Effects of estrogen on vein grafts.

The effect of estrogen on veins was evaluated in vitro and in vivo in three species. 17 beta-estradiol did not significantly alter 3H-thymidine uptake in vitro in segments from either canine femoral or human saphenous veins. In vivo in a rabbit carotid vein graft model, 17 beta-estradiol administration did not affect the development of intimal hyperplasia but was associated with a higher rate of graft thrombosis. These data suggest that the effects of estrogen on veins differs from the effects reported in arteries. These differences were seen both in vitro in veins taken from their normal location and in vivo in veins placed in the arterial circulation.     

Arterialization of reversed autogenous vein grafts: quantitative light and electron microscopy of canine jugular vein grafts harvested and implanted by standard or improved techniques

To provide sequential, quantitative analysis of the cellular events occurring in reversed autogenous vein grafts after implantation and potential modifications of these events, two groups of veins were evaluated. Veins prepared by standard techniques of unmonitored pressure distension with cold heparinized saline solution, tributary ligation adjacent to the wall, and storage at 4 degrees C were morphometrically compared with veins harvested by means of a modified protocol of papaverine irrigation, tributary ligation away from the graft wall, pressure distension to 100 mm Hg with heparinized blood containing papaverine at body temperature, storage in identical solution at 4 degrees C, and implantation while distended. Unilateral jugular veins harvested from dogs with the modified technique (IRJV,N = 9) or standard technique (SRJV,N = 9) were implanted into carotid arteries, retrieved at 30 minutes, 2 days, and 10 days postoperatively along with the contralateral control vein after perfusion fixation in situ, and examined microscopically to quantitate intimal-medial thickness and endothelial damage (denudation and ultrastructural alterations). All IRJVs remained endothelialized, whereas SRJVs had 19% and 40% endothelial denudation at 30 minutes and 2 days, respectively, as well as massive neutrophil, platelet, and monocyte involvement. In contrast, IRJVs had only a modest infiltration of monocytes beginning early after implantation and culminating in their localization beneath endothelial cells; these endothelial cells increased in number during the 10-day period. Although SRJVs exhibited nearly complete reendothelialization over the luminal surface of macrophages by 10 days, endothelial damage was consistently higher than that of IRJVs at all periods and intimal-medial thickness was significantly greater at 10 days (65 +/- 0 vs. 57 +/- 0 micron, respectively; p less than 0.001). These findings suggest that endothelial preservation with improved harvesting techniques inhibits thrombosis and limits wall thickening and also that macrophages may play a protective role by promoting endothelial proliferation.     

Histologic fate and endothelial changes of distended and nondistended vein grafts.

Sixty-two autogenous cephalic vein segments were grafted into the femoral arteries of 31 mongrel dogs, the left side receiving non-distended (control) grafts and the right side distended (experimental) grafts. Distending media were heparinized blood and saline. Veins were distended at 600 mm Hg for 2 minutes. Specimens were taken at intervals from 15 minutes to 3 months, and were studied by gross inspection, surface observations (light scanning stereoscope to X70 scanning electron microscope to X6,000) and routine histologic techniques (light microscope to X 1000). In general, grafting of veins in the arterial system was followed by progressive degenerative changes in all layers of the vein, including endothelial cell involution, desquamation and re-endothelialization. Often a variable degree of subendothelial fibrous and/or myoepithelial proliferation occurred which might compromise even a lumen lined by healthy endothelium. Distention caused these changes to occur earlier (2-4 weeks) and to be more pronounced. Distention with saline caused more damage to the endothelium than did distention with blood. We conclude that preimplant distention of vein grafts (to overcome spasm) should be employed sparingly, as it adversely affects the endothelial covering of the flow surface, accelerates the development of degenerative changes, and may predispose the graft to early thrombotic complications.     

Effects of implanted Doppler flowmeters on femoral vein autografts.

Thirteen femoral vein autografts were placed into the corresponding ipsilateral femoral arteries of 8 mongrel dogs. Cuff-type Doppler (ultrasonic) flowmeters were placed around six of the grafts. None of the vessels thrombosed. Blood flow velocities were measured in all vessels up until the time of sacrifice (mean 95 +/- 5 days after surgery) or accidental death (one dog, 49 days after surgery). The only case of graft failure was attributed to infection at the flowmeter site. With this single exception, the vein grafts exhibited uniformity in histological appearance from dog to dog. These data suggest that implantation of properly designed Doppler flow transducers may have clinical applications. This technique permits continuous or intermittent assessment of blood flow characteristics through a graft without additional trauma or cost to the patient. It is free of the many inherent disadvantages of chronically implanted electromagnetic flowmeters and may negate the need in some instances for followup angiographic studies.     

Coronary bypass graft fate. Angiographic study of 1,179 vein grafts early, one year, and five years after operation

A total of 1,179 vein grafts were studied angiographically in 353 (45%) unselected survivors (male, mean age 45.5 years) of 786 coronary bypass operations. Studies were conducted early (0.96 months), 1 year (12.8 months), and 5 years (59.7 months) postoperatively. A previously described technique was used to grade the patency of the grafts, and a new technique was used to assess intimal irregularity, presumably caused by atherosclerosis; this new technique indicated both intimal surface distribution of disease and profile (relief or elevation). Ten percent, 17%, and 26% of grafts were occluded early, at 1 year, and at 5 years, respectively. Distal anastomotic defects were the commonest cause for low grades in the patency classification. Irregularities in patent grafts increased from 9% at 1 year to 42% at 5 years, with 11% of all the 1 year lesions and 20% of all the 5 year lesions having a high profile (more than 50% graft stenosis); of the lesions categorized as showing the widest surface spread, 17% were in high relief at 1 year and 34% at 5 years. Thus, the lesions we believed to be atherosclerotic proliferated in both surface spread and elevation. All severely diseased grafts at the 1 year study had been normal in outline early; 79% at the 5 year study had been disease free at 1 year. All newly occluded grafts at the 1 year study had been normal in outline and 82% had had good patency early; 78% of newly occluded grafts at the 5 year study had been disease free at 1 year and 77% had had good patency. Normal appearance of the intima in grafts studied at 1 year had no prognostic value for 5 year findings. However, 62% of all grafts with the appearance of intimal disease at 1 year showed deterioration by 5 years, and 28% were occluded. The differences between these outcomes are highly significant (p less than 0.0005). In conclusion, the appearance of intimal irregularity compatible with atherosclerosis in a coronary bypass graft 1 year after operation carried a poor prognosis for adverse angiographic change at 5 years. On the other hand, normally appearing intima at 1 year had no predictive valve for the 5 year study despite a generally better prognosis for nondiseased grafts.     

The evolution of morphologic and biomechanical changes in reversed and in-situ vein grafts.

A comparative study of experimental reversed (RV) and in-situ (INS) vein grafts with respect to the evolution of morphologic and compliance characteristics was done in a canine model. In addition, the compliance characteristics in a series of human INS vein grafts were recorded as a function of time after operation. At 6 months after implantation, all experimental grafts displayed well-developed intimal hyperplasia. There was no significant difference in either absolute intimal thickness (INS 0.133 +/- 0.09 mm vs. RV 0.085 +/- 0.06 mm; NS) nor in the percentage of the total wall thickness occupied by the intima when experimental INS grafts were compared with RV grafts after 6 months. Similarly, compliance values of INS and RV vein grafts were similar at all time intervals examined up to 6 months after operation. Thirty-three human INS vein grafts had a mean compliance value of 1.74 +/- 0.72 (percent radial changes per mmHg X 10(-2) at a median postoperative interval of 14 weeks. This value did not differ significantly from those measured in the INS vein grafts. Although all vein grafts examined retained their native viscoelastic properties, this study suggests that functioning human INS vein grafts are less compliant than previously suspected on the basis of prior ex-vivo and clinical studies of RV saphenous vein grafts. The purported clinical superiority of the INS vein graft cannot be explained on the basis of superior biomechanical performance or failure to develop intimal hyperplasia.     

Effects of different graft preparation techniques on the acute thrombogenicity of autologous vein grafts. An experimental study in sheep

The effects of different techniques of preparing autologous vein grafts on acute thrombogenicity have been studied in a sheep model. Storing grafts at room temperature or rinsing with different solutions seemed to be of minor importance, whereas distending them to a pressure of 400 mm Hg significantly reduced patency and increased platelet accumulation and thrombus formation.     

The value of vein graft surveillance in bypasses performed with small-diameter vein grafts

We assessed the impact of preoperative diameter of the venous conduit on reintervention rate and outcome following infrainguinal vein graft bypass. Consecutive infrainguinal vein bypasses between January 2001 and December 2006 were reviewed. All patients underwent preoperative measurement of vein graft diameter (VGD). Grafts were classified into those with VGD <3.5 mm and those with VGD > or =3.5 mm. All patients were enrolled in a duplex surveillance program. The association between VGD and reintervention rate was assessed. Graft patency and amputation rates were compared. There were 377 bypasses followed up for a median of 23 months (range 8-67). VGD was <3.5 mm in 139 grafts (36.9%) and > or =3.5 mm in 238 grafts (63.1%). A higher proportion of smaller vein grafts (32.3%) required reintervention to maintain graft patency compared with larger conduits (20.2%) (chi(2) = 7.7, p < 0.001). VGD (odds ratio [OR] = 2.87, 95% confidence interval [CI] 1.63-3.81; p < 0.001), smoking (OR = 1.83, 95% CI 1.39-3.20; p = 0.02), and type of bypass (OR = 1.86, 95% CI 1.49-2.47; p = 0.02) were variables associated with higher reintervention rate. There was no difference in graft patency (p = 0.13) or amputation rates (p = 0.35) between the two groups. Use of smaller vein grafts was associated with a higher reintervention rate. Provided that these grafts are surveyed and where necessary repaired, the use of smaller vein grafts is successful and expands the availability of autogenous conduit for infrainguinal arterial reconstruction.     

Biologic fate of valves in reversed and nonreversed arterial vein grafts

The cusps of valve-bearing segments of canine cephalic, femoral, and jugular veins were completely divided and were used in interposition grafts in the femoral and carotid arteries in the nonreversed position. Three control grafts had intact valves in the reversed position, and one control graft in the reversed position had division of the leaflets. Nine grafts were studied up to 2 months postoperatively with gross and microscopic observations. The cusp tissue, which shrinks immediately after complete division, disappears very early in the postoperative period in the reversed and nonreversed positions. Two reversed intact valves were still grossly microscopically normal 5 and 7 weeks postoperatively. The complete disappearance of the divided valve with a nonreversed coronary graft 101/2 months postoperatively has been documented at autopsy for the first time in a human subject. The significance of these findings and the superiority of the valveless nonreversed autogenous vein graft in clinical cardiovascular surgery has been discussed.     

Management of infected lower extremity autologous vein grafts by selective graft preservation.

Between 1975 and 1991, we treated 16 patients with infected lower extremity autologous vein grafts performed for limb salvage by complete graft preservation. Traditional treatment of these infections includes immediate graft excision and complex revascularization procedures to prevent limb loss. The infection involved an intact anastomosis in 12 patients or the body of a patent graft in 4 patients. None of the patients was systemically septic. All patients were treated with appropriate intravenous antibiotics. Six patients were treated by placement of autologous tissue on the exposed graft (4 rotational muscle flaps, 2 skin grafts), and 10 were treated with antibiotic-soaked dressing changes and repeated operative débridements to achieve delayed secondary wound healing. This treatment resulted in a 19% (3 of 16) mortality rate and an 8% (1 of 13) amputation rate in survivors. Of the six patients managed by autologous tissue placement onto the infected graft, five patients had wounds that healed without complications, and one died of a myocardial infarction. Of the 10 patients treated by delayed secondary wound healing, 2 developed anastomotic hemorrhage, which resulted in death in 1 patient and above-knee amputation in the other, 1 died of a myocardial infarction, 1 developed graft thrombosis, and 6 had wounds that healed. Placement of autologous tissue to cover an exposed, infected patent vein graft with intact anastomoses may prevent graft dessication, disruption, and thrombosis, which renders graft preservation an easier, safer method of treatment compared with routine graft excision.     

Long-term fate of the internal mammary artery and saphenous vein grafts

Thirty-four patients, each receiving internal mammary artery (IMAG) as well as saphenous vein grafts (SVGs), returned with symptoms 3 to 12 years after operation and underwent angiographic studies. At a mean follow-up period of 6.8 years, two (6%) IMAGs were occluded and 33 (94%) were in excellent condition. Of the 57 SVGs, 28 (48%) were totally occluded, 12 (22%) had severe atherosclerosis, and only 17 (30%) were in good condition. Seven patients (20%) had new significant lesions in the ungrafted coronary arteries. Failure of SVGs was the predominant cause of symptoms in this group of patients. Late failure of the SVGs appears to be due to progressive atherosclerosis in the grafts. The IMAGs tend to remain free from atherosclerosis and perform much better than the SVGs in the long run.     

Femorodistal vein grafts: The utility of graft surveillance criteria

Purpose: This retrospective review of femorodistal vein grafts was analyzed to determine the usefulness of various graft surveillance criteria.Method: The surveillance schedule involved evaluations at 1 month, every 3 months the first year, and then every 6 months. Salvage intervention or graft occlusion occurring within the next follow-up interval defined surveillance end points. One hundred two grafts (329 surveillance visits) had an ankle/brachial index (ABI). A duplex scanning – determined midgraft peak systolic flow velocity (PSFV) was available for 81 grafts (262 visits). Forty-eight grafts (137 visits) had both a PSFV and entire graft duplex scanning (EGDS) to determine stenosis greater than 50%, whereas 40 grafts (91 visits) had simultaneous ABI and EGDS.Results: When a greater than 15% decrease in ABI denoted an abnormal surveillance study result, a positive predictive value (PPV) of 24.3% and negative predictive value of 94.5% were noted. Similarly, a PSFV cutoff of less than 35 cm/sec demonstrated values of 26.3% and 94.2%, respectively. When an EGDS of greater than 50% stenosis or a PSFV of less than 35 cm/sec were the cutoff criteria, the PPV was 36.7% and negative predictive value 99.1%, whereas characterizing abnormal results further with ABI (>15%↓) increased the PPV to 83.3%.Conclusion: The combination of an EGDS, midgraft PSFV, and ABI provides optimal follow-up for our patients with a femorodistal vein graft. (J V ASC S URG 1995; 21:127-34.)     

Intimal integrity and fibrinolytic potential of reversed and in situ vein grafts

The improved patency rates of in situ vein grafts are attributed to better flow characteristics, anastomotic "fit," and intimal preservation. This study compared the early changes in intimal morphology and fibrinolytic activity of in situ and reversed vein bypass grafts from mongrel dogs. Four to six centimeter in situ and reversed vein segments were used to bypass left and right femoral and internal carotid arteries, respectively. Heparin (100 U/kg) was administered before arterial clamping. Anastomoses were fashioned end to side and the intervening artery was ligated. Fifty-two grafts were harvested at day 1 (12 grafts), day 7 (16 grafts), day 14 (12 grafts), and 12 weeks (12 grafts). The veins were analyzed for histologic changes by light microscopy and scanning electron microscopy. The fibrinolytic activity of the grafts was assayed by the fibrin slide and fibrin plate techniques. There were no significant differences in morphology or fibrinolytic activity between the reversed and in situ grafts at any time period. These findings indicate that the improved patency rates associated with in situ grafts are not dependent on improved preservation of intimal structure or fibrinolytic activity.     

Vascular graft infection: an analysis of sixty-two graft infections in 2411 consecutively implanted synthetic vascular grafts

Among 2411 consecutive arterial reconstructions performed with synthetic prosthetic material in Denmark during a 4-year period, 62 patients (2.6%) developed graft infection. Graft infection occurred only when the groin had been incised. The incidence of infection and the spread of infection along the graft did not relate to the graft material used (Dacron velour, Dacron woven, polytetrafluoroethylene, and umbilical vein). Retrospective analysis disclosed predisposing or precipitating factors in 50 of the 62 cases; the most important seemed to be unsatisfactory surgical technique. Fifty-three percent of the graft infections occurred within 30 days. Gram-positive cocci were the most common pathogen. The 62 patients had been in the hospital for a mean of 90 days and had undergone an average of 1.4 operations for graft infections. Of the patients, 25.8% died and 30.6% underwent amputations. Vascular graft infection is still one of the major problems in vascular surgery; greater care should be taken to improve antiseptics, improve surgical technique, and establish a rational prophylactic antibiotic regimen. A prophylactic antibiotic regimen of a combination of cephalosporin and ampicillin is recommended.     

Bacteremic infectability of vascular grafts: the influence of pseudointimal integrity and duration of graft function.

This report describes an experimental study in which dogs with prosthetic graft replacement of the infrarenal abdominal aorta were challenged at progressive time intervals following graft placement with a single intravenous infusion of Staphylococcus aureus in order to determine the duration of susceptibility to graft infection of bacteremic origin. The results demonstrate that the susceptibility of a prosthetic graft to infection by bacteremic seeding virtually was 100 percent up to 1 month following graft placement. The incidence of infection then began to progressively drop but never was eliminated as demonstrated by a 30 percent incidence of graft infection in dogs so challenged 1 year graft placement. Careful scrutiny of the intimal surface of the harvested grafts, 3 weeks following bacteremic challenge, revealed that all grafts in which the pseudointimal coverage was complete were insulated effectively from infection by bacteremic seeding in that their cultures were negative. All grafts that had positive cultures for Staphylococcus aureus were noted to have either an incomplete or absent pseudointimal lining.