Prosthetic Vascular Graft Research Articles

Development of prosthetic vascular graft covered with autogenous canine endothelial cells—Basic research

Development of prosthetic vascular graft covered with autogenous canine endothelial cells—Basic research

Endothelial linings in prosthetic vascular grafts.

Endothelial linings in prosthetic vascular grafts.

Improved patency of collagen-impregnated grafts after in vitro autogenous endothelial cell seeding.

Currently available prosthetic vascular grafts remain sufficiently thrombogenic to preclude their use as small-caliber arterial substitutes. However, thrombogenicity may be significantly reduced by the presence of an endothelial monolayer on the luminal surface. The present study was undertaken to test the efficacy of lining a small-caliber prosthesis with autogenous endothelial cells in vitro so that the graft may subsequently be implanted with an established confluent endothelial lining. For this purpose, cells were obtained from canine external jugular vein, harvested enzymatically, and passaged in culture. Dacron grafts (4 X 150 mm) were then seeded in vitro and maintained for 48 to 72 hours before implantation in the femoral position of the same animal. Seeded grafts were implanted contralateral to unseeded control grafts and explanted after 1 month. Seeded grafts demonstrated an 86% patency rate at explanation in contrast to the significantly lower 14% patency rate of the unseeded control grafts. This study justifies further investigation directed toward the feasibility of endothelializing intravascular prostheses in vitro before implantation.

Improved patency of collagen-impregnated grafts after in vitro autogenous endothelial cell seeding

Currently available prosthetic vascular grafts remain sufficiently thrombogenic to preclude their use as small-caliber arterial substitutes. However, thrombogenicity may be significantly reduced by the presence of an endothelial monolayer on the luminal surface. The present study was undertaken to test the efficacy of lining a small-caliber prosthesis with autogenous endothelial cells in vitro so that the graft may subsequently be implanted with an established confluent endothelial lining. For this purpose, cells were obtained from canine external jugular vein, harvested enzymatically, and passaged in culture. Dacron grafts (4 × 150 mm) were then seeded in vitro and maintained for 48 to 72 hours before implantation in the femoral position of the same animal. Seeded grafts were implanted contralateral to unseeded control grafts and explanted after 1 month. Seeded grafts demonstrated an 86% patency rate at explanation in contrast to the significantly lower 14% patency rate of the unseeded control grafts. This study justifies further investigation directed toward the feasibility of endothelializing intravascular prostheses in vitro before implantation.

Primary graft infections

An amputation rate of 8% to 52% and a mortality rate of 13% to 58% make vascular prosthetic graft infections the most dreaded complication facing a vascular surgeon. In 1978 a randomized prospective double-blind study reported a statistically significant decrease in wound infections in patients treated with prophylactic antibiotics whereas the graft infection difference only approached statistical significance. The present study reviews 2614 arterial prosthetic grafts implanted from January 1975 through June 1986. Twenty-four patients were identified as having a prosthetic graft infection, yielding an overall infection rate of 0.92%. Staphylococcus aureus was the most common organism, occurring in one third of the cases. The most common graft material was polytetrafluoroethylene (PTFE) (33%) followed by Dacron (29%), composite PTFE and Dacron (20%), and umbilical vein grafts (9%). Diabetes was a common factor in one third of the patients. Symptoms of infection were present in 15 patients (63%) within 3 months of operation, with 11 patients showing symptoms within 30 days. The longest interval between operation and onset of symptoms was 48 months. Prophylactic antibiotics were administered to 22 of the 24 patients, but in only 7 of the 22 (29.5%) were they given according to our usual practice. All patients required removal of the infected prosthesis, with limb loss in 17% and death in 17%.

The 111In-granulocyte scan in prosthetic vascular graft infections: imaging technique and results.

Fourteen patients were examined between 3 weeks and 11 years after implantation of an aortobifemoral vascular graft with 111In labelled leukocytes isolated with discontinuous gradient centrifugation. The camera acquisition was performed with a three phase technique (acquisitions at 30 min, 4 h and 24 h p.i.). The presence and extent of a graft or perigraft infection including complicating fistulas could be correctly diagnosed in six of eight patients with surgically proven infections. Leukocyte uptake index was calculated as 1.77 +/- 0.4 (30 min p.i.) and 2.4 +/- 0.7 (24 h p.i.). All infections could be diagnosed by 30 min p.i., fistulas only could be seen 24 h p.i. In two of eight patients, false positive results were observed. These patients suffered from suspected perigraft hematomas and noninfected aortic graft aneurysms. Both had a negative 30 min scan and a slight uptake in the late scans comparable to bone marrow activity. Six patients with fever of unknown origin showed true negative scans. There were no false negative scans. We conclude that only the leukocyte scan can diagnose the presence and the extent, including fistulas, of vascular graft infections. The three phase technique is recommended to localize the blood pool in the 30 min scan and to diagnose complications 24 h p.i. In cases of a negative 30 min scan and positive 4 h and 24 h scans, false positive results should be suspected. All infections have a leukocyte uptake index higher than 1.2.

Endothelial linings: The effect of serine protease inhibition

The purpose of this investigation was to determine if the inhibition of the serine proteases, thrombin and plasmin, by heparin and ϵ-aminocaproic acid (EACA) would improve endothelial cell retention on synthetic grafts. Endothelium was harvested from the external jugular veins of mongrel dogs using an enzymatic technique. The cells were grown in tissue culture for 3–4 weeks, labeled with 111In oxine, inoculated (2000 cells/mm 2) into fibronectin-coated 4 mm-diameter tubes of polyester eleastomer (PE, Hytrel 4056, DuPont), and cultured for 18 hr. Each animal received iv heparin (100 U/kg) prior to implantation, and a 4 × 30-mm segment of the culture-lined PE was interposed in the dog's own carotid artery. After 6 hr of flow the grafts were perfusion fixed; the percentage of endothelial retention was determined by 111In counting, and the surfaces of the grafts were analyzed by scanning electron microscopy. Six experiments were performed in each of three treatment groups. Animals in Group I received no additional drugs. Group II animals received a continuous infusion of heparin at 30 U/kg/hr. Group III animals received a bolus of 200 mg/kg of EACA with the initial heparin dose and a continuous infusion of heparin at 30 U/kg/hr and EACA at 200 mg/kg/hr. Group I grafts retained an average of 36.1 ± 23.3% of the cells; Group II retained 67.5 ± 24.9%; and Group III retained 83.4 ± 9.8%. Although continuous heparin infusion resulted in a trend ( P = 0.067) toward better retention, a combined infusion of heparin and EACA resulted in significantly better retention ( P = 0.002.) We conclude that a combination of serine protease inhibitors improves cell retention on endothelium-lined prosthetic vascular grafts.

Glycocalyx Enhances Prosthetic Vascular Graft Infection

AbstractCoagulase-negative staphylococci are major pathogens in prosthetic implant infections, and the capability of certain strains to produce glycocalyx enhances their infectivity. We investigated the importance of glycocalyx in an animal model of prosthetic vascular graft infection. Coagulasenegative staphylococci (5×108) and 1 cm2pieces of Dacron or polytetrafluoroethylene (PTFE) grafts were placed in subcutaneous pockets of adult Sprague-Dawley rats. Two strains of bacteria were used, one producing and the other not producing glycocalyx. At 5 days, uninfected grafts were incorporated into the surrounding tissues whereas infected grafts were surrounded by fluid. Grafts were excised and adherent bacteria dislodged by sonication and quantitated. Scanning electron microscopy confirmed the presence of bacteria and glycocalyx, and the efficiency of bacterial dislodgement by sonication. The bacterial adherence (CFU/cm2mean ± SE) of glycocalyx-producing staphylococci was 3.7±1.1×107and 3.5±1.0×105to Dacron and PTFE, respectively (both < 0.05). Nonglycocalyx producing bacteria had decreased adherence to both Dacron (1.4±0.8×104) and PTFE (0.9±0.4±104). Antibiotic administration reduced the adherence of the nonglycocalyx producing strain by one log to both materials (p<0.05) but did not affect the glycocalyx-producing strain. These data demonstrate that glycocalyx production enhances the adherence of coagulase-negative staphylococci to prosthetic vascular graft materials. Prophylactic antibiotic administration does little to inhibit the adherence of glycocalyxproducing bacteria but does affect nonglycocalyx producing strains.

111 In-labeled leukocytes in the detection of prosthetic vascular graft infections.

Making a clinical diagnosis of infection in prosthetic vascular grafts is difficult but when undiagnosed, this condition has a high mortality rate. Using Indium-111-labeled white-blood cells, 30 scans were performed in 21 patients suspected of having a prosthetic graft infection. The diagnosis of infected graft was confirmed by surgery in all cases, and lack of infection was established by resolution of symptoms with conservative therapy. Twenty-four hour scans of autologous Indium-111 leukocytes were obtained, and correlative CT studies were done in 11 cases. There were 13 infected grafts at surgery (purulent material present), and scans were positive in all (100% sensitivity); of 17 scans, there were 15 true negatives and two false positives (88% specificity). Using the criteria of gas or fluid around the graft, the sensitivity of CT was only 37% in a small subset of these patients. One-half of the cases in which infection was suspected clinically had no infection and had negative scans. Various types of grafts and graft materials were used, and there was no correlation with presence or absence of infection on the basis of the type of graft. Extragraft infection sites were found in five patients. In conclusion, use of Indium-111 leukocytes has been found to be an accurate and valuable diagnostic method for evaluation of suspected prosthetic vascular graft infection, and to have higher diagnostic accuracy than CT.

Bacterial adherence to vascular prostheses: A determinant of graft infectivity

An in vitro model was developed to quantitatively measure bacterial adherence to the surface of prosthetic vascular graft material. Four strains of bacteria (Staphylococcus aureus, nonmucin-producing S. epidermidis [SP-2], mucin-producing S. epidermidis [RP-12], and Escherichia coli) were used to inoculate expanded polytetrafluoroethylene (cPTFE), woven Dacron, and velour knitted Dacron graft material. After graft specimens were incubated in a 107 suspension of bacteria, they were washed to remove nonadherent organisms and ultrasonically oscillated to dislodge adherent organisms. Quantitative culture of the sonication effluent was used to calculate bacterial adherence, expressed as the number of colony-forming units found in each square centimeter of graft material per 107 inoculum. All bacterial strains had a greater affinity to velour knitted Dacron graft than to ePTFE (p < 0.025). E. coli and S. aureus adhered to velour knitted Dacron in greater numbers than to woven Dacron (p < 0.04). The production of extracellular polysaccharide (mucin) by the RP-12 strain significantly increased adherence to both ePTFE and Dacron grafts compared with the other three bacterial strains tested (p < 0.04). Although E. coli was less adherent to ePTFE than nonmucin-producing staphylococcal strains (S. aureus and SP-2), no difference in adherence to knitted or woven Dacron graft material was demonstrated. The differential adherence of bacteria to prosthetic vascular grafts pays an important role in the pathogenesis of graft sepsis and determines relative graft infectivity. The in vitro model developed is well suited for further study of the mechanisms by which bacteria adhere to and colonize vascular grafts.

On the correlation between the failure of vascular grafts and their structural and material properties: a critical analysis.

A statistical investigation of reported vascular graft failures over a period of 30 years is undertaken. The most important causes of graft failure are underlined, as well as the time to failure and relative frequency of each failure mechanism. This brings out the need for a critical review of the properties of basic textile structures used in today's vascular prosthetic grafts. The physiologic and structural factors which contribute to mechanical failure of arteries and artery/implant composite systems are analyzed. The importance of obtaining the complete set of time-dependent elastic constants of the artery--which is viewed as an anisotropic material--is pointed out. Future research areas important for characterizing the mechanical behavior of artery/implant systems are suggested, with the aim of establishing rational standards for prosthesis evaluation.

Morphology of Healing in Vascular Prostheses

Vascular grafts differ in shape and size, material, mode of construction, and porosity. The latter was found to be of great importance with respect to tissue response of the host to the graft. The first reaction of the host after implantation represents the phase of exsudation. An aggregate of platelets and fibrin will cover most of the luminal and external surface of the graft, which is also seen between the interstices. The following phase of resorption develops within 2 weeks. It is characterized by replacement of the fibrinous material on the outer surface and between the interstices by capillaries, histiocytes, and myofibroblasts. Organisation of the outer capsule will then occur, and is also seen inside the transprosthetic bridges within one month. However, organization of the luminal lining remains very slow and is almost never completed. Healing depends on blood flow and local hemodynamic factors, and a mismatch in mechanical properties between the graft and host vessel may be important. Sources of endothelium in graft healing are anastomotic sites, pluripotent cells growing through the graft wall or deposition of pluripotent cells from the blood. Early failure of a prosthetic vascular graft occurs mainly as a result of separation at its sites of attachment. Late complications may be the result of mechanical failure (anastomotic sites or within the graft), kinking, inadequate or incomplete healing, and infection. The incidence of infectious complications varies from 0.25% to 6.0%, usually associated with high mortality rates.

The effect of fibronectin coating on endothelial cell kinetics in polytetrafluoroethylene grafts.

Despite the proven experimental success of endothelial cell seeding of prosthetic vascular grafts, the process has not been widely accepted for clinical use because of its complexity and the need for a relatively large length of autologous vein to provide the requisite number of cells. Using autologous endothelial cells radiolabeled with indium 111-oxine, we studied the effect of fibronectin coating of polytetrafluoroethylene grafts in a canine carotid interposition model on initial endothelial cell adherence and subsequent cell retention for up to 72 hours following restoration of blood flow. Since the number of harvested endothelial cells varied widely depending on the diameter and length of available vein, cellular adherence was best expressed as a percentage of the original cell harvest. More than twice as many (46.7% vs. 19.8%) endothelial cells initially adhered to fibronectin-coated grafts compared with uncoated control grafts. Fibronectin did not appear to influence the loss of cells within the first 30 minutes following restoration of blood flow. However, over the next 24 hours, it clearly reduced the mean cell loss from 3.7%/hr to 2.2%/hr and resulted in a sixfold increase (21.3% vs. 3.4%) in the number of retained cells at the end of a 24-hour period. When the endothelial cell preclot was performed with a solution of culture medium 199, as opposed to heparinized whole blood, there was no significant difference in endothelial cell retention.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of fibronectin coating on endothelial cell kinetics in polytetrafluoroethylene grafts

Despite the proven experimental success of endothelial cell seeding of prosthetic vascular grafts, the process has not been widely accepted for clinical use because of its complexity and the need for a relatively large length of autologous vein to provide the requisite number of cells. Using autologous endothelial cells radiolabeled with indium 111-oxine, we studied the effect of fibronectin coating of polytetrafluoroethylene grafts in a canine carotid interposition model on initial endothelial cell adherence and subsequent cell retention for up to 72 hours following restoration of blood flow. Since the number of harvested endothelial cells varied widely depending on the diameter and length of available vein, cellular adherence was best expressed as a percentage of the original cell harvest. More than twice as many (46.7% vs. 19.8%) endothelial cells initially adhered to fibronectin-coated grafts compared with uncoated control grafts. Fibronectin did not appear to influence the loss of cells within the first 30 minutes following restoration of blood flow. However, over the next 24 hours, it clearly reduced the mean cell loss from 3.7%/hr to 2.2%/hr and resulted in a sixfold increase (21.3% vs. 3.4%) in the number of retained cells at the end of a 24-hour period. When the endothelial cell preclot was performed with a solution of culture medium 199, as opposed to heparinized whole blood, there was no significant difference in endothelial cell retention. Assuming that such increases in seeding density will result in more rapid growth to confluence of the endothelial layer, pretreatment with fibronectin may shorten the period during which grafts remain vulnerable to thrombosis and infection and may significantly reduce the length of autologous vein necessary to seed a given length of prosthesis.

Prosthetic vascular graft, its present situation and problems to be solved in future

Prosthetic vascular graft, its present situation and problems to be solved in future

Are seeded endothelial cells the origin of neointima on prosthetic vascular grafts?

Although endothelial cell seeding has been demonstrated to be effective in producing uniform endothelial coverage on prosthetic grafts, no one has demonstrated that the seeded cells are the genetic precursors of the endothelial cells that ultimately line the graft. This study was performed to determine whether seeded endothelial cells were the source of the neoendothelial surface on Dacron vascular grafts implanted in the pig. Eight pairs of littermate male and female pigs were selected at birth and allowed to grow until their weight reached 20 to 25 kg. Endothelial cells were enzymatically harvested from the jugular vein of the female siblings and seeded onto 8 mm diameter grafts, 25 cm in length. The grafts were then implanted as a thoracoabdominal bypass into the male siblings. Seven other randomly selected pigs of similar size (four males and three females) had thoracoabdominal bypass with similar grafts, which were preclotted with autologous blood only, but not seeded. After 4 weeks, grafts in both groups were covered with a neointima that was more than 90% thrombus-free. The graft surface cells were grown in culture and were documented to be endothelium. Chromosome analysis demonstrated that the surface cells on the seeded grafts were from the male host and did not originate from the donor female cells. We conclude that seeded endothelial cells are not the source for the neointima on Dacron grafts in the porcine model. In addition, we have again documented that spontaneous endothelial coverage of grafts does occur without endothelial seeding.

Are seeded endothelial cells the origin of neointima on prosthetic vascular grafts?

Are seeded endothelial cells the origin of neointima on prosthetic vascular grafts?

Mucin production by Staphylococcus epidermidis. A virulence factor promoting adherence to vascular grafts.

The production of an exopolysaccharide (mucin) by some Staphylococcus epidermidis strains facilitates bacterial adhesion to prosthetic vascular grafts and may play an important role in adherence-mediated growth. An in vitro model was developed to measure the differential adherence of mucin-producing (RP-12) and nonmucin-producing (SP-2) S epidermidis strains onto expanded polytef and velour knitted Dacron graft material. After incubation in a 10(7)/mL suspension of organisms, graft specimens were repeatedly washed to remove nonadherent organisms and then sonicated to dislodge adherent organisms. Bacterial adherence was calculated from a quantitative culture of the sonication effluent. Both S epidermidis strains adhered in ten to 100 times greater numbers to the knitted Dacron graft material than to expanded polytef. The production of an exopolysaccharide by the RP-12 strain significantly increased adherence to both graft types compared with the SP-2 strain. The increased adherence of the RP-12 strain was inhibited by adding D-mannosamine to the inoculum. The in vitro model developed is well suited for further study of the mechanisms by which bacteria adhere to and colonize vascular grafts.

Prosthetic Graft Infections: A Review of 720 Arterial Prosthetic Reconstructions

Six-hundred-and-three patients who underwent 720 vascular prosthetic graft operations caudal to the diaphragm were studied retrospectively. Wound complications appeared in 99 patients. Prophylactic antibiotics were not used. Serous secretion was found after 27 arterial graft procedures (3.8%), superficial wound infection after 41 (5.7%), and prosthetic graft infection after 31 (4.3%). Of the 31 patients with prosthetic graft infection, 10 recovered (32%). Four of these patients recovered after removal of the Staphylococcus aureus-infected prosthesis. Three received a replacement prosthesis with systemic antibiotic treatment and closed antibiotic irrigation, and one patient's prosthesis was replaced with an autologous vein graft with antibiotic treatment. Twelve patients (39%) underwent amputation and 9 died. The frequency of graft occlusion was greater when the prosthesis was infected with Staphylococcus aureus than with other microorganisms. The aggressive approach used in the 4 above-mentioned cases could be a treatment modality in prosthetic graft infection with Staphylococcus aureus, especially because of the high incidence of graft occlusion associated with these microorganisms.

Mycotic pseudoaneurysm of an aortic bypass graft and contiguous vertebral osteomyelitis due to aspergillus fumigatus

Fungal osteomyelitis is rare in patients who are not immunocompromised. This report documents that Aspergillus vertebral osteomyelitis may, however, be associated with infection of an adjacent prosthetic vascular graft in the absence of overt immunosuppression. A 73-year-old man is described with a mycotic pseudoaneurysm of a Dacron aortic bypass graft and contiguous vertebral osteomyelitis due to Aspergillus fumigatus. The patient was successfully treated with resection of the infected graft and administration of amphotericin B in a total dose of 2 g. Infection may have occurred intraoperatively as a result of inoculation with airborne fungal elements.