Infrainguinal vein graft stenosis

Phlebosclerosis in lower extremities veins - a systematic review

Phlebosclerosis is a venous wall degenerative disease which has gained little popularity in the literature due to its uncertain clinical significance. The objective of this review is to evaluate the epidemiology, etiology and clinical significance of phlebosclerosis in lower extremities veins, particularly the effect of preexisting phlebosclerosis of the great saphenous vein on vein graft patency. Medline was searched from inception until November 1, 2019. Reference lists of included studies were scanned. Only articles published after 1949 were included. Two reviewers independently screened titles/abstracts and full-text papers for any study design in relation to phlebosclerosis in lower extremities veins and abstracted data. A total of 16 Cohort studies and one case-control study (3708 participants, mean age 61.8 years, 59.3 % men, and 40.7 % women) were included after screening 317 titles and abstracts, and 80 full-text articles. The incidence of phlebosclerosis ranged from 1.5-9.7 % depending on the radiological features. On the contrary, the incidence of the phlebosclerotic great saphenous vein prior to its use as a vein graft was 26.9-91 % on histological examination. The small saphenous vein was the most common location of phlebosclerosis followed by the great saphenous vein. There is a link between phlebosclerosis and age, venous insufficiency and haemodialysis. As for the vein graft patency seven studies demonstrated a correlation between preexisting phlebosclerosis and vein graft stenosis, whereas three studies failed to prove any association. In conclusion, the radiological incidence of phlebosclerosis depended on the ultrasound findings. Its presence in the great saphenous vein prior to its use as a vein graft is established on histological examination. The small saphenous vein is mainly affected. Risk factors included age, haemodialysis, and venous insufficiency. Preexisting wall thickness of the great saphenous vein graft seemed to affect negatively its patency in bypass surgery.

A versatile hybrid agent-based, particle and partial differential equations method to analyze vascular adaptation

Peripheral arterial occlusive disease is a chronic pathology affecting at least 8–12 million people in the USA, typically treated with a vein graft bypass or through the deployment of a stent in order to restore the physiological circulation. Failure of peripheral endovascular interventions occurs at the intersection of vascular biology, biomechanics, and clinical decision making. It is our hypothesis that the majority of endovascular treatment approaches share the same driving mechanisms and that a deep understanding of the adaptation process is pivotal in order to improve the current outcome of the procedure. The postsurgical adaptation of vein graft bypasses offers the perfect example of how the balance between intimal hyperplasia and wall remodeling determines the failure or the success of the intervention. Accordingly, this work presents a versatile computational model able to capture the feedback loop that describes the interaction between events at cellular/tissue level and mechano-environmental conditions. The work here presented is a generalization and an improvement of a previous work by our group of investigators, where an agent-based model uses a cellular automata principle on a fixed hexagonal grid to reproduce the leading events of the graft’s restenosis. The new hybrid model here presented allows a more realistic simulation both of the biological laws that drive the cellular behavior and of the active role of the membranes that separate the various layers of the vein. The novel feature is to use an immersed boundary implementation of a highly viscous flow to represent SMC motility and matrix reorganization in response to graft adaptation. Our implementation is modular, and this makes us able to choose the right compromise between closeness to the physiological reality and complexity of the model. The focus of this paper is to offer a new modular implementation that combines the best features of an agent-based model, continuum mechanics, and particle-tracking methods to cope with the multiscale nature of the adaptation phenomena. This hybrid method allows us to quickly test various hypotheses with a particular attention to cellular motility, a process that we demonstrated should be driven by mechanical homeostasis in order to maintain the right balance between cells and extracellular matrix in order to reproduce a distribution similar to histological experimental data from vein grafts.

Neointima development in externally stented saphenous vein grafts

Introduction

The main limitation of coronary artery bypass grafting (CABG) is rapid neointimal hyperplasia leading to graft failure.

Aim

To assess plaque formation in saphenous vein grafts (SVG) covered by an external Dacron stent in comparison with the classical technique.

Material and methods

In the study group vein grafts covered by external stent mesh made of Dacron were implanted. An intravascular ultrasonography (IVUS) study was performed in 35 aorto-coronary SVG covered by an external Dacron stent and in 64 normal SVG during the first year after CABG. In each SVG 25 mm of good quality IVUS image, volumes of lumen, plaque (neointima), outer border of the vein graft (external SVG) and adventitia were calculated in three time periods: 0–130 days, 130–260 days and 260–390 days.

Results

Between the first and second time period, lumen volume (mm³) was reduced from 10.33 ±4.4, to 6.80 ±2.23 in the second period and 5.69 ±1.26 in the third one. This effect was much less marked in normal grafts. The corresponding lumen volume (mm³) was: 10.90 ±3.9, 9.15 ±2.94 and 8.92 ±2.93 in consecutive time periods. Plaque volume (mm³) did not change in control grafts during the course of the study, but it increased very significantly in stented grafts from 0.86 ±1.24 in the first period to 2.70 ±1.58 in the second and 3.29 ±2.66 in the third one.

Conclusions

The experimental technique of implanting SVG covered with an external elastic Dacron stent seems to be inferior to traditional ones. This is probably due to the more complicated process of vein implantation and higher micro-injury occurrence during the surgery.

Distal runoff and the development of degenerative changes in autologous reversed saphenous vein femoropopliteal bypass

MATERIAL

A total of 10 patients randomly selected from those who had reversed saphenous vein femoropopliteal bypass at our Institution and who had a postoperative angiogram were included into the study.

METHODS

The occurrence of degenerative changes at the control angiography was correlated to the quality of the distal runoff as seen at the preoperative angiography and to the level of the index of distal resistances, calculated as the difference between the upper calf pressure and that at the ankle, divided by the arm pressure.

RESULTS

Three patients had degenerative changes which were more common in case of poor distal runoff and high index of distal resistances.

CONCLUSIONS

Degenerative changes in reversed saphenous vein grafts are more common in case of poor distal runoff and high distal resistance. These factors should be added to the many risk factors that have been analyzed previously.

Folic acid administration reduces neointimal thickening, augments neo-vasa vasorum formation and reduces oxidative stress in saphenous vein grafts from pigs used as a model of diabetes

AIMS/HYPOTHESIS

There is evidence that plasma homocysteine augments vein graft failure and that it augments both micro- and macro-angiopathy in patients with diabetes mellitus. It is therefore suggested that homocysteine may augment vein graft thickening, a major cause of vein graft failure, in diabetic patients, as well as impairing adaptive growth of a new vasa vasorum, possibly through overproduction of superoxide. In order to test these proposals, the effect of folic acid administration, which lowers plasma homocysteine, on vein graft thickening and microvessel density was studied in pigs used as a model of diabetes.

METHODS

Non-ketotic hyperglycaemia was induced in Landrace pigs by intravenous injection of streptozotocin, and folic acid was fed daily for 1 month. Vein grafts were excised and the thickness of the neointima and media and microvessel density were assessed by planimetry and superoxide formation.

RESULTS

Plasma total homocysteine was significantly reduced by folic acid in both control and diabetic pigs, whereas glucose was unchanged. Compared with controls, diabetic pigs showed increased neointimal thickness and superoxide formation and decreased adventitial microvessel density. Folic acid reduced neointimal thickness and superoxide formation and augmented microvessel density in diabetic but not in control pigs.

CONCLUSIONS

Folic acid administration reduces neointimal thickening, augments vasa vasorum neoformation and reduces oxidative stress in saphenous vein grafts from diabetic pigs. Folic acid may therefore be particularly effective in reducing vein graft failure in diabetic patients.

An experiment-based model of vein graft remodeling induced by shear stress

Vein graft intimal hyperplasia induced by shear stress is considered to be one of the major causes of vein graft failure. We have developed a mathematical model of vein graft intimal hyperplasia induced by shear stress based on experimental data. Intimal thickness and the rate of intimal thickness change are expressed as functions of shear stress and time. The model coefficients are derived from animal experiments where bilateral rabbit carotid vein grafts are exposed to different shear stress levels. Morphology data of the vein grafts are obtained over multiple time points. The model describes the well-known behavior of intimal thickening, which is inversely related to shear stress. It also depicts the time-dependent behavior of vein graft intimal hyperplasia. Finally, the model is used to simulate the intimal growth around a focal stenosis, which was created by ligating the middle of a vein graft using a suture. Simulation results and experimental data agree qualitatively, and demonstrate that the intima thickens more distal to the stenosed area. These experiments establish the potential of the general experiment-based approach for predicting human vein graft remodeling. Other mechanical and biological factors can be included following a similar approach in order to obtain a more accurate vein graft remodeling model.

A model of vein graft intimal hyperplasia

When vein graft is implanted in the arterial system, the vein graft wall becomes thicker as an adaptive process. We have developed a model of early adaptive vein graft intimal thickening induced by shear stress. Intimal thickness and the rate of intimal thickening are expressed as functions of shear stress and time based on experimental data. The model describes the behavior of intimal thickening which is inversely related to shear stress. It also depicts the time-dependent behavior of the vein graft intimal thickening.

Interactive Effects of Homocysteine and Copper on Angiogenesis in Porcine Isolated Saphenous Vein

BACKGROUND

After coronary artery bypass grafting procedures with saphenous vein, there is a protracted elevation of plasma homocysteine and copper. These interact to elicit endothelial dysfunction through promotion of superoxide. It has been suggested that angiogenesis and the formation of a neovasa vasorum is important in mediating vein graft patency. A novel in vitro model of angiogenesis in isolated pig saphenous veins was therefore developed to study the effect of homocysteine and copper and the role of superoxide on tubule growth, an index of angiogenesis.

METHODS

Two-millimeter rings of porcine saphenous veins were embedded in fibrin, incubated for 2 weeks with homocysteine and copper chloride, and tubules counted.

RESULTS

Tubule growth in cultured saphenous veins, which was inhibited by angiostatin, occurred in a time-dependent manner during a 14-day period. Copper chloride alone at 1 microM and 10 microM augmented microtubule formation, whereas homocysteine alone at up to 1 mM had no effect. Homocysteine and copper chloride together markedly inhibited microtubule formation. Significant inhibition of tubule formation and superoxide formation was elicited with inhibitors of nicotinamide adenine dinucleotide phosphate oxidase, mitochondrial respiration, and xanthine oxidase. Copper chloride augmented superoxide formation, but homocysteine had no effect. Homocysteine and copper chloride together also augmented superoxide formation.

CONCLUSIONS

These data indicate that the increase in plasma homocysteine and copper may exert a deleterious effect on graft patency by preventing the formation of a neovasa vasorum, thereby promoting hypoxia. This effect is mediated by a mechanism independent of superoxide which actually promotes angiogenesis in this model.

Local and Global Geometric Influence on Steady Flow in Distal Anastomoses of Peripheral Bypass Grafts

We consider the effect of geometrical configuration on the steady flow field of representative geometries from an in vivo anatomical data set of end-to-side distal anastomoses constructed as part of a peripheral bypass graft. Using a geometrical classification technique, we select the anastomoses of three representative patients according to the angle between the graft and proximal host vessels (GPA) and the planarity of the anastomotic configuration. The geometries considered include two surgically tunneled grafts with shallow GPAs which are relatively planar but have different lumen characteristics, one case exhibiting a local restriction at the perianastomotic graft and proximal host whilst the other case has a relatively uniform cross section. The third case is nonplanar and characterized by a wide GPA resulting from the graft being constructed superficially from an in situ vein. In all three models the same peripheral resistance was imposed at the computational outflows of the distal and proximal host vessels and this condition, combined with the effect of the anastomotic geometry, has been observed to reasonably reproduce the in vivo flow split. By analyzing the flow fields we demonstrate how the local and global geometric characteristics influences the distribution of wall shear stress and the steady transport of fluid particles. Specifically, in vessels that have a global geometric characteristic we observe that the wall shear stress depends on large scale geometrical factors, e.g., the curvature and planarity of blood vessels. In contrast, the wall shear stress distribution and local mixing is significantly influenced by morphology and location of restrictions, particular when there is a shallow GPA. A combination of local and global effects are also possible as demonstrated in our third study of an anastomosis with a larger GPA. These relatively simple observations highlight the need to distinguish between local and global geometric influences for a given reconstruction. We further present the geometrical evolution of the anastomoses over a series of follow-up studies and observe how the lumen progresses towards the faster bulk flow of the velocity in the original geometry. This mechanism is consistent with the luminal changes in recirculation regions that experience low wall shear stress. In the shallow GPA anastomoses the proximal part of the native host vessel occludes or stenoses earlier than in the case with wide GPA. A potential contribution to this behavior is suggested by the stronger mixing that characterizes anastomoses with large GPA.

Intimal Hyperplasia in Mouse Vein Grafts Is Regulated by Flow

Altered flow conditions are presumed to cause stenosis in vein grafts due to exaggerated neointimal formation. The aim of this study was to establish a mouse model of flow-regulated intimal hyperplasia (IH) in vein grafts. The caval vein was grafted into the common carotid artery of 38 mice, followed by modulation of the blood flow, resulting in vein grafts with high (HF) and low flow (LF). The vessel wall thickening was evaluated after 3, 14 and 42 days by morphometric analyses and immunohistochemistry. There was an immediate significant change in flow, which was persistent throughout the time of observation. After 42 days, flow was increased 2.7 times in HF animals compared to LF animals. The vessel wall was composed of two layers where the inner layer was positive for alpha-actin and considered as IH. The area of neointimal formation was 74% larger in the LF group compared to the HF group. The present study demonstrates that flow regulates IH in vein grafts in mice. This model gives the potential to study the effect of shear stress on vascular biology in genetically modified animals.

Long-term reduction of medial and intimal thickening in porcine saphenous vein grafts with a polyglactin biodegradable external sheath

OBJECTIVES

The development of neointimal hyperplasia with subsequent atherosclerotic deposition has been proposed to cause most late vein graft failures. Our unit has previously demonstrated that placement of a macroporous, loose-fitting polyester external stent prevents neointimal thickening in porcine vein grafts, and has been proposed as a therapeutic strategy to prevent late vein graft failure. To reduce any potential long-term complications of the permanent polyester stent, a study was undertaken to investigate the effect of a biodegradable external stent on porcine vein graft thickening at 1 month and to identify its longer term effects at 6 months.

METHODS

Bilateral saphenous vein to common carotid artery interposition grafting was performed in Large White pigs (25-32 kg; n = 6 per time course group) according to UK Home Office guidelines. A commercially constructed loose-fitting 8-mm-diameter polyglactin stent was placed externally around the vein graft on one side, and the contralateral side remained unstented to serve as control. The external stent was designed to biodegrade and hence disappear within 90 days. Grafts were left in situ for 1 month in 1 group of animals, and for up to 6 months in the other group, before explantation. Graft morphometric features were assessed with computer-aided planimetry.

RESULTS

At 1 month the vein grafts fitted with the polyglactin stent demonstrated a statistically significant decrease in neointimal thickening (0.038 mm; interquartile range [IQR], 0.035-0.039 mm) compared with the unstented control grafts (0.13 mm; IQR; 0.11-0.19; P = .0012), and also in medial thickening (0.09 mm; IQR, 0.086-0.093) compared with unsheathed control grafts (0.302 mm; IQR, 0.272-0.414; P = .0012). The 6-month polyglactin stented grafts also demonstrated a statistically significant reduction in neointimal thickening (0.049 mm; IQR, 0.047-0.07; P = .0012) compared with control grafts (0.178 mm; IQR, 0.164-0.19), and also in medial thickening (0.105 mm; IQR, 0.095-0.143) compared with unstented grafts (0.421 mm; IQR, 0.35-0.44; P = .0012, Mann-Whitney U test).

CONCLUSION

The loose-fitting biodegradable polyglactin external stent reduces porcine vein graft thickening at 1 month, which persists in the long term, even after degradation of the stent itself. This effective removal of the stent may therefore reduce the long-term risks for infection and mechanical complications associated with implanted prosthetic material while still eliciting the primary objective of preventing graft thickening over the long term. Biodegradable external stents therefore have potential advantages over permanent stent material in clinical application.

CLINICAL RELEVANCE

Arteriovenous bypass graft failure has a huge economic effect on health care resources, and a devastating effect o the patient. The attenuation of vein wall thickening, with subsequent luminal narrowing and occlusion, is a major goal in improving the longevity of the venous graft, to reduce secondary percutaneous and surgical interventions. The biodegradable external stent demonstrated in this study has possible clinical applications in bypass procedures with autogenous venous tissue, and represents a novel approach to ameliorating the problem of intimal hyperplasia that plagues these grafts.

Transduction of peptide analogs of the small heat shock-related protein HSP20 inhibits intimal hyperplasia

BACKGROUND

Human saphenous vein (HSV) is the autologous conduit of choice for peripheral vascular reconstructions. However, vasospasm can lead to early graft failure. The leading cause of delayed graft failure is intimal hyperplasia.

OBJECTIVE

To develop a proteomic approach to prevent vein-graft spasm and intimal hyperplasia.

METHODS

Biomimetic peptide analogs of the small heat shock-related protein HSP20, containing a protein transduction domain (PTD), a phosphorylated serine, and a sequence of HSP20 surrounding the phosphorylation site (PTD-pHSP20), or a scrambled sequence of the same amino acids surrounding the phosphorylation site (PTD-scHSP20) were synthesized. The peptides were used in muscle bath and organ culture experiments with human saphenous vein (HSV) segments. Cultured smooth muscle cell lines were used to determine the effect of the peptides on proliferation and migration.

RESULTS

In HSV rings precontracted with norepinephrine, PTD-pHSP20 but not PTD-scHSP20 led to relaxation. There was no significant difference in smooth muscle cell proliferation in cells treated with PTD-pHSP20 compared with PTD-scHSP20. Treatment with PTD-pHSP20 significantly inhibited cellular migration compared with PTD-scHSP20. Control, untreated, and PTD-scHSP20-treated saphenous veins had significant increases in intimal thickness after culture. This intimal thickening was completely inhibited by treatment with PTD-pHSP20.

CONCLUSIONS

Protein transduction of biologically active motifs of HSP20 can affect pathologic and physiologic responses of HSV and represents a novel proteomic-based therapeutic approach.

CLINICAL RELEVANCE

We have been a part of the genomics era and are now viewing the emergence of "proteomics." The genome is linear and relatively easy to examine; however the proteome is much more complex and dynamic. In essence, the purpose of gene therapy is to manipulate the genome to produce a particular protein. This manuscript describes a new proteomic approach in which the biologically active part of a protein is directly introduced into vascular cells. Peptides were synthesized which contained a total of 24 amino acids, 11 of which represent a protein transduction domain or "carrier" while the other 13 are the biologically active "cargo." These synthetic peptides prevent spasm (contraction) and intimal hyperplasia in segments of human saphenous vein treated ex vivo. Preclinical development is currently underway to develop these molecules as a proteomic-based vein harvest solution to enhance vein-graft patency.

Arterial flow induces changes in venous endothelium which are modified by calcium channel blockers

INTRODUCTION

Adaptation of saphenous vein to arterial flow may be critical to the results of bypass. The present paper summarizes work recently presented as a Hunterian Lecture. Work includes in vitro investigation of the response of saphenous vein endothelium to arterial flow and assessment of its clinical importance using a cohort of patients undergoing vein bypass surgery.

METHODS

Freshly excised human saphenous vein segments were placed in an in vitro flow circuit to simulate arterial and venous flow conditions. Changes in the endothelial expression of proteins were assessed using a combination of immunohistochemistry and Western blotting. The role of ion channels in the changes seen induced by arterial flow in the saphenous vein endothelium was assessed by addition of ion channel blocking medication to the medium perfusing vein segments. A cohort of patients undergoing vein bypass surgery were followed to assess graft patency and the influence of prescribed medication on its outcome.

RESULTS

After arterial flow conditions, the staining area for the endothelial adhesin ICAM-1 and nitric oxide synthase were increased, while that of the anticoagulant protein thrombomodulin was decreased. The concentration of the important stimulant of the clotting cascade tissue factor was unaffected by arterial flow. These changes were modulated by the addition of ion channel blocking drugs to the vein perfusate. In particular, nifedipine abolished the reduction in thrombomodulin, but increased the amount of tissue factor. In a series of 236 patients undergoing primary infra-inguinal vein grafts, prescription of calcium channel blocker was associated with improved primary patency.

CONCLUSIONS

Important changes in the venous endothelium are induced by arterial flow. Ion channel blocking drugs have the potential to modulate these responses.

A bioabsorbable (polyglactin), nonrestrictive, external sheath inhibits porcine saphenous vein graft thickening

OBJECTIVE

External, nonrestrictive, macro-porous polyester stents prevent neointima formation in porcine vein grafts and have been proposed as a therapeutic approach to the prevention of late vein graft failure. These stents are nonbiodegradable and therefore may promote long-term foreign body problems including infection and inflammation. The effect of external macro-porous biodegradable (polyglactin) sheaths on neointimal and medial thickening in porcine vein grafts was therefore investigated.

METHODS

Bilateral saphenous vein-carotid artery interposition grafting was performed in white Landrace pigs (n = 8) with external placement of polyglactin (Vicryl) sheaths (8 mm in diameter) on 1 side, with the contralateral side acting as a control. One month after surgery, grafts were explanted and wall dimensions measured on histological sections using computer-aided planimetry, and an immunocytochemical appraisal was carried out.

RESULTS

All grafts were patent at explantation. Polyglactin sheaths significantly reduced intimal thickness, medial thickness, and the percentage of proliferating cells compared with unsheathed controls. There was a pronounced accumulation of macrophages, giant cells, endothelial cells, and microvessels within and surrounding the biodegradable sheath compared with controls.

CONCLUSIONS

A nonrestrictive, biodegradable (polyglactin), external sheath reduces medial and intimal thickening in experimental saphenous vein grafts, possibly through inflammatory cell-mediated angiogenesis. If subsequent long-term studies confirm preservation of this beneficial effect, once the sheath biodegrades, this approach may have an advantage over the permanent polyester stent when applied clinically.

External supports and the prevention of neointima formation in vein grafts

AIMS AND METHODOLOGY

the aim of this review is to provide an overview of the aetiology of neointima formation in vein grafts and to highlight the use of an external support to modulate this phenomenon. A systematic literature review was performed via computerised search on MEDLINE, OVID and the Cochrane Library. The search terms initially employed were broad-based; "vein graft", "neointima" and "external stent". Subsequently, more specific search terms were utilised; "perivenous mesh", "external prosthesis" and "varicose vein". Articles from indexed journals relevant to the objective, external venous supports, from the earliest reports in the 1960's to the latest in 2001 were included to obtain an exhaustive list. Reviews, abstracts and proceedings of scientific meetings, case reports and the results of both animal model investigations and human clinical trials in all languages were included. Articles describing an external support employed in both peripheral and aortocoronary bypass investigations were included.

Intraoperative endothelial damage is associated with increased risk of stenoses in infrainguinal vein grafts

OBJECTIVES

Saphenous vein injury is believed to predispose to vein graft stenoses. The aims of this study were to assess the endothelial injury associated with infrainguinal vein bypass surgery by serial measurements of serum thrombomodulin concentration as well as by platelet scintigraphy, and to relate these findings with the postoperative development of stenoses.

METHODS

In 35 patients undergoing vein bypass surgery serum thrombomodulin concentration was measured pre- and postoperatively. Autologous 111-indium labelled platelets were administered into the common femoral artery immediately after restoration of flow in the graft and scintigraphic images were obtained 4 and/or 24 h later.

RESULTS

Serum thrombomodulin increased markedly from median 17 ng/ml preoperatively to 32 ng/ml 1 day after surgery (p =0.00002). Platelet scintigraphy revealed a total of 62 focal activity accumulations, the majority being located in the anastomotic regions. Among the 30 patients with grafts remaining patent at 30 days stenoses occurred in nine (16%) of 55 regions with scintigraphic platelet accumulations as compared to only four (4%) of 94 regions without platelet accumulations (p =0.03).

CONCLUSIONS

The very high predictive value of a negative platelet scintigraphy (96%) strongly suggests that localised perioperative endothelial injury is an important pathogenetic factor in the development of vein graft stenoses.

Arterial flow induces changes in saphenous vein endothelium proteins transduced by cation channels

OBJECTIVES

expression of leukocyte adhesins and proteins controlling thrombosis is likely to be an important determinant of graft patency early following vein bypass. We have previously demonstrated rapid increase in endothelial ICAM-1 and nitric oxide synthase (eNOS) concentrations in human saphenous vein exposed to arterial flow. The aim of this study was to investigate whether ion-channel-blocking drugs could alter these flow-induced changes.

METHODS

human saphenous vein segments, freshly excised from patients, were placed in a validated in vitro circuit using flow conditions shown to simulate arterial or venous circulations for 90 min, in the presence or absence of ion-channel blockers. The concentrations of ICAM-1, VCAM-1, eNOS and tissue factor (TF) were assessed by quantitative immunohistochemistry in vein exposed to flow and compared with that in freshly excised vein from the same patient. The endothelial protein concentration was calculated as the mean area of staining as percentage of that for the control protein CD31, using computer-aided image analysis.

RESULTS

after arterial flow conditions the area ratio of ICAM-1 increased from 21.4+/-1.4 to 44.6+/-2.0%, of eNOS increased from 50.0+/-5.6 to 70.1+/-5.0%, of VCAM-1 decreased from 16.6+/-3.4 to 3.6+/-1.0%, whereas TF staining area ratio was unchanged. Inclusion of the non-selective K(+)channel blocker, tetraethylammonium, in the arterial perfusion solution abolished all these arterial flow-induced changes. Inclusion of the K(+)ATP channel blocker, glibenclamide, selectively abolished the arterial flow-induced changes in ICAM-1 and VCAM-1. Inclusion of the calcium channel blocker, nifedipine, abolished the arterial flow-induced changes in eNOS and VCAM-1 but increased the TF staining area ratio from 3.0+/-0.4 to 8.5+/-0.7%, p=0.01. Inclusion of the stretch-activated cation-channel blocker, gadolinium, enhanced the arterial flow-induced increase in eNOS, but prevented the arterial flow-induced increase in ICAM-1.

CONCLUSIONS

perfusion of veins under arterial flow conditions with gadolinium was associated with low endothelial concentrations of ICAM-1, VCAM-1 and TF, but high levels of eNOS. Such a concentration of endothelial proteins may be advantageous in newly implanted vein grafts. In contrast, nifedipine could have adverse effects by promoting increase in TF concentration.

Ultrastructural analogies between intimal alterations in veins from diabetic patients and animals with STZ-induced diabetes

The aim of this study was to document similarities and differences between veins from human diabetic patients and an experimentally induced diabetic animal model. The saphenous vein and posterior tibial vein from diabetic patients and the femoral vein from rats were studied. An increase in the extracellular matrix with migration of smooth muscle cells and endothelial alterations were observed in the intima of all specimens. These findings demonstrate that there is a high degree of similarity between the pathological changes in the venous wall during human diabetes mellitus and streptozotocin (STZ) induced-diabetes. This finding validates STZ induced-diabetes in rats as a model for further experimental study to clarify the fate of the diabetic venous wall when used as a graft.

Sustained reduction of neointima with c-myc antisense oligonucleotides in saphenous vein grafts

BACKGROUND

Treatment of saphenous veins with c-myc antisense oligomers during preparation for grafting reduces medial cellular proliferation and macrophage infiltration, and preserves medial smooth muscle content at 3 days. Accordingly, the purpose of this study was to examine whether c-myc antisense oligomers have an impact on late vein graft remodeling.

METHODS

Sixty-two pigs underwent unilateral saphenous vein-carotid artery interposition grafting. Harvested veins were incubated either in saline (control group) or 20-micromol/L or 200-micromol/L concentrations of c-myc antisense oligomers (treated groups) for 30 minutes intraoperatively. Three months after surgery, vein graft histology was assessed.

RESULTS

Forty-five of 62 randomized animals survived the experiment; no differences in animal survival or graft patency among the groups were observed (p = NS, chi2). C-myc antisense oligomers significantly decreased neointimal and wall thickness, as well as increased lumenal index, in treated groups (p<0.04, p<0.03, and p<0.001, respectively, analysis of variance). In contrast, there was no difference in medial thickness or perivascular wound healing.

CONCLUSION

Intraoperative treatment of saphenous veins with c-myc antisense oligomers decreased neointimal formation at 3 months after grafting. In conjunction with our previous reports, these findings suggest that early inhibition of cellular proliferation and inflammatory infiltration results in a sustained reduction in neointimal formation and favorable graft remodeling.

Endothelin-B receptors mediate intimal hyperplasia in an organ culture of human saphenous vein

OBJECTIVE

Although a number of pharmacologic agents have been shown to reduce intimal hyperplasia in animal models of restenosis, to date no systemic agent has conclusively been shown to be effective in humans. Recently, considerable attention has been directed towards endothelin (ET), a potent vasoconstrictor and a powerful mitogen for vascular smooth muscle cells, as a mediator of intimal hyperplasia. Endothelin-1 has been shown to be mitogenic for human saphenous vein smooth muscle cells, and expression also is elevated in human vein graft stenosis. The aim of this study was the investigation of whether ET receptor antagonists can attenuate neointima formation in a laboratory model of vein graft intimal hyperplasia and the determination of whether the effects are mediated by a specific ET receptor subtype.

METHODS

We used an organ culture of human saphenous vein, a well-validated model of vein graft intimal hyperplasia. Paired segments of human long saphenous vein were cultured with and without the following antagonists: bosentan, a nonselective ET receptor antagonist; BQ 123, a specific endothelin-A antagonist; or BQ 788, a specific endothelin-B (ETB) antagonist. After 14 days in the culture, the segments were fixed and processed and the sections were immunostained to facilitate the measurements of neointimal thickness with a computerized image analysis system.

RESULTS

The nonselective antagonist bosentan and the ETB selective antagonist BQ 788 significantly reduced neointima formation by 70% (P = .001) and 50% (P = .03), respectively, but the ETA antagonist BQ 123 had no significant effect on the reduction of neointima formation (P = 1.0).

CONCLUSION

The results of this study imply an important role for ET as a mediator of human vein graft intimal hyperplasia and imply further that a specific ETB antagonist may have a therapeutic potential for the prevention of vein graft stenosis.

Marimastat inhibits neointimal thickening in a model of human vein graft stenosis

BACKGROUND

There is now accumulating evidence that matrix metalloproteinases (MMPs), the physiological mediators of matrix deposition and degradation, play an important role in the development of intimal hyperplasia following arterial bypass. This study investigated the effect of marimastat, an orally active specific MMP inhibitor, on neointima formation in cultured human saphenous vein.

METHODS

Segments of human saphenous vein obtained from ten patients undergoing arterial bypass surgery were cultured for 14 days in serum-supplemented RPMI medium (controls) or in control medium supplemented with marimastat at three different concentrations (treatment groups). Following culture, half of each segment was prepared for histological examination and MMPs were extracted from the other half for gelatin zymography.

RESULTS

Marimastat inhibited neointimal thickening in a concentration-dependent manner; inhibition was significant at 10(-5) and 10(-6) mol/l (P=0.006). This observation was paralleled by a significant reduction in the levels of MMP-2 and MMP-9 in the tissues.

CONCLUSION

Marimastat significantly reduced neointimal thickening in this laboratory model. MMP inhibitors may offer a potential therapeutic strategy in the prevention of intimal hyperplasia.

Locally applied antisense oligonucleotide to proliferating cell nuclear antigen inhibits intimal thickening in experimental vein grafts

This study examines the effect of antisense oligonucleotide to proliferating cell nuclear antigen (PCNA) on the formation of vein graft intimal hyperplasia in vivo, using localized administration. Twenty-four New Zealand white rabbits had a right carotid interposition bypass graft using the external jugular vein and were sacrificed on the 28th postoperative day. To determine the effect of PCNA on the development of intimal hyperplasia, 6 animals had their grafts coated with a pluronic gel containing 18 base antisense oligonucleotide to PCNA (1 mg/ml), 6 received a pluronic gel containing an 18 base nonsense oligonucleotide (1 mg/ml), and 12 animals were controls (6 with and 6 without pluronic gel). These grafts were harvested for morphology and videomorphometry. There was no change in the intimal thickness between the control and gel-treated groups. (70 +/- 4 microm versus 72 +/- 4 microm; mean +/- s.e.m.; p = ns). The presence of nonsense oligonucleotide had no further effect. Antisense PCNA produced a 26% decrease in intimal thickness to 50 +/- 4 microm in the treated vein grafts (p < 0.03) without a change in medial thickness. This study shows that a local single application of antisense oligonucleotide to PCNA will reduce the intimal hyperplasia in experimental vein grafts over 28 days.

Local effects of nitric oxide supplementation and suppression in the development of intimal hyperplasia in experimental vein grafts

OBJECTIVES

The universal response of vein grafts after insertion into the arterial circulation is the development of intimal hyperplasia; smooth muscle cell proliferation and connective tissue deposition, which may be modulated in part by dysfunctional endothelial nitric oxide (NO) metabolism. This study examines the effects of single dose, local application by pluronic gel of a NO donor, S-nitroso-N-acetylpenicillamine (SNAP) and an NO synthase inhibitor nitro-L-arginine methyl ester (L-NAME) on the formation of intimal hyperplasia.

MATERIALS

Forty New Zealand white rabbits underwent jugular vein interposition grafting of the common carotid artery.

DESIGN

Ten animals were controls, 10 animals had the outer surface of the vein graft coated with 30% pluronic gel (2.5 ml), and 10 each were immersed for 15 min prior to insertion in Ringer lactate containing 10(-3) M of SNAP or L-NAME and then had their vein grafts coated with 2.5 ml of gel containing either SNAP (10(-3) M) or L-NAME (10(-3) M), which allows for sustained delivery for up to 6 h. On the 28th post operative day, the animals were sacrificed and vein grafts were harvested for morphology by electron microscopy (SEM and TEM) and dimensional analysis by videomorphometry.

RESULTS

All vein grafts developed intimal hyperplasia. On SEM the vein grafts had a confluent layer of endothelial cells with multiple layers of smooth muscle cells representing intimal hyperplasia in TEM. There were no demonstrable morphological differences between the four groups. Local treatment with SNAP produced a significant 36% decrease in mean intimal thickness (72 +/- 4 microns vs. 45 +/- 4 microns; mean +/- S.E.M.; p < 0.01) without a change in medial thickness compared to gel-only treated groups (58 +/- 6 microns vs. 61 +/- 7 microns; p = ns). Inhibition of NO synthase by L-NAME had no effect on the development of intimal hyperplasia (72 +/- 4 microns vs. 79 +/- 10 microns; p = ns); medial thickness was also unchanged.

CONCLUSION

These data confirm the protective effect of NO in vascular injury and suggest that NO synthase activity is either absent or reduced to such a level that further inhibition in this short time course is not relevant to the pathophysiology of vein graft intimal hyperplasia.

Histopathological features of in situ vein bypass stenoses

OBJECTIVES

To analyse the histopathological features of in situ vein bypass stenoses.

MATERIALS AND METHODS

Nineteen specimens of primary (n = 16) or recurrent (n = 3) vein graft stenoses obtained from 17 patients during surgical revision were prepared for light microscopy and immunohistochemical investigation. The median time interval from bypass surgery to stenosis excision was 5 months (range 2-52 months). Twenty-seven saphenous vein segments obtained from patients undergoing primary bypass surgery served as controls.

RESULTS

Graft stenoses were characterised by moderate to severe intimal hyperplasia composed of actin positive but desmin negative cells, interspersed with areas of fibrosis. A single layer of factor VIII positive endothelial cells were identified on the luminal surface. The media, separated from the intima by a poorly defined elastic lamina, usually appeared normal or mildly hyperplastic and consisted of smooth muscle cells, which stained positive for actin as well as for desmin. The adventitia was composed of loose connective tissue in which lymphocytes, plasma cells and giant cells were occasionally seen. Atheromatous material was absent from intragraft lesions, but was observed in one specimen, which was harvested from a proximal anastomotic lesion. The majority of pre-bypass vein segments showed evidence of intimal thickening whereas medial hyperplasia was less common.

CONCLUSIONS

In situ vein bypass stenoses mainly consisted of intimal hyperplasia and varying degrees of fibrosis. Similar but less pronounced morphological changes were found in pre-bypass vein segments. The nature of the actin positive but desmin and factor VIII negative intima cells is uncertain, and further studies are needed to characterise this cell type.

Vein grafts: haemodynamic forces on the endothelium--a review

OBJECTIVE

To review the mechanisms believed to be important in the development of vein graft stenosis, with particular attention placed on the adaptation of saphenous vein endothelium to a new haemodynamic environment.

DESIGN AND METHODS

Discussion based on review of published research.

RESULTS

The aetiology of vein graft stenosis remains to be established and appears to be multi-factorial. The increasing evidence for an important role of haemodynamic forces is discussed, particularly via the interaction of these force with the endothelium.

CONCLUSION

Further understanding of the interaction between haemodynamic forces, blood constituents and the newly implanted vein graft is required. Use of in vitro models is contributing increasing knowledge to this area, but ultimately better non-invasive methods of assessing haemodynamic forces in vivo are required.

Antibodies to cardiolipin may increase the risk of failure of peripheral vein bypasses

OBJECTIVES

To assess the association between antibodies to cardiolipin and infrainguinal vein graft patency.

MATERIALS AND METHODS

Plasma levels of antibodies to cardiolipin, haemostatic factors, lipids and the smoking marker carboxyhaemoglobin were determined preoperatively and 6 weeks postoperatively in 80 patients undergoing infrainguinal vein bypass surgery. Bypass patency was assessed by ankle blood pressure measurements and ultrasound duplex scanning at 1 week, 6 weeks, 3, 6, 9 and 12 months. A localised increase in the graft peak systolic velocity by a factor of 2.5 or more was considered to indicate a significant stenosis.

RESULTS

Antibodies to cardiolipin were identified in seven (9%) patients preoperatively. In four of these seven patients the bypasses thrombosed within 3 months after surgery and another two developed stenoses. At 6 months the primary bypass patency, i.e. patency without stenosis, was 14% (95% confidence interval (CI) 0-33%) in patients with antibodies to cardiolipin, as opposed to 57% (95% CI 45-69%) in patients without these antibodies (log rank test: p = 0.03). Diabetes mellitus was also associated with a reduced 6 months primary bypass patency (38% (95% CI 16-60%) vs. 58% (95% CI 45-71%), p = 0.006). A Cox regression analysis showed that both the presence of antibodies to cardiolipin and diabetes independently contributed towards predicting the overall risk of bypass failure.

CONCLUSION

Antibodies to cardiolipin were identified in 9% of patients undergoing infrainguinal vein bypass surgery and appeared to be associated with increased risk of bypass failure.

Pre-bypass quality assessment of the long saphenous vein wall with ultrasound and histology

OBJECTIVES

Pre-existing unsuspected wall changes in saphenous vein grafts have been implicated in the graft outcome. Pre-bypass assessment of the vein may identify grafts at high risk for failure. This study was conducted to evaluate preoperatively the quality of the long saphenous vein (LSV) wall with ultrasound and histology.

DESIGN

Prospective clinical study.

MATERIAL AND METHODS

Three particular LSV segments, ankle, knee and mid-thigh, were evaluated preoperatively by ultrasound in 40 limbs of 38 patients, candidates for coronary artery bypass grafting. The venous wall was characterised based on its thickness and echogenicity in three categories: normal, moderately and severely fibrotic. LSV specimens taken from the above sites were also grouped into the same three categories based on their fibrotic content found on histology.

RESULTS

In total, 89 vein specimens were evaluated. On ultrasound, 81 specimens were detected as normal (91%), seven as moderately (8%) and one as severely fibrotic (1%). On histology, only eight specimens were found normal (9%), 75 with moderate (84%) and six with severe fibrosis (7%). Similar wall characterisation with both examinations was found in only 19% (17/89) of the specimens. Eighty-one specimens (91%) had some degree of fibrosis on histology. Different grades of fibrosis were found on histology in different sites of the same vein.

CONCLUSIONS

Pre-existing wall changes are very common in vein grafts used for bypass surgery. However, the ultrasonic characterisation of the venous wall preoperatively cannot reliably identify these changes.

Detection of "functional" valves in reversed saphenous vein bypass grafts: identification with duplex ultrasonography

PURPOSE

Although venous valve lesions have been cited as a mechanism of graft failure, the fate of venous valves in reversed saphenous vein (RSV) bypass grafts is unclear. The basis for this uncertainty is the difficulty in postoperative identification and follow-up of valve sites and the infrequent pathologic submission of vein graft lesions. This report describes the features of "functional" valves (FV) visualized in RSV grafts by ultrasonic duplex scanning.

METHODS

Sixty-six RSV infrainguinal vein grafts were prospectively studied with duplex ultrasonography from January 1992 to December 1995. Grafts were studied at 1, 2, 3, 4, 6, 9, 12, 18, and 24 months, then annually. FV identification was based on a characteristic ultrasound Doppler waveform and color flow pattern and visualization of the leaflets by B-mode imaging. The waveform consists of end-systolic valve closure followed by variable degrees of reflux. Immediate postoperative reactive hyperemia precludes detection, because flow reversal in the graft is needed for identification.

RESULTS

Since August 1994, 14 FV have been identified in 11 (17%) of 66 RSV grafts. The mean time to FV recognition after implantation was 10 months (range, 1 to 52 months), and the average follow-up was 15 months. One valve was completely competent. Seven (50%) of the FV were associated with the development of a < 50% diameter reducing stenosis by Doppler velocity criteria. None of the FV has required intervention.

CONCLUSIONS

"Functional" vein valves in RSV grafts are common and can be identified by ultrasonic duplex imaging. Awareness of the characteristics of FV during routine duplex graft surveillance will undoubtedly increase detection. The variable time course to identification of FV and duration of "function" warrants continued follow-up to determine the relationship of these valves to the development of stenotic lesions and graft failure.

Antisense oligonucleotide to proto-oncogene c-myb inhibits the formation of intimal hyperplasia in experimental vein grafts

BACKGROUND

The development of intimal hyperplasia is a major cause of early vein graft failure. The study examines the effects of locally delivered antisense oligonucleotides to the proto-oncogene c-myb on the development of vein graft intimal hyperplasia.

METHODS

Common carotid vein bypass grafting procedures were performed on 60 New Zealand White rabbits. Seventeen grafts were controls, 14 had grafts coated with a commercial gel, 17 had grafts coated with gel containing 200 micrograms of an antisense c-myb oligonucleotide, and 6 rabbits each had grafts coated with gel containing one of two control oligonucleotides. Grafts were harvested 28 days after surgery, and sections were taken for dimensional analysis, morphologic evaluation, and vasomotor function. Grafts were also harvested at 1 day for oligonucleotide uptake/localization analysis and at 3 days for c-myb mRNA analysis.

RESULTS

Oligonucleotides were uniformly distributed within the media and adventitia by 1 day. A 38% reduction occurred in mean intimal thickness in the vein grafts coated with antisense to c-myb compared with the other groups. No difference in medial thickness was seen among groups. By scanning and transmission electron microscopy all vein grafts showed a confluent endothelium. In contrast to control vein grafts, which did not relax to acetylcholine, most of the gel and all of the gel/oligonucleotide-coated grafts relaxed by more than 40% of precontracted tension. Responses to a panel of contractile agents were unchanged in the treated groups compared with those in the control group.

CONCLUSIONS

Locally delivered antisense oligonucleotides to proto-oncogene c-myb significantly reduces intimal hyperplasia with preservation of acetylcholine-mediated endothelium-dependent relaxation in experimental vein grafts. These findings suggest that targeting a common regulatory pathway of vascular smooth muscle mitogenesis can be successful in reducing the early development of intimal hyperplasia.

Early vein bypass thrombectomy is associated with an increased risk of graft related stenoses

OBJECTIVES

To assess the risk of graft stenoses following early thrombectomy of peripheral vein bypasses.

DESIGN

Prospective study of 371 vein bypasses performed at the Vascular Service, Rigshospitalet, Copenhagen from January 1991 through December 1992.

MATERIALS AND METHODS

Thirty-six vein bypasses reopened by thrombectomy within 30 days postoperatively (group I) and 335 bypasses not subjected to early thrombectomy (group II) were studied by ultrasound duplex scanning 3, 6, 9, 12, 18, 24, 36 and 48 months postoperatively. A localised increase in the peak systolic velocity of 250% or more was considered an indicator for significant stenosis.

RESULTS

In the perioperative period nine (2%) patients died, 30 (8%) bypasses occluded and 14 (4%) patients were lost to follow-up. Among the 318 patients remaining at risk at 1 month graft stenoses were identified in 39% (9/23) in group I compared to 17% (51/295) in group II, p = 0.03. Late bypass revisions were required in 35% (8/23) in group I as opposed to 9% (28/295) in group II, p = 0.004. Despite this high number of revisional procedures the 12-months secondary bypass patency was lower in recanalised grafts (38% vs. 82%, p < 0.00001).

CONCLUSION

Early vein bypass thrombectomy is associated with a two-fold increased risk of graft related stenoses and a reduced secondary bypass patency.

Arteriovenous fistulas aggravate the hemodynamic effect of vein bypass stenoses: an in vitro study

PURPOSE

The purpose of this study was to assess the impact of arteriovenous fistulas combined with varying degrees of stenosis on distal bypass hemodynamics and Doppler spectral parameters.

METHODS

In an in vitro flow model bypass stenoses causing 30%, 55%, and 70% diameter reduction were induced 10 cm upstream of a fistula with low outflow resistance. Flow and intraluminal pressure were measured proximal to the stenosis and downstream of the fistula. The waveform parameters peak systolic velocity, end-diastolic velocity, pulsatility index, and pulse rise time were determined from midstream Doppler spectra obtained 10 cm downstream of the fistula. All measurements were carried out with open and clamped fistula.

RESULTS

At 30% diameter reducing stenosis opening of the fistula induced a 12% systolic pressure drop across the stenosis but had no adverse effect on the Doppler waveform parameters. At 55% stenosis the pressure drop increased from 16% to 31% after fistula opening. This increased pressure drop was associated with a further reduction in peak systolic velocity, a decrease in pulsatility index, and an enhanced pulse rise time prolongation. Fistula opening at 70% stenosis increased the systolic pressure drop from 31% to 48% and had significant impact on all waveform parameters.

CONCLUSIONS

Distal arteriovenous fistulas enhance pressure loss across stenoses and affect downstream velocity waveform configuration. The presence of a combined fistula and a stenosis mimics the distal hemodynamic conditions of a more severe stenosis. Assessment of the hemodynamic impact of fistulas must be undertaken in the evaluation of in situ vein bypass stenoses.

Balloon catheter injury and vein graft morphology and function

Endovascular interventions to salvage failing vein bypass grafts are often associated with suboptimal outcomes. This study examines the effect of experimental vein graft catheter injury on vein graft morphology and vasomotor function. Thirty New Zealand white rabbits underwent a right common carotid interposition vein bypass graft. Ten grafts were harvested at 14 days, 10 were harvested at 28 days, and 10 had a balloon catheter injury induced at 14 days (4 F Fogarty catheter, 0.6 to 0.75 ml water inflation, 3 passes) and these 10 grafts were harvested after an additional 14 days. Morphologic and morphometric determinations (n = 5) or in vitro contractile studies (n = 5) were performed on segments of the vein grafts. Intimal thickness, without any intervention, increased by 84% from 14 to 28 days (p < 0.01), whereas catheter injury at 14 days induced a twofold increase (p < 0.001) in the formation of intimal hyperplasia by 28 days. Scanning electron microscopy demonstrated near-complete endothelial denudation after balloon catheter injury. In the 14- and 28-day control vein grafts, and in the balloon-injured vein grafts, the vascular surfaces had confluent endothelial linings. However, the ultrastructural features of the endothelial cells were group specific. Transmission electron microscopy of the same specimens confirmed this. There were no significant differences in contractility between the 28-day control and the catheter-injured vein grafts. This study demonstrates that balloon catheter injury doubles the rate at which intimal hyperplasia develops in vein grafts without significantly altering the physiologic phenotype of the smooth muscle cells as defined by their vasomotor function.

Suppression of intimal hyperplasia in experimental vein grafts by oral l-arginine supplementation and single ex vivo immersion in deferoxamine manganese

PURPOSE

Vein grafts undergo morphologic and functional changes after insertion into the arterial circulation with the development of intimal hyperplasia, as well as significant alterations in endothelial and smooth muscle cell physiologic responses.

METHODS

Forty New Zealand white rabbits underwent jugular vein interposition grafting of the common carotid artery. Ten animals were controls, 10 animals received 2.25% L-arginine supplementation in their drinking water (200 ml/day; 2 gm/kg) 7 days before surgery and continued thereafter until harvest, in 10 animals the veins were immersed in deferoxamine manganese (DFMn; 10(-3) mol/L in heparinized Ringer's lactate for 15 minutes) before implantation, and 10 received both L-arginine supplementation and either histologic (n=6) or isometric tension studies (n=4). The function of the vein grafts was compared with that of jugular veins.

RESULTS

Treatment with DFMn, l-arginine, amd DFMn L-arginine produce increases in mean intimal thickness of 39% (51 +/ -7 microm; p<0.05), 51% (41 +/- 7 microm; p<0.05), and 65% (29 +/- 6 microm; p< 0.01), respectively, compared with control vein grafts (83 +/- 12 microm). Compared with the control group, the intimal ratio ([intima]/[intima + media]) decreased by 16% (difference not significant), 8% (difference not significant), and 47% (p<0.01) in the DFMn-, L-arginine- and and DFMn/L-arginine-treated vein grafts, respectively. Jugular veins relaxed to acetylcholine (53% +/- 12% maximal relaxation), whereas control vein grafts did not relax. In contrast, vein grafts from each of the experimental groups relaxed to acetylcholine with maximal relaxations of 26% +/- 7% (p<0.05 compared with the jugular vein), 22% +/- 8% (p<0.05), and 44% +/- 14% (difference not significant) in the DFMn, L-arginine, DFMn/L-arginine groups, respectively. Neither DFMn nor l-arginine had a significant effect on the alterations in smooth muscle contractility that occur in control vein grafts.

CONCLUSION

This study demonstrates that an agent that modulates free radical production combined with a precursor of nitric oxide formation will lead to a significant decrease in the formation of intimal hyperplasia in arterial vein grafts with the preservation of endothelial-derived relaxation.

Preferential use of vein for above-knee femoropopliteal grafts

OBJECTIVES

Many centres preferentially use polytetrafluoroethylene (PTFE) for above-knee femoropopliteal bypass as surgery is simplified and patency rates are comparable to vein, which is preserved for subsequent revisions or for distal disease progression. In this Unit, vein remains first choice graft material. The aim of this study was to audit our results with respect to above-knee bypass to establish the demand for vein for secondary reconstruction and to document the ultimate fate of the limb.

PATIENTS

Between 1983 and 1992, 112 above-knee reconstructions were performed on 109 patients (89 vein and 23 PTFE grafts). PTFE was used where vein was absent or inadequate. Life table analysis of primary graft patency, limb salvage and patient survival up to 36 months follow-up concurs with previously reported series.

RESULTS

Twenty-eight vein grafts (31%) and 11 PTFE grafts (48%) occluded during a median follow-up of 64 months (8-116 months). In only four cases was vein required for secondary procedures. The remainder were salvaged by thrombectomy and local procedures for technical problems. Amputation rates following graft occlusion were 12% in the vein group (20% of these being above-knee) as against 26% in the PTFE group (80% above knee).

CONCLUSIONS

The demand for vein for secondary procedures is low. Amputation rates when vein grafts do occlude are half those of PTFE and amputation level is significantly influenced by graft type. We advocate preferential use of vein in above-knee femoropopliteal bypass.

The influence of the combined presence of diabetes mellitus and hypercholesterolaemia on the function and morphology of experimental vein grafts

OBJECTIVES

Diabetes and hypercholesterolaemia are known risk factors for the development of atherosclerosis and are considered to influence the development of vein graft intimal hyperplasia. This study examines the combined effect of diabetes for 12 weeks (alloxan-induced) and hypercholesterolaemia for 8 weeks (1% cholesterol diet) on the formation of intimal hyperplasia and the vasomotor function of vein grafts. MATERIALS AND DESIGN: Thirty-two New Zealand White rabbits underwent a carotid vein bypass graft. Eight were controls, eight were diabetic, eight were hypercholesterolaemic and eight had both diabetes and hypercholesterolaemia. All vein grafts were harvested at 4 weeks postoperatively for morphology (n = 4) or contractility studies (n = 4).

RESULTS

Compared to controls, both diabetes and hypercholesterolaemia increased intimal thickness by 20% and 63% respectively; medial thicknesses of these vein grafts were unchanged compared to control. In contrast, diabetes with hypercholesterolaemia dramatically increased intimal and medial thickness (1.8 fold and 1.6 fold respectively, compared to control). Smooth muscle cell contractility was enhanced in both the diabetic and hypercholesterolaemic groups. The presence of diabetes with hypercholesterolaemia did not further alter the enhanced smooth muscle cell contractile responses.

CONCLUSIONS

This study suggests that the combination of both the atherogenic risk factors, hypercholesterolaemia and diabetes, significantly augments the formation of intimal hyperplasia in experimental vein grafts.

Hemodynamic parameters of failing infrainguinal bypass grafts

PURPOSE

To assess the relationship of duplex ultrasound hemodynamic parameters in stenotic vein grafts with events such as graft thrombosis or surgical revisions.

PATIENTS AND METHODS

We studied 35 patent infrainguinal bypass grafts that were observed by means of color duplex graft mapping using a surveillance protocol.

RESULTS

During the 11.2 month mean follow-up interval, 10 grafts developed complications. Two stenotic grafts (1 already revised) thrombosed spontaneously, and arteriography was obtained on the basis of either clinical indications or a decreased ankle/brachial index of greater than 0.15 on 9 bypasses, leading to 12 procedures (multiple procedures on 2 grafts). The 14 duplex examinations preceding an event showed these bypasses had increased focal peak systolic velocities that ranged from 250 to 600 cm/s and velocity ratios that ranged from 3.4 to 25.0 at the stenotic segment of the graft, anastomosis, or outflow artery. None of the grafts with a stenotic peak systolic velocity less than 250 cm/s or a velocity ratio less than 3.4 thrombosed spontaneously or required revision.

CONCLUSION

We conclude that stenotic vein grafts with a focal peak systolic velocity of at least 250 cm/s or a velocity ratio of at least 3.4 are at increased risk for thrombosis or need for revision. Asymptomatic stenotic vein grafts with focal peak systolic velocities and ratios less than the above values may be safely observed without immediate risk for thrombosis.

Percutaneous transluminal angioplasty of infrainguinal vein graft stenosis: long-term outcome

The aim of this prospective study was to examine the long-term outcome of infrainguinal vein graft stenosis managed by percutaneous transluminal angioplasty (PTA) as first-line treatment. Thirty-three infrainguinal vein graft stenoses detected by graft surveillance during a 44-month period were treated initially by PTA. The median (range) follow-up after angioplasty was 39 (18-56) months. Although 19 stenoses were successfully treated by a single PTA, 14 stenoses recurred at a median (range) interval of 8.5 (1-39) months. Restenosis occurred more frequently in the distal third of a graft (P = 0.002) compared with that in the proximal or mid-grafts, and restenosis was more common in in situ than reversed vein grafts (P = 0.03). It is concluded that infrainguinal vein graft stenoses were successfully treated by single PTA. There was, however, a high restenosis rate after angioplasty of stenosis in the distal third of a vein graft and, while approximately one third of such stenoses can be treated by a single PTA, the optimal management of recurrent stenosis requires further investigation.

Pathophysiology of vein graft failure: a review

Vein bypass grafting is an integral component of cardiovascular surgical practice for both arterial and venous diseases. However, many of these grafts will eventually fail due to either intrinsic or extrinsic causes. This review examines the current understanding and knowledge of venous histology, vein graft pathology and the associated endothelial and smooth muscle cell physiology and pharmacology. In addition, the status of research on the therapeutic control of vein graft intimal hyperplasia and accelerated atherosclerosis is assessed.