimal area (2.25 vs. 2.65 mm(2), P = 0.034), neointimal height (204.46 vs. 299.41 microm, P = 0.048), percentage stenosis (38.25 vs. 50.42%, P = 0.019), and inflammation score (0.12 vs. 0.30, P = 0.029). Complete re-endothelialization was seen in both stent types at both intervals.

CONCLUSION

At long-term follow-up, the superior results of PTFEP-coated stents were characterized by a noteworthy reduction of neointimal growth and inflammatory response.

Aortoiliac Kissing Stents:Long-term Results and Analysis of Risk Factors Affecting Patency

PURPOSE

To present the early and long-term results of aortoiliac kissing stents implantation and evaluate the risk factors affecting patency.

METHODS

The data were retrospectively reviewed on 68 patients (64 men; mean age 55+/-11, range 32-77) who underwent kissing stents implantation during a 12-year period. The majority of patients (64, 94%) had claudication; 4 patients had rest pain. All were smokers. There were bilateral or unilateral stenoses in 42 (62%) patients, and unilateral occlusion and contralateral stenosis in 26 (38%). Lesions were treated with simultaneous implantation of self-expanding (n=52) or balloon-expandable (n=16) stents. After the procedure, patency was determined with Doppler ultrasonography or angiography at 1, 3, 6, and 12 months and annually thereafter. Primary, assisted primary, and secondary patency rates were calculated with Kaplan-Meier analysis on an intention-to-treat basis, and risk factors affecting the patency rates were determined with the Cox regression analysis.

RESULTS

All procedures were technically and clinically successful. Complications occurred in 12%, but none required surgery. The follow-up period was 35+/-31 months. Primary, assisted primary, and secondary patency rates, respectively, were 76%, 90%, and 94% at 1 year; 63%, 86%, and 92% at 3 years; and 63%, 64%, and 81% at 5 years. In multivariate analysis, age <50 years and presence of iliac occlusion were identified as risk factors for reduced primary and assisted primary patency; a crossed configuration of kissing stents was identified as a risk factor for reduced primary patency.

CONCLUSION

Implantation of kissing stents is a safe and effective alternative in the treatment of aortoiliac obstructions. However, overall primary and assisted primary patency rates are inferior to those reported for surgery. Long-term patency comparable to surgery may be obtained in patients >50 years and in those without an iliac occlusion, particularly if a favorable stent configuration is achieved.

Conformation of Adjacent Self-expanding Stents: A Cross-Sectional In Vitro Study

We examined the proximal conformation of three commonly used self-expanding stents when the stents were deployed adjacent to one another in a tubular model, simulating a "kissing" stent technique. The stent pairs were evaluated by computed tomogrphy to determine the cross-sectional area excluded by the stents within the model. The mean areas associated with each stent pair were compared and significance evaluated by a t-test. A statistically significant difference was found when the area excluded by adjacent Wallstents was compared with both the Luminexx and SMART stents (p < 0.001 and p < 0.002, respectively). The difference in the area excluded and differences in conformation might play a role in the lower patencies that have been observed in "kissing" stent series.

A New Polymer Concept for Coating of Vascular Stents Using PTFEP (poly(bis(trifluoroethoxy)phosphazene) to Reduce Thrombogenicity and Late In-Stent Stenosis

OBJECTIVES

We sought to evaluate the new polymer PTFEP (poly(bis(trifluoroethoxy)phosphazene) for (1) its ability to reduce thrombogenicity and late in-stent stenosis and (2) its effect on endothelialization in a rabbit iliac artery model.

MATERIALS AND METHODS

Nanocoated ( approximately 50 nm) and bare stainless-steel stents were implanted bilaterally in the iliac arteries of 30 New Zealand White rabbits (1, 4, 8, 12, and 16 weeks follow-up) and evaluated by angiography, light, and scanning electron microscopy.

RESULTS

Bilateral stent placement was successful in 27 of 30 rabbits. Thrombus depositions occurred in none of the 27 coated but in 4 of the 27 bare stents (P=0.037). A normal angiogram was obtained in 18 of 22 coated stents at risk for restenosis (follow-up >or=4 weeks) but only in 13 of 22 bare stents (P=0.023). Marked restenosis (luminal loss >30%) was found in 6 bare stents (P=0.011) but not in any coated stents. The neointima was 47.7-73.9 mum on coated and 66.9-115.2 mum on bare stents (statistically significant at 4, 8, and 16 weeks). Scanning electron microscopy detected full endothelialization in all stents from 4 weeks on (22 stents in both groups).

CONCLUSION

PTFEP nanocoating successfully showed thromboresistance and reduced late in-stent stenosis. Endothelialization was equal in both stent types. Studies in more human-like models and human feasibility studies in human arteries are encouraged.

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.

Flow patterns in an endovascular stent-graft for abdominal aortic aneurysm repair

Endovascular exclusion of the abdominal aortic aneurysm (AAA) has been carried out in selected patients during the past decade. The deployment of a complex multicomponent endovascular device in an aneurysmal aorta may alter the local haemodynamics and lead to thrombosis and intimal hyperplasia development. The aim of this in vitro study was to investigate the flow patterns using flow visualisation and laser Doppler anemometry in a commercial bifurcated stent-graft. Two configurations of the stent-graft, endo-stent and exo-stent, were investigated in an idealised planar AAA model. The flow structures in the main trunk in both configurations of the stent-graft are three-dimensional with complex secondary structures. However, these flow structures were not entirely caused by the stent-graft. The stent struts in the endo-stent configuration cause localised alteration in the flow pattern but the overall flow structures were not significantly affected. Low velocity regions in the main trunk and flow separation in the stump region and the curved segment of the iliac limbs were observed. These areas are associated with thrombosis in the clinical situation. Improvements in the design of endovascular devices may remove these areas of unfavourable flow patterns and lead to better clinical performance.

Augmentation of wall shear stress inhibits neointimal hyperplasia after stent implantation: inhibition through reduction of inflammation?

BACKGROUND

Low wall shear stress (WSS) increases neointimal hyperplasia (NH) in vein grafts and stents. We studied the causal relationship between WSS and NH formation in stents by locally increasing WSS with a flow divider (Anti-Restenotic Diffuser, Endoart SA) placed in the center of the stent.

METHODS AND RESULTS

In 9 rabbits fed a high-cholesterol diet for 2 months to induce endothelial dysfunction, 18 stents were implanted in the right and left external iliac arteries (1 stent per vessel). Lumen diameters were measured by quantitative angiography before and after implantation and at 4-week follow-up, at which time, macrophage accumulation and interruption of the internal elastic lamina was determined. Cross sections of stent segments within the ARED (S+ARED), outside the ARED (S[minus]ARED), and in corresponding segments of the contralateral control stent (SCTRL) were analyzed. Changes in WSS induced by the ARED placement were derived by computational fluid dynamics. Computational fluid dynamics analysis demonstrated that WSS increased from 0.38 to 0.82 N/m2 in the S+ARED immediately after ARED placement. This augmentation of shear stress was accompanied by (1) lower mean late luminal loss by quantitative angiography ([minus]0.23+/-0.22 versus [minus]0.58+/-0.30 mm, P=0.02), (2) reduction in NH (1.48+/-0.58, 2.46+/-1.25, and 2.36+/-1.13 mm2, P<0.01, respectively, for S+ARED, S[minus]ARED, and SCTRL), and (3) a reduced inflammation score and a reduced injury score. Increments in shear stress did not change the relationship between injury score and NH or between inflammation score and NH.

CONCLUSIONS

The newly developed ARED flow divider significantly increases WSS, and this local increment in WSS is accompanied by a local reduction in NH and a local reduction in inflammation and injury. The present study is therefore the first to provide direct evidence for an important modulating role of shear stress in in-stent neointimal hyperplasia.

Shear stress, vascular remodeling and neointimal formation

The role of shear stress in atherosclerosis has been well documented. However, its role in restenosis was underexposed. In this paper a novel in vivo measuring technique and several of its applications related to restenosis will be described. The technique consists of a combination of 3D reconstruction of blood vessels and computational fluid dynamics (CFD). The 3D imaging techniques use either of 3D intravascular ultrasound (IVUS) as a stand-alone technique or a fusion of biplane angiography and IVUS (ANGUS). CFD is applied in order to relate local shear stress distribution to the morphology of the vessel wall. In the applications of these techniques it will be demonstrated that shear stress plays a role in the prediction of neointimal formation in in-stent restenosis and in vascular remodeling after balloon angioplasty. Attempts to locally increase shear stress by a newly developed flow divider indicate that shear stress reduce in-stent neointimal formation by 50%.

Effects of abciximab on the acute pathology of blood vessels after arterial stenting in nonhuman primates

OBJECTIVES

This study was designed to assess the effect of abciximab on platelet and leukocyte deposition 60 min after stent insertion in nonhuman primates.

BACKGROUND

Although it is well established that abciximab improves both short- and long-term clinical outcomes after stent placement, there have been no studies assessing its effect on early platelet and leukocyte deposition.

METHODS

Cynomolgus monkeys were pretreated with aspirin and either saline or a 0.4 mg/kg bolus of abciximab, and then subjected to angioplasty and Palmaz-Schatz stent placement in the common iliac artery or abdominal aorta. After 60 min, animals were euthanized and the stented artery was evaluated by immunohistochemistry and morphometry.

RESULTS

Complete occlusion of the stented vessel with a thin fibrin(ogen) meshwork and trapped blood occurred in two saline-treated and two abciximab-treated animals. In the four remaining saline-treated animals, a layer of erythrocytes trapped in a network of fibrin(ogen) was noted close to the vessel wall, and this was covered by a layer of large, irregular platelet thrombi. Leukocytes formed a monolayer on top of the platelets and near stent struts. In the four remaining abciximab-treated animals, the mean erythrocyte area was 65% smaller (p = 0.070), the platelet aggregate area was 89% smaller (p = 0.049) and the luminal area was 59% larger (p = 0.004). A monolayer of leukocytes also formed on top of the platelets and near stent struts.

CONCLUSIONS

In control stented blood vessels in this study, platelet thrombi formed not at the vessel wall, but on top of an erythrocyte-rich layer, and platelets recruited leukocytes. Abciximab decreased the size of platelet thrombi, but did not prevent leukocyte recruitment.

Radiological Investigation and Treatment of the Critically Ischemic Limb—A Review

The contribution of radiological investigation and treatment in the management of the critically ischemic lower limb is reviewed. The methods of classifying and assessing the cause, level, and severity of the arterial disease causing the ischemia are discussed with comparison of the relative merits of the various invasive and noninvasive techniques of investigation. The development of the methods of interventional radiological management is described with an indication of the relative success of the different techniques. Newer interventional developments, including intravascular brachytherapy and gene therapy are discussed.

Malignant portal venous obstructions treated by stent placement: significant factors affecting patency

PURPOSE

To identify factors affecting stent occlusion after stent placement in the portal vein in patients with malignant portal vein invasion.

MATERIALS AND METHODS

Forty patients were studied. Twenty-three patients had hepatocellular carcinoma, nine patients had pancreatic cancer, and eight patients had bile duct cancer. Stents were placed in the portal venous system across stenotic (n = 28) or obstructive (n = 12) lesions after percutaneous transhepatic portography. Bare stents were used in 33 patients and covered stents were used in seven patients. Twenty-two variables were analyzed with use of univariate and multivariate analyses to identify significant factors affecting stent occlusion.

RESULTS

Stents remained patent during a mean follow-up period of 11.9 months (range, 2-61 mo) in 60% of the patients. Stent occlusion was found in 40% of the patients, with a mean period until occlusion of 3.7 months (range, 0.2-16 mo). In the univariate analysis, the following five factors were significantly associated with a higher probability of stent occlusion: (i) splanchnic vein involvement, (ii) Child-Pugh class C, (iii) obstruction of the portal venous system, (iv) pancreatic cancer, and (v) lack of anticancer treatment after stent placement. In the multivariate analysis, the first three factors were found to have independent value for stent occlusion.

CONCLUSIONS

Splanchnic vein involvement, severe hepatic dysfunction, and obstruction of the portal venous system are the most important factors affecting stent occlusion in patients with malignant portal vein invasion.

Evaluation of thrombogenicity of fluoropassivated polyester patches following carotid endarterectomy

The use of a patch after carotid endarterectomy (CE) is recommended to reduce the incidence of restenosis. Most studies on this subject report the implantation of saphenous vein or PTFE patches, because polyester has always been considered to be a thrombogenic material. The purpose of this study was to evaluate the thrombogenicity of a knitted polyester patch passivated by fluoropolymer surface treatment (FPD patch), which experimental studies have demonstrated to be less thrombogenic than other materials. This prospective, randomized study was performed in 22 patients who underwent CE. In 11 patients the arteriotomy was sutured directly, while in the other 11 an FPD patch was applied. Patients' 111in-oxine labeled platelets were reinjected on the first postoperative day, and scintigraphies were performed after 4, 24, and 48 hr, respectively. The study confirmed that an FPD patch is no more thrombogenic than a simple carotid endarterectomy. The application of the patch, therefore, can be recommended to reduce restenosis without any adjunctive thromboembolic risk.

Portal venous stent placement in patients with pancreatic and biliary neoplasms invading portal veins and causing portal hypertension: initial experience

PURPOSE

To evaluate the clinical usefulness of portal venous stent placement in patients with pancreatic or biliary neoplasms invading portal veins and causing portal hypertension.

MATERIALS AND METHODS

Thirteen patients underwent portal venous stent placement because of gastrointestinal bleeding (n = 8), risk of gastroesophageal varix rupture (n = 4), ascites (n = 4), thrombocytopenia (n = 3), and/or portal venous thrombosis (n = 3). The main portal vein or both the intrahepatic and main portal veins were invaded in six patients (group A). The main portal vein and splanchnic veins were involved in seven patients (group B). Stents were placed across the stenotic (n = 8) or occluded (n = 5) lesions after percutaneous transhepatic portography. Changes in portal venous pressure, stent patency, and survival were evaluated.

RESULTS

Mean portal venous pressure decreased significantly immediately after stent placement, from 24.9 mm Hg +/- 5.9 (SD) to 15.8 mm Hg +/- 4.6 (P <.001). In group A, blood flow through the stent was maintained and the symptoms had subsided at follow-up (mean, 12.5 months). In group B, symptoms were improved in five patients, but the stents were occluded in all but one patient at a mean follow-up of 1.5 months. There was a significant difference in stent patency between the patients with (14%) and those without (100%) splanchnic venous involvement (P <.01).

CONCLUSION

Stent placement helped to relieve portal hypertension symptoms. Splanchnic venous involvement was associated with worse stent patency.

Influence of stent edge angle on endothelialization in an in vitro model

PURPOSE

To investigate the influence of topographic features in the path of migrating endothelial cells, specifically the effect of edge angle of intravascular metallic material on endothelialization.

MATERIALS AND METHODS

Flat 1-cm x 1-cm 316-L pieces of stainless steel were placed on confluent monolayers of human aortic endothelial cells. The thickness of each metal piece was ground to achieve an edge angle of 35 degrees, 70 degrees, 90 degrees, or 140 degrees (n = 6 each) in relation to the endothelial surface. Migration distance and density of endothelial cell coverage on the metal pieces were measured in groups of six each under static conditions at 4, 7, and 11 days and flow conditions (16 dynes/cm(2)) at 4 days.

RESULTS

Endothelial cell migration distance along the surface of the pieces with edge angles of 35 degrees was significantly greater than that with those with larger angles (P < .05) under static and flow conditions. The migration distances on the 35 degrees piece were 87.5%, 47.3%, 57.1%, and 66.1% greater than those on the 90 degrees piece at the upstream, downstream, right, and left edges, respectively. There were no significant differences in cell density among different angle groups under flow or static conditions.

CONCLUSION

The edge angle of intravascular metallic material has an influence on the rate of endothelialization. A smaller edge angle facilitates endothelialization over metallic material when compared to a larger angle. These results demonstrate the importance of metallic stent profile on endothelialization rate.

Placement of a flexible endovascular stent across the femoral joint: an in vivo study in the swine model

PURPOSE

To investigate the effects of joint motion on the structural integrity of periarticular stents and on the development of neointimal hyperplasia within these devices.

MATERIALS AND METHODS

In four juvenile farm swine, Wall-stents were implanted in the common femoral arteries and contralateral common femoral veins, centered at the point of maximal conformational change during passive hip flexion. Control stents were placed in the aortae and iliac veins. Angiography and transcatheter blood pressure measurements were obtained across each stent, with periarticular stents studied in flexion and extension. Two animals underwent repeated evaluation after 1 month, the others after 3 months. Findings were correlated with gross and histopathologic findings in the harvested stents.

RESULTS

No stent fractures occurred. One femoral vein was injured during stent placement and was occluded 1 month later at follow-up. Hemodynamically significant stenoses were identified in one arterial stent and one venous stent at 3 months. The amount of neointimal hyperplasia was greater in periarticular stents than in controls and greater in animals studied at 1 month than in those studied at 3 months. The pattern of neointimal hyperplasia within mobile arteries was circumferentially asymmetric and thicker at the distal ends of the stents. Venous neointimal hyperplasia was thicker and markedly different in character than that seen in arterial stents from the same animals.

CONCLUSIONS

Periarticular Wallstents and the underlying vascular anatomy remained structurally intact despite the stresses of repetitive motion during a 3-month period. Stents deployed across joints or in venous locations may be at greater risk for neointimal hyperplasia development and eventual occlusion than those deployed in immobile vessels and arteries. Neointimal hyperplasia may decrease in thickness after an initial period of exuberant development. Additional studies are necessary to determine long-term outcomes.