Processes human umbilical veins as arterial substitutes--evaluation in canine models.

Human umbilical cord vein segments have been used as vessel substitutes for damaged or occluded arteries, as aorto-coronary by-passes and as arterio-venous fistulae for dialysis. The Dardik-Biograft fixed with glutaraldehyde and the Mindich-Bioflow, fixed with ethanol and dialdehyde starch, are commercially available. They were implanted in dogs as replacements for a segment of the abdominal aorta. Post-implantation status was followed by angiography. They were evaluated after removal from sacrificed animals with the aid of scanning electron microscopy and histological techniques. Attention was focused on vessel patency, dimensional stability, integrity of the anastomosis line, lumen wall microstructure, evidence of suture damage and thrombus deposition pattern. Both types of grafts gave functional by-passes for at least until 6 months post-implantation. The Dardik-Biograft appeared more prone to thrombus formation near the anastomosis. Sparse cellular development was also noted. The Mindich-Bioflow gave rise to a prosthesis of superior thromboresistance which was more subject to mechanical damage.

[The Sparks-Mandril arterial prosthesis. An ingenious concept, a total failure. What can we learn from it?]. / Le Sparks-Mandril comme prothèse artérielle. Un concept ingénieux, un échec complet. Que faut-il en retenir?

In spite of its ingenuity, the Sparks-mandril concept has failed to generate a satisfactory arterial substitute. Pathological analysis of prostheses retrieved from humans and explanted from dogs as part of a controlled laboratory study has demonstrated that the tissue laid down during the autogenous generation stage contains neither elastin fibers nor smooth muscle cells capable of providing the required dimensional stability of a blood vessel. The supporting polyester mesh tube has been found to stretch in vivo, resulting in dilation and lengthening of the prosthesis and the formation of aneurysm and thrombosis. It is recommended that the use of devices relying on the Sparks-mandril concept not to be reintroduced until such time as the mechanism of growth promoting factors for angiogenesis are fully understood.

[Polyethylene terephtalate (Dacron) prostheses as arterial substitutes. Value of commercial grafts as abdominal aorta substitutes in the dog (author's transl)]. / Les prothèses en polyéthylène téréphtalate (Dacron) comme substituts artériels. Evaluation des greffes commerciales comme substitutes de l'aorte abdominale de chiens.

Most of the presently available Dacron fabric grafts are either woven or knitted; some are velours. Whereas the various configurations and textures can be easily recognized and classified with respect to morphology, structure, porosity and fabric tenacity, it is also necessary to establish their post-implantation healing characteristics. Canine models have been used to investigate the healing characteristics of 18 types of prostheses over implantation periods from one to six months using techniques of scanning electron microscopy and conventional light microscopy. Velours exhibit superiar tissue ingrowth but the internal tissue lining does seldom embeds all of the fibres. Complete neoendothelialization is not achieved; the process appears more closely linked to haemodynamic factors such as shear forces acting postfacto on blood deposits as opposed to graft porosity facilitating ingrowth. More meaningful criteria of performance must be found to allow a closer matching between the available products and the individual clinical needs of each situation.

[Ruptured abdominal aortic aneurysm: long-term survival]. / Anéurysmes de l'aorte abdominale rompus: survie à long terme.

Despite technological improvement, surgery for ruptured aortic abdominal aneurysm (AAA) only gets about 50% of patients to survive past the operative period. This series addresses the long-term outcome of those survivors. Eighty consecutive patients operated on for ruptured AAA between January 1983 and June 1990 at l'hôpital du Saint-Sacrement by three vascular surgeons, were studied and compared to 279 patients submitted to elective aneurysm surgery during the same period. The operative mortalities were respectively of 45% (ruptured) and 6.1% (elective). Five year survivals added up to 30 and 68%. When the 5 year survivals were recalculated, including only patients who were discharged from hospital, we found no statistically significant difference (p greater than 0.05) between the ruptured (55%) and the elective groups (68%). Data from this series demonstrate that long-term survival of patients undergoing ruptured AAA surgery is good and compares with that of AAA elective surgery. Therefore, aggressive treatment of ruptured AAA remains justified.

[Experimental staphylococcal colonization of a Dacron arterial prosthesis (author's transl)]. / Colonisation expérimentale d'une prothèse artérielle en Dacron par un staphylocoque.

Infection is certainly the most dramatic complication of reconstructive vascular surgery, even after long periods following the operation. A hematogenous mechanism is often implicated in late infections ; colonization of an arterial graft appears to depend on the material used and cicatrization processes. Animal studies have the disadvantage of requiring repeated operations. We have developed an in vitro infusion system in order to reproduce the bacteremic phenomenon, and to study the conditions necessary for colonization by a staphylococcus of a textile prosthesis (Dacron) in velvet, placed in the "Ex vivo" circulation of a dog for 2 hours. The prosthetic material is colonized very much more easily than a fragment of aorta used a control. The bacterial deposit (y) is a linear function of the inoculum (x) and, by approximation, y = 10(4) x (p 0.01). Colonization is independent of the infusion rate when this varies between 5 and 20 cm/sec. The reproducibility of the results, their quantification, and the ease with which these tests can be employed suggest that such models could be used to assess resistance to bacterial colonization of various materials used for arterial substitution.

[Glutaraldehyde - fixed human umbilical cord vein as a small diameter arterial substitute. Experimentation on the monkey]. / La veine ombilicale humaine traitée au glutaraldéhyde comme substitut artériel de petit diamètre. Expërimentation sur le singe.

Autologous saphenous veins, the preferred substitute material for aorto-coronary, femoro-popliteal and femoro-tibial by-pass, are usable in only 70% of individuals in need of such procedures. The development of small diameter substitute arteries is therefore essential to broaden the pool of patients who could benefit from this class of cardiovascular surgery. Existing substitutes, however, present major difficulties and have had limited success. In this laboratory, an attempt has been made to develop a vessel of 3 millimetres or less in diameter derived from human umbilical cord processed in glutaraldehyde. This substitute can be stored in 45% ethanol or dessicated by critical point drying. This device had been implanted as a segment of abdominal aorta in eight primates (Macaca fascicularis). Preliminary results are disappointing. The indicate that retention of a patency for more than a year post-implantation is difficultly achievable and that connective tissue hyperplasia leading to occlusion at the anastomoses is a major problem. Similar but larger diameter by-passes in the order of 6-8 millimetres should be investigated in greater detail, in order to better establish the "in-vivo" behavior of this class of tissue prosthesis. This would address the more fundamental issues pertaining to the clinical usefulness of fixed biological tissue by-pass devices.

[On preclotting of woven Dacron vascular prostheses (author's transl)]. / La précoagulation des prothèses vasculaires en Dacron tissé.

The role and the clinical value of common protocols of preclotting for a woven Dacron vascular prosthesis have been investigated. A comparative study of blood loss was carried out for Standard Woven De Bakey protheses inserted in a specially constructed extracorporeal blood circuit with canine models. The system detected transport of blood across the wall of the prostheses. These measurements were supplemented by gravimetric assessment of blood clot density and scanning electronmicroscopy examination of the internal surfaces of the prostheses. The pre-operative protocols investigated included : absence of pre-treatment, precoagulation with anticoagulant-free blood and various techniques using heparinized blood subsequent to an initial blood contact (modified method of Sauvage). The effect of using heparinized animals was also investigated. Leakages in unclotted prostheses could be reduced almost five fold by any precoagulation technique. Heparinization did not cause a significant increase in leakage and considerably improved the quality of the newly deposited blood product lining on the prostheses which consisted almost entirely of fibrin and eliminated any embolization.

[Evaluation of two commercial bovine vascular heterografts (author's transl)]. / Evaluation de deux hétérogreffes bovines commerciales pour le remplacement vasculaire.

Two commercially available grafts made from chemically modified bovine carotif arteries, Artegraft (Surgikos Corp. U.S.A.) and Solcograft (Solco A.G. Switzerland), were evaluated. Preliminary evaluation indicates that these products compare favorably with other more common chemically treated grafts of biological origin. Morphological characteristics, inflammatory response and thrombogenic potential were measured. Their structure suggest that each of the processes conserve the collagen morphology of the media and the adventitia originally present in the precursor arteries. Test implantations in dogs reveal a tendency to undergo stenosis near the anastomoses within a few months. After six months of in-vivo function, these grafts are not invaded with the expected neo-formed cells and new collagen in their central portion; this process takes place only near the anastomoses.

Arterial reconstruction to the foot vessels: is it worth the trouble?

Between 1974 and 1988, 32 patients with severe rest pain and ischemic ulcerations of lower extremities underwent 34 arterial reconstructions to the foot vessels, using, in the majority of cases, the in-situ vein technique. There were 10 early graft failures, resulting in the loss of five extremities. The indication for surgery, presence of diabetes and type of bypass were not predictive of early thrombosis. Five-year primary and secondary patency rates were 52.8% and 62.6%, with a foot salvage rate of 74%. Although a number of these long bypass grafts fail early because of the severity of tibial disease, this procedure appears to be durable in a selected group of patients.

Erythromycin-associated ergotamine intoxication: arteriographic and electrophysiologic analysis of a rare cause of severe ischemia of the lower extremities and associated ischemic neuropathy.

Vasospasm associated with ergotamine is a well-known phenomenon. In this case report we present a rare drug interaction between erythromycin and ergotamine at normal doses causing lower extremity ischemia in a 36-year-old woman. Nitroprusside proved to be the treatment of choice. The response was dramatic and took place in a matter of hours in this patient. Ischemic monomelic neuropathy is a recently described entity in which axonal necrosis is caused by a loss of distal extremity blood flow. The association between erythromycin and ergotamine may be a dangerous pharmacologic combination; drugs that have a hepatic cycle with ergotamine derivatives must be used with caution.

Experimental colonization of vascular grafts with Staphylococcus aureus.

In an attempt to solve the problem of infection of arterial grafts, the authors designed an experimental model to reproduce, in vitro, hematogenous seeding of grafts with Staphylococcus aureus. The inoculum, containing an average of 10(7) viable bacterial cells per millilitre, was circulated through grafts of various types. Normal dog aortas were used as controls. They entrapped a mean of 8 bacteria/cm2. The prosthetic grafts, previously placed in dogs as femorofemoral arteriovenous bypasses for 2 hours, trapped many more cells: expanded polytetrafluoroethylene, 23 cells/cm2; bovine heterograft, 607 cells/cm2 and Dacron velour, 2801 cells/cm2. All cell counts were significantly (p less than 0.001) different from control values. Thoracoabdominal aortic bypass grafts implanted in dogs 2 months previously gave the following mean numbers of trapped bacteria: expanded polytetrafluoroethylene, 19 122 cells/cm2; bovine heterograft, 863 cells/cm2 and Dacron velour, 3500 cells/cm2. Polytetrafluoroethylene had significantly (p less than 0.001) higher numbers of trapped bacteria than any other type of prosthesis. The bacteria were located mainly on irregular fibrin strands and on surface defects of the grafts. The addition of cefazolin during the seeding process at concentrations 10 to 25 times the minimal inhibitory concentration did not decrease the numbers of bacteria in any graft. Bacterial colonization of prosthetic arterial grafts depends on the graft material and on the duration of implantation, but this study provided no answer to the controversial question of how to prevent arterial graft infections with antimicrobial agents in patients who undergo vascular procedures that expose them to bacteremia.

The fate of human umbilical vein grafts as an infrarenal aortic substitute in monkeys.

The literature contains conflicting reports about the potential value of the processed human umbilical vein graft as an arterial substitute. With a view to a better understanding of the ultimate fate of this device, a series of long-term implantation was undertaken with a nonhuman primate model. Dardik Biografts were implanted as an infrarenal aortic substitute in 13 monkeys. Nine were put to death following complications after post-operative periods ranging from 3 months to 3 years, while four animals remain alive. No calcification or lipid infiltration was found, presumably because the animals were healthy. The patency rate was poor because of complications associated with thrombotic deposits and thinning of the graft wall after implantation, which led to stenosis and fibrous hyperplasia along the anastomoses. The external polyester mesh was found to encourage external tissue proliferation, which could not prevent the graft from dilating since it contained neither elastin nor smooth muscle cells. Because the places where the graft had been damaged before or during processing were the sites of thrombotic accumulation and initial collagen degeneration, it is essential to use only defect-free material. As a consequence the long-term durability of this graft continues to be questioned.

Thoraco-abdominal bypass as a method of evaluating vascular grafts in the dog.

Seven Vasculour d grafts, five Gore-Tex grafts and seven Solco-graft, 8 mm by 30 cm, implanted as thoraco-abdominal bypasses in dogs. Sixteen were retrieve at two months. Graft size was assessed angiographically in representative dogs of each group prior to sacrifice. Initial examination of the retrieved specimens revealed pannus extensions at both anastomoses on all graft types, and a variable midgraft appearance from smooth and glistening to partially thrombus coated. Histological assessment of graft segments revealed widely differing healing responses on the three graft types. Tissue attachment to both graft surfaces and varying degrees of tissue incorporation were observed in the Vasculour D and Gore-Tex prostheses. The Solco-graft specimens showed no evidence of tissue incorporation of the wall at two months. Tissue on the graft surfaces remains loosely attached and unincorporated. Pannus extensions were thickest on the Solco-graft. Variably thin fibrin is scattered over the luminal surface of the three graft types. Vascularization of the wall particularly the internal capsulae was noted in the Vasculour D grafts. Although biological responses in the dog are difficult to extrapolate to man, the types of comparison testing allowed by the use of the thoraco-abdominal by-pass procedure can provide valuable information of degree of dilation, relative tissue attachment, tissue incorporation into various types of prostheses and kidney infarcts study. The greatest value of the thoraco-abdominal by-pass lies in graft sizes and length without special regard for patency: assessment of graft size post-implantation and structural changes is then made possible.

A SEM investigation of the trauma to prostheses and arteries during vascular reconstruction procedures.

Scanning electron microscopy was used to diagnose incidents of trauma and the pattern of healing following surgical implantation of microporous blood vessel substitutes. Vascular reconstruction procedures using autogenous or synthetic prosthetic materials inflict damage to the adjacent tissues as well as the prosthesis. This effects the thrombotic behavior and healing pattern of the area. The prognoses for long term success are, as a consequence, directly influenced. Various vessel occluding devices were evaluated on canine models with respect to their ability to damage blood vessels at the clamped site. The impact of suture needles on tissues and prosthetic materials was also considered. Of the various vessel clamping devices which are commercially available, those which have elastomeric shields on the clamping components were found to be the most satisfactory. The development of less traumatic surgical devices and possible modifications in the surgical protocols are discussed with the aim of further reducing surgical trauma.

Another look at the Sparks-Mandril arterial graft precursor for vascular repair. - Pathology by scanning electron microscopy.

The Sparks-Mandril blood vessel precursor system, an autogenous tissue growth-promoting device, in spite of its ingenuity and its surgical elegance, has received only limited usage. At technique for peripheral blood vessels by several authors. In the latter period, this laboratory also undertook similar work. The results of seven implantations in dogs and two in patients are reported here in the context of a program on the evaluation of blood vessel substitutes, their mode of operation and their long term performance. The clinical status and the pathology of the grafts at time of failure were investigated using techniques of scanning electron microscopy. This work confirms the findings of other centres regarding the generally unsatisfactory performance of the Sparks-Mandril system. Possible causes for failure in mandril-formed blood vessels are discussed.

Cardiovascular sutures as assessed by scanning electron microscopy.

Nine types of commercial sutures were investigated with respect to their suitability in cardiovascular surgery involving anastomosis of arterial prostheses. Polyester, nylon, silk and polypropylene in the form of multifilaments and monofilaments with or without coatings were included. The gross structure of the suture and the needle, the uniformity of the fibres and the coatings, the mechanical properties, before and after surgical use and the quality of the resulting anastomoses in canine models were evaluated. Although all surveyed products were potentially usable for the purpose intended, some appeared more suitable. Intraoperative damage to the sutures was found to be extensive and may play an important part in the long-term security of the anastomoses.