Functional Injury of Vein Graft Endothelium

Preservation of Adrenoceptor and Endothelin Receptor Mediated Vasoconstriction and of Endothelium-Dependent Relaxation after Cold Storage of Explanted Blood Vessels for ex vivo Analyses

INTRODUCTION

Adrenoceptor and endothelin (ET) receptor-mediated vasoconstriction as well as endothelium-dependent vasodilation of human saphenous veins were compared before and after 20 h of cold storage.

METHODS

Contractile responses to potassium chloride (KCl), norepinephrine (NE), and ET-1 as well as vasodilator responses to acetylcholine (ACh) were evaluated.

RESULTS

Storage in HEPES-supplemented Dulbecco's modified Eagle's medium (HDMEM) diminished KCl induced contractile forces to 71% (p = 0.002) and NE induced contractions to 80% (p = 0.037), in contrast to HEPES-supplemented Krebs-Henseleit solution (HKH) and TiProtec solution. KCl-normalized NE contractions were not affected by storage. NE EC50 values were slightly lower (7.1E-8 vs. 7.5E-8, p = 0.019) after storage in HKH, with no changes after storage in the other solutions. Endothelium-dependent responses to ACh were not affected by storage. ET-1 induced contractions were attenuated after storage in HDMEM (77%, p = 0.002), HKH (75%, p = 0.020), and TiProtec (73%, p = 0.010) with no changes in normalized constrictions. ET-1 EC50 values were not affected by storage.

CONCLUSION

Loss of contractility after storage in HDMEM may reflect the lower content of dextrose. There was no specific attenuation of adrenoceptor, ET-receptor, or ACh receptor mediated signal transduction after storage in any of the media. HKH or TiProtec are equally suitable cold storage solutions for ex vivo measurements.

The effect of distension pressure on endothelial injury and vasodilatation response in saphenous vein grafts: conversion of a bypass graft to a dead pipe

Introduction

Endothelial damage caused by high pressure applied for spasm relaxation during graft preparation is one of the most plausible theories explaining early graft failure.

Aim of the study

We aimed to demonstrate the extent of endothelial damage in saphenous vein grafts distended to different pressure levels by using immunohistochemical methods and in vitro tissue baths.

Material and methods

Saphenous vein grafts (SVGs) of 25 patients who underwent isolated elective CABG surgery were used in this study. By using a specific mechanism, SVGs were distended to five different pressure levels for two minutes: 0 mmHg, 50 mmHg, 100 mmHg, 200 mmHg, 300 mmHg. In vitro tissue baths and immunohistochemical examinations were performed.

Results

None of the grafts distended to 300 mmHg pressure were functional in the tissue bath system. The relaxation response to carbachol of SVGs distended to 0, 50, 100 and 200 mmHg was 97.87 ± 4.47%, 98.52 ± 3.95%, 93.78 ± 3.64%, and 30.87 ± 4.11%, respectively. There were no statistically significant differences in terms of relaxation responses between samples distended to 0, 50, and 100 mmHg (p = 0.490). The relaxation response of samples distended to 200 mmHg was significantly decreased (p = 0.021). The endothelia of samples distended to 0 mmHg were almost intact in CD31 staining. Endothelial cell loss occurred at all tested distension pressures at different degrees.

Conclusion

In vitro and immunohistochemical studies revealed that distending an SVG used for coronary artery bypass grafting with pressures of 100 mmHg or less results in less endothelial damage and increases graft patency.

Conduits for coronary bypass: vein grafts

The saphenous vein has been the principal conduit for coronary bypass grafting from the beginning, circa 1970. This report briefly traces this history and concomitantly presents one surgeons experience and personal views on use of the vein graft. As such it is not exhaustive but meant to be practical with a modest number of references. The focus is that of providing guidance and perspective which may be at variance with that of others and recognizing that there may be many ways to accomplish the task at hand. Hopefully the surgeon in training/early career may find this instructive on the journey to surgical maturity.

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.

Intraluminal pressure modulates eicosanoid enzyme expression in vascular endothelium of intact human conduit vessels at physiological levels of shear stress

OBJECTIVE

Biosynthesis of eicosanoid metabolites in blood vessels regulates vascular tone and platelet function. We investigated whether intraluminal pressure modulates gene and protein expression of key eicosanoid enzymes in intact human conduit vessels and/or release of their vasoactive metabolites.

METHODS

Paired segments of human umbilical veins were perfused under laminar flow for 1.5, 3 and 6 h at high versus low intraluminal pressure (40/20 mmHg) with identical shear stress (10 dyn/cm(2)). Endothelial cell mRNAs encoding cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), prostaglandin synthase (PGS), and thromboxane synthase (TXS) were measured by quantitative real-time RT-PCR. Secretion of PGI2 and TXA2 to the perfusion medium was measured by enzyme immunoassay of their metabolites 6-keto-prostaglandin F(1alpha) and TXB2.

RESULTS

Intraluminal pressures were 39.9 +/- 0.02 and 20.0 +/- 0.03 mmHg (P < 0.0001) in high and low pressure circuits, and shear stress levels were 10.6 +/- 0.60 and 9.7 +/- 0.36 dyn/cm(2) (NS, not significant). COX-1 mRNA was significantly up-regulated after 1.5 h of high pressure stimulation and continued up to 3 h, but fell thereafter significantly below baseline after 6 h. COX-2 mRNA was initially significantly down-regulated, followed by a significant up-regulation after 6 h. Gene expressions of PGS and TXS were significantly induced after 6 h of high pressure perfusion. High pressure depressed the production of PGI(2) (P < 0.05) but did not alter TXA(2) formation.

CONCLUSIONS

Intraluminal pressure has differential effects on gene and protein expression of key eicosanoid enzymes and biosynthesis of prostanoid metabolites in intact human conduit vessels. The new, computerized biomechanical perfusion system may be a useful tool to elucidate specific effects of various biomechanical forces on intact mammalian conduit vessels.

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.

Femoropopliteal bypass: in situ or reversed vein grafts? Ten-year results of a randomized prospective study

One hundred femoropopliteal bypass procedures performed in 91 patients between October 1980 and January 1985 were randomly divided into two statistically comparable groups including 50 in situ vein grafts and 50 reversed vein grafts. The indication for bypass was chronic critical ischemia in 97% of cases. The lower anastomosis was made on the distal popliteal artery in 75% of cases. Follow-up ranged from 10 years (for the last patient included) to 14 years. Three patients have been lost to follow-up. Median survival was 54 months in the in situ graft group and 76.5 months in the reversed graft group. Actuarial survival at 10 years was 30.8% in the in situ graft group and 29.5% in the reversed graft group. Actuarial limb salvage at 10 years was 73.5% in the in situ graft group and 74.4% in the reversed graft group. Graft occlusion was observed in 10 cases during the perioperative period (six in the in situ graft group and four in the reversed graft group) and in 19 cases during the late postoperative period (12 in the in situ graft group and seven in the reversed graft group). Reoperation during follow-up was required in 13 cases in the in situ graft group (11 patients) and in nine cases in the reversed graft group (five patients). Discounting residual arteriovenous fistulas (FAV) (five ligations in four patients), the incidence of lesions involving the bypass and anastomoses threatening graft patency was 6% in the in situ graft group and 8% in the reversed graft group. Actuarial primary patency at 10 years was 41.7% in the in situ graft group and 64.5% in the reversed graft group (p < 0.05). Actuarial secondary patency at 10 years was 64.8% in the in situ graft group and 70.2% in the reversed graft group (NS). As a function of vein diameter, actuarial secondary patency at 10 years in the in situ graft group was 37.5% for bypasses using veins with a diameter of 4 mm or less and 80.6% for bypasses using veins larger than 4 mm (p < 0.05). In the reversed graft group the patency rate was 71.2% for bypasses using veins with a diameter of 4 mm or less and 65.5% for bypasses using veins larger than 4 mm. In addition to requiring a training period the in situ technique raises the problem of valve removal especially for small diameter veins. The absence of these disadvantages makes the reversed technique the procedure of choice for femoropopliteal bypass.

Functional and morphological evaluation of canine veins following preservation in different storage media

Injuries of endothelial and smooth muscle cells of autologous vein due to preservation in standard storage media may be responsible for graft failure. The effects of vein preservation with University of Wisconsin solution (UWs) on endothelial and smooth muscle cell function and morphology were compared to the effects of preservation with autologous whole blood (AWB) and normal saline (NS), which are frequently used in cardiovascular surgery. Canine external jugular and common femoral vein segments were preserved in the different solutions at 4 degrees C for 45 min and 24 hr. Rings (4-5 mm in length) from control and preserved veins were evaluated by isometric tension studies at 37 degrees C and by scanning and transmission electron microscopy. Differences between groups were evaluated by Student's t test or Mann-Whitney U test and by analysis of the variance, and considered to be significant at P < 0.05. Sensitivities to norepinephrine (NE) showed that a 45-min vein storage in AWB (5.7 +/- 0.2 mumol/L) but not in NS (5.8 +/- 0.2 mumol/L) or UWs (6.5 +/- 0.2 mumol/L) had a deleterious effect on function of smooth muscle (P < 0.05) when compared to control veins (6.6 +/- 0.2 mumol/L). Maximum contractile responses and sensitivities to NE were significantly altered (P < 0.05) after 24-hr vein storage in AWB (0.09 +/- 0.02 g/mm2 and 5.4 +/- 0.07 mumol/L) and NS (0.12 +/- 0.03 g/mm2 and 5.6 +/- 0.08 mumol/L) but not in UWs (0.36 +/- 0.06 g/mm2 and 6.4 +/- 0.07 mumol/L). With both storage times, acetylcholine-induced endothelium-dependent maximum relaxations and sensitivities were significantly reduced (P < 0.05) in veins stored in AWB and NS, but not in UWs, compared with controls. Similarly, transmission electron microscopy revealed marked neutrophil migration beneath the intimal surface of vessels and extensive separation and desquamation of endothelial cells with exposure of subendothelial structures in veins stored in AWB and NS. The results suggest that UWs is a suitable storage medium when compared to AWB and NS.

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.

Neointima formation is promoted by surgical preparation and inhibited by cyclic nucleotides in human saphenous vein organ cultures

Intimal thickening is an important cause of late coronary vein graft occlusion, which no variation of surgical technique or pharmacologic intervention has been shown to reduce. We used a recently developed quantitative organ culture of human saphenous vein to investigate whether surgical preparative injury promotes neointima formation. We also investigated the effects on neointima formation of the lipid-soluble cyclic nucleotide analogs, 8-Br-cyclic adenosine monophosphate and 8-Br-cyclic guanosine monophosphate, and the phosphodiesterase inhibitor, isobutylmethylxanthine. These agents are pharmacologic mimetics of endothelium-derived prostacyclin and nitric oxide, which elevate vascular smooth muscle cyclic adenosine monophosphate and cyclic guanosine monophosphate concentrations, respectively, and may normally suppress neointima formation. Surgical preparation was found to promote intimal thickening and neointimal smooth muscle cell proliferation by 42% and 48%, respectively. 8-Br-cyclic adenosine monophosphate, 8-Br-cyclic guanosine monophosphate, or isobutylmethylxanthine (which elevated endogenous cyclic adenosine monophosphate concentrations) inhibited intimal thickening by 80%, 40%, and 72%, respectively, at a concentration of 0.1 mmol/L. The results imply that surgical techniques that avoid preparative injury and vasodilator drugs that act by elevating cyclic adenosine monophosphate or cyclic guanosine monophosphate concentrations may reduce neointima formation in vein grafts.

Endothelium-dependent relaxation after short-term preservation of vascular grafts

As the integrity of graft endothelium seems to be essential to successful long-term patency in coronary operations, its preservation demands the utmost care. The aim of the present study was to investigate the effects of currently used solutions on endothelium-dependent relaxation after short-term storage of vessels at room temperature or at 4 degrees C. The infrarenal rat aorta was selected for study because its use enabled standardization of the investigation, which was performed in organ baths on 672 vessel segments from 112 Sprague-Dawley rats. Stable vasoconstriction was obtained with the thromboxane analogue U-46619. Acetylcholine was used to elicit endothelium-dependent relaxation. The results obtained for vessels preserved for 2 hours were compared with those for autologous vessels studied immediately after harvesting. Vessel contractility was unaffected by the preservation solutions, except in the Ringer's acetate group, where it was reduced by 50% (p < 0.05). Endothelium-independent relaxation, tested with papaverine, was unaffected in all groups. Ringer's lactate, Krebs solution, and Perfadex (a low-potassium-dextran-glucose solution) did not significantly affect endothelium-dependent relaxation either at room temperature or at 4 degrees C, although a tendency to impaired relaxation was seen in these three groups after cold storage. Standard Ringer's solution and fresh heparinized blood each significantly reduced endothelium-dependent relaxation in vessels stored at room temperature (p < 0.05), but not in those stored at 4 degrees C. Endothelium-dependent relaxation was significantly reduced after storage in normal saline solution (p < 0.05) and in Ringer's acetate (p < 0.01), both at room temperature and at 4 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Vein graft factors in the outcome of femorodistal bypass

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

Alteration of reactivity of native arteries induced by venous graft placement

Occlusion of aortocoronary venous grafts can be due to thrombosis, atherosclerosis, or vasospasm. Investigations have focused on properties of the graft itself, and little is known about the vascular reactivity and function of the native arteries proximal and distal to the vein graft, although spasm of the native artery distal to the graft site has been observed in patients. We hypothesized that the function of the endothelium of the native arteries may be altered after surgery. Autogenous venous grafts were placed in femoral arteries of rabbits to study the reactivity of the native arteries after grafting. Four weeks after graft implantation, the vein graft, ipsilateral vein, and native artery proximal and distal to the graft were removed for in vitro studies. Morphological evaluation by scanning electron microscopy and fluorescence microscopy after labeling with acetylated low density lipoprotein labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate indicated the presence of an intact, metabolically active endothelial layer. There was no alteration in the contractile responses to phenylephrine of the arteries, vein grafts, or veins. Precontracted vein grafts, veins, and arterial segments proximal to the grafts relaxed when exposed to endothelium-dependent vasodilators (acetylcholine, arachidonic acid, and substance P), but the native arteries distal to the grafts did not. In bioassay cascade experiments, the distal artery did not release any measurable relaxing factor when exposed to acetylcholine. We conclude that the endothelium of the distal artery did not function normally. The extent and reversibility of altered endothelial function remain to be determined. This observation may help to explain the occurrence of myocardial infarction after aortocoronary bypass grafting in some patients.

The endothelium: a key to the future

The vascular endothelium is a complex modulator of a variety of biological systems and may well be the key to definitive success in the treatment of cardiovascular disorders. Surgically-induced endothelial injury may occur preoperatively during cardiac catheterization and intraoperatively from mechanical manipulation, ischemia, hypothermia, and exposure to cardioplegic solutions. The normal endothelium is antithrombogenic and yet promotes platelet aggregation and coagulation if injured. Vasospasm, occlusive intimal hyperplasia, and accelerated arteriosclerosis can also all occur as a result of endothelial injury. Furthermore, endothelial injury is harmful even in the absence of disruption of its monolayer integrity. Thus, preservation of the endothelium should be an additional objective for all cardiovascular surgeons. Synthetic vascular grafts, cardiac valves, and artificial ventricles do not spontaneously endothelialize and thus usually require some form of anticoagulation to maintain patency. Hence, endothelialization of prosthetic implants became an attractive concept. A number of different methods of obtaining an endothelial lining of prosthetic material has since been developed; these include facilitated endothelial cell migration, and endothelial cell seeding by using either venous or microvascular endothelial cells. Manipulating the endothelium might well provide the next major advancement for therapeutic and preventive measures for cardiovascular disease.

Prostacyclin release from the human saphenous vein in diabetics in lower than in nondiabetics

The balance between prostacyclin and thromboxane has been suggested to be of great importance for the maintenance of patency in veins. In order to investigate prostacyclin and thromboxane release, segments from the human saphenous veins were investigated in 53 patients. Twenty-seven patients (10 males, 17 females) underwent surgery for varicose veins. Twenty-six patients (14 nondiabetics, 12 diabetics) underwent surgery for lower limb ischemia (rest pain or gangrene) with use of the saphenous vein as arterial conduit. Vein segments were gently excised and perfused ex vivo for five 15 minute periods, with a balanced salt solution and determination of the stable degradation products 6-keto-PGF1 alpha and TxB2. Saphenous veins from patients with varicose veins had an initial prostacyclin release of 61 +/- 13 pg/mm2/15 min declining to 4 +/- 1 pg/mm2/15 min after 60 min (p < 0.001) and increasing after addition to arachidonic acid to 37 +/- 7 pg/mm2/15 min (p < 0.001). Segments from nondiabetic patients with lower limb ischemia did not differ from those of varicectomy patients, but diabetic segments had a significantly lower prostacyclin release than both these groups, 34 +/- 11 pg/mm2/15 min, 1 +/- 1 pg/mm2/15 min, and 7 +/- 5 pg/mm2/15 min, respectively (p < 0.05). The addition of arachidonic acid failed to increase the prostacyclin release in diabetics. Three patients from each group were studied regarding thromboxane release and there was almost no detectable thromboxane in any group. These findings suggest that diabetics have a lowered prostacyclin release from the saphenous vein and that the deficiency is at the cyclo-oxygenase level.(ABSTRACT TRUNCATED AT 250 WORDS)

Vein compliance: a preoperative indicator of vein morphology and of veins at risk of vascular graft stenosis

Compliance measurements of 53 long saphenous veins before femorodistal bypass have been performed using a duplex scanner with venous occlusion for distension. These have been compared with the histological features of the veins. There was significantly more moderate or severe focal hyperplasia and circular muscle hypertrophy in distal long saphenous vein than in its proximal counterpart (P < 0.01 and P < 0.05 respectively). The mean (95 per cent confidence interval) compliance of distal vein with moderate or severe hyperplasia was 0.16 (0.13-0.19) compared with 0.29 (0.22-0.36) for that with no, minimal or mild hyperplasia (P = 0.001). The mean compliance of distal vein with moderate or severe muscle hypertrophy was 0.19 (0.17-0.21) and of vein with no, minimal or mild hypertrophy 0.25 (0.21-0.29) (P = 0.14). The mean lowest compliance in seven patients who developed stenosis was 0.10 (0.07-0.13) compared with 0.21 (0.16-0.26) in the rest (P < 0.001). Preoperative measurement of vein compliance can be used to identify vein with marked pre-existing intimal hyperplasia and as a predictor of future graft stenosis.

Storage in sodium chloride does not impair arterial prostacyclin release

Heparinised sodium chloride solution is often used for the storage of veins and to prevent clotting in the arterial tree during vascular surgery. Sodium chloride deranges the morphology of endothelial cells and has therefore been interpreted as "toxic" to the endothelial cell. Perfused human saphenous veins and rabbit aortas show the same pattern of prostanoid release even though veins have a lower release than arteries. Excised rabbit aortas were stored in either (a) 0.9% sodium chloride or (b) 0.9% sodium chloride with heparin 5 I.U. ml-1 prior to being mounted in a perfusion model. The vessels were perfused ex vivo for 5 x 15 min with either Hanks' balanced salt solution (HBSS), calcium- and magnesium-free HBSS or 0.9% sodium chloride. For the last period, arachidonic acid (AA) 4 micrograms ml-1 was added. The release of prostacyclin, measured as the stable degradation product 6-keto-PGF1 alpha by radioimmunoassay, was not altered by storage in sodium chloride, or 0.9% sodium chloride plus heparin when compared with control segments. Perfusion with 0.9% sodium chloride did, however, significantly (p greater than 0.05) decrease the prostacyclin production when AA was added. This is most likely to be due to the low pH of the sodium chloride solution. It is concluded that short-term storage of rabbit aorta in sodium chloride plus heparin or 0.9% sodium chloride does not impair the prostacyclin cascade from the vessel wall, which might be of importance when choosing storage medium for reversed veins and veins used for coronary bypass surgery.

The influence of harvesting technique on endothelial preservation in saphenous veins

To study optimal conditions of preparation of saphenous veins as coronary artery bypass grafts, segments of saphenous veins were obtained from 29 consecutive patients undergoing coronary artery bypass grafting. The saphenous vein segments were divided into three groups. In Group I, 10 saphenous vein segments were harvested using a "no-touch" technique without any other preparation aids. In Group II, 10 saphenous vein segments were removed while distended at 70-120 mm Hg with a balanced pH electrolyte solution at 37 degrees C. In Group III, consisting of 10 saphenous vein segments, nitroglycerin (1 microgram/ml) was added to the distending solution used in Group II. Samples of saphenous vein were assessed in a blind study using light and scanning electron microscopy to estimate endothelial cell preservation by the three harvest techniques. Saphenous veins receiving only a no-touch dissection technique without distention solution (Group I) revealed significantly better endothelial preservation (P less than 0.005). The administration of distention solution alone, or with nitroglycerin, to saphenous veins in situ using our operative technique during harvest does not appear to protect endothelial-integrity and may be harmful.

Blowout of carotid venous patch angioplasty

Two cases of vein patch blowout were observed five and seven days after carotid bifurcation endarterectomy with patch angioplasty. Both patients died in spite of emergency reoperation. One patient developed respiratory failure with subsequent fatal cardiac arrest seven days after reoperation; the other died of extensive hemispheric infarction on the fifth postoperative day. At reoperation both ruptures were found to be located in the middle of the patch whereas the suture lines were intact. Both patients were hypertensive. In the first case, an accessory saphenous vein retrieved from the calf had been the only venous material available for the patch, while the other patient had varicose veins in the contralateral leg. Pathology revealed central transmural tissue necrosis in one of the disrupted patches. A review of the literature regarding morphologic alterations of free vein grafts placed within the arterial circulation as well as hemodynamics in patched arterial segments may provide additional insight as to the inherent benefits and risks of vein patch angioplasty after carotid endarterectomy. When considering vein patch angioplasty, particular attention should be directed to the gross aspect of the vein to be used as well as to any antecedent history of phlebitis.

Simulated blood flow and the effects on prostacyclin production in the dog femoral artery

Effects of blood flow on the production of prostacyclin (PGI2) were examined in the canine femoral artery perfused ex vivo. Each artery was perfused in situ with medium 199, under conditions of simulated blood flow. To simulate the normal and abnormal blood flow waveforms at the same mean flow rate, we developed a flow apparatus capable of making various waveforms by changing the duration when the electromagnetic valve in the circuit was open. Group I (n = 7) was exposed to a steep acceleration waveform followed by a steep deceleration, as the normal flow waveform; group II (n = 7) was exposed to a gentle sloping waveform in the deceleration phase, as the abnormal flow waveform. PGI2 was measured as 6-ketoprostaglandin F1 alpha. PGI2 production was estimated as the cumulative production for the first 5 minutes (acute response) and as the production rate after the first 30 minutes (stable production rate). Under conditions of normal flow, the acute response was 5.87 +/- 2.16 ng/cm2/5 min, whereas under conditions of abnormal flow, the rate was 2.20 +/- 0.27 ng/cm2/5 min (p less than 0.01). Stable production rates were 82.5 and 37.5 pg/cm2/min, respectively (p less than 0.05). Both the acute response and the stable production rate of PGI2 production were greater under conditions of simulated normal flow as compared with findings in the case of an abnormal flow. Our working hypothesis is that the decreased production of PGI2, as well as a deterioration in the implanted graft, under conditions of abnormal blood flow leads to a loss of late patency of the reconstructed arteries.

Regional variability of prostacyclin biosynthesis

To investigate the regional variability in arterial and venous endothelial prostacyclin (PGI2) biosynthesis, we obtained 1-cm segments of carotid arteries, external jugular veins, femoral arteries and veins, iliac arteries and veins, inferior venae cavae (IVC), and aortas from 17 dogs. Vessel luminal PGI2 production was measured in the basal state by radioimmunoassay of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha). A total of 90 arterial specimens (57, 19, and 14 segments, respectively, of femoral/carotid arteries, iliac arteries, and aorta) and 41 venous specimens (15, 10, and 16 segments, respectively, of femoral/jugular veins, iliac veins, and IVC) were analyzed. Overall, arterial endothelial 6-keto-PGF1 alpha was higher than venous (8.1 +/- 0.5 ng/ml vs. 4.9 +/- 0.7 ng/ml, p less than 0.0004); 6-keto-PGF1 alpha levels were greater in the arteries than in their corresponding veins [femoral/carotid arteries (6.3 +/- 0.4 ng/ml) vs. femoral/jugular vein (2.1 +/- 0.4 ng/ml), p less than 0.0002; iliac arteries (9.3 +/- 1.0 ng/ml) vs. iliac veins (4.8 +/- 0.9 ng/ml), p less than 0.005; aorta (14.0 +/- 1.6 ng/ml) vs. IVC (7.5 +/- 1.4 ng/ml), p less than 0.006].(ABSTRACT TRUNCATED AT 250 WORDS)

Prostacyclin and thromboxane release from the vessel wall--comparison between an incubation and a perfusion model

Prostacyclin (measured as its stable degradation product 6-keto-PGF1 alpha) and thromboxane (measured as its stable degradation product TxB2) produced by the vascular wall were measured by radioimmunoassay (RIA). Four pieces from the rabbit aorta and four from the caval vein were used. One piece was incubated in Hank's balanced salt solution (HBSS), one piece with additional indomethacin, and the other pieces were mounted in a perfusion system so that only the endothelium was exposed to the buffer solution with or without indomethacin. There was a higher release in the piece incubated in the buffer than in the piece which was perfused, indicating that not only the endothelium releases prostacyclin and thromboxane from the vascular wall. The 6-keto-PGF1 alpha/TxB2 ratio was higher in the perfused than in the incubated samples suggesting that 6-keto-PGF1 alpha release is higher in the endothelium than in the other wall layers and/or that TxB2 production is higher in the outer layers than in the inner layers. No correlation was found between the release from the incubated vessel and from the perfused vessel. There was a higher release of 6-keto-PGF1 alpha from aortas than from caval veins, when incubated or perfused, whereas there was a tendency to a higher release of TxB2 from veins than aortas.

In situ versus reversed saphenous vein for femoropopliteal bypass: a prospective randomized study of 100 cases

With the purpose of comparing results using the greater saphenous vein in situ or as a reversed conduit, 100 femoropopliteal bypasses, performed in 91 patients between October 1980 and January 1985, were randomized into two statistically comparable groups of 50 procedures of each type. Seventy-five percent of patients had cutaneous signs of ischemia and 20% had isolated rest pain. Average follow-up was 32 months for the in situ group and 33.4 months in the reversed bypass group. The quality of the vein was statistically better in the in situ group (p less than 0.01). There were six cases of early thrombosis in the in situ group compared to four in the reversed bypass group. In the in situ group, half of the thromboses could be attributed to inadequate valvular destruction. Seven delayed thromboses were noted in the in situ group whereas there were two in the reversed saphenous vein bypass group. The actuarial rates of bypass patency at three years in the reversed and in situ groups were 88.2 and 70.8%, respectively (chi 2 = 2.62; NS). Analysis of results suggests that: 1) the reversed saphenous vein bypass provides excellent results if vein harvest and preparation are as atraumatic as possible; 2) expertise in rendering the valves incompetent markedly increases patency in the in situ technique; 3) during the first 12 months, Doppler follow-up of measured distal pressures is necessary in order to detect pathologic changes of the bypass and adjacent arterial tree.

Biochemical (functional) adaptation of "arterialized" vein grafts

Canine venous autografts and allografts were interposed in the femoral and carotid arterial positions in 29 dogs; grafts were harvested at three postoperative intervals (1-2 weeks, 4-6 weeks, and 8-10 weeks) for light and scanning electron (SEM) microscopy and lumenal surface prostacyclin (PGI2) production. Normal veins and arteries were used as controls. Radioimmunoassay for tritiated 6-k-PGF1 alpha, the stable metabolite of PGI2, was performed using a flow surface template incubation chamber during basal and arachidonic acid stimulated conditions. Using SEM, the autografts revealed normal endothelial cell (EC) surfaces at all time intervals; conversely, allografts exhibited extensive EC loss at 1-2 weeks with gradual reparation by 10-12 weeks (such that the EC surface was virtually indistinguishable from that of control veins or autografts). PGI2 production was significantly greater in control arteries than veins (p = 0.0001). At 1-2 weeks and 4-6 weeks, lumenal production of PGI2 in both the autografts and allografts was not significantly different from control vein; however, PGI2 production after 10-12 weeks was identical to normal arterial levels (and significantly [p less than 0.0044] higher than venous levels) in both basal and stimulated conditions. Although the mechanisms responsible for this functional (biochemical) "arterialization" process remain conjectural, increased biosynthesis and/or release of PGI2 by endothelial cells, acute phase inflammatory cells (allografts) mediated by interleukin-1 or myointimal cells seems most likely. Further elucidation of these sources of PGI2 is necessary, but these data demonstrate for the first time that venous grafts placed in the arterial circulation undergo complete functional adaptation (in addition to the well known morphological changes).

Compliance changes in in-situ femoropopliteal bypass vein grafts

Changes in wall structure, including neo-intimal proliferation and medial fibrosis, have been implicated as a cause of late occlusion in reversed femoropopliteal vein grafts. These changes can be measured indirectly as a fall in compliance. It has been suggested that long-term patency might be improved by the in situ technique because the nutrient vasa vasorum are left intact and therefore wall structure preserved. We have measured the compliance of 62 in situ vein grafts, with times after operation ranging from 2 days to 6 years, and also compared the compliance changes, in the first 3 months after operation, of 15 undisturbed in situ vein grafts with 15 fully mobilized in situ vein grafts. Compliance was derived non-invasively from the pulse wave velocity using Doppler ultrasound. There was a significant fall in compliance after operation (P less than 0.001) and no difference could be found between the undisturbed and mobilized in situ vein grafts (P greater than 0.1). Histological examination of 6 grafts suggested that the fall in compliance was due to neo-intimal proliferation which still occurred although medial fibrosis was reduced. Any potential improvement in long-term patency rates using the in situ technique must be due to other factors.

Maximizing the use of autogenous vein using the in situ (valve incision) technique

Bypass grafting to vessels beyond the popliteal bifurcation is an established method for treating severe limb ischaemia. Failure rate is high, however, especially when prosthetic vascular substitutes have to be used. When left in situ, saphenous vein can be used down to much smaller diameters than would be possible with reversed vein. With this method, vein utilization of around 90% can be achieved with respective increases in patency and limb salvage. Our early results with 26 in situ grafts are presented. In two cases the presence of a suitable tributary of the saphenous vein allowed a 'bifurcated' or 'femorotibial' graft to be performed. All patients (17 males, nine females) were admitted with limb threatening ischaemia. Mean ankle pressure index was 0.29 (s.d. = 0.09), range 0.18-0.53. Average graft intra-operative flow rate measured 96 ml/min. Twenty grafts remain patent while six grafts have failed. In three of these failures, performed early in the series, the graft could not be made to function at the time of surgery. The mean postoperative ankle pressure index was 0.87 (s.d. = 0.19). Cumulative patency rate at 24 months is 74%. This rises to 83% if the three 'on table' failures are excluded. Five amputations were required; four as a result of graft failure and one despite a functioning graft. Four grafts clotted within 24 h but have remained patent following immediate thrombectomy. One patient required ligation of an arteriovenous fistula on the third postoperative day.