The histopathology of infrainguinal vein graft stenoses

Femoropopliteal Venous Bypass Studied with Intravascular Ultrasound: A Case Report

Purpose:

To describe the ability of intravascular ultrasound (IVUS) to document the status of the greater saphenous vein during bypass surgery, the long-term changes in the bypass, and the effects of balloon angioplasty on vein graft stenoses.

Methods:

An 80-year-old female underwent in situ femoropopliteal venous bypass grafting. Vein graft stenosis developed 6 months later, necessitating balloon angioplasty. The angioplasty failed, and a polytetrafluoroethylene (e-PTFE) interposition graft was placed. Ten months after bypass surgery, balloon angioplasty was performed for new stenoses. This procedure also failed, and the venous bypass and interposition graft were removed and replaced by an e-PTFE graft. IVUS images obtained during the first surgery were compared with those obtained 10 months later. Histologic sections were used to confirm the IVUS findings.

Results:

IVUS detected a distinct narrowed venous segment, pre-existent intimal thickening, and disrupted valves. Over the follow-up period, both the pre-existent intimal thickening and the narrowed segment evolved into stenoses, necessitating treatment. Luminal gain after balloon angioplasty of graft stenosis was associated with vascular damage.

Conclusions:

This report shows that IVUS has the ability to document long-term venous bypass alterations and to demonstrate the effect of balloon angioplasty on venous bypass stenoses.

The role of oral vitamin K antagonists in the outcome of infrainguinal bypass procedures

We investigated the role of oral vitamin K antagonists (VKAs) in graft patency, limb salvage, major and minor bleeding rates in patients undergoing infrainguinal bypass surgery. Five randomized-controlled trials (RCTs; n = 3746 patients) comparing VKA versus non-VKA treatment outcomes in patients undergoing infrainguinal bypass surgery were analyzed. The VKA treatment was associated with improved graft patency rates when a vein graft was used (risk ratio [RR]: 0.74; P = .0004), while there was no difference with prosthetic grafts (RR: 1.07; P = .39). The VKA treatment was also associated with improved limb salvage rates (RR: 0.33; P = .0008). Major and minor bleeding complications were higher in the VKA group. In conclusion, VKA treatment is associated with improved graft patency and limb salvage rates when a vein graft is used at the price of an increased risk of bleeding. Due to the inconsistent results, further well-designed RCTs are needed.

Stenosis of reverse great saphenous vein graft in infrainguinal arterial revascularization

OBJECTIVE

The aim of this study was to evaluate the prevalence of hemodynamically significant infrainguinal bypasses stenosis using reverse great saphenous vein graft.

METHODS

From March of 2008 to March of 2009, 56 infrainguinal bypasses were performed with reverse great saphenous vein graft in 56 patients. On the 30th post-operative day, 32 out of 56 patients were submitted to vascular ultrasonography. The prevalence of significant graft stenosis was determined. In addition, the diagnosis of stenosis was related to the clinical and surgical characteristics of the patients. The variables analyzed at the moment of diagnosis were the localization of the graft stenosis, the risk factors associated with stenosis and the association of vascular ultrasonography findings with ankle brachial pressure index (ABI).

RESULTS

The overall prevalence of significant graft stenosis was 48.4%. Out of the total number of observed stenosis, 19.4% were considered severe, and 29% mild or moderate. There was no significant association between the presence of significant stenosis and the following variables: gender, diabetes, hypertension, smoking, hipercholesterolemia, graft diameter, site of the distal anastomosis, and graft composition. There was a weak agreement between ABI and vascular ultrasonography in detecting stenosis in general (K = 0.30; CL95% 0.232 - 0.473; p = 0.018). However, there was a substantial agreement in detecting severe stenosis (K = 0.75; CL95% 0.655 - 0.811; p = 0.0001).

CONCLUSION

There was a high prevalence of stenosis on the 30th post-operative day, mostly localized in the proximal half of the vein graft. There was no significant association of stenosis with clinical and surgical factors analyzed. ABI and vascular ultrasonography had weak agreement with the diagnosis of stenosis in general and an important agreement for the diagnosis of severe stenosis.

Detrimental effects of mechanical stretch on smooth muscle function in saphenous veins

OBJECTIVE

This study evaluated the smooth muscle functional response and viability of human saphenous vein (HSV) grafts after harvest and explored the effect of mechanical stretch on contractile responses of porcine saphenous vein (PSV).

METHODS

The contractile responses (stress, 10(5) N/m(2)) of deidentified, remnant HSV grafts to depolarizing potassium chloride and the agonist norepinephrine were measured in a muscle organ bath. Cellular viability was evaluated using a methyl thiazole tetrazolium (MTT) assay. A PSV model was used to evaluate the effect of radial, longitudinal, and angular stretch on smooth muscle contractile responses.

RESULTS

Contractile responses varied greatly in HSV harvested for autologous vascular and coronary bypass procedures (0.04198 ± 0.008128 × 10(5) N/m(2) to 0.1192 ± 0.02776 × 10(5) N/m(2)). Contractility of the HSV correlated with the cellular viability of the grafts. In the PSV model, manual radial distension of ≥ 300 mm Hg had no impact on the smooth muscle responses of PSV to potassium chloride. Longitudinal and angular stretch significantly decreased the contractile function of PSV by 33.16% and 15.26%, respectively (P < .03).

CONCLUSIONS

There is considerable variability in HSV harvested for use as an autologous conduit. Longitudinal and angular stretching during surgical harvest impairs contractile responsiveness of the smooth muscle in saphenous vein. Avoiding stretch-induced injuries to the conduits during harvest and preparation for implantation may reduce adverse biologic responses in the graft (eg, intimal hyperplasia) and improve patency of autologous vein graft bypasses.

Dose-dependent inhibition of myointimal hyperplasia by orally administered rapamycin

Myointimal hyperplasia (MIH) after vascular intervention is a major problem. Recent reports describing elimination of within-stent restenosis by means of rapamycin-eluting stents prompted us to examine the effect of systemic oral rapamycin on MIH induced by arterial trauma. We studied the effect of oral rapamycin on MIH after rabbit aorta balloon injury. Thirty-five New Zealand white rabbits (2.5-3 kg) had aortic injury and were given either no rapamycin (control), 0.1 (low dose) rapamycin mg/kg/day, or 0.4 mg/kg/day (high dose). Rapamycin was started 1 week before injury and continued for 3 (4 weeks total) or 6 weeks (7 weeks total) post-injury. Sections were analyzed to measure aortic intima/media area ratios (I:M) at either 3 or 6 weeks. At 3 weeks, the I:M (mean +/- SD) for controls was 0.53 +/- 0.1; for low dose, 0.17 +/- 0.13; and for high dose, 0.24 +/- 0.07 (p < 0.001 vs. control). At 6 weeks, the I:M for controls was 0.52 +/- 0.12; for low dose-4 weeks, 0.29 +/- 0.15; low dose-7 weeks, 0.33 +/- 0.07; and high dose-4 weeks, 0.47 +/- 0.16. At 6 weeks only the difference between the low dose-4 weeks and control I:M ratios was significant (p = 0.018). The results confirm earlier studies showing that systemic rapamycin inhibits MIH after arterial injury when drug therapy is started before injury. Therapy for 3 or 6 weeks after injury yields similar inhibition, indicating that exposure to the drug early in the response to injury is more important than prolonged exposure. We observed a paradoxical relation between dose and degree of MIH inhibition, with the low dose being more effective than the high dose at both time intervals studied. Overall, the results suggest that oral rapamycin therapy might be a useful adjunct to clinical interventions at risk for development of MIH.

Rotational in vitro compliance measurement of diverse anastomotic configurations: a tool for anastomotic engineering

Anastomotic configurations with a small internal diameter are prone to intimal hyperplasia which can cause occlusion within weeks or months. A link between intimal hyperplasia and inhomogenities of the elastic profile of the anastomosis has been established, making anastomotic engineering directed towards smoothing the compliance profile at the anastomotic site essential. Methods to date restrict the anastomotic compliance measurement to one plane. We present a method by which the anastomotic configurations are rotated, thereby allowing an anastomotic elastic profile assessment in multiple planes. Eight end-to-end anastomoses (ovine common carotid artery) and three end-to-side anastomoses (e-PTFE graft to ovine common carotid artery) were prepared and mounted in an artificial circulation system. Anastomotic circumferential compliance (maximal-minimal diameter/(maximal-minimal pressure.minimal diameter)) was measured by means of a laser-scan-micrometer and a Statham pressure transducer. By rotating end-to-end anastomoses, the compliance was measured in three, and in end-to-side anastomoses in four different planes. Multiplanar compliance variability in areas remote to both end-to-end and end-to-side anastomoses was approximately 9%. At the suture line the variability was approximately 22% in end-to-end anastomoses and 78% in end-to-side anastomoses. These results show that local factors result in different compliance profiles when utilizing a multiplanar technique, particularly in end-to-side anastomoses. The rotational apparatus is a tool which can be used to more accurately engineer a homogeneously compliant anastomosis, with the ultimate goal of prolonging anastomotic patency.

Improving the patency of vascular bypass grafts: the role of suture materials and surgical techniques on reducing anastomotic compliance mismatch

BACKGROUND

compliance mismatch is an important factor in the development of myointimal hyperplasia in both coronary and vascular anastomoses. This mismatch may be reduced by the use of newer suture materials and techniques. This review discusses the current techniques and materials used to date in generating anastomoses in both coronary and vascular applications and to correlate these with the degree of inherent compliance achieved.

METHODS

PubMed, ISIS, CAS and PAS database searches were performed. Other articles were cross-referenced.

RESULTS AND CONCLUSION

continuous suture is still the most used technique in both cardiac and vascular surgery for the generation of anastomoses due to the reduced time and improved haemostasis. However, continuous suture results in a greater compliance mismatch than the interrupted technique. Vein cuffs and patches improve compliance and transmission of pulsatile blood flow and offer improvement of graft patency. Alternative to sutures are biological glue, clips and laser generated solders all of which have shown promising results, but further work is required before they become applicable for routine use.

The role of matrix metalloproteinases in vascular disease

There is growing interest in the role of matrix metalloproteinases in vascular diseases. These conditions are often characterized by excessive tissue remodelling, and increased matrix metalloproteinase activity has been demonstrated in aneurysms, intimal hyperplasia and atherosclerotic plaque disruption. These enzymes represent a potential target for therapeutic intervention to modify vascular pathology. The core of this review is derived from a MEDLINE database literature search. The review found that there is convincing evidence of increased matrix metalloproteinase activity in a spectrum of vascular disease. Evidence for an imbalance promoting increased matrix degradation is less well documented. However, studies of matrix metalloproteinase inhibition in vascular disease models suggest potential therapeutic benefit. In conclusion, in vivo studies of matrix metalloproteinase inhibition are required to further study the potential for reversal or deceleration of the excessive tissue remodelling that accompanies vascular disorders.

Intraoperative flow predicts the development of stenosis in infrainguinal vein grafts

OBJECTIVE

There are data to suggest that the development of myointimal hyperplasia is affected by long-term alterations in blood flow. However, the clinical relevance of these findings has not been demonstrated.

METHODS

In this retrospective clinical study, intraoperative volume flow measurement with transit time flowmeter was performed in 257 infrainguinal vein grafts carried out in 241 patients. The patients were enrolled in an intensive duplex scanning-based surveillance program. The relationship between the intraoperative graft flow and subsequent occlusion or development of stenosis was evaluated and controlled for other pertinent risk factors.

RESULTS

The median follow-up time was 13.6 months. A graft stenosis was found in 58 grafts. The mean graft flow for event-free grafts was 98 mL/min, which was significantly higher compared with 78 mL/min for stenosed or 69 mL/min for occluded grafts. The patients were divided into four groups according to quartiles of the sample distribution of graft flow measurements. The respective 2-year primary and assisted primary patency rates in the lowest to the highest graft flow groups were 39%, 49%, 47%, and 72% (P =.003) and 55%, 67%, 71%, and 84% (P =.01). Analogous significant differences were observed for maximal flow capacity measurements. Female sex (P =.009) and low graft flow in maximal flow capacity measurements (P =.003) were independent predictors of stenosis development in the multiple regression model.

CONCLUSION

Intraoperative graft volume flow is a predictor of bypass occlusion after infrainguinal bypass. In addition, this study verifies an association between the development of clinically evident graft stenoses and low graft flow.

Vascular clips have no significant effect on the cellular proliferation, intimal changes, or peak systolic velocity at anastomoses in rabbit vein grafts

OBJECTIVE

This study compares vascular closure staples (VCSs) with conventional sutures in the rabbit carotid vein graft model to determine whether anastomotic technique affects cellular proliferation, blood velocity, or intimal changes when measured over a period of 3 months postoperatively.

METHODS

Twenty-six New Zealand White rabbits weighing 3.0-3.2 kg underwent interposition of jugular vein grafts in left carotid arteries. Half of the animals had anastomoses performed with small VCSs (n = 13) and half had anastomoses performed with 8-O interrupted polypropylene suture. Animals were allowed to survive for 1 week (n = 4, VCS; n = 4, suture), 2 weeks (n = 4, VCS; n = 4, suture), and 3 months (n = 5, VCS; n = 5, suture). The peak systolic velocity (PSV) at the distal anastomosis was measured after completion of the graft and again at sacrifice in the 3-month survival groups. At sacrifice, sections were taken from the middle and distal end of the vein graft and the distal carotid artery. Vascular cell proliferation was measured using 5-bromo-2'-deoxyuridine labeling and intimal changes were measured using digitized microscopic images.

RESULTS

All 26 grafts were open at the time of sacrifice. PSV at the distal clipped anastomosis was 40.52 cm/s (t = 0) and 34.3 cm/s (t = 3 months, P = 0.31). PSV at the distal sutured anastomosis was 38.30 cm/s (t = 0) and 39.23 cm/s (t = 3 months, P = 0.82). There was no difference between the two techniques at either t = 0 or t = 3 months (P = 0.51 and P = 0.31, respectively). Endothelial cell proliferation and smooth muscle cell proliferation at the anastomosis was highest during the 2 weeks after the procedure, then returned to baseline levels by 3 months. But there was no significant difference between the clipped and sutured groups with respect to vascular cell proliferation postoperatively. The intimal thickness changed significantly in the vein graft at the anastomosis for both the clipped and sutured groups (P = 0.0007 and P = 0.002). But there was no difference when the intimal changes for each technique were compared (P = 0.94).

CONCLUSION

No differences were observed when peak systolic velocity, vascular cell proliferation, and intimal changes were compared between sutured and stapled anastomoses in rabbit vein interposition grafts over a period of 3 months after surgery.

Marimastat inhibits neointimal thickening in a model of human arterial intimal hyperplasia

OBJECTIVE

matrix metalloproteases (MMPs) produced by vascular smooth-muscle cells (VSMCs) degrade extracellular matrix and facilitate the migration of these cells. This is a fundamental process in arterial intimal hyperplasia. This study investigated whether Marimastat (a selective but non-specific MMP inhibitor) can prevent intimal hyperplasia in cultured human internal mammary artery (IMA).

MATERIALS AND METHODS

segments of IMA from 8 patients were prepared and cultured for 14 days in serum-supplemented medium (control) or in medium supplemented with Marimastat at 2 concentrations (treatment groups). The tissue was fixed, sectioned, stained and neointimal thicknesses measured by computer-aided image analysis. Further sections were cultured in the same manner and prepared for gel enzymography to quantify the production of MMPs.

RESULTS

neointimal thickness was significantly reduced by Marimastat in a dose-dependent manner when compared to controls (p =0.008 Wilcoxon). Gel enzymography demonstrated a reduction in levels of MMP2 and MMP9. This was most significant for the active forms of the enzymes ( p =0.03).

CONCLUSIONS

our results suggest that there is a potential therapeutic role for specific inhibition of the gelatinases in the prevention of human arterial restenosis.

Production and inhibition of the gelatinolytic matrix metalloproteinases in a human model of vein graft stenosis

OBJECTIVES

human vein graft stenoses are caused by intimal hyperplasia, a process which is characterised by extensive degradation and accumulation of extracellular matrix. This study investigated the role of the matrix metalloproteinases (MMPs) - the principal physiological mediators of extracellular matrix degradation - in the development of intimal hyperplasia in cultured human long saphenous vein.

DESIGN

experimental study.

MATERIALS AND METHODS

paired venous segments with the endothelium intact or denuded were cultured in standard conditions for 14 days. At the termination of culture, MMPs were extracted from one half of the tissue, whilst the remainder of the vein was prepared for histological examination.

RESULTS

stereologic analysis revealed that the endothelium intact veins developed a significantly thicker neointima when compared to the denuded venous segments (20 micron v. 0 micron, p=0.006). Quantification of MMPs by substrate gel enzymography demonstrated that the development of a neointima was associated with increased production of the gelatinolytic MMP-9 (p=0. 03) in intact veins. Immunocytochemistry showed that the MMP-9 localised to the internal elastic lumina, which suggested a role in facilitating smooth-muscle-cell migration into the intima. The role of MMPs-2 and -9 in intimal hyperplasia was further investigated by culturing intact venous segments with a therapeutic concentration of doxycycline--a potent MMP inhibitor. These experiments demonstrated that a therapeutic dose of doxycycline significantly reduced neointimal thickness (control 21 micron, doxycycline 10 mg/l-5.5 micron), in conjunction with a significant reduction in the production of MMP-9.

CONCLUSIONS

these data suggest that elevated levels of MMPs may play a significant role in the development of human intimal hyperplasia and that inhibition of these enzymes may offer a potential therapeutic strategy for the prevention of hyperplastic lesions.

Lower limb surveillance following autologous vein bypass should be life long

BACKGROUND

The aim of the study was to investigate whether infrainguinal vein graft surveillance can be stopped at 1 year without prejudicing graft or leg survival.

METHODS

Data were collected prospectively on 351 infrainguinal vein bypass grafts (326 patients) that had been entered into a vein graft surveillance programme between 1988 and 1997.

RESULTS

Some 104 grafts (30 per cent) developed significant new vein graft stenoses, 95 (91 per cent) of which occurred within 12 months. After 1 year, the risk of developing a significant graft stenosis was 3 per cent per year. Sixty-nine grafted limbs (20 per cent) developed new arterial inflow or run-off stenoses that required intervention, but only 37 (54 per cent) occurred within the first year, after which the risk was 9 per cent per year. The overall risk of developing a new vein graft or arterial stenosis after 1 year was 10 per cent per year.

CONCLUSION

The incidence of vein graft stenosis decreases significantly 1 year after operation but there is still at risk of developing potentially graft-threatening arterial stenoses. Legs that have undergone infrainguinal vein bypass grafting should continue to be monitored in a surveillance programme for life.

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.

Local inhibition of tyrosine kinase activity markedly attenuates the development of intimal hyperplasia in experimental vein grafts

BACKGROUND

Intimal hyperplasia is due to the migration and proliferation of vascular smooth muscle cells after bypass surgery. Tyrosine kinases are involved in many signal transduction pathways including cell proliferation. This study examines the effects of local treatment with the tyrosine kinase inhibitor, tyrphostin AG-51, on the formation of intimal hyperplasia in vein grafts.

MATERIALS AND METHODS

Thirty-nine New Zealand White rabbits underwent interposition bypass grafting of the carotid artery using the jugular vein. In the first group (TKI), tyrphostin AG-51 (5 mg), dissolved in 600 microliter of dimethyl sulfoxide and Ringer's lactate (2:1, v:v), was used to incubate the veins ex vivo prior to grafting and delivered locally in 2.5 ml of 30% pluronic gel after grafting. The second group (DMSO) received the same treatment but without tyrphostin. In the third group (control), tyrphostin and DMSO were omitted from the incubation and gel delivery solutions. Postoperatively, vein grafts were harvested on Day 3 for Western analysis using an antiphosphotyrosine antibody (PY-20) to assess for tyrosine kinase activity, and on Day 28 for either morphologic or contractile function studies.

RESULTS

Local application of the TKI to vein grafts resulted in a 49% reduction in intimal hyperplasia compared to DMSO-treated vein grafts (31 +/- 4 micrometer vs. 61 +/- 5 micrometer, P < 0.01). Treatment with DMSO alone reduced intimal hyperplasia by 28% compared to control (85 +/- 4 micrometer, P < 0.05). The contractile responses in the DMSO and TKI-treated vein grafts were equivalent. Western analysis showed a 39-fold decrease in tyrosine phosphorylation with TKI treatment compared to control.

CONCLUSION

This study demonstrates that local short-term treatment with TKI produces a 49% reduction in intimal hyperplasia and suggests that phosphorylation of tyrosine residues is involved in the signaling pathways leading to the development of intimal hyperplasia in vein grafts.

Bilateral infrainguinal vein grafts and the incidence of vein graft stenosis

OBJECTIVES

To elucidate the incidence of significant vein graft stenosis in patients who have undergone bilateral infrainguinal vein grafts.

MATERIALS

Between 1987 and 1996, 22 patients were identified from our vascular studies database as having undergone bilateral infrainguinal vein bypass grafting.

METHODS

Data was obtained from the vascular studies database and by case note review. All patients had been part of a vein graft surveillance programme.

RESULTS

Of the 22 patients with bilateral vein grafts, eight were excluded from further analysis because one or more of their grafts failed within 30 postoperative days. In the remaining 14 patients (28 vein grafts) there were 15 primary vein graft stenoses. Six patients (43%) had bilateral vein graft stenoses, which is significantly higher (p = 0.0008) than the predicted value of 9%, for developing bilateral vein graft stenoses. For those patients who developed a vein graft stenosis in their first grafted limb (9/14), 67% (6/14) subsequently developed a vein graft stenosis in their second grafted limb.

CONCLUSION

Patients who develop vein graft stenosis in one limb are at a greater risk of developing a contralateral vein graft stenosis if that limb is grafted. This may well be due to individual vein morphology or unidentified systemic factors that play a role in the aetiology of vein graft stenosis.

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.

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.

Vein quality influences neointimal hyperplasia in an organ culture model of human saphenous vein

OBJECTIVES

The severity of pre-existing pathological changes in human saphenous vein (HSV) correlates with the development of vein graft stenosis and graft patency. The aim of this study was to investigate the influence of pre-existing intimal hyperplasia on development of the neointima in vitro, using an organ culture model.

MATERIALS AND METHODS

Segments of HSV were harvested during coronary artery bypass surgery. Histology was performed on part of the vein; the remainder was maintained in culture. Pre-existing intimal thickness (PIT) in HSV from day 0 and neointimal thickness (NIT) in cultured HSV were measured using computerised image analysis on histological sections. Day 0 and 14 veins were compared with respect to intimal hyperplasia.

RESULTS

Twelve pairs of veins were examined. A mean tissue ATP of 297 nmoles/g wet weight for cultured. HSV confirmed cell viability. Mean PIT was 180 microns (CI: 86-274) and mean NIT was 60 microns (CI: 48-72), with a significant correlation between them using the Spearman Rank test (Rs = 0.72; p = 0.008).

CONCLUSIONS

Pre-existing vein quality as measured by PIT correlates with the development of neointimal hyperplasia in culture, adding further support to clinical evidence that poor vein quality predisposes to vein graft stenosis due to an inherent susceptibility to intimal hyperplasia.

Oral monoterpene therapy (perillyl alcohol) reduces vein graft intimal hyperplasia

The development of intimal hyperplasia is recognized as a major impediment to graft patency. D-Limonenes are monoterpenes with a recognized cytostatic effect on cell proliferation by inhibiting posttranslational isoprenylation of p21ras and other small G-proteins. This study examines the effect of perillyl alcohol, an oral hydroxylated D-limonene, on the development of intimal hyperplasia and its associated smooth muscle cell physiological responses in an experimental model of vein bypass grafting. Twenty New Zealand white rabbits had a right carotid interposition bypass graft using the ipsilateral external jugular vein. Ten animals received chronic oral therapy with a perillyl alcohol (200 mg/kg/day; begun 5 days before surgery and continued until harvest) and 10 control animals received vehicle only. All animals were sacrificed on the 28th postoperative day. Vein grafts were harvested either for morphology/videomorphometry (n = 6 per group) or for in vitro isometric tension studies (n = 4; four 5-mm rings per graft). The cell proliferation and incorporation of [3H]thymidine into the cellular DNA of serum-stimulated rabbit aortic smooth muscle cells was also assessed in the presence of increasing concentrations of perillyl alcohol (10(-9)-10(-4) M). Perillyl alcohol treated vein grafts showed a 22% reduction in overall mean intimal thickness (54 +/- 4 microns vs 69 +/- 3 microns; P = 0.006) but a 25% increase in overall mean medial thickness (86 +/- 4 microns vs 61 +/- 3 microns). The intimal ratio of the perillyl alcohol treated vein grafts decreased by 27% compared to controls. Perillyl alcohol induced norepinephrine and serotonin hypersensitivity in vein grafts compared to controls. The IC50 for perillyl alcohol was 176 nM with maximal inhibition at 5 microM. Incubation of smooth muscle cell cultures with increasing concentrations of perillyl alcohol showed a dose-dependent decrease in in vitro cellular proliferation, maximal at 1 microM. Therapy with perillyl alcohol alters the early development of intimal hyperplasia reducing the intimal response but increasing the medial response without significant changes in the physiological responses of the smooth muscle cells. Modulating G-proteins will affect the intimal hyperplastic response in vein grafts.

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.

Femoropopliteal venous bypass studied with intravascular ultrasound: a case report

PURPOSE

To describe the ability of intravascular ultrasound (IVUS) to document the status of the greater saphenous vein during bypass surgery, the long-term changes in the bypass, and the effects of balloon angioplasty on vein graft stenoses.

METHODS

An 80-year-old female underwent in situ femoropopliteal venous bypass grafting. Vein graft stenosis developed 6 months later, necessitating balloon angioplasty. The angioplasty failed, and a polytetrafluoroethylene (e-PTFE) interposition graft was placed. Ten months after bypass surgery, balloon angioplasty was performed for new stenoses. This procedure also failed, and the venous bypass and interposition graft were removed and replaced by an e-PTFE graft. IVUS images obtained during the first surgery were compared with those obtained 10 months later. Histologic sections were used to confirm the IVUS findings.

RESULTS

IVUS detected a distinct narrowed venous segment, pre-existent intimal thickening, and disrupted valves. Over the follow-up period, both the pre-existent intimal thickening and the narrowed segment evolved into stenoses, necessitating treatment. Luminal gain after balloon angioplasty of graft stenosis was associated with vascular damage.

CONCLUSIONS

This report shows that IVUS has the ability to document long-term venous bypass alterations and to demonstrate the effect of balloon angioplasty on venous bypass stenoses.

Human saphenous vein organ culture: a useful model of intimal hyperplasia?

OBJECTIVES

Although cell culture techniques and animal models of intimal hyperplasia have increased our current understanding of the aetiology of vein graft stenosis, the results of such studies have been difficult to relate to the human situation.

DESIGN

The present study was designed to validate an organ culture of human saphenous vein by comparing the changes occurring in cultured vein with those seen in pathological vein graft stenoses and to identify a suitable marker of cell proliferation.

MATERIALS AND METHODS

Saphenous vein segments were cultured for 14 days, fixed in formalin and processed for immunohistochemistry. Freshly excised stenoses were fixed and processed similarly. A number of markers of cell proliferation were evaluated in the culture system in order to identify the one best suited to this particular model.

RESULTS

Marked similarities were observed in the cellular and extracellular matrix composition, and electron microscopy revealed that both the neointima of the cultured vein and the pathological lesion contained an abundance of smooth muscle cells of a secretory phenotype. Bromodeoxyuridine proved to be the most reliable proliferation marker and revealed that early proliferation in the superficial layers of the vein intima gave rise to the formation of neointima. Both proliferation and neointimal thickness were maximal by day 14 in culture. Proliferation declined rapidly thereafter, and the neointima was maintained.

CONCLUSIONS

The changes occurring in cultured vein and graft stenoses bore many similarities, thereby justifying the use of organ culture as a valuable experimental tool.

The "ad hoc" estimation of outflow does not predict patency of infrainguinal reconstructions

OBJECTIVES

This prospective study was performed to evaluate the clinical implication of the adhoc estimation (also called SVS score) of outflow on patency of infrainguinal in situ femoropopliteal or -distal bypasses.

METHODS

The bypasses were followed with Duplex scanning at 1, 3, 6, and 12 months after surgery. Fifty-three bypasses were recruited for the study, 20 of which were performed in 17 diabetics. In 47% the adhoc scoring was < or = 4.5 and in 53% it was between 5 and 10 (1 corresponds to an excellent outflow and 10 to a blind segment).

RESULTS

Within the first 30 days eight occlusions occurred, all of which were surgically corrected. The adhoc score for these bypasses was 4.2 vs. 4.9 (NS) for those who did not occlude. During follow-up, revisions were performed in 21 cases (40%) with 30 interventions. At the end of 1 year, 68% of the bypasses were patent (80% among diabetics and 64% among non-diabetics, NS). Patency at 1 year was not influenced by the adhoc classification.

CONCLUSION

The estimation of outflow from angiography seems to be of no value in predicting graft patency in infrainguinal grafting.

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.

Pathobiology of intimal hyperplasia

In the current vascular interventional environment, high restenosis rates have increased awareness of the significance of intimal hyperplasia, a chronic structural lesion that develops after vessel wall injury, and which can lead to luminal stenosis and occlusion. Intimal hyperplasia may be defined as the abnormal migration and proliferation of vascular smooth muscle cells with associated deposition of extracellular connective tissue matrix. The pathology of intimal hyperplasia is reviewed with particular attention to its physiology, pharmacology, cell biology and molecular biology.

The aetiology of vein graft stenoses

The aetiology of vein graft stenosis is poorly understood. In a cohort of 88 patients, the mean internal diameter of the vein grafts that developed a stenosis was 3.7 (3.1-4.2) mm compared to 4.7 (4.4-5.0) mm in those that did not (p = 0.006). The mean lowest compliance value in the 11 patients who developed a stenosis was 0.1 (0.07-0.13) % per mmHg compared to 0.21 (0.19-0.23) % per mmHg in the rest (p < 0.001). The presence of vein incompetence, site of tributaries or valves and the degree of endothelial cell loss were not related to the development of vein graft stenoses. The presence of a macrophage infiltrate (p < 0.001), lymphocyte infiltrate (p < 0.025) and subendothelial smooth muscle cells (p < 0.05) were all significantly more common in those grafts that developed a stenosis. Vein quality is an important factor in the development of graft stenoses.

Vein graft factors in the outcome of femorodistal bypass

Various vein factors affect the outcome of femorodistal bypass using vein in the treatment of lower limb ischaemia. In this review, the effect of factors such as vein size, compliance and morphology are discussed.

Human venous endothelium can promote intimal hyperplasia in a paracrine manner

PURPOSE

Vein graft stenoses resulting from the development of intimal hyperplasia are the major cause of graft failure in the first postoperative year. This study uses an organ culture of human saphenous vein to model vein graft intimal hyperplasia and assess the involvement of the endothelium in its development.

METHODS

Organ cultures of saphenous vein were established comprised of intact vein, vein denuded of endothelium, or cocultures of intact plus denuded vein for 14 days in serum-supplemented medium. At the end of the culture period, veins were processed and sections prepared for immunostaining with monoclonal alpha-smooth muscle actin, Millers elastin, QB END.10, and bromodeoxyuridine.

RESULTS

After culture, a cellular neointima developed in the intact veins that was significantly thicker than in those denuded of endothelium (24.5 vs 2.5 microns; p = 0.0001). Denuded veins in coculture with intact veins developed a thicker neointima than did denuded veins alone (12 vs 0 microns; p = 0.01) but less than that of intact veins (12 vs 28 microns; p < 0.01). Proliferation indexes followed the same trend (i.e., intimal smooth muscle cell proliferation was greatest in intact and least in denuded veins).

CONCLUSION

The endothelium can promote neointimal formation in cultured human saphenous vein through a paracrine action on the vascular smooth muscle cell.

Pre-bypass morphological changes in vein grafts

Random vein samples taken prior to bypass surgery have shown certain pathological features. Long saphenous vein was taken from the groin (proximal) and knee to mid-calf (distal) of 85 patients undergoing femoro-distal bypass over a 2-year period. During this period only four patients had cephalic arm vein used; this was also studied. Histological examination was performed using haematoxylin and eosin and van Geison stains. Intimal hyperplasia was seen in 62 (73%) proximal and 74 (87%) distal samples. There were significantly more distal veins with moderate to severe focal hyperplasia and circular muscle hypertrophy (p < 0.05 and p < 0.001). Changes of diffuse intimal hyperplasia were seen in three of the cephalic veins. Muscle hypertrophy occurred in 58 (68%) of proximal segments compared to 75 (88%) of distal segments (p < 0.005). This study shows that significant pathological changes are seen in long saphenous and cephalic veins thought to be "normal". These changes are more evident in the distal long saphenous vein. These changes may have a significant effect on the outcome of vein bypass.

The effects of intraoperative vasodilators and angiographic contrast medium on the endothelium and smooth muscle cells of vein grafts

Cellular injury is a major cause of intimal hyperplasia in vein grafts. The effects of exposure of vein samples to iopamidol, papaverine and iloprost were studied in vitro in an organ chamber to determine whether these agents cause endothelial and/or smooth muscle cell injury. Smooth muscle cell function was assessed by eliciting a dose response curve to noradrenaline. Endothelial cell function was assessed by measuring the degree of endothelial-dependent relaxation of sub-maximally contracted vein samples. Iopamidol and iloprost did not have any deleterious effect on endothelial or smooth muscle cell function. Papaverine did not affect endothelial-dependent relaxation but did produce a significant decrease in smooth muscle contraction. The use of these intraoperative agents during femorodistal bypass does not appear to cause functional injury to the endothelial or smooth muscle cells.