Changes in vein grafts following aorto-coronary bypass induced by pressure and ischemia

Sequential Versus Individual Saphenous Vein Grafting During Coronary Arterial Bypass Surgery

BACKGROUND

Although multiarterial grafting or bilateral mammary artery use is being increasingly emphasized for contemporary coronary artery bypass grafting (CABG) practice, saphenous vein graft (SVG) is still the most frequently used CABG conduit, and it accounts for 80% of all CABG conduits. Research focusing on modifiable surgical factors such as anastomosis technique, however, is scarce. This study aimed to compare clinical outcomes and graft patency according to anastomosis methods of vein grafting.

METHODS

From January 2005 through December 2016, patients who underwent CABG using SVG either by a sequential or an individual grafting technique were enrolled in this study. Graft patency was evaluated with coronary computed tomographic angiography. Propensity-score matching was used to compare the clinical outcomes and graft patency of these 2 grafting techniques to reduce treatment selection bias.

RESULTS

Overall 2515 eligible patients, 1,037 in the sequential SVG graft group (41.3%) and 1478 (58.8%) in the individual SVG graft group were enrolled. After propensity-score matching, 901 matched pairs of patients and 891 matched pairs of grafts were included in the final outcome analysis. There were no significant differences in unadjusted (P = .83) and adjusted overall mortality (hazard ratio [HR], 0.96; 95% confidence interval [CI], 0.79 to 1.17; P = .67). The composite outcome of death, nonfatal myocardial infarction, and repeat revascularization also did not significantly differ between the sequential SVG and the individual SVG groups for both before (P = .20) and after matching (HR, 0.91; 95% CI, 0.75 to 1.09; P = .30). The sequential grafts showed superior patency as compared with the individual grafts for both before (P = .015) and after adjustment (HR, 0.61; 95% CI, 0.45 to 0.82; P < .001).

CONCLUSIONS

The sequential grafting technique of SVG showed fairly acceptable safety and efficacy with superior long-term graft patency than individual grafts. Sequential SVG grafts perhaps can be a reasonable option as a second graft in CABG in some clinical situations.

Loss of Tachyphylaxis and Increased Sensitivity to Angiotensin II in Experimental Vein Grants

Intimal hyperplasia and atherosclerosis have been implicated in the pathophysiology of vein graft failure. Several recent studies have also reported alterations in the vasoreactivity of vein grafts. These alterations in vasoreactivity could contribute to vein graft spasm and lead to graft occlusion. This study examined the vasomotor responses of experimental vein grafts to angiotensin II, the most potent natural vasoconstrictor known. The right carotid artery was divided and bypassed in 12 rabbits with use of the right external jugular vein. The left external jugular vein was used as a control.

Eight vein grafts and jugular veins were harvested after fourteen days and 4 vein grafts after twenty-eight days. Segments of vein graft and control vein were mounted under isometric tension in an organ bath, and the dose response curves to angiotensin II obtained. On day 14, the response of the jugular veins was triphasic, while the respnse of the vein grafts was sigmoidal. The vein grafts were hypersensitive to angiotensin II. The ED50 was reduced from 8.4 ± 2.5 x 10-6 M in the jugular veins to 1.62 ± 0.24 x 10-8 M in the vein grafts (p < 0.005). The maximal response to angiotensin II was also increased from 342 ± 24 mg in the jugular veins to 558 ± 108 mg in the vein grafts on day 14 (p < 0.05). There was no significant difference in either the ED50 or the maximal response of the vein grafts on day 14 or 28. Tachyphylaxis (desensitization with repeated doses of agonist) was observed in the jugular veins but not in the vein grafts. The results show that experimental vein grafts are hypersensitive to angiotensin II, with either single or repeated exposure. This increased vasoreactivity to angiotensin II may have important clinical implications, particularly when vein grafts are used in patients with renovascular hypertension.

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.

Gene Therapy for the Extension of Vein Graft Patency: A Review

The mainstay of treatment for long-segment small-vessel chronic occlusive disease not amenable to endovascular intervention remains surgical bypass grafting using autologous vein. The procedure is largely successful and the immediate operative results almost always favorable. However, the lifespan of a given vein graft is highly variable, and less than 50% will remain primarily patent after 5 years. The slow process of graft malfunction is a result of the vein's chronic maladaptive response to the systemic arterial environment, its primary component being the uncontrolled proliferation of vascular smooth muscle cells (SMCs). It has recently been suggested that this response might be attenuated through pre-implantation genetic modification of the vein, so-called gene therapy for the extension of vein graft patency. Gene therapy seems particularly well suited for the prevention or postponement of vein graft failure since: (1) the stimulation of SMC proliferation appears to largely be an early and transient process, matching the kinetics of current gene transfer technology; (2) most veins are relatively normal and free of disease at the time of bypass allowing for effective gene transfer using a variety of systems; and (3) the target tissue is directly accessible during operation because manipulation and irrigation of the vein is part of the normal workflow of the surgical procedure. This review briefly summarizes the current knowledge of the incidence and basic mechanisms of vein graft failure, the vector systems and molecular targets that have been proposed as possible pre-treatments, the results of experimental genetic modification of vein grafts, and the few available clinical studies of gene therapy for vascular proliferative disorders.

Saphenous vein graft failure after coronary artery bypass surgery: pathophysiology, management, and future directions

OBJECTIVE

To review our current understanding of the epidemiology and pathogenesis of vein graft failure (VGF), give an overview of current preventive and interventional measures, and explore strategies that may improve vein graft patency.

BACKGROUND

VGF and progression of native coronary artery disease limit the long-term efficacy of coronary artery bypass graft surgery.

METHODS

We reviewed the published literature on the pathophysiology, prevention, and/or treatment of VGF by searching the MEDLINE (January 1, 1966-January 1, 2012), EMBASE (January 1, 1980-January 1, 2012), and Cochrane (January 1, 1995-January 1, 2012) databases. In addition, we reviewed references from the selected articles for studies not identified in the initial search. Basic science and clinical studies were included; non-English language publications were excluded.

RESULTS

Acute thrombosis, neointimal hyperplasia, and accelerated atherosclerosis are the 3 mechanisms that lead to VGF. Preventive measures include matching and quality assessment of conduit and target vessel, lipid-lowering drugs, antithrombotic therapy, and cessation of smoking. Treatment of VGF includes medical therapy, percutaneous intervention, and redo coronary artery bypass graft surgery. In patients undergoing graft intervention, the use of drug-eluting stents, antiplatelet agents, and embolic protection devices may improve clinical outcomes.

CONCLUSIONS

Despite advances in management, VGF remains one of the leading causes of poor in-hospital and long-term outcomes after coronary artery bypass graft surgery. New developments in VGF prevention such as gene therapy, external graft support, fully tissue-engineered grafts, hybrid grafts, and synthetic conduits are promising but unproven. Future efforts to reduce VGF require a multidisciplinary approach with a primary focus on prevention.

Saphenous vein graft disease: review of pathophysiology, prevention, and treatment

Saphenous vein graft (SVG) disease after coronary artery bypass grafting (CABG) occurs in three phases: thrombosis, intimal hyperplasia, and atherosclerosis. Within the first month, thrombosis plays a major role. From month 1 to month 12, intimal hyperplasia occurs. Beyond 12 months, atherosclerosis becomes the primary cause for late graft failure. Endothelial damage has been shown to be the major underlying pathophysiology of SVG disease. Many factors contribute to endothelial damage from the moment the vein is harvested to when the vein is grafted into an arterial environment. To address this disease process, various therapeutic modalities, from surgical methods to medical treatment, have been evaluated. Surgically, the technical method of harvesting the vein has been shown to affect SVG patency. From a pharmacologic perspective, only two guideline class I recommended medications, aspirin and statins, have been shown to improve short- and long-term SVG patency after CABG. Despite these surgical and medical advances, SVG disease remains a significant problem with 1-year patency rates of 89% dropping to 61% after 10 years. This review discusses the pathogenesis of SVG disease, predictors of SVG failure, and current surgical and pharmacologic therapies to address SVG disease, including possible future treatment.

Drug-eluting versus bare-metal stent for treatment of saphenous vein grafts: a meta-analysis

BACKGROUND

Saphenous vein grafts develop an aggressive atherosclerotic process and the efficacy of drug eluting stents (DES) in treating saphenous vein graft (SVG) lesions has not been convincingly demonstrated. The aim of this study was to review and analyze the current literature for controlled studies comparing DES versus bare metal stents (BMS) for treatment of SVG stenoses.

METHODOLOGY/PRINCIPAL FINDINGS

We searched several scientific databases and conference proceedings up to March 15, 2010 for controlled studies comparing target vessel revascularization (TVR) between DES and BMS. Summary odds ratios (OR) for the primary endpoint TVR and secondary endpoints infarction, stent thrombosis and death were calculated using random-effect models. A total of 29 studies (3 randomized controlled trials RCT) involving 7549 (202 in RCT) patients were included. The need for target vessel revascularization in the DES group tended to be lower compared to BMS for the 3 RCT (OR 0.50 [0.24-1.00]; p = 0.051) and for observational studies (0.62 [0.49-0.79]; p<0.001). There was no significant difference in the risk for myocardial infarction in the RCT (OR 1.25 [0.22-6.99]; p = 0.250) but a lower risk for DES based on the observational studies 0.68 [0.49-0.95]; p = 0.023. The risk for stent thrombosis was found to be non-different in the RCT (OR 0.78 [0.03-21.73], p = 0.885) while it was in favor of DES in the observational studies (0.58 [0.38 - 0.84]; p<0.001). The mortality was not significantly different between DES and BMS in the RCT's (OR 2.22 [0.17 - 29.50]; p = 0.546) while the observation studies showed a decreased mortality in the DES group (0.69 [0.55-0.85]; p<0.001).

CONCLUSION

DES may decrease TVR rate in treatment of SVG stenoses. No differences in reinfarction rate, stent thrombosis or mortality was found between the DES and BMS groups in the RCT's while the observational data showed lower risk for myocardial infarction, stent thrombosis and death in the DES group. This may be a result of patient selection bias in the observational studies or represent a true finding that was not the detected in the RCT analysis due to limited statistical power.

No touch vein harvesting technique for CABG improves the long-term clinical outcome

OBJECTIVES

To investigate the long-term clinical outcome, averaging 8.5 years, of two saphenous vein harvesting techniques for CABG; no touch (NT) versus conventional (C).

DESIGN

In a randomized study, 49/52 in group NT and 44/52 in group conventional were evaluated for reangina, myocardial infarction, new revascularization, functional class, risk factors and medical treatment. The vein grafts and the native coronary arteries were correlated to the occurrence of reangina.

RESULTS

There were significantly more patients free from angina and in NYHA class I (67.3 versus 43.2%; p =0.02) in group NT compared to group C. No cardiac death was found in group NT versus three in group C. There were trends towards fewer patients with cardiac death or myocardial infarction (3.8 vs. 13.4%; p =0.16), more patients free from angina (75.5 vs. 63.6%; p =0.26) and fewer patients with graft occlusion (24.3 vs. 43.2% (p =0.14) in group NT.

CONCLUSIONS

The results of the NT-technique are encouraging with no cardiac deaths, significantly more asymptomatic patients and a trend towards impact on hard clinical endpoints compared to the conventional technique.

Comparison of the rheologic parameters in left internal thoracic artery grafts with those in saphenous vein grafts

BACKGROUND

Left internal thoracic artery (LITA) grafts have superior patency to saphenous vein grafts (SVG). Because shear stress augments the release of nitric oxide throughout the LITA endothelium, shear stress and shear rate in coronary artery bypass grafts (CABG) may play an important role in the higher patency, so the aim of the present study was to evaluate and compare the rheologic parameters in CABG using LITA and SVG.

METHODS AND RESULTS

Rheologic examinations were done in 197 patients using a vacuum-suction glass tube viscometer after CABG surgery was completed. Shear stress and shear rate were calculated from the geometry of the graft, blood flow in the graft and blood viscosity. Of 197 patients, 177 underwent LITA grafting to the left anterior descending artery (LAD) and 160 had SVG anastomosis to coronary arteries. Mean wall shear stress in the LITA grafts to the LAD (13.8+/-1.0 dyne/cm2) was nearly 4-6-fold larger than that in the SVG grafts. Mean shear rate (559.1+/-57.0 s(-1)) of LITA-LAD grafts was approximately 2-3-fold higher than that of SVG.

CONCLUSION

These results suggest that high wall shear stress and shear rate play an important role in the higher patency rate of LITA grafts.

Modulation of phosphatidylinositol 3-kinase signaling reduces intimal hyperplasia in aortocoronary saphenous vein grafts

OBJECTIVES

Fifty percent of human aortocoronary saphenous vein grafts are occluded after 10 years. Intimal hyperplasia is an initial step in graft occlusion and consists of vascular smooth muscle cell proliferation. Phosphatidylinositol 3-kinase and its downstream regulator, the inositol 3-phosphatase PTEN (phosphatase and tensin homolog deleted on chromosome 10), are important regulators of vascular smooth muscle cell proliferation, migration, and cell death. This study tests whether overexpression of PTEN in aortocoronary saphenous vein grafts can reduce intimal hyperplasia.

METHODS

Adult dogs underwent aortocoronary bypass grafting to the left anterior descending artery by using the autologous saphenous vein. Saphenous vein grafts were treated with phosphate-buffered saline (n = 9), empty adenovirus (n = 8), or adenovirus encoding for PTEN (n = 8). Arteriography at 30 and 90 days assessed saphenous vein graft patency. A subset received saphenous vein grafts treated with a marker transgene (beta-galactosidase, n = 3), empty adenovirus (n = 4), or adenovirus encoding for PTEN (n = 4) and were killed on postoperative day 3 to confirm expression. Vascular smooth muscle cells were isolated from canine saphenous vein infected with adenovirus encoding for PTEN, and immunoblotting and proliferation assays were performed.

RESULTS

Saphenous vein graft transgene expression was confirmed by means of immunohistochemistry, immunoblotting, and polymerase chain reaction. Arteriograms revealed all saphenous vein grafts to be patent. Saphenous vein grafts treated with adenovirus encoding for PTEN demonstrated reduced intimal area compared with those treated with empty adenovirus and phosphate-buffered saline (1.39 +/- 0.11 vs 2.35 +/- 0.3 and 2.57 +/- 0.4 mm 2 , P < .05), and the intima/media ratio was lower in saphenous vein grafts treated with adenovirus encoding for PTEN (0.50 +/- 0.05 vs 1.43 +/- 0.18 and 1.11 +/- 0.14, P < .005). PTEN overexpression in vascular smooth muscle cells inhibited platelet-derived growth factor-induced phosphorylation of Akt, a downstream effector of phosphatidylinositol 3-kinase. PTEN-treated vascular smooth muscle cells demonstrated decreased basal, platelet-derived growth factor-stimulated, and serum-stimulated proliferation.

CONCLUSION

This study demonstrates that PTEN overexpression in aortocoronary saphenous vein grafts reduces intimal hyperplasia. The mechanism of this antiproliferative effect in vascular smooth muscle cells is likely due to inhibition of phosphatidylinositol 3-kinase signaling through Akt, with resultant decreases in vascular smooth muscle cell growth and survival. Therefore modulation of the phosphatidylinositol 3-kinase pathway through PTEN overexpression might represent a novel therapy to prevent saphenous vein graft intimal hyperplasia after coronary artery bypass grafting.

Modulation of vascular remodeling induced by a brief intraluminal exposure to the recombinant R7020 strain of Herpes simplex-1

OBJECTIVE

Vascular remodeling in response to injury or low shear stress (or both) is characterized by neointimal hyperplasia and luminal contraction. When profound, the response leads to restenosis after percutaneous endovascular intervention as well as to de novo stenosis in vein grafts. It has recently been reported that exposure of vein patches to neurovirulence-attenuated Herpes simplex virus-1 (HSV-1) decreases neointimal hyperplasia and increases luminal area. This experiment tested the hypothesis that R7020, a more highly attenuated mutant of HSV-1, would modulate the vascular remodeling response of experimental vein grafts chronically exposed to low shear stress.

METHODS

The external jugular veins of 31 New Zealand white rabbits were clamped and intraluminally exposed to vehicle (phospate-buffered saline solution, n = 11), R7020 2.5 x 10(8) plaque forming units [PFU]/mL (n = 8), or R7020 2.5 x 10(9) PFU/mL (n = 12) for 10 or 30 minutes at an average pressure of 80 mm Hg. After exposure, an end-to-side distal external jugular-to-common carotid artery anastomosis was created, resulting in a widely patent arteriovenous fistula. The external jugular was suture-ligated just proximal to the thoracic inlet, distal to a small 10- to 50-microm venous tributary, creating a reversed vein "graft" segment immediately and abruptly exposed to arterial pressure (48 +/- 3 mm Hg) and low shear stress (0.12 +/- .02 dyne/cm(2)). In the 29 animals (N = 31) that survived to harvest, 26 grafts were found to be patent and were analyzed further. Nine grafts were harvested within the first week after operation, snap frozen in liquid nitrogen, and assayed for the presence of the Herpes viral immediate-response protein ICP0 by Western blot analysis. The 17 remaining grafts were perfusion-fixed, excised, stained, and analyzed morphometrically by digital planimetry.

RESULTS

In patent grafts, the hemodynamic environment of low shear stress was maintained (shear stress at harvest, 0.26 +/- .06 dyne/cm(2)). Western blot analysis revealed the presence of ICP0 in R7020-exposed vein grafts after 2, 3, 7, and 14 days; ICP0 was not detected in unexposed vein grafts or adjacent carotid arteries. After 4 weeks, vein grafts exposed to R7020 exhibited a statistically significantly increased ratio of luminal radius to wall thickness, indicating altered remodeling (vehicle, 6.7 +/- 1.3; R7020 2.5 x 10(8), 9.1 +/- 1.3; R7020 2.5 x 10(9) ratio, 11.3 +/- 1.4; P < .05 for high dose compared with vehicle).

CONCLUSION

A brief exposure of the neurovirulence-attenuated HSV-1 strain R7020 results in an increased ratio of luminal radius to wall thickness in experimental vein grafts chronically exposed to low shear stress.

Saphenous Vein Grafts: To Use or Not to Use?

The choice of the graft conduit is crucial to the success of coronary artery bypass grafting (CABG) because the patency of a coronary conduit is closely associated with an uneventful postoperative course and better long-term patient survival. From the beginning of coronary bypass surgery venous conduits particularly the great saphenous veins (GSV) have been the most frequently used coronary conduit from the beginning of the coronary bypass surgery. However, over the last decade or so, coronary bypass graft surgery with arterial revascularization of all diseased coronaries has shown to be efficient because arterial grafts have better long-term patency, especially left internal mammary artery (LIMA), compared with venous grafts. Early vein graft failure coupled with occlusion is the most important limitation of saphenous vein grafts. Nevertheless, vein grafting is still an integral part of cardiac surgical practice. This review provides a summary of the patency rates, technical features and certain characteristics of the venous conduits. It also 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 existing and the emerging strategies to combat and control vein graft intimal hyperplasia and accelerated atherosclerosis are reviewed in detail.

Saphenous Vein Grafts: to Use or Not to Use?

The choice of the graft conduit is crucial to the success of coronary artery bypass grafting (CABG) because the patency of a coronary conduit is closely associated with an uneventful postoperative course and better long-term patient survival. From the beginning of coronary bypass surgery venous conduits particularly the great saphenous vein (GSV) has been the most frequently used coronary conduit. However, over the last decade or so, coronary bypass graft surgery with arterial revascularization of all diseased coronaries has shown to be efficient because arterial grafts have better long-term patency, especially left internal mammary artery (LIMA), compared with venous grafts. Early vein graft failure coupled with occlusion is the most important limitation of saphenous vein grafts. Nevertheless, vein grafting is still an integral part of cardiac surgical practice. This review provides a summary of the patency rates, technical features and certain characteristics of the venous conduits. It also 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 existing and the emerging strategies to combat and control vein graft intimal hyperplasia and accelerated atherosclerosis are reviewed in detail.

Altered expression of vascular endothelial growth factor and its receptors in normal saphenous vein and in arterialized and stenotic vein grafts

BACKGROUND

Myointimal thickening is a major cause saphenous vein graft failure. The prominence of medial and adventitial microvessels in stenotic vein grafts and the known angiogenic effects of vascular endothelial growth factor (VEGF) lead us to investigate the expression of VEGF and its receptors in vein graft arterialization and stenosis.

METHODS

Normal and arterialized vein graft segments were evaluated by reverse transcription-polymerase chain reaction (RT-PCR) for expression of VEGF-R1 (flt), VEGF-R2 (KDR), and neuropilin-1. The cells expressing VEGF, VEGF-R1, VEGF-R2, and neuropilin-1 were identified in normal, stenotic, and arterialized vein graft segments by immunohistochemistry.

RESULTS

Vascular endothelial growth factor, detected in the wall in endothelial cells and adventitial microvessels in normal vein, localized to smooth muscle cells, endothelial cells and adventitial microvessels in arterialized and stenotic vein. VEGF-R1 and VEGF-R2 were expressed infrequently on endothelial cells, macrophages, and smooth muscle cells in arterialized and stenotic vein. Neuropilin-1 was detected in all specimens. RT-PCR demonstrated significantly greater expression of neuropilin-1 in normal vein compared with arterialized vein (P <0.05).

CONCLUSIONS

The differential expression of VEGF and its receptors in normal, arterialized, and stenotic vein grafts suggests that alterations in VEGF/VEGF-R2/neuropilin-1 interactions may be important determinants of the adaptive response of vein grafts to arterialization.

Intimal changes in varicose veins: an ultrastructural study

In order to study the structural changes in the intimal layer of varicose veins, we prospectively collected a total of 23 vein specimens from both the normal proximal thigh long saphenous (LSV) in 3 young trauma patients and from the unstripped proximal LSV near the sapheno-femoral junction and the distal calf blowouts in 10 primary varicose veins patients. Paraffin sections stained with hematoxylin and eosin were examined under the light microscope while ultra-thin sections were examined under the transmission electron microscope (TEM). Compared with the normal control LSV, varicose vein sections showed increase in the diameter of the lumen, hypertrophy of the wall and elongation and invagination of the intima. Along these invaginations, endothelial cells were compressed, elongated and thinned out. The cells also showed progressive degeneration and were finally lost into the lumen, leaving only the basal lamina to form the luminal surface. This invited blood components like platelets and red blood cells to stick to the bare intima and to penetrate through the wall. This may form the basis of the clinical condition of superficial thrombophlebitis, which sometimes complicates cases of varicose veins. In conclusion, varicose veins showed increased diameter of the lumen and hypertrophy, elongation and invagination of the intima. There was marked degeneration of the endothelial cells and desquamation of the endothelial layer.

Improved patency in vein grafts harvested with surrounding tissue: results of a randomized study using three harvesting techniques

BACKGROUND

The technique of harvesting the saphenous vein for coronary artery bypass grafting influences the fate of vein grafts. The patency rate of a novel "no-touch" technique in which the vein is harvested with a pedicle of surrounding tissue and not distended was compared with two other techniques.

METHODS

One hundred fifty-six patients who underwent coronary artery bypass grafting were randomized to three saphenous vein harvesting groups: group C (conventional)--the vein was stripped, distended, and stored in saline; group I (intermediate)--the vein was stripped, local application of papaverine was used instead of distention, and the vessel was then stored in heparinized blood; and group NT (no-touch)--the vein was harvested with surrounding tissue, not distended, and stored in heparinized blood. Surgical and clinical factors that might influence graft occlusion were recorded. One hundred twenty-seven vein grafts in group C, 116 in group I, and 124 in group NT, as well as 118 left internal mammary artery grafts, were angiographically assessed at 18 months mean follow-up time.

RESULTS

The vein graft patency was 88.9% in group C, 86.2% in group I, and 95.4% in group NT. There was a statistically significant difference between the patency of the single-vein grafts in NT and the other two groups (p = 0.025). The higher the flow, the better the patency irrespective of the technique used. A higher attrition rate was found in vein segments taken from the knee area in group I. Poor vein quality affected patency in all groups. Forty-seven of all 51 sequential grafts (92.2%) were patent. The patency of left internal mammary artery grafts was 108 of 118 (91.5%).

CONCLUSIONS

We conclude that preservation of the surrounding tissue of the saphenous vein using this no-touch technique abolishes venospasm intraoperatively and plays an important role in maintaining vein graft function and patency.

Prevention of venous graft sclerosis with clopidogrel and aspirin combined with a mesh tubing in a dog model of arteriovenous bypass grafting

OBJECTIVE

to investigate the effect of clopidogrel combined with aspirin or aspirin alone on fibromyointimal hyperplasia (FIMH) in a bypass model with native vein grafts (NVG) and biocompound grafts (BCG).

DESIGN

twelve Beagle dogs were randomised into two equal groups. In each animal NVG and a BCG were interposed in the common carotid arteries. Postoperatively, Group 1 received clopidogrel (200 mg/d) and aspirin (100 mg/d) and Group 2 received aspirin (100 mg/d) alone.

METHODS

the BCG was constructed by sheathing the ipsilateral jugular vein with highly flexible metal mesh tubing. After 30 days the grafts were harvested and pressure fixed. FIMH was determined by morphometry.

RESULTS

the average wall thickness of the BCG was significantly lower than that of the NVG in both groups (0.26 (SD)0.02 mm vs 0.47 (SD)0.15 mm, p = 0.04 and 0.28 (SD)0.05 mm vs 0.70 (SD)0.29 mm, p = 0.01, respectively). For BCG treated with aspirin, the wall cross section area was lower (5.0 (SD)0.6 mm(2)vs 9.1 (SD)3.3 mm(2), p = 0.02) and the lumen larger (25.2 (SD)5.9 mm(2)vs 9.7 (SD)3.4 mm(2), p < 0.01) than for the NVG. There was also a difference in the lumen cross section area of the NVG, which was larger after combined therapy with clopidogrel and aspirin (17.9 (SD)7.8 mm(2)vs 9.7 (SD)3.4 mm(2), p = 0.04).

CONCLUSIONS

in this dog model the sheathing of vein grafts effectively prevents FIMH following bypass surgery. Clopidogrel is effective in NVG.

The effect of supplemental oxygen on the transarterial wall oxygen gradients at a prosthetic vascular graft to artery anastomosis in the rabbit

Artery wall hypoxia has been proposed to contribute to many kinds of artery wall pathology, including atherosclerosis and intimal hyperplasia. The purpose of this study was to determine the effect of supplemental oxygen on the transarterial wall oxygen gradients at a prosthetic vascular device (PVG)-to-artery anastomosis. The transarterial wall oxygen gradient in the infrarenal aorta of New Zealand White rabbits housed for 42 days in a 40% supplemental oxygen was measured with an oxygen microelectrode 2 mm distal to a PVG-to-artery anastomosis. Oxygen tensions were significantly increased throughout the artery wall at all time points in the supplemental oxygen groups compared to those in non-oxygen-supplemented groups. Within the oxygen-supplemented groups, the outer artery wall had diminished oxygen tensions immediately following creation of the anastomosis, with a slow return to control oxygen tensions on postanastomosis day 42 which correlated with a return of the vasa vasorum. These changes were noted without differences in blood pressure or arterial blood oxygen concentrations within the oxygen-supplemented group. Artery wall hypoxia noted following the creation of a PVG-to-artery anastomosis can be eliminated and artery wall oxygen tensions significantly increased by the administration of supplemental oxygen.

Vein adaptation to arterialization in an experimental model

PURPOSE

The events preceding myointimal thickening in vein grafts after vascular reconstructions are not well characterized. Indeed, the injury response associated with vein graft arterialization may be different than that observed in the balloon angioplasty model. Therefore, we used a rat model to study the early cellular response after arterialization of vein grafts.

METHODS

Epigastric veins were placed as femoral artery interposition grafts in 37 male Lewis rats (weight range, 350-400 g). Vein grafts and contralateral epigastric veins were harvested at different time points (6 hours, 1 day, 2 days, 3 days, 7 days, 14 days, 21 days, 30 days, and 70 days). Tissue specimens were processed for histology and immunohistochemistry with antibodies for the proliferating cell nuclear antigen (PCNA) and for different cell types. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay was used as a means of determining the presence of apoptosis. Electron microscopy was used as means of assessing the integrity of the endothelial cell surface (SEM) and confirming the presence of apoptosis (TEM). Specimens were also snap frozen in liquid nitrogen for RNA isolation and molecular analysis.

RESULTS

At 1 day, endothelial denudation with platelet deposition on the surface was shown by means of SEM. Both apoptosis and necrosis of smooth muscle cells (SMCs) were present in the media, along with monocyte infiltration. Cellular proliferation and apoptosis were most intense within the first week of implantation. PCNA staining was first seen in the adventitial fibroblasts and microvessels, then in the medial SMCs at 3 days. With reverse transcriptase polymerase chain reaction, upregulation of vascular endothelial growth factor (VEGF) messenger RNA (mRNA) was noted at 1 day. Myointimal thickening progressively developed, with no apparent diminution of the luminal area as long as 70 days after implantation. By means of the analysis of the transforming growth factor beta1, mRNA showed expression during intimal thickening and accumulation of extracellular matrix. Reendothelialization was complete at 30 days.

CONCLUSIONS

These observations indicate that the cellular composition in our vein graft model is similar to human stenotic explants. Endothelial denudation is observed in rat vein grafts with complete regeneration by 30 days. VEGF mRNA is upregulated at 1 day, followed by proliferation of microvessel endothelial cells in the adventitia. Cellular proliferation and apoptosis are minimal after 21 days, with progressive intimal thickening likely to be the result of matrix accumulation.

The biocompound method in coronary artery bypass operations: surgical technique and 3-year patency

BACKGROUND

Complete arterial revascularization may be unsafe in patients with a high operative risk. In patients with varicose ectatic veins, the biocompound technique, which uses unsuitable autologous veins, enables the surgeon to influence the bypass graft wall stress levels and diameter. This report summarizes the 3-year patency of 53 patients, the survival rate of 200 patients, and operative technical considerations.

METHODS

Biocompound grafts were used for aortocoronary bypass in 200 patients who were considered inappropriate subjects for complete arterial revascularization and who had unsuitable saphenous veins.

RESULTS

The mortality rate (30 days) of 200 patients was 3.5%. The 3-year survival rate was 88.5%. The patency rate of the left internal thoracic artery (LITA) after 3 years was 97.3%, of the native vein was 68.7%, and of the biocompound graft was 68.3%. The LITA showed a superior patency rate (p = < 0.05).

CONCLUSIONS

The LITA is the first choice in coronary bypass operation. The biocompound technique is a reliable method to achieve complete revascularization in patients with a lack of suitable saphenous veins.

Transarterial wall oxygen gradients at the deployment site of an intra-arterial stent in the rabbit

Intimal hyperplasia, common at the deployment site of an intra-arterial stent, may be caused by artery wall hypoxia. The purpose of this study was to determine the effect of an intra-arterial stent on artery wall oxygen concentrations. Transarterial wall oxygen gradients were measured by microelectrode at stent deployment sites in New Zealand White rabbits. Thinned artery walls and decreased oxygen tensions were noted throughout the artery wall immediately following stent deployment with a return toward control values at 28 days. Angioplasty alone had no acute effect on artery wall oxygen concentrations. Larger stent deployment diameters yielded acutely lower artery wall oxygen tensions. Using a linear one-dimensional model for the oxygen profile, we noted that stent deployment resulted in acute changes in oxygen consumption in the inner artery wall that rapidly returned to control values. Changes were noted without differences in blood pressure or arterial blood oxygen concentrations. Oxygen delivery to and consumption within the artery wall are altered by intra-arterial stent deployment. A role for artery wall hypoxia in artery wall pathology at the deployment site of an intra-arterial stent is supported by these findings.

Development of an ex vivo model to investigate the effects of altered haemodynamics on human bypass grafts

The insertion of vein grafts into the arterial circulation may contribute to vessel wall thickening and accelerated atherosclerosis, a common feature of late vein graft failure. We aimed to develop a model suitable for investigation of the effects of altered haemodynamics on human saphenous vein following its implantation into the arterial circulation. Segments of human saphenous vein obtained from patients undergoing coronary artery bypass surgery were sutured at each end to PTFE and placed into a flow system. Pressure and flow rates to stimulate the arterial and venous systems were achieved. A theoretical model of the flow chamber was created and computational fluid dynamics software (FLOTRAN, Swanson Analysis Systems) was used to determine the flow profile within the model. In summary, a flow model has been developed to investigate the effect of altered haemodynamics on the molecular and pathological changes that occur in vein grafts incorporated into the arterial circulation.

Intimal growth and neovascularization in human stenotic vein grafts

BACKGROUND

Myointimal thickening and microvessel ingrowth are commonly observed in vein graft stenosis, which complicates a third of infrainguinal bypass procedures. But a direct correlation between these two features has not been established. Our purpose was to analyze the relationship between neovascularity and intimal thickness in human vein grafts.

STUDY DESIGN

Twenty-two explant stenotic vein grafts (STVG), 8 nonstenotic arterialized vein grafts (AVG), and 20 age-matched control greater saphenous veins (CGSV) were analyzed histologically and compared morphologically by light microscopy. Digitized computer image analysis was used to measure intimal thickness and quantitate microvessel ingrowth. Immunolocalization of endothelial cells around the lumen and in microvessels was determined using antibodies to factor VIII and to endothelial nitric oxide synthase (eNOS), respectively.

RESULTS

Focal areas of endothelial disruption and thrombus deposition were present in 23% (5 of 22) of stenotic vein grafts. The neointima of STVG grafts was two- and fourfold thicker than that of AVG and CGSV, respectively (p < 0.0001). Microvessels were most frequently observed in the adventitia and media of STVG and increased in number with increasing intimal thickness (p < 0.001 by ANOVA).

CONCLUSIONS

A fourfold increased neointimal thickness in critically stenotic vein grafts is associated with increased medial and adventitial neovascularization. Remodeling alone with doubling of the intimal thickness in nonstenotic arterialized vein grafts does not appear to be associated with enhancement of the graft microvasculature. More specific observations using an experimental model may allow us to further define the role of angiogenesis in vein graft stenosis and to determine the therapeutic implications of such observations.

Transarterial wall oxygen gradients at a prosthetic vascular graft to artery anastomosis in the rabbit

PURPOSE

Artery-wall hypoxia has been proposed to contribute to many kinds of artery-wall pathologic conditions, including atherosclerosis and intimal hyperplasia. Intimal hyperplasia is common at sites of arterial injury, including an anastomosis. The purpose of this study was to determine the effect of a prosthetic vascular graft (PVG)-to-artery anastomosis on the delivery of oxygen to the artery wall.

METHODS

The transarterial wall oxygen gradient in the infrarenal aorta of New Zealand White rabbits 2 mm distal to a PVG-to-artery anastomosis was measured with an oxygen microelectrode.

RESULTS

Oxygen tensions were significantly decreased in the outer artery wall immediately after the creation of the anastomosis and showed a further decrease in oxygen tensions at days 7 and 14, which correlated with the absence of a vasa vasorum. After day 14, the oxygen tensions gradually increased, returning to normal by postanastomosis day 42, correlating with a return of the vasa vasorum. These changes were noted without differences in blood pressure or arterial blood oxygen concentrations.

CONCLUSION

The delivery of oxygen to the artery wall is altered by the creation of a PVG-to-artery anastomosis. Low arterial oxygen tensions at a PVG-to-artery anastomosis support a role for artery-wall hypoxia in the formation of intimal hyperplasia at the site of a PVG-to-artery anastomosis.

Reduction of intimal and medial thickening in sheathed vein grafts

BACKGROUND

Arterial pressures are described as an important factor in the development of graft degeneration and in reduced patency rate in vein bypass grafts. Sheathing of the graft with a pressure resistant mesh tubing might slow down this development.

METHODS

Saphenous vein grafts were implanted into the carotid arteries of five pigs in order to evaluate the influence on myointimal hyperplasia of a compliant Phynox mesh tubing (a wrought Cobalt-Chromium-Nickel-Molybdenum-Iron Alloy), which surrounded autologous vein grafts that were exposed to arterial pressure. Each pig was operated on using a sheathed vein graft (biocompound-graft, a hybrid vascular prosthesis) on one side and an untreated saphenous vein on the other.

RESULTS

After 4 weeks intimal hyperplastic changes were found in all histological sections. The wall thickness (medial and intimal layer) varied from 351 microm to 432 microm in the biocompound-graft and from 391 microm to 1196 microm in the native vein grafts (p < 0.05, n = 5). Severe myocytial and fibroblast proliferation was only found in the control grafts. Cellularity of the medial layer differed at sites of maximal cellular density and ranged from 11 to 12 cells in the biocompound-graft and from 17 to 18 cells per counting field in the native vein grafts (p < 0.05, n = 5).

CONCLUSIONS

External support of vein grafts reduces intimal and medial layer proliferation. The findings of this study are in accordance with the results reported by other research groups.

Influence of Vasodilator Drugs on Perioperative Blood Pressure

Survey results are given of the incidence and the etiology of perioperative hypertension in patients sub jected to coronary artery surgery. Over the years, numer ous types of antihypertensives have been used for intravenous administration with the aim of preventing or treating perioperative hypertension. Nitrovasodilator compounds such as sodium nitroprusside and nitroglyc erin (NTG), a few calcium antagonists (nifedipine, nicar dipine and isradipine), the short-acting β-blocker esmo lol, clonidine, and the multifactorial compounds labetalol and ketanserin are discussed in detail. Perioperatively, there is an increasing level of plasma catecholamines, causing α-adrenoceptor stimulation. This indicates that α-adrenoceptor blockade with appropriate antagonists is a logical approach for the treatment of perioperative hypertension. For this reason, the multifactorial agent urapidil, which is an α-adrenoceptor blocker and a 5-HT1A agonist, is discussed extensively.

Early injury to the media after saphenous vein grafting

BACKGROUND

Injury to the smooth muscle cells of the media affects the remodeling process of vein grafts. The purpose of this study was to determine whether different techniques of surgical preparation influence the degree of medial smooth muscle injury.

METHODS

Carotid-saphenous vein interposition grafting was performed in crossbred pigs (n = 32), using distended (n = 16) or nondistended (n = 16) conduits. After 3 to 90 days, the media was evaluated for the presence of smooth muscle cells (desmin stains), myofibroblast formation (transient alpha-SM actin expression), and apoptosis (TdT-mediated dUTP nick end-labeling [TUNEL]).

RESULTS

Smooth muscle loss was uniformly severe; only 5% +/- 5% (p < 0.01) and 14% +/- 9% (p < 0.01) of the medial area of distended and nondistended veins were desmin positive in comparison with 80% +/- 9% of controls. Apoptosis appeared to contribute to medial smooth muscle loss (5.7% +/- 4.3% in vein grafts versus 0.0% +/- 0.0% of TUNEL-positive cells in controls; p = 0.05). There was a time dependent increase in medial myofibroblast formation (p < 0.05).

CONCLUSIONS

Severe medial smooth muscle loss occurs in vein grafts, even when prepared without distension. Apoptosis contributes to the early disappearance of smooth muscle cells. Adjunctive measures, in addition to ideal surgical techniques, should be developed to prevent medial muscle loss.

Nitric oxide modulation of neutrophil-endothelium interaction: difference between arterial and venous coronary bypass grafts

OBJECTIVES

This study sought to evaluate the relation between the pattern of neutrophil-endothelial adhesion in saphenous vein (SV) and internal mammary artery (IMA) grafts and the endothelial production of nitric oxide (NO).

BACKGROUND

Autologous IMA and SV grafts (SVGs) are increasingly used as conduits for coronary bypass grafting. Previous studies have demonstrated a greater production of endothelial-derived relaxing factor (NO) from IMA than from SVGs. Because of the well known role of NO in modulating the adhesion of polymorphonuclear leukocytes to the endothelium, we studied the pattern of neutrophil adhesion to the endothelium of IMA and SVs under basal conditions and after inhibition of NO synthesis.

METHODS

Segments of IMA and SVs were obtained from 20 patients undergoing coronary artery bypass graft surgery. We evaluated the adhesion of both unstimulated and activated neutrophils to the endothelial surface of IMA and SVs in both basal conditions and after inhibition of NO synthesis with Nomega-nitro-L-arginine methyl ester.

RESULTS

Under basal conditions, no difference in unstimulated neutrophil adhesion to endothelium was observed between the two vessel conduits. After neutrophil activation, a significantly (p < 0.05) greater adhesion of neutrophils was observed in the SV than in the IMA. After inhibition of NO release, the adhesion of activated neutrophils increased in both vessels, and no significant difference between them was observed. The increased adhesion was attenuated by both L-arginine and sodium nitroprusside.

CONCLUSIONS

The lesser neutrophil adhesion to the endothelium of the IMA is a consequence of enhanced release of NO at this level; this effect could be responsible for the better early and long-term patency of this conduit over the SVG in coronary bypass grafting.

The effects of potassium channel openers on saphenous vein exposed to arterial flow

OBJECTIVES

To assess the sensitivity of saphenous vein to potassium channel opening drugs (KCOs).

METHODS

Saphenous vein, harvested at bypass surgery or high ligation for correction of varicose veins, was exposed to an in vitro flow circuit and vasomotor responses assessed by organ bath pharmacology.

OUTCOME MEASURES

Effective drug concentrations for 50% reduction in vein ring tension (IC50).

RESULTS

Vein rings pre-contracted with phenylephrine showed a concentration-dependent relaxation to all the KCOs tested with a potency ranking of HOE 234 > cromakalim > pinacidil > diazoxide. The relaxation to cromakalim was endothelium-independent and was inhibited by glibenclamide (an ATP-sensitive K+ channel blocker). The sensitivity of vein rings to cromakalim increased after exposure to arterial flow conditions for 90 minutes (IC50 before 1.7 +/- 0.25 microM and after 0.25 +/- 0.08 microM, p > 0.001). This effect was not evident after 90 min of venous flow conditions, 2.19 +/- 0.49 microM. When the workload on vein, exposed to arterial flow conditions, was reduced mechanically by external stenting with PTFE the increased sensitivity to cromakalim was abolished.

CONCLUSIONS

Saphenous vein has ATP-sensitive K+ channels responsive to KCOs. The increased sensitivity to cromakalim, induced by arterial flow conditions, may represent an endogenous protective mechanism limiting ischaemic damage resulting from the higher workload imposed on grafted vein.

Should angiographically disease-free saphenous vein grafts be replaced at the time of redo coronary artery bypass grafting?

BACKGROUND

Controversy exists regarding the management of angiographically disease-free saphenous vein grafts at the time of redo coronary artery bypass grafting (CABG). Some authorities favor replacement of these disease-free grafts, arguing that occlusion is likely in the near future. Others believe that these grafts are "biologically privileged" and should not be replaced.

METHODS

One hundred thirty-two consecutive patients (113 men, 19 women, aged 46 to 88 years, mean 67 years) underwent redo revascularization with one or more angiographically disease-free saphenous vein grafts at the time of redo CABG. Thirty-six patients had the disease-free grafts replaced (R) and 96 did not (NR). The mean interval from the first CABG was 9.25 years.

RESULTS

Surgical mortality was comparable in the NR and R groups (5 of 96 or 5.2% versus 3 of 36 or 8.3%, respectively; p < 0.5). Survival at 1 and 3 years was higher in the NR group than the R group (98% versus 80%, and 95% vs. 66% respectively; p < 0.0001). Late myocardial infarction was less common in the NR group than in the R group (12 of 91 or 12.9% versus 12 of 33 or 36.4%; p < 0.003). Recurrent angina was less common in the NR than in the R group (21 of 91 or 23.1% versus 15 of 33 or 45.5%; p < 0.015). Cardiac hospitalization was required less commonly in the NR than in the R group (11 of 91 or 12.1% versus 12 of 33 or 36.4%; p < 0.002). In nondiseased grafts undergoing angiographic evaluation late after redo CABG, rate of new stenosis was lower in NR grafts than in R grafts (2 of 12 or 16.7% versus 2 of 3 or 66.7%; p < 0.05).

CONCLUSIONS

With a conservative approach that does not replace nondiseased saphenous vein grafts at redo CABG (1) there is no increase in operative mortality, (2) good late survival is obtained, (3) clinical ischemia related to the NR saphenous vein grafts is uncommon, and (4) NR grafts continue to be patent. We conclude that disease-free vein grafts may not require routine replacement at redo CABG. A randomized study is required for definitive resolution.

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.

Mucosal biopsy findings and venous abnormalities in idiopathic myointimal hyperplasia of the mesenteric veins

Idiopathic myointimal hyperplasia of the mesenteric veins (IMHMV) is a rare cause of intestinal ischemia secondary to venous compromise. A patient with this condition who presented with crampy abdominal pain, diarrhea, and rectal bleeding initially attributed to inflammatory bowel disease had several colonoscopies and ultimately a sigmoid colectomy. The colonic mucosa in biopsies performed at initial presentation and subsequently and in the resection specimen contained numerous hyperplastic, thick-walled, hyalinized vessels in the lamina propria, which have not been described in this entity previously. Examination of the mucosa in 27 resection specimens of ischemic enterocolitis of various etiologies, in five resections of prolapsed rectum, and in seven colostomy specimens revealed no instance in which there were similar histologic abnormalities. When seen on biopsy, therefore, these features should lead to inclusion of IMHMV in the differential diagnosis. Furthermore, the characteristic lesions of the submucosal and extramural veins in IMHMV were compared with those of 14 examples, from several organs, of veins subjected to arterial pressure and 21 cases of venous hypertension. The marked similarity of the arterialized veins to the mural veins of IMHMV suggests a role for arteriovenous fistulization in the pathogenesis of IMHMV, and a mechanism by which this might occur is proposed.

Long-term evaluation of EC-IC bypass patency

The EC-IC Bypass Study Group could not detect any benefit from surgery compared to medical management in the prevention of stroke in 1985 [15]. During the past years surgical revascularization was re-evaluated and considered as an appropriate treatment for a small subgroup of patients with recurrent focal cerebral ischaemia and impaired haemodynamics. This retrospective study examines the long-term benefit and patency rate of bypass. We present a follow-up of 5.6 years of 47 patients, all of whom underwent bypass surgery after 1985. Forty patients suffered recurring transient ischaemic attacks due to uni- or bilateral internal carotid artery occlusion. Examination included neurologic status, TCD with CO2 or Diamox challenge, angiography, CT and SPECT scans. Neurological improvement was seen in 23% of patients with better results after early surgery, a worsening in 22% suffering further ischaemic events on a postoperative average of 2.8 years. Patency rate for vein graft material was 50%, for the STA-MCA procedure 91%. Occlusion of the vein graft occurred on an average after 1.4 years, other anastomosis after 2.7 years. We conclude that only few patients derived long-term benefit from EC-IC bypasses. Functioning of the bypass worsens over time, suggesting a role for surgery predominantly in the first year of ischaemic events due to insufficient collateral supply. Actual indications for bypass surgery may be patients with failure of maximal medical therapy and progressive ischaemia and haemodynamic compromise.

A comparative study of endothelium-derived relaxing factor-mediated relaxation and smooth muscle cell function in arterial and venous vein bypass grafts

The development of intimal hyperplasia in reversed vein grafts is associated with altered endothelial and vasomotor function. This study examines the effect of surgery on the morphology and vasomotor function of experimental arterial and venous vein bypass grafts. Twelve reversed vein grafts, 12 in situ vein grafts and 12 venovenous grafts were placed in 24 New Zealand White rabbits. All grafts remained patent and were harvested after 28 days. Isometric contraction to norepinephrine, histamine, bradykinin, serotonin and relaxation to acetylcholine and sodium nitroprusside following pre-contraction with prostaglandin F(2 alpha) were determined on the grafts and on contralateral jugular veins. Compared to the contralateral jugular veins, norepinephrine supersensitivity was induced in the reversed vein grafts, and venovenous vein grafts but not in the in situ vein grafts. Decrease in histamine sensitivity occurred in all grafted vessels. Bradykinin responses were significantly reduced in the in situ vein grafts and reversed vein grafts. Contractile responses to serotonin developed in the in situ vein grafts and reversed vein grafts only. Acetylcholine-induced endothelium-derived relaxing factor-mediated relaxation of the contralateral jugular veins was preserved in both venovenous grafts and in situ vein grafts but was lost in reversed vein grafts. All tissues relaxed to sodium nitroprusside in dose-dependent manner. The data suggest that norepinephrine supersensitivity in reversed vein grafts results from excision of the vessel. Attenuation of bradykinin responses and the enhanced contractile responses to serotonin appear predominantly to result from arterialization. Decreases in histamine sensitivity appear related both to excision and to arterialization. Neither the excision of the vein nor arterialization individually influences the alterations in endothelium-derived relaxing factor-mediated relaxation. However, a combination of excision and arterialization results in the altered endothelium-derived relaxing factor-mediated relaxation. This study suggests that the surgical preparation of the vein and the surgical procedure used have significantly different effects on endothelium-derived relaxing factor-mediated relaxation and smooth muscle contractility in vein grafts.

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.

Use of ketanserin in the treatment of hypertension following coronary artery surgery

Ketanserin, a selective S2-serotonin receptor blocker with alpha 1-adrenergic blocking effects, may be a suitable antihypertensive medication after coronary artery surgery and lacks side effects seen with other vasodilators. Fifty patients with systolic blood pressures greater than 150 mmHg after coronary artery surgery were given, in a randomized double-blind fashion, either ketanserin (K) or saline (S). Each patient received six successive boluses of 1 mL of S or 1 mL of K (5 mg) at 2-minute intervals. After the last injection, sodium nitroprusside was started whenever the systolic blood pressure exceeded 150 mmHg. In the K group, the following significant (P < 0.05) changes occurred: systolic and diastolic arterial pressure -12% and -11%, respectively; heart rate -3%; systolic and diastolic pulmonary artery pressure -5% and -6%; central venous pressure -5%; pulmonary capillary wedge pressure -5%; systemic vascular resistance -16%; pulmonary vascular resistance -8%; stroke index +6%. None of these parameters changed significantly in the S group. There was no change in pulmonary shunt fraction in either group. In the K group, five patients did not require any further antihypertensive therapy during the 120 minutes following the last bolus injection. Twenty patients needed sodium nitroprusside during this period. This occurred 37 minutes (+/- 17 min) after the last bolus. In conclusion, after coronary artery bypass surgery, K is an effective antihypertensive medication, which does not cause reflex tachycardia or an increase in pulmonary shunt fraction. Exceeding the recommended dose of 10 (or 20) mg, as done in this study, does not seem to improve effectiveness or prolong the duration of action.

Effect of chronic native flow competition on internal thoracic artery grafts

Residual competitive flow from the native coronary artery has been proposed as a mechanism that reduces flow in an internal thoracic artery graft (ITA), resulting in narrowing and ultimately failure of the graft. Results from acute experiments have indicated that competitive flow from a fully patent native artery did not abolish ITA graft flow. The present study was designed to examine the consequences of dynamic flow competition between the native vessel and the ITA graft in a chronic model. Fifteen mongrel dogs underwent coronary artery bypass grafting using the pedicled left ITA anastomosed to the normal, fully patent circumflex (CFX) coronary artery. The procedure was performed through a sterile thoracotomy, without systemic cardiopulmonary bypass, using a brief local occlusion to construct the anastomosis. Intraoperatively, ITA flow was measured in situ on the chest wall, before the pedicle was mobilized. Internal thoracic artery graft and distal CFX flow were measured after the anastomosis was completed, with and without brief occlusion of the proximal CFX. Angiography was performed 72 hours, 4 weeks, and 8 weeks later; graft patency and diameter were evaluated. After 8 weeks, open-chest direct flow measurements comparable with the intraoperative assessment were obtained. Two grafts (13%) occluded early, the technical result of poor anastomotic construction. In the 13 remaining animals, all grafts were widely patent at all time points. Internal thoracic artery flow in situ averaged 10.9 +/- 7.8 mL/min (mean +/- standard deviation), and was maintained after grafting (11.5 +/- 4.4 mL/min; p = not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of low molecular weight heparin on intimal hyperplasia in vein grafts

Intimal hyperplasia due to smooth muscle cell proliferation is a well recognised cause of vascular graft failure. In experimental studies heparin and its low molecular weight derivatives can inhibit this proliferative response. This study examines the effect of subcutaneous low molecular weight heparin (LMWH) therapy on intimal hyperplasia in a model of arterial vein grafting. Twenty-four New Zealand White rabbits underwent interposition vein grafting of the carotid artery. Animals were randomly assigned to a control or treated group. Treated animals received 60 anti Xa units/kg of subcutaneous LMWH daily for 1 month. Animals were then sacrificed, graft patency assessed and the vessels then harvested for analysis of intimal hyperplasia. Intimal hyperplasia in carotid arteries and vein grafts was measured using a computerised image analysis system and was expressed as an intimal:medial area ratio. A statistically significant reduction in the degree of intimal hyperplasia seen in the arterial component of the distal anastomoses of carotid vein grafts was achieved using subcutaneous LMWH [Control 0.44 (0.37-0.55): LMWH 0.27 (0-0.37) p < 0.05]. There was no difference in the degree of intimal hyperplasia seen in the vein grafts themselves. [Control 0.21 (0-0.54): LMWH 0.23 (0-0.72)]. This study suggests that subcutaneous LMWH can inhibit the development of intimal hyperplasia in arteries undergoing vascular grafting but does not influence intimal hyperplasia within vein grafts. This has important implications for the further evaluation of antithrombotic agents following vascular surgery.

The integrity of experimental vein graft endothelium--implications on the etiology of early graft failure

INTRODUCTION

the vascular endothelium serves as a functional barrier between the circulating blood and the vessel wall. It is an essential element for the maintenance of vascular homeostasis and is implicated in the pathogenesis of vascular disease. Reversed vein bypass grafting is considered to be a devastating procedure for the endothelial cell layer of the graft during the first 7 days. At this time, smooth muscle cell proliferation, the forerunner of intimal hyperplasia, begins. Loss of endothelial cell integrity is cited as an important factor in this smooth muscle cell response. The integrity of the vein graft endothelial lining after grafting was examined in this study.

METHODS

reversed vein bypass grafting of the common carotid artery using external jugular vein was performed in 24 New Zealand white rabbits. All grafts were pressure fixed (80 mmHg) in situ, at 0 and 10 min, 6 h and 1, 3, 5, 7 and 14 days postoperatively. The endothelial cell layer was examined by light microscopy (LM), scanning (SEM) and transmission electron microscopy (TEM) and immunohistochemistry (Factor VIII) using standard histological procedures.

RESULTS

the endothelium was observed by SEM and confirmed by both LM, Factor VIII and TEM in all specimens. It covered almost the entire surface examined. At 0 and 10 min, endothelial cells were present and displayed minimal evidence of injury. At 6 h and 1 day, numerous red cells, polymorphonucleocytes (PMNs), platelets and fibrin were adherent to the luminal surface. Blood cells were also seen beneath the endothelium. At day 3, the adherent fibrin and cellular elements were reduced with most of the endothelial lining intact. Within 10 min, TEM demonstrated that these cells were stretched, very thin with few microvesicles and a blurred cytoplasm, which would indicate viability but a degree of cellular injury. By day 1, the endothelial cells were lifted from their underlying structures by subendothelial oedema and an infiltrate predominantly of PMNs. By day 5, the blood cells and fibrin which were adherent to the endothelium had been dispersed and the subendothelial infiltrate was to a large extent replaced by disintegrated PMNs. On days 7 and 14, a viable confluent endothelial cell layer was present and a degree of intimal hyperplasia was noted. The endothelial cells appeared to have enlarged nucleoli and cytoplasms filled with a considerable quantity of rough endoplasmic reticulum.

CONCLUSION

the endothelium of reversed vein grafts is preserved at the time of implantation and at all time intervals studied in this model. These findings do not support the assumption that endothelial denudation is a prerequisite for intimal hyperplasia. Endothelial cell dysfunction and morphological changes are maximal within the first 3 days after grafting but appear to recover by the 5th postoperative day. The gross preservation of the endothelial cell layer implies that therapeutic approaches, to mitigate endothelial cell injury and its consequences, should be focused on the preoperative period and the first 5 days following implantation.

Experimental microsurgical vein grafts: quantitative temporal analysis of progressive media fibroplasia

The sequential histopathologic changes in microvenous grafts placed in a microarterial system were studied. In 48 Sprague Dawley rats, a 1 cm segment of epigastric vein was interposed into a defect created in the femoral artery. Grafts were explored at 1, 2, 4, and 12 weeks. After an initial smooth muscle hyperplasia, a progressive fibroplasia of the media was observed. Only small focal areas of intimal hyperplasia were seen. The width of the media was measured with an eyepiece micrometer. A statistically significant (P < 0.01) increase in width from 17 microns at 1 week to 462 microns at 12 weeks was noted. Although this process has been described before, this is the first quantitative assessment.

Noninvasive color Doppler inspection of small-diameter vascular grafts implanted in canine carotid and femoral arteries

To noninvasively evaluate a small-diameter vascular graft (approx. 4 mm in diameter) developed for coronary artery bypass application, a state-of-the-art color Doppler flow mapping system was applied to inspect various grafts implanted in 5 canines. The grafts, including Denaflex, Gore-Tex ePTFE, and Bioflow, were implanted interpositionally in the carotid and femoral arteries. Inspections were conducted with a 5 MHz linear vascular transducer at 6 weeks postimplantation and 12 weeks postimplantation, immediately prior to retrieval. In the carotid artery position, all 5 Denaflex grafts were patent throughout the implantation period while 2 of the 5 Gore-Tex grafts were occluded at 6 weeks, and 1 more was occluded at 12 weeks. In the femoral artery position, all 5 Denaflex grafts were patent at 6 weeks; however 2 were occluded at 12 weeks. For the Bioflow grafts at 6 weeks, 3 were patent, and 2 were occluded. The same results were observed at 12 weeks. The color Doppler inspection results indicated a higher patency rate in the carotid artery position than in the femoral artery position. Furthermore, the volumetric flow rate and the wall shear stress measured with the pulsed Doppler in the carotid artery were greater than in the femoral artery. These findings suggest that the hemodynamic "environment" in which the graft was implanted may affect the graft patency rate. The Doppler inspection results obtained at 12 weeks, identical with those observed after retrieval, demonstrated that color Doppler flow mapping is a reliable method to noninvasively inspect blood flow through small-diameter vascular grafts.