Changes in saphenous veins used as aortocoronary bypass grafts

The anatomical sources of neointimal cells in the arteriovenous fistula

Neointimal cells are an elusive population with ambiguous origins, functions, and states of differentiation. Expansion of the venous intima in arteriovenous fistula (AVF) is one of the most prominent remodeling processes in the wall after access creation. However, most of the current knowledge about neointimal cells in AVFs comes from extrapolations from the arterial neointima in non-AVF systems. Understanding the origin of neointimal cells in fistulas may have important implications for the design and effective delivery of therapies aimed to decrease intimal hyperplasia (IH). In addition, a broader knowledge of cellular dynamics during postoperative remodeling of the AVF may help clarify other transformation processes in the wall that combined with IH determine the successful remodeling or failure of the access. In this review, we discuss the possible anatomical sources of neointimal cells in AVFs and their relative contribution to intimal expansion.

Ventricular Fibrillation Due to Aortocoronary Vein Graft Spasm During Angiography: Case Report and Literature Review

A 69-year-old man underwent coronary angiography 7 years after coronary artery bypass. Saphenous vein graft spasm was observed during contrast injection, resulting in ventricular fibrillation. Angiography 6 years later showed graft patency. Vein graft spasm after coronary artery bypass grafting is rarely described. Further investigation is needed regarding incidence, mechanism, and clinical outcomes. (Level of Difficulty: Beginner.).

A Brief Comment on Vasa Vasorum of Human Saphenous Vein: relevance for Coronary Artery Bypass Surgery

The importance of the vasa vasorum and blood supply to the wall of human saphenous vein (hSV) used for coronary artery bypass grafting (CABG) is briefly discussed. This is in the context of the possible physical link of the vasa vasorum connecting with the lumen of hSV and the anti-ischaemic impact of this microvessel network in the hSV used for CABG.

A multicompartment vascular implant of electrospun wintergreen oil/ polycaprolactone fibers coated with poly(ethylene oxide)

Background

The aim of the present study was to fabricate double layered scaffolds of electrospun polycaprolactone (PCL) and poly(ethylene oxide) (PEO). The electrospun PCL fibers were functionalized with wintergreen oil (WO) as a novel approach to prevent vascular grafts failure due to thrombosis by adjusting biomaterial–blood interactions.

Methods

PCL tubular scaffolds were prepared by electrospinning approach and coated with PEO as a hydrophilic polymer. The single and double layered scaffolds were characterized in terms of their morphological, chemical properties -as well as-hemocompatibility assays (i.e. prothrombin time, hemolysis percentage and platelets adhesion). Moreover, the antioxidant potential of WO-PCL samples were measured by 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH) free radical assay.

Results

The results demonstrated that incorporation of WO during the electrospinning process decreased the PCL fiber diameter. In addition, the prothrombine time assay shows that WO could be used to lower the electrospun PCL fiber tendency to induce blood clotting. Moreover, SEM observations of platelets adhesion of both single and double layered PCL/PEO scaffolds fiber shows an increase of platelets number, compared with the scaffolds containing WO.

Conclusions

The antioxidant potential and blood compatibility measurements of WO-PCL/PEO samples highlight the approach made so far as an ideal synthetic small size vascular grafts to overcome autogenous grafts shortages and drawbacks.

Early Stage of Atherosclerosis in Aortocoronary Saphenous Vein Grafts: Intravascular Ultrasound Study

Introduction

Angiographically visible plaques in patent vein grafts are usually detected years after surgery. Our aim was to examine early plaque formation in vein grafts.

Methods

Bypass angiography and intravascular ultrasonography (IVUS) examination were performed on 77 aortocoronary saphenous vein grafts (SVGs) implanted in 36 patients during the first 2 years after CABG. In each graft, a good quality 25 mm ultrasound image was analyzed. We measured: plaque area, lumen area, external elastic membrane (EEM) area, graft area and wall area. For the comparative assessment of SVGs, the index plaque area/EEM area was calculated. Data were analyzed for the following 4 time periods: I – 0-4 months (22 grafts), II – 5-8 months (23 grafts), III – 9-12 months (19 grafts) and IV – 13-16 months (13 grafts) after CABG. Student’s t and Fisher-Snedecor tests were used for the purpose of statistical analysis in this retrospective study.

Results

In period I, plaque formation (neointimal) was observed in 10 grafts (45%), with a mean plaque area of 1.59 mm., in 6 grafts (26%) in period II, with a mean plaque area of 1.03 mm. and in 15 grafts (71%) in period III, with a mean plaque area of 1.41 mm., and in all (100%) grafts in period IV, with mean plaque area of 2,3 mm.. Average index plaque area/EEM area in periods I, II, III and IV were 0.12, 0.08, 0.13 and 0.22. We have showed a significant plaque increase between periods II and IV(P=0.038).

Conclusion

IVUS showed plaque in about 40% of venous grafts during the first year after CABG. Between 13-16 months plaque was visible in all studied grafts.

Vascular Smooth Muscle Remodeling in Conductive and Resistance Arteries in Hypertension

Cardiovascular disease is a leading cause of death worldwide and accounts for >17.3 million deaths per year, with an estimated increase in incidence to 23.6 million by 2030. ¹ Cardiovascular death represents 31% of all global deaths ² -with stroke, heart attack, and ruptured aneurysms predominantly contributing to these high mortality rates. A key risk factor for cardiovascular disease is hypertension. Although treatment or reduction in hypertension can prevent the onset of cardiovascular events, existing therapies are only partially effective. A key pathological hallmark of hypertension is increased peripheral vascular resistance because of structural and functional changes in large (conductive) and small (resistance) arteries. In this review, we discuss the clinical implications of vascular remodeling, compare the differences between vascular smooth muscle cell remodeling in conductive and resistance arteries, discuss the genetic factors associated with vascular smooth muscle cell function in hypertensive patients, and provide a prospective assessment of current and future research and pharmacological targets for the treatment of hypertension.

Biomechanics and Mechanobiology of Saphenous Vein Grafts

Within several weeks of use as coronary artery bypass grafts (CABG), saphenous veins (SV) exhibit significant intimal hyperplasia (IH). IH predisposes vessels to thrombosis and atherosclerosis, the two major modes of vein graft failure. The fact that SV do not develop significant IH in their native venous environment coupled with the rapidity with which they develop IH following grafting into the arterial circulation suggests that factors associated with the isolation and preparation of SV and/or differences between the venous and arterial environments contribute to disease progression. There is strong evidence suggesting that mechanical trauma associated with traditional techniques of SV preparation can significantly damage the vessel and might potentially reduce graft patency though modern surgical techniques reduces these injuries. In contrast, it seems possible that modern surgical technique, specifically endoscopic vein harvest, might introduce other mechanical trauma that could subtly injure the vein and perhaps contribute to the reduced patency observed in veins harvested using endoscopic techniques. Aspects of the arterial mechanical environment influence remodeling of SV grafted into the arterial circulation. Increased pressure likely leads to thickening of the medial wall but its role in IH is less clear. Changes in fluid flow, including increased average wall shear stress, may reduce IH while disturbed flow likely increase IH. Nonmechanical stimuli, such as exposure to arterial levels of oxygen, may also have a significant but not widely recognized role in IH. Several potentially promising approaches to alter the mechanical environment to improve graft patency are including extravascular supports or altered graft geometries are covered.

In vivo morphologic comparison of saphenous vein grafts and native coronary arteries following non-ST elevation myocardial infarction

OBJECTIVE

This study aimed to assess the pathophysiological differences between saphenous vein grafts (SVG) and native coronary arteries (NCA) following presentation with non-ST elevated myocardial infarction (NSTEMI).

BACKGROUND

There is accelerated pathogenesis of de novo coronary disease in harvested SVG following coronary artery bypass (CABG) surgery, which contributes to both early and late graft failure, and is also causal in adverse outcomes following vein graft PCI. However in vivo assessment, with OCT imaging, comparing the differences between vein grafts and NCAs has not previously been performed.

METHODS

We performed a retrospective, observational, analysis in patients who underwent PCI with adjunctive OCT imaging following presentation with NSTEMI, where the infarct-related artery (IRA) was either in an SVG or NCA.

RESULTS

A total of 1550 OCT segments was analysed from thirty patients with a mean age of 66.3 (±9.0) years were included. The mean graft age of 13.9 (±5.6) years in the SVG group. OCT imaging showed that the SVG group had evidence of increased lipid pool burden (lipid pool quadrants, 2.1 vs 2.7; p = 0.021), with a reduced fibro-atheroma cap-thickness in the SVG group (45.0 μm vs 38.5 μm; p = 0.05) and increased burden of calcification (calcified lesion length = 0.4 mm vs 1.8 mm; p = 0.007; calcified quadrants = 0.2 vs 0.9; p = 0.001; arc of superficial calcium deposits = 11.6° vs 50.9°; p = 0.007) when compared to NCA.

CONCLUSION

This OCT study has demonstrated that vein grafts have a uniquely atherogenic environment which leads to the development of calcified, lipogenic, thin-capped fibro-atheroma's, which may be pivotal in the increased, acute and chronic graft failure rate, and may underpin the increased adverse outcomes following vein graft PCI.

Cyclic stretch-induced Crp3 sensitizes vascular smooth muscle cells to apoptosis during vein arterialization remodeling

Vein graft failure limits the long-term patency of the saphenous vein used as a conduit for coronary artery bypass graft. Early graft adaptation involves some degree of intima hyperplasia to sustain the hemodynamic stress, but the progress to occlusion in some veins remains unclear. We have demonstrated that stretch-induced up-regulation of cysteine and glycine-rich protein 3 (Crp3) in rat jugular vein and human saphenous vein in response to arterialization. Here, we developed a Crp3-KO rat to investigate the role of Crp3 in vascular remodeling. After 28 days jugular vein arterialization, the intima layer was 3-fold thicker in the Crp3-KO that showed comparable smooth muscle cells (SMC) proliferation but an absence of early apoptosis observed in the wild-type rat (WT). We then investigated the role of Crp3 in early integrin-mediated signaling apoptosis in isolated jugular SMC. Interestingly, under basal conditions, ceramide treatment failed to induce apoptosis in both WT and Crp3-KO SMC. Under stretch, Crp3 expression increased in WT SMC and ceramide induced apoptosis. Immunoblotting analysis indicated that ceramide stretch-induced apoptosis in SMC is accompanied by a decrease in the phosphorylation status of both Fak and Akt, leading to an increase in Bax expression and caspase-3 cleavage. In contrast, ceramide failed to decrease Fak and Akt phosphorylation in Crp3-KO SMC and, therefore, there was no downstream induction of Bax expression and effector caspase-3 cleavage. Taken together, we provide evidence that stretch-induced Crp3 modulates vein remodeling in response to arterialization by sensitizing SMC to apoptosis.

Replacing the Anterior Mitral Valve Leaflet With Autologous Jugular Vein in a Sheep Model

BACKGROUND

This study evaluated the use of an autologous vein graft, supported by expanded polytetrafluoroethylene (ePTFE) chordae tendineae, to replace an anterior mitral valve leaflet.

METHODS

A double-layered autologous jugular vein graft, supported by ePTFE chords, was used to create an anterior mitral valve leaflet in 21 sheep. Mitral valve function was monitored with echocardiography for up to 10 months. Surviving sheep were euthanized between 6 and 10 months later, and vein implants were examined histologically.

RESULTS

One sheep died intraoperatively. Fourteen sheep had trace to mild mitral regurgitation (MR), 5 had mild to moderate MR, and 1 had moderate to severe MR. Ten sheep died between 2 days and 6.2 months. Echocardiography at 6 months showed MR progression in 8 of 11 sheep. The vein leaflet developed intimal fibroplasia and fibrous proliferation in response to the increased stress on the tissue, but the vein remained flexible without shortening or contracture. The 6- to 10-month vein implants showed viability with intact endothelium, myofibroblasts, collagen, and elastin. A normal healing pattern was seen at the suture lines, and no calcification was observed in the vein leaflet apart from the ePTFE sutures.

CONCLUSIONS

Autologous vein has the potential to function as a mitral valve leaflet substitute because it adapted morphologically and remained viable in the intracardiac position. Technical refinement in creating and implanting the leaflet is needed to improve the progression of MR.

Conduits Used in Coronary Artery Bypass Grafting: A Review of Morphological Studies

There is a significant variety of vascular conduits options for coronary bypass surgery. Adequate graft selection is the most important factor for the success of the intervention. To ensure durability, permeability, and bypass function, there must be a morphological similarity between the graft and the coronary artery. The objective of this review was to analyze the morphological characteristics of the grafts that are most commonly used in coronary bypass surgery and the coronary arteries that are most frequently occluded. We included clinical information regarding the characteristics that determine the behavior of the grafts and its permeability over time. Currently, the internal thoracic artery is the standard choice for bypass surgery because of the morphological characteristics of the wall that makes less prone to developing atherosclerosis and hyperplasia. The radial and right gastroepiploic arteries are the following second and third best options, respectively. The ulnar artery is the preferred choice when other conduits are not feasible.

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.

Angiographic and Intravascular Ultrasonographic Findings after Endovascular Stent Implantation

The study was an attempt to evaluate the benefit of intravascular ultrasound imaging (IVUS) as a supplement to follow-up angiography after endovascular stent implantation. A consecutive series of 15 patients underwent stent implantation in the peripheral or coronary arteries. Ten Palmaz stents, 3 Palmaz-Schatz stents and 2 Wallstents were used. After a period from 1 to 6 months (mean 3.2 months) follow-up angiography was performed. In 12 cases the angiography was combined with IVUS of the stent and the adjacent vessel segments. In one case IVUS failed due to the tortuous course of the vessel, in another case the stent was occluded, and in one case IVUS was considered too hazardous. In stents of diameter ≥5 mm, ultrasound (US) did not reveal more information concerning vessel and stent diameter, stent stenosis and intraluminal surface contact than angiography alone. Smaller stents were insufficiently visualized by conventional radiologic methods. In small stents only IVUS permitted an exact stent identification and differentiation between stent stenosis and stenosis of the native vessel. At US imaging artifacts, caused by the highly reflectant metallic stent struts, interfered with the native vessel wall and partly obscured its structural details.

Quality of the Long Saphenous Vein Conduits Used for Coronary Artery Bypass Grafting Operations

The aim of this study was first to select preoperatively suitable long saphenous vein (LSV) segments by using color flow duplex imaging (CFDI) and second to evaluate the quality of the harvested LSVs histologically. Forty LSVs in 38 consecutive patients (mean age 63 years) were examined by CFDI for patency and luminal diameter. None of the patients had documented previous deep venous thrombosis or superficial thrombophlebitis. Perioperatively, 79 LSV specimens were harvested from the ankle, knee, and midthigh regions and examined histologically for wall calcification and fibrosis. According to the amount of fibrosis present the specimens were classified as being normal or mildly, moderately, or severely affected.

All LSVs were found patent and nonvaricose, and their diameter ranged from 0.18 to 0.54 cm at the ankle, 0.29 to 0.69 cm at the knee, and 0.25 to 0.77 cm at the midthigh level. On histology 11% of the specimens were found to be normal, and 43% were mildly, 38% moderately, and 8% severely fibrotic. Also, various grades of fibrosis were found in different sites of the same vein. None of the specimens had calcification.

It is concluded that the majority of the LSVs used for coronary artery bypass grafting have some degree of fibrosis. The histologic appearance of the LSV wall in a particular site cannot predict the condition of vein throughout its length. CFDI can be useful in the perioperative conduit selection.

Distribution of saphenous vein valves and its practical importance

OBJECTIVE

Among the veins used as a graft in myocardial revascularizations and ends, great saphenous vein is the most used. Knowing the presence and location of valves has great importance when evaluating the surgical anatomy of the great saphenous vein. Despite major surgical application and many works involving great saphenous vein, the number of valves present in it from the saphenous hiatus to the medial epicondyle of the femur is still described inaccurately. The objective of this study is to quantify the valves of the great saphenous vein from the saphenous hiatus to the medial epicondyle of the femur to determine the best portion of the great saphenous vein to perform revascularization surgeries.

METHODS

This is a cross sectional observational study in which it was analyzed great saphenous vein extracted from 30 cadavers. It was measured the length of the veins; (diameter) at its proximal, middle and distal, quantifying the number of valves in each one and the total number of valves at the great saphenous vein.

RESULTS

The frequency of valves in the great saphenous vein taken from the medial epicondyle of the femur to the saphenous hiatus was 4.82, ranging between 2 and 9. Moreover, there is a significant difference in the number of valves in the proximal and distal relative to the average.

CONCLUSION

the median and distal portions of the saphenous vein in the thigh, are the best options for the realization of bridges due to the fact that these portions have fewer valves which therefore would tend to decrease the risk of complications connected with the valves in these grafts.

Myofibroblast-mediated adventitial remodeling: an underestimated player in arterial pathology

The arterial adventitia has been long considered an essentially supportive tissue; however, more and more data suggest that it plays a major role in the modulation of the vascular tone by complex interactions with structures located within intima and media. The purpose of this review is to summarize these data and to describe the mechanisms involved in adventitia/media and adventitia/intima cross-talk. In response to a plethora of stimuli, the adventitia undergoes remodeling processes, resulting in positive (adaptive) remodeling, negative (constrictive) remodeling, or both. The differentiation of the adventitial fibroblast into myofibroblast (MF), a key player of wound healing and fibrosis development, is a hallmark of negative remodeling; this can lead to vessel stenosis and thus contribute to major cardiovascular diseases. The mechanisms of fibroblast-to-MF differentiation and the role of the MF in adventitial remodeling are highlighted herein.

Prolonged hypercholesterolemia-induced tissue factor expression in rabbit vein grafts: a potential mechanism for graft failure

OBJECTIVES

To evaluate tissue factor (TF) expression in vein grafts interposed in the arterial circulation of hypercholesterolemic rabbits. Veins implanted in the arterial circulation of normocholesterolemic rabbits respond by inflammation and infiltration by monocytes with transient TF expression. In a hypercholesterolemic milieu these monocytes may differentiate into macrophages capable of enhanced TF synthesis, which may facilitate hyperplasia and thrombosis.

METHODS

Autologous jugular veins interposed in the carotid artery of hypercholesterolemic rabbits were harvested at 1, 2, 4, 6, and 8 weeks after surgery and examined for presence and localization of rabbit TF antigen. Protein extracted from vein segments was evaluated for procoagulant activity by bioassay and for TF protein content by western blotting.

RESULTS

Rabbit TF antigen was observed mostly in the subendothelium of vein grafts. Peak TF procoagulant activity observed at 1-2 weeks postsurgery (2.3+/-1.8 pg/mg, P<0.006) declined to 0.9+/-0.5, 0.2+/-0.1, and 0.15+/-0.06 pg/mg at 4, 6, and 8 weeks, respectively (P<0.03). Western blotting showed a time-dependent pattern for rabbit TF protein with prolonged expression peaking at 6 weeks.

CONCLUSION

Prolonged expression of biologically active rabbit TF and TF protein were shown within jugular vein grafts of hypercholesterolemic rabbits. This response, reported for the first time and attributed to increased cholesterol levels, may possibly contribute to enhanced hyperplasia. These results suggest that TF expression could serve as another mechanism underlying vein graft failure and that hypercholesterolemia in bypass patients should be treated aggressively beginning within the weeks after surgery.

Dimensional analysis of human saphenous vein grafts: Implications for external mesh support

OBJECTIVE

Constrictive external mesh support of vein grafts was shown to mitigate intimal hyperplasia in animal experiments. To determine the degree of constriction required for the elimination of dimensional irregularities in clinically used vein grafts, a detailed anatomic study of human saphenous veins was conducted.

METHODS

In 200 consecutive patients having coronary artery bypass grafting, harvested saphenous veins (length 34.4 +/- 10.8 cm) were analyzed regarding diameter irregularities, side branch distribution, and microstructure.

RESULTS

The mean outer diameter of surgically distended saphenous veins was 4.2 +/- 0.6 mm (men, 4.3 +/- 0.6 mm vs women, 3.9 +/- 0.5 mm; P < .0001). Although the outer diameter significantly decreased over the initial 18 cm (-7.6%; P < .0001), the overall increase between malleolus and thigh was not significant (+11.2%). Smaller-diameter veins (<3.5 mm) had more pronounced diameter fluctuations than larger veins (31.8% +/- 11.0% vs 21.2% +/- 8.8%; P < .0001), with more than 71% of all veins showing caliber changes of more than 20%. There was 1 side branch every 5.4 +/- 4.3 cm, with a significantly higher incidence between 20 and 32 cm from the malleolus (P < .0001 to distal, P < .0004 to proximal). Generally, women had more side branches than men (0.30 +/- 0.15 cm(-1) vs 0.25 +/- 0.12 cm(-1); P = .0190). Thick-walled veins (565.7 +/- 138.4 mum) had a significantly higher number of large side branches (P < .0001), and thin-walled veins (398.7 +/- 123.2 mum) had significantly more small side branches (P < .0001). Pronounced intimal thickening ("cushions") was found in 28% of vessels (119.8 +/- 28.0 mum vs 40.1 +/- 18.2 mum; P < .0001).

CONCLUSION

Although the preferential location of side branches may be addressed by the deliberate discarding of infragenicular vein segments, a diameter constriction of 27% on average would eliminate diameter irregularities in 98% of vein grafts.

Cellular, molecular and immunological mechanisms in the pathophysiology of vein graft intimal hyperplasia

Coronary artery disease, leading to myocardial infarction and ischaemia, affects millions of persons and is one of the leading causes of morbidity and mortality worldwide. Invasive techniques such as coronary artery bypass grafting are used to alleviate the sequelae of arterial occlusion. Unfortunately, restenosis or occlusion of the grafted conduit occurs over a time frame of months to years with a gradual reduction in patency, especially in vein grafts. The events leading to intimal hyperplasia (IH) formation involve numerous cellular and molecular components. Various cellular elements of the vessel wall are involved as are leucocyte-endothelial interactions that trigger the coagulation cascade leading to localized thrombus formation. Subsequent phenotypic modification of the medial smooth muscle cells and their intimal migration is the basis of the lesion formation that is thought to be propagated by an immune-mediated reaction. Despite intense scrutiny, the pathophysiology of IH remains an enigma. Although several growth factors, cytokines and numerous other biomolecules have been implicated and their relationship to prohyperplasia pathways such as the phosphatidyl-inositol 3-kinase (PI3K)-Akt pathway has been established, many pieces of the puzzle are still missing. An in-depth understanding of early vein graft adaptation and progression is necessary to improve the long-term prognosis and develop more effective therapeutic measures. In this review, we have critically evaluated and summarized the literature to elucidate and interlink the numerous established and emerging factors that play a key role in the development of IH leading to vein graft restenosis.

Mechanical protection of cardiac microcirculation during percutaneous coronary intervention of saphenous vein grafts

Saphenous vein bypass grafts permeability is one of the most important limitations of open heart surgery. The risks associated with surgical re-intervention are greater than those associated with the initial procedure. While native coronary arteries usually have fixed, fibrotic or calcified atherosclerotic plaques, the disease in the vein grafts contains soft material. When this material is compressed during percutaneous angioplasty, there is an unfavorable immediate outcome due to distal embolization of thrombus and plaque debris. In addition, the risk of post-procedure adverse events are higher when the grafts have a long time of implantation, due to a greater risk of branch occlusion or no-reflow at the adjacent microcirculation. The clinical consequence is a Non-Q-Wave Myocardial Infarction that is reflected in the increased serum cardiac enzymes. It is because of this complication that the distal protection devices were developed. The purpose of this paper is to review and discuss the current data on the distal protection devices available now for the treatment of degenerative saphenous vein graft disease. Currently, there are two distal protection devices approved in the United States: the Guardwire Balloon and Aspiration (Export) System and the Filter Wire EX. Other devices like the Triactiv System, Angioguard XP/ECW, DOW, MedNova Cardioshield, Medtronic-AVE DPD and the E-Trap Filter are still being studied. The first observational studies showed the safety and efficacy of the approved devices. A large randomized trial initially confirmed a significant decrease of in-hospital and 30-day cardiac adverse events, mainly Non-Q-Wave Myocardial Infarction, when angioplasty was performed with the assistance of the Guardwire System. Subsequently, another randomized study showed an equivalence between the Guardwire System and the Filter Wire EX. Distal protection devices have an acceptable performance, however, further technological improvements are warranted for a quick preparation, delivery and/or retrieval of these devices.

Adaptation of the endothelium to fluid flow: in vitro analyses of gene expression and in vivo implications

Biomechanical forces generated by blood flow play an important role in the pathogenesis of vascular disease. For example, regions exposed to non-uniform shear stresses develop early atherosclerotic lesions while areas exposed to uniform shear stresses are protected. A variety of in vitro flow apparatuses have been created to apply well-characterized flow patterns to endothelial cells in an effort to dissect the cellular and molecular pathways involved in these distinct processes. Recent advances in biotechnology have permitted large-scale transcriptional profiling techniques to replace candidate gene screens and have allowed the genome-wide examination of biomechanical force-induced endothelial gene expression profiles. This review provides an overview of biomechanical force-induced modulation of endothelial phenotype. It examines the effect of sustained laminar shear stress (LSS), a type of uniform shear stress, on in vitro endothelial gene expression by synthesizing data from the early candidate gene and differential display polymerase chain reaction (PCR) approaches to the numerous, recent, high throughput functional genomic analyses. These studies demonstrate that prolonged LSS regulates the expression of only a small percentage (approximately 1-5%) of endothelial genes, and this transcriptional profile produces an endothelial phenotype that is quiescent, being protected from apoptosis, inflammation and oxidative stress. These observations provide a possible molecular mechanism for the strong correlation between patterns of blood flow and the occurrence of vascular pathologies, such as atherosclerosis, in vivo.

Mechanisms of death in the early postoperative period following coronary artery bypass grafting for acquired heart disease. A clinicopathological study of 32 cases

OBJECTIVES

A retrospective cardiopathological and clinical study was conducted in order to determine causes of perioperative death following coronary artery bypass grafting (CABG).

EXPERIMENTAL DESIGN

Between January 1992 and June 1995, a total of 5749 CABG procedures were performed at the Heart Center Duisburg (Germany). Following the procedures, 218 patients died in hospital (mortality rate 3.8%). Fifty-eight were autopsied at the Institute of Pathology, Bethesda Hospital, Duisburg, and 32 autopsied cases were amenable to our study. Basis for selection was accessibility of clinical and morphological data and a postoperative death within 30 days.

METHODS

In each case, morphological analysis of the heart and an evaluation of surgical and clinical data were performed in order to draw a conclusion on the mechanism of death.

RESULTS

Using criteria defined by us, the following causes of death were determined: (1) surgical complications (43%); (2) severe coronary artery disease with incomplete revascularization (41%); (3) congestive heart failure (13%); (4) non-cardiac complications (3%).

CONCLUSION

Criteria defined in this study may be useful in evaluations of causes of death after open heart surgery and may help to compare results in future series. Determination of the cause of death is important for the cardiac surgeon to reconsider indications and quality of surgical procedure.

Adenoviral delivery of a constitutively active retinoblastoma mutant inhibits neointima formation in a human explant model for vein graft disease

Intimal hyperplasia resulting from vascular injury remains a major obstacle in the long-term success of coronary artery bypass grafts. Inhibition of smooth muscle cell (SMC) proliferation using adenoviral gene transfer of cell cycle inhibitors resulted in reduced neointima formation in various animal models. However, little is known about the effect on human SMCs and neointima formation. Here we report the effects of infection with an adenoviral vector encoding a constitutively active form of the retinoblastoma gene (Ad. delta Rb) on proliferation of human saphenous vein SMCs (HSVSMCs) and neointima formation in organ cultures of human saphenous vein. Proliferation of SMCs was inhibited dose-dependently after infection with Ad. delta Rb. A near-total inhibition was found at an Ad. delta Rb concentration of 10(8) pfu/ml. Organ cultures of human saphenous vein segments were used to evaluate the effect of Ad. delta Rb infection on neointima formation and vein graft disease. Segments cultured for 4 weeks develop a neointima that is morphologically highly similar to early initimal lesions found in pathological vein grafts in vivo. Infection of saphenous vein segments with 2 x 10(9) pfu/ml Ad. delta Rb resulted in a 59% reduction of neointimal area when compared to uninfected counterparts, whereas infection with control adenovirus, Ad.LacZ, had no significant effect. The results of this study show that Ad. delta Rb gene transfer might be an efficient approach to prevent neointima formation in human saphenous vein grafts.

Smooth muscle changes in the cephalic vein of renal failure patients before use as an arteriovenous fistula (AVF)

Complications in arteriovenous fistula (AVF) occur in up to 35% of renal failure patients on hemodialysis. The most frequent complication is thrombosis, usually from stenotic lesions in the venous outflow system. To study the pre-existing smooth muscle changes in the cephalic vein of these patients, we prospectively collected a total of 17 cephalic vein specimens from 3 normal controls and 14 renal failure patients undergoing primary AVF construction on the chosen limb. After preparation, ultrathin sections were stained with uranyl and lead acetate and were examined under the transmission electron microscope (TEM). Compared with the normal controls, abnormal fibrous infiltration of the intima and the media and varying degrees of smooth muscle degenerative changes were observed in all the cephalic vein sections of renal failure patients. Smooth muscle cells (SMCs) lost their normal fusiform shape and were widely separated by increased amount of irregularly disposed, extracellular collagen fibers. Other cellular abnormalities included irregular cell membrane, granular cytoplasm, Peri- and Paranuclear vacuoles and mega mitochondria. SMCs also showed morphological expression of phagocytosis of collagen and elastic fibers as a sign of remodeling of the vein wall. In conclusion, pre-existing wall and smooth muscle changes were observed in all the cephalic vein sections of renal failure patients, which may contribute to the later complications of AVFs.

Purinergic receptor distribution in endothelial cells in blood vessels: a basis for selection of coronary artery grafts

Expression levels of the purinergic P2X receptor subunits (P2X(1) to P2X(7)) and P2Y(2) were examined in the endothelial cell layer of internal mammary artery (Ann. Thorac. Surg. 54 (1992) 652), radial artery (Ann. Thorac. Surg. 16 (1973) 111) and saphenous vein (Ann. Thorac. Surg. 20 (1975) 628) samples obtained at surgery for coronary artery bypass grafts using immunohistochemistry and confocal microscopy. Similar levels of P2X(1), P2X(2), P2X(3), P2X(7) and P2Y(2) were found in the endothelial cells in all vessels examined while the levels of P2X(5) and P2X(6) were uniformly lower. A clear difference was measured in P2X(4) expression between arteries and veins. Both radial and internal mammary arteries exhibited very low levels of P2X(4) whereas the level in the saphenous vein was 14.6 fold higher (P<0.0001), approaching that of the major receptor subtypes. These data showing strong expression of P2X(4) in veins have implications for the choice of vessels used in coronary artery bypass grafts given that P2X(4) is involved in calcium influx into endothelial cells, modulates blood vessel contractility and is up-regulated in situations involving intima proliferation suggesting vein grafts are more susceptible to developing atherosclerosis.

Accelerated atherosclerosis in saphenous vein bypass grafts: a spectrum of diffuse plaque instability

Our understanding of plaque instability may be extended to vein graft atherosclerosis, which appears to represent the end of a continuum of plaque instability. Compared with plaque in native coronary arteries, vein graft atheroma is more diffuse and vulnerable to rupture, and the consequences of plaque rupture in vein grafts seem to be associated with almost certain thrombotic occlusion within 7 to 12 years after surgery.

Impaired contractility of left-over vein grafts used for CABG and the possible trauma caused by air exposure

OBJECTIVE

The patency of vein grafts limits the long-term results after bypass surgery. Vein graft trauma may contribute to the clinical results.

DESIGN

Left-over pieces of vein after routine coronary bypass surgery were compared with references of the same vein that were stored with maximum care. Blood perfusion (20 h, 37 degrees C) was also tested to evaluate possible recovery. Vessel rings were measured by isometric tone recordings.

RESULTS

Left-over veins showed a contractile dysfunction compared to reference (p < 0.01-0.001, n = 13), and that did not recover after blood perfusion. Four trauma models were tested, using saphenous vein graft (SVG)-references (n = 5). Chemical exposures (0-90 min) to NaCl-papaverin or cardioplegic medium affected the baseline (p < 0.05-0.01). With mechanical distension, up to 450 mmHg leak testing, an increased norepinephrine (NE) reactivity appeared. Air contact, 20 min, reduced the NE reactivity to half maximum (p < 0.05). Longer exposures (40-60 min) completely abolished the contractility.

CONCLUSIONS

The saphenous vein smooth muscle function appeared permanently traumatized following routine harvesting and handling. Air exposure gave dramatic deterioration and could in theory contribute to hamper the long-term results after bypass surgery.

Risk assessment of slow or no-reflow phenomenon in aortocoronary vein graft percutaneous intervention

Slow or no-reflow phenomenon (SNR) complicates 10%-15% of cases of percutaneous intervention (PCI) in aortocoronary saphenous vein grafts (SVG). At present, there are no uniform, effective strategies to predict or prevent this common and potentially serious complication. The purpose of our study was to characterize variables correlated with the risk of SNR in SVG PCI in the era of stenting and glycoprotein IIb/IIIa receptor inhibitors. We identified 2,898 consecutive patients who had PCI, of whom 163 underwent PCI of at least one SVG. The clinical and angiographic characteristics of patients who developed SNR (SNR group) were compared with those who did not (no-SNR group). A total of 23 patients experienced SNR and 140 did not. Using a stepwise multivariate logistic regression analysis, four independent predictors for SNR were detected: probable thrombus (OR 6.9; 95% CI, 2.1-23.9; P = 0.001), acute coronary syndromes (OR 6.4; 95% CI, 2.0-25.3; P = 0.003), degenerated vein graft (OR 5.2; 95% CI, 1.7-16.6; P = 0.003), and ulcer (OR 3.4; 95% CI, 0.99-11.6; P = 0.04). The risk of developing SNR could be estimated according to the number of predictors found: low-grade risk (1%-10%) if < or = one variable was present, moderate risk (20%-40%) if two variables were present, and high risk (60%-90%) if three or more variables were present. We identified and quantified current risk factors for SNR and concluded that the risk of developing SNR during PCI in SVG can be predicted by simple clinical and angiographic variables obtained before PCI. This information may be useful when the risk of PCI has to be balanced against alternative strategies such as medical therapy or redo-bypass surgery or in the selection of those patients that will most benefit from the use of protection devices during PCI.

Three-dimensional numerical simulations of flow through a stenosed coronary bypass

This work analyzes the flow patterns at the anastomosis of a stenosed coronary bypass. Three-dimensional numerical simulations are performed using a finite elements method. We consider a geometrical model of the host coronary artery with and without a 75% severity stenosis for three different locations from the anastomosis. The flow features - velocity profiles, secondary motions and wall shear stresses - are compared for different configurations of the flow rate and of the distance of the anastomosis from the site of occlusion (called distance of grafting). The combination of the junction flow effects - counter rotating vortices - with the stenosis effects - confined jet flow - is particularly important when the distance of grafting is short. Given that the residual flow issued from the pathologic stenosis being non-negligible after two weeks grafting, models without stenosis cannot predict the evolution of the wall shear stress in the vicinity of the anastomosis.

Application of a continuous regression model of restenosis to saphenous vein grafts after successful percutaneous transluminal coronary angioplasty or directional coronary atherectomy

OBJECTIVES

To evaluate a quantitative model of restenosis in patients with vein graft disease undergoing percutaneous transluminal coronary angioplasty (PTCA) or directional coronary atherectomy (DCA).

BACKGROUND

A quantitative relationship between acute gain and late loss has been developed to describe the late changes in lumen dimension after native vessel coronary intervention. This same relationship may also be seen after treatment of saphenous vein graft disease.

METHODS

Patients with native coronary artery stenoses (CAVEAT-I) or saphenous vein graft lesions (CAVEAT-II) were randomized to either DCA or PTCA, and data from these trials were analyzed retrospectively. Angiographic results of the target lesions were reviewed, and each lesion was assessed for vessel caliber and reference diameter, absolute minimal lumen diameter, percent diameter stenosis, percent stenosis of the cross-sectional area, acute gain and late loss. Linear regression models were used to determine late loss and to detect differences in angiographic outcomes.

RESULTS

Vein grafts had significantly larger reference vessel diameters than native coronary arteries; they also had significantly more acute gain and more late loss. Directional coronary atherectomy was associated with a larger acute gain in both studies. Patients undergoing DCA also experienced greater late loss although the effect was statistically significant only in the CAVEAT-I study. After adjusting for the acute gain, the treatment effect on late loss became nonsignificant in both studies.

CONCLUSIONS

In patients undergoing DCA or PTCA of saphenous vein graft narrowings, the relationship between late loss and acute gain is also demonstrated, similar to the device-independent relationships seen in native coronary lesions. In CAVEAT-II, larger degrees of acute gain were also associated with higher degrees of late lumen loss.

Endoscopic and traditional saphenous vein harvest: a histologic comparison

BACKGROUND

Vein trauma after saphenectomy by endoscopic or longitudinal techniques may influence the progression of medial and intimal hyperplasia and ultimately affect graft patency. This study compared the histologic characteristics of saphenous veins after endoscopic and longitudinal harvest.

METHODS

One hundred seventy patients who underwent elective coronary artery bypass grafting had saphenectomy performed endoscopically (n = 88) or by a longitudinal incision (n = 82). Cross-sectional specimens from endoscopically (n = 151) and longitudinally (n = 158) harvested veins were submitted for hematoxylin-eosin, trichrome, and elastin staining. Blinded histologic evaluation involved graded analysis of endothelial, smooth muscle, and elastic lamina continuity in addition to medial and adventitial connective tissue uniformity.

RESULTS

Regardless of harvest technique, endothelial, elastic lamina, and smooth muscle continuity as well as medial and adventitial connective tissue uniformity were not significantly different.

CONCLUSIONS

Minor histologic alterations occur during saphenectomy, however, endoscopically and longitudinally harvested saphenous veins are histologically similar.

Changes in venous histology in chronic hemodialysis patients

Because most hemodialysis access fails at the venous side, we studied samples of brachial vein obtained during access creation in 15 patients with end-stage renal disease who gave consent. Veins were examined by computer-assisted histomorphometry, and the results correlated with the patients' clinical data. The mean venous medial width was 239 +/- 31 microm, and mean intimal width was 6.0 +/- 0.9 microm. Mean venous medial width was 358 +/- 74 microm and mean venous intimal width was 9.2 +/- 1.2 microm in the 4 patients who had been undergoing dialysis more than 6 months, compared with 196 +/- 23 microm and 4.9 +/- 0.8 microm, respectively, in the 11 patients undergoing dialysis less than 6 months (P < 0.01). The number of months undergoing hemodialysis correlated well with venous medial width (r = 0.79; P < 0.001). Correlation between number of months undergoing dialysis and intimal width did not reach statistical significance. Medial and intimal widths of the 4 patients with diabetes were not significantly different from those of the patients without diabetes. Serum parathyroid hormone level did not correlate with either medial or intimal venous width. We conclude there may be changes in the veins of hemodialysis patients with time that cause thickening of layers, even in veins not directly used for access. This may affect the creation or survival of subsequent vascular accesses.

Adaptive mechanisms of arterial and venous coronary bypass grafts to an increase in flow demand

OBJECTIVE

To compare the mechanisms by which arterial and venous grafts increase their flow during pacing induced tachycardia, early and later after coronary bypass surgery.

DESIGN

43 grafts (13 epigastric artery, 15 mammary artery, 15 saphenous vein) evaluated early (9 (3) days (mean (SD)) after bypass surgery were compared with 41 other grafts (15 epigastric, 11 mammary, 15 saphenous vein) evaluated later after surgery (mean 23 months, range 6 to 168 months) by quantitative angiography and intravascular Doppler velocity analysis during atrial pacing. Controls were 17 normal coronary arteries.

RESULTS

Baseline graft flow tended to be lower later after surgery than early (41 (16) v 45 (21) ml/min, NS). Blood flow increased during pacing by 30 (16)% early after surgery, less than later after surgery (+46 (18)%, p < 0.001) and less than in normal coronary arteries (+54 (27)%, p < 0.001 v early grafts; NS v late grafts). There was no difference between venous and arterial grafts. No significant vasodilatation was observed during pacing early after surgery in arterial and venous grafts. Later after surgery, significant vasodilatation was observed only in arterial grafts (mammary and epigastric grafts), from 2.41 (0.37) to 2.53 (0. 41) mm (+5.1% v basal, p < 0.001). Early after surgery and in venous grafts later after surgery, the increase in flow was entirely due to an increase in velocity. In later arterial grafts, the relative contribution of the increase in velocity to the increase in flow during pacing was lower in arterial grafts (70 (22)%) than in venous grafts (102 (11)%, p < 0.001) and similar to normal coronary arteries (68 (28)%).

CONCLUSIONS

Early and later after surgery, arterial grafts and venous grafts both increase their flow similarly during pacing. Early arterial grafts and venous grafts increase their flow only through an increase in velocity. Later after surgery, arterial grafts act as more physiological conduits and increase their flow in the same way as normal coronary arteries, through an increase in velocity and calibre mediated by the endothelium.

Arterialization of human vein grafts is associated with tenascin-C expression

OBJECTIVES

This study was performed to test the hypothesis that tenascin-C (TN-C), an extracellular matrix (ECM) protein with counteradhesive chemotactic and vascular growth-promoting effects, is expressed in "arterialized" human saphenous vein grafts (SVGs).

BACKGROUND

Tenascin-C is expressed in the vessel wall after vascular injury in the experimental model, where it has been implicated in the formation of neointima. Overexpression of TN-C has also been implicated in the development and progression of pulmonary hypertension. Saphenous vein grafts are exposed to hemodynamic stress when interposed in the arterial circulation and mechanical stress upregulates expression of TN-C, whereas stress-relaxation suppresses its synthesis. We hypothesized that the hemodynamic stress of increased arterial pressure could also induce TN-C expression in SVG.

METHODS

We examined the expression of TN-C protein and mRNA in normal vein and "arterialized" human SVG using immunohistochemistry and in situ hybridization, respectively.

RESULTS

TN-C protein was not detected in control human saphenous veins; however, it was uniformly and strongly expressed in the adventitia and media of patent human vein grafts, with minimal or no expression in the neointima (n = 27, 100%). In situ hybridization showed that TN-C mRNA was not detected in the neointima, but was strongly upregulated in the adventitia and media, corroborating immunostaining data (n = 10, 100%). Unlike patent SVG, TN-C was not expressed in the adventitia of occluded grafts, except for a low level of expression around the newly formed vessels in neointima (n = 5, 100%). Smooth muscle cell-specific staining demonstrated that the lack of expression of TN-C in occluded vein grafts is not due to the lack of presence of smooth muscle cells in the graft.

CONCLUSIONS

These findings suggest that placement of a venous graft in the arterial system leads to expression of TN-C, which may in turn facilitate graft remodeling. Conversely, loss of flow and intravascular pressure, associated with vein graft occlusion, is accompanied by disappearance of TN-C expression.

Morphologic comparison of atherosclerotic lesions in native coronary arteries and saphenous vein graphs with intracoronary angioscopy in patients with unstable angina

BACKGROUND

Coronary vein grafts develop accelerated atherosclerosis after aortocoronary bypass surgery. Previous pathologic studies have suggested that the morphologic appearance of atherosclerotic lesions in saphenous vein grafts may have subtle differences compared with those of native coronary arteries and may be more prone to disruption and thrombus formation. However, a comparative in vivo assessment of the angioscopic morphology differences between these two types of vessels has not been reported previously. We compared the angioscopic lesion morphology of native coronary arteries and saphenous vein grafts in patients with unstable angina.

METHODS AND RESULTS

Percutaneous coronary angioscopy was performed in 60 consecutive patients with unstable angina. Plaque color, texture, friability, and the presence of atherosclerotic plaque ulceration or intracoronary thrombus were noted in the culprit lesion. The culprit lesion was located in native coronary arteries in 42 (70%) patients and in a saphenous vein graft in 18 (30%) patients. There were no significant differences in age, sex, and coronary risk factors including tobacco use, hypertension, hypercholesterolemia, or diabetes mellitus between the two populations. There were also no significant differences between the two groups in terms of plaque color, surface texture, or the incidence of complex plaque morphology (plaque ulceration and intracoronary thrombosis). Loosely adherent, friable plaque, detected by angioscopy, was absent in native coronary arteries and was present in 44% of the saphenous vein grafts (p < 0.0001).

CONCLUSIONS

The results of our angioscopic study indicate that other than a high incidence of plaque friability in vein grafts, the surface morphology of culprit lesions in unstable angina patients is quite similar for saphenous vein grafts and native coronary arteries.

Saphenous vein graft protection: effects of c-myc antisense

OBJECTIVE

Saphenous vein grafting is associated with extensive medial remodeling, characterized by cellular proliferation, loss of smooth muscle cells, and an inflammatory response. In this study, we examined whether unfavorable responses to vein grafting could be modified by the intraoperative application of c-myc antisense oligomers.

METHODS

The intragraft cell proliferation, macrophage infiltration, and medial preservation were examined in a porcine model in the control and antisense-treated groups (n = 36).

RESULTS

Saphenous veins showed transmural distribution of oligomers within 30 minutes of the ex vivo incubation. A concentration-dependent inhibition of cell proliferation in the media of saphenous grafts was noted 3 days later (0 to 200 mumol/L, p = 0.005). The growth inhibition was sequence-specific, because control oligomers produced only insignificant effects (20 mumol/L). Vascular effects of c-myc antisense were associated with a significant attenuation of macrophage infiltration in saphenous grafts. A concentration-dependent decrease in tissue edema (p = 0.0005) and the attenuated loss of smooth muscle cells (p = 0.002) were noted in the media of the arterialized venous conduits after c-myc antisense.

CONCLUSIONS

Direct application of synthetic DNA to harvested saphenous veins resulted in a rapid transmural distribution. The inhibition of the intragraft cell proliferation in vivo after c-myc antisense was sequence dependent. Decrease in vein graft injury resulted in an attenuated inflammatory response and better medial preservation. These findings provide a rationale for assessment of the long-term effects of vein graft protection with c-myc antisense.

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.

Remodeling of autologous saphenous vein grafts. The role of perivascular myofibroblasts

BACKGROUND

Aortocoronary saphenous vein grafts (SVGs) undergo structural changes that render them susceptible to atherosclerosis. Accordingly, the origin of neointimal hyperplasia-was examined in porcine arterialized SVGs to determine the mechanism of vein graft remodeling.

METHODS AND RESULTS

At 2 to 4 days after surgery, the percentage of cells lacking differentiation markers characteristic for smooth muscle (SM) cells (ie, alpha-SM actin, desmin, and SM myosin) increased within the media of SVGs interposed in the carotid arteries (P < .001). At 7 to 14 days, these cells acquired a differentiated phenotype (ie, alpha-SM-actin positive/ variable desmin/SM-myosin negative) and accumulated in the neointima. At 3 months, the neointima was positive for alpha-SM actin but mostly negative for desmin, which contrasted with medial SMCs that were invariably positive for alpha-SM actin, desmin, and SM myosin. To determine the role of nonmuscle cells in the above process, perivascular wound fibroblasts were selectively labeled and found to translocate through the media of newly placed SVGs, contributing to neointimal formation. These migrating cells differentiated to myofibroblasts exhibiting sustained alpha-SM-actin expression. The intima of human SVGs, retrieved during repeat aortocoronary bypass surgery, exhibited the profile of cytoskeletal proteins that resembled myofibroblasts seen in porcine SVGs.

CONCLUSIONS

Perivascular fibroblasts may infiltrate injured media of arterialized SVGs, differentiate to myofibroblasts (acquiring alpha-SM actin), and contribute to vein graft remodeling. The similarities between porcine and human SVGs regarding the repertoire of cytoskeletal proteins suggest the involvement of myofibroblasts in graft remodeling in the clinical setting.

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.

Cryopreserved veins in myocardial revascularization: possible mechanism for their increased failure

BACKGROUND

Cryopreserved veins are used as conduits for myocardial revascularization. However, a high failure rate associated with their use has been reported anecdotally.

METHODS

To find an explanation for the poor performance of cryopreserved vein grafts, we conducted a retrospective 5-year study on all patients at a single institution in whom cryopreserved vein grafts were used. We further performed in vitro studies measuring cell adhesion, nitric oxide production, and contractile capacity of saphenous vein, internal thoracic artery, and cryopreserved veins. RESULTS; Forty-one patients were identified in whom one or more cryopreserved veins were used as a last resort. Sixteen had events (death or recatheterization). Seven deaths occurred (17%). Event-free survival was 50% at 12 months. Activated granulocyte/monocyte endothelial adherence could be lowered in internal thoracic arteries and saphenous veins with morphine incubation (50% and 57%, respectively), but not in cryopreserved veins. Simultaneous increases in nitric oxide release were also found in internal thoracic arteries and saphenous veins, but not cryopreserved veins. In addition, cryopreserved veins showed a diminished contractile capacity under experimental conditions.

CONCLUSIONS

In this highly select group of patients, cryopreserved veins had a high early failure rate, which may be partially due to the inability of the endothelium to participate in immunovascular processes.

Preserved vasodilatory response to nitroglycerin in saphenous vein bypass grafts

BACKGROUND

Uncertainty exists regarding the effects of nitroglycerin on atherosclerotic segments of coronary arteries, and information on vasoreactivity of saphenous vein bypass grafts is sparse. Intravascular ultrasound enables identification of atherosclerosis in angiographically normal segments and allows continuous determination of alterations in cross-sectional lumen areas.

METHODS AND RESULTS

Patients with documented coronary atherosclerosis were studied. Vessel morphology and lumen area at baseline and after 100 to 200 micrograms nitroglycerin were assessed at 10-second intervals for 60 seconds in vessel segments without angiographically apparent lesions. Coronary artery saphenous vein bypass grafts from 11 patients were compared with native coronary arteries in 16 different patients. Atherosclerosis was present in all vessel segments studied. There was a rapid increase in lumen area compared with baseline after intravascular nitroglycerin in both native coronary arteries and saphenous vein bypass grafts. Maximum lumen area dilatation was 19.6 +/- 12.2% in saphenous vein bypass grafts and 19.7 +/- 13.1% in native coronary arteries. An earlier peak response in saphenous vein bypass grafts (34.5 +/- 6.9 seconds) compared with native coronary arteries (44.7 +/- 8.5 seconds; P = .003) was found. Vessel wall area remained constant during vasodilation, but there was a significant reduction in measured wall thickness (P = .034).

CONCLUSIONS

In patients with documented coronary artery disease, intravascular ultrasound reveals substantial atherosclerosis in angiographically normal vessel segments. In these vessel segments, both native coronary arteries and saphenous vein bypass grafts exhibit prompt vasodilation with the intravascular administration of nitroglycerin. The vasodilatory capacity in response to nitroglycerin seems to be preserved in transposed, denervated, and devascularized saphenous veins.

Use of intravascular ultrasound for in vivo assessment of changes in intimal thickness of angiographically normal saphenous vein grafts one year after aortocoronary bypass surgery

OBJECTIVE

To use intravascular ultrasound in vivo to evaluate changes in the intimal thickness of angiographically normal saphenous vein grafts one year after implantation.

DESIGN

Fifteen saphenous vein grafts in 12 patients were examined one month and 12 months after aortocoronary bypass graft surgery with intravascular ultrasound using a 30 MHz transducer. None of the grafts examined showed any angiographic abnormalities. The intimal thickness and intimal area of the graft in the proximal portion were measured on intravascular ultrasound images obtained one month and 12 months after operation.

SETTING

General hospital.

PATIENTS

Twelve patients who underwent aortocoronary bypass graft surgery.

RESULTS

The ultrasound images showed a thin-walled graft with a thin intima one month after operation (mean (SD)) (0.31 (0.09) mm). The intimal thickness of the graft increased significantly to 0.65 (0.08) mm (P < 0.001) 12 months after operation. The intimal area of the graft was 0.90 (0.80) mm2 one month after operation. 12 months after operation the intimal area had increased significantly to 5.26 (1.38) mm2 (P < 0.001).

CONCLUSION

Intravascular ultrasound in vivo showed that one year after implantation angiographically normal saphenous vein grafts had a thicker intima than one month after implantation.

Duplex sonography of venous atheromatosis found in the venous part of hemodialysis fistula

Manifestation of atherosclerosis is one of the alterations in venous bypass grafts. Its progression and morphology usually cannot be described by sonography. The venous part of a hemodialysis fistula can be compared to a venous bypass graft. The authors investigated the venous part of hemodialysis fistula in 16 patients. They found atherosclerosis in 7 patients. The morphologic findings were similar to arterial atherosclerosis. Looking at the venous part of hemodialysis fistulas may be an adequate model to investigate the initiation and progression of atherosclerotic lesions in venous bypass grafts.

Absence of focal compensatory enlargement or constriction in diseased human coronary saphenous vein bypass grafts. An intravascular ultrasound study

BACKGROUND

No in vivo data are available on the occurrence of compensatory enlargement or vessel constriction in diseased human coronary saphenous vein bypass grafts (SVBGs). The aim of this intravascular ultrasound (IVUS) study was to examine to what extent lumen reduction is accompanied by (1) vessel wall thickening and (2) arterial wall constriction in SVBGs.

METHODS AND RESULTS

We used IVUS to examine 43 SVBGs from 42 patients (32 men, 10 women; mean age, 72 +/- 5 years) 8 to 23 (11 +/- 4) years after SVBG. IVUS images were obtained with a 3.5F monorail ultrasound catheter with a 30-MHz frequency and were analyzed at the lesion site, the reference site, and an intermediate site. The lumen area was significantly (P < .01) decreased; the vessel wall area (SVBG cross-sectional area minus lumen area) and the plaque area (area within the external elastic lamina minus lumen area) were significantly (P < .01) increased from the reference site through the lesion site. However, SVBG cross-sectional area was the same at these three sites (24.0 +/- 8.1 versus 24.4 +/- 8.6 versus 24.5 +/- 8.6 mm2, P = NS), and the external elastic lamina area was also quite constant in each vessel (17.8 +/- 6.0 versus 17.7 +/- 6.4 versus 17.6 +/- 6.2 mm2, P = NS).

CONCLUSIONS

These in vivo IVUS data from human coronary SVBGs demonstrate that (1) no focal compensatory enlargement or vessel constriction occurred in stenotic segments compared with the reference segments and that (2) the absence of focal compensatory enlargement appears to be a potentially important factor in the progression of stenoses in coronary SVBGs.

Long-term structural alterations to endothelial cells in vein-to-artery grafts: a quantitative electron microscopic study

The intracellular structure of endothelium lining vein-to-artery grafts in rats was analysed, using transmission electron microscopy and morphometry, to determine the ultrastructural adaptations of endothelial cells in this altered vascular environment. Autogenous 4-mm sections of iliolumbar veins were inserted microsurgically into the left common iliac arteries of 16 male Wistar rats. At 3, 6, 26 and 52 weeks the cytoplasmic-vesicular, mitochondrial and rough endoplasmic reticular contents of endothelial cells lining the grafts, the opposite iliac arteries and the remaining ilio-lumbar veins were analysed morphometrically. There was a significant increase in the amount of all these cytoplasmic structures in endothelial cells at 3, 6 and 26 weeks, at 52 weeks there was also a significant increase in the volumes of mitochondria and cytoplasmic vesicles, but not in rough endoplasmic reticulum. It was concluded that the ultrastructure of endothelial cells lining these grafts is changed chronically after graft insertion, and we propose that this may be attributable to altered haemodynamic stresses within the graft.