Paul-Emile Roy

In vitro and in vivo characterization of an impervious polyester arterial prosthesis: the Gelseal Triaxial® graft

Over the years, textile polyester arterial prostheses have acquired an excellent reputation for easy handling and good healing characteristics. Until recently, the main drawback in using them was the need for preclotting. This, however, is no longer true. Nonporous polyester grafts which have been coated with an impervious bioerodible layer during manufacture are now commercially available. The Gelseal Triaxial prosthesis is one of this new generation of grafts. It is manufactured by impregnating a Triaxial prosthesis with a gelatin coating. An in vivo and in vitro evaluation of this new device has found that its water permeability is almost zero. It has good handling and conformability characteristics, and its bursting strength is slightly greater than that of the uncoated prosthesis due, no doubt, to the presence of the gel. The rates of degradation of the gelatin coating have proven to be rapid under both in vitro and in vivo conditions. In fact, only a few traces of the gel were found remaining on the graft after 2 wk in the canine thoracic aorta. In addition, this study has demonstrated that the use of a bioerodible gelatin coating, with its ability to promote cellular regeneration, is a feasible approach with which to achieve earlier and more complete biological healing.

Collagen coatings as biological sealants for textile arterial prostheses

Two collagen-coated grafts were studied: Hemashield (bovine collagen cross-linked with formaldehyde vapours and softened by exposure to glycerol) and Tascon (collagen fibres cross-linked with glutaraldehyde solution). The weight of the coating was 310 +/- 5 mg/g for Hemashield and 45 +/- 2.5 mg/g for Tascon. However, notwithstanding these differences, both coatings were efficient in making the walls of the grafts impervious to blood. The water permeabilities for the Hemashield and the Tascon were 8.7 and 5.9 ml.min-1.cm-2 at 120 mmHg respectively. The Hemashield collagen coating was rapidly eroded in vitro (4 h) after exposure to buffer, trypsin or pancreatin solutions, whereas the Tascon collagen coating remained well preserved after 7 d incubation. Both coatings were safe and did not interfere with the physical properties of the graft which was used as a skeleton. The healing properties of the Hemashield were similar to that observed with preclotted polyester prostheses, except in the early hours following graft implantation. On the other hand, the absence of erosion in the coating of the Tascon seemed to contribute to early antithrombogenicity. It also induced marked inflammatory reactions in the surrounding tissues and thus the healing appeared to be delayed.

QUÉBEC BEER-DRINKERS’MYOCARDOSIS: PATHOLOGICAL ASPECTS

Last winter, a peculiar epidemic of myocardosis occurred in the Lower Town of QuCbec City, and we had the opportunity to study the pathology of some of these cases.l-j A total of 20 deaths occurred, and the autopsy findings in all cases revealed the same degenerative changes in the myocardium. In addition, biopsy material from heart, liver, and skeletal muscle of patients who survived was available for study. In this paper, we are limiting ourselves to a description of the cardiac and thyroid lesions. The complete data of the autopsy findings will be published el~ewhere.~

Degradability of crosslinked albumin as an arterial polyester prosthesis coating in in vitro and in vivo rat studies.

In order to avoid the preclotting procedure in knitted polyester arterial prostheses and in woven models, compound polyester grafts have been proposed, containing preadsorbed collagen or albumin. Since we are currently investigating grafts impregnated with crosslinked albumin, it was decided to establish the degradation rate of this coating after stabilization with either glutaraldehyde (GA) or carbodiimide (CDI). Tests were performed in vitro by incubation in either PBS, plasma or pancreatin and in vivo by implantation in the abdominal cavity of rats. In PBS or plasma in vitro, the coatings were very stable (2% degradation after 144 h incubation), however, in pancreatin the CDI crosslinked albumin degraded much faster than the GA crosslinked albumin (more than 50% degradation in 12 h compared to less than 30% in 48 h). In vivo the degradation rates of the two types of crosslinked albumin were similar (almost all of the albumin having been lost after 4 weeks) but the cellular response was very different: a mild tissue reaction was observed with the CDI crosslinked coating whereas many foreign body giant cells were present on the GA crosslinked material.

Ultrastructural comparative study on lymphatic capillaries of the subendocardium, myocardium, and subepicardium of the heart left ventricle

A comparative study, with quantitative analysis, was done on the fine structure of the lymphatic capillaries in the subepicardium, myocardium, and subendocardium of the left ventricle from dog hearts. In the three layers, the vesicular system of lymphatic capillaries was quite similar. More than 63% of the plasmalemmal vesicles are in contact with the abluminal or luminal endothelial membrane of cardiac lymphatic capillaries. Volume density measurements showed that plasmalemmal vesicles occupied between 8.0 and 9.3% of the endothelial cytoplasm. Overlapping and interdigitation contacts were frequent, whereas end to end contacts were scarce. The frequency of open junctions wider than 50 nm was inferior to 1%. The intercellular cleft was often obstructed by a focal tight junction (macula occludens). Intercellular spaces without specialized junctions were more frequent with subepicardial and myocardial lymphatic capillaries as compared with subendocardial vessels. Important quantitative variations of the fine structure were encountered on the abluminal side of the endothelial wall. In the subendocardium, the basement membrane covered 33% of the lymphatic endothelium whereas for the subepicardium and myocardium lymphatic capillaries, the values were reduced significantly to 18% (P less than 0.05) and 10% (P less than 0.001), respectively. An inverse relation was observed between the proportion of endothelium covered by basement membrane and the frequency of abluminal endothelial projections associated with the endothelial wall. Endothelial projections (EP) decreased in the following order: myocardium (19 EP/100 micron), subepicardium (15 EP/100 micron), and subendocardium (10 EP/100 micron). Quantitative morphological variations in the fine structure of lymphatic capillaries are believed to result from physiological (muscular movements, metabolic activity) and morphological (thickness of the connective tissue support surrounding lymphatic capillaries) differences existing between the three cardiac layers.

A Pathological Study of Arterial Prostheses Surgically Excised after Overt Clinical Infection

Infection caused regarding vascular grafts in vascular surgery still remains a major problem. To reduce this problem and the complications which follow, the surgeon must be able to apply the best surgical management and also be confident with the vascular substitute used. There are two important factors to be considered: the biomaterial must have low propensity to infection and good stability if and when infected. In an attempt to verify this problem, 93 vascular grafts surgically excised for overt infection were examined. Techniques used for examinations were gross morphology, histopathology and scanning electron microscopy (SEM) evaluation. There were 23 human umbilical vein (HUV) grafts, 51 Dacron grafts and 19 expanded polytetrafluoroethylene (ePTFE) grafts. Histopathological signs of infection were absent in 57% of the ePTFE and Dacron grafts and in 17.4% of the HUV grafts. The latter were more heavily histologically infected and in some cases the walls were destructed. Histopathological signs of infection were seen on all the prosthetic walls in 36% of all the specimens and were mainly on the external portion of the grafts for the remaining prostheses. Bacteria were seen in respectively 21.7, 15.7 and 20% of the HUV, Dacron and ePTFE grafts with the Gram stain and in 86.9, 84.3 and 94.7% with SEM. The implantation period was shorter for the bioprostheses compared to that of the synthetic grafts because of the site and the indication of implantation. The stability of the bioprostheses was lower compared to that of the synthetic grafts when infected, leading to a breakdown of the wall along the length of the graft. The infection was found on the external capsule of the grafts rather than on the luminal surface.

Per-operative uncontrollable bleeding at polyester (Dacron) arterial prosthesis implantation.

An aortobifemoral knitted polyester graft was placed in a 58-year-old woman with aorto-iliac occlusive disease. Although the prosthesis was preclotted in the usual manner, it never became impervious to blood under normal intra-arterial pressure. Examination of the graft showed lipid infiltration not ordinarily seen. We recommend that when a knitted prosthesis fails to preclot a woven graft should be used instead.

A preliminary histological study of chemically processed porcine heart valves stored in glutaraldehyde for up to 72 months

Abstract The effect of different storage times in glutaraldehyde was evaluated in porcine valve heterografts prior to implantation. Histological, scanning and transmission electron microscopy examinations were performed on 6 glutaraldehyde-treated porcine aortic valves (St. Jude-Bioimplant®). The bioprostheses were manufactured 2–72 months before the analyses (2, 24, 36, 48, 60 and 72 months) during which time they were preserved in a 0·5% buffered glutaraldehyde solution. Structural changes due to varying soaking times in glutaraldehyde were observed in porcine aortic valvular heterografts. Histomorphometric studies indicated that there was a decrease of collagen content in fibrosa after more than three years of storage. Scanning electron microscopy revealed mild morphological modification on inflow and outflow surfaces. However, because of the limited number of valves investigated, it was not possible to precisely determine the shelf-life of the valves stored in glutaraldehyde with accuracy.

Postoperative thrombocytopenia and haemolytic anaemia in peripheral arterial reconstruction involving collagen-impregnated grafts

Abstract Two patients operated on for atherosclerotic occlusive disease (Case no. 1) and aneurysm resection (Case no. 2) were implanted with an aortobifemoral vascular prosthesis HemashieidR, a knitted double velour graft impregnated with collagen. This graft does not require preclotting. In Case no. 1, the graft thrombosed eight days postoperatively and was replaced because of the failure of the thrombectomy. The graft was devoid of collagen. In Case no. 2, the patient died five weeks postoperatively, following complications. The graft was well encapsulated and the collagen fibrils remained present. The dissolution of the impregnated collagen was variable.