Antigenicity of vascular heterografts

The Carotid Artery as a Coronary Bioprosthesis: Five Potential Donor Species

Bovine, porcine, ovine, caprine and canine carotid arteries were chosen for study as potential sources of aortocoronary bypass biologic prostheses for use in patients undergoing reconstructive surgery. Anatomic and histologic evalua tions, structural measurements and static mechanical property tests were per formed. The canine carotid arteries have an average length of about 20 to 21 cm with the considerable advantage that there is only one branch, located near the distal end. They also offer the most uniform luminal diameter of 3.0 to 4.0 mm and the most uniform wall thickness (approximately 0.5 mm). The suitable lu minal diameter and wall structure provide a good match to the coronary arte rial anastomosis. Although the canine carotid artery has a thinner wall, static mechanical property tests demonstrate that wall strength and elasticity are com parable to the four other species studied. The canine carotid artery appears to best fit the suggested criteria for a biologic aortocoronary bypass prosthesis from a readily available source. As such, the canine carotid artery in a properly processed form appears worthy of experimental study for aortocoronary bypass surgery.

Carotid Endarterectomy with Bovine Pericardium Patch Angioplasty: Mid-Term Results

The objective of this study was to assess the efficacy of bovine pericardium (BP) as a patch material in carotid endarterectomy (CEA) in terms of peri- and postoperative complications and the incidence of recurrent stenosis. During a 4-year period, 148 CEAs were performed in 138 consecutive patients. The study group included elective, emergency, and combined with cardiac operation CEAs in both symptomatic and asymptomatic carotid artery disease patients. Patch angioplasty using the BP followed the standard CEA in all patients. Postoperative follow-up included clinical examination and periodical color duplex scans at 3, 6, and 12 months and yearly thereafter. Surgical outcome was evaluated by the operation-related parameters, early and late mortality and morbidity rates, and the incidence of recurrent stenosis. All CEAs were performed without any unfavorable event. In the early postoperative period, there were no deaths and the morbidity consisted of transient cranial nerve paresis (4.7%) in seven patients and two ipsilateral strokes (1.4%). During the follow-up period, three patients (2%) developed significant carotid restenosis, though they remain asymptomatic, while there were no deaths related to the CEA. Patch angioplasty of the carotid artery using BP showed unwittingly early and mid-term surgical outcome. Our results demonstrate the BP to be a suitable patch material for routine use in carotid surgery.

Pseudoaneurysm formation in a subset of patients with small intestinal submucosa biologic patches after carotid endarterectomy

BACKGROUND

The carotid artery is frequently patched after carotid endarterectomy (CEA) to minimize the risks of early postoperative thrombosis and late recurrent stenosis. The small intestinal submucosa (SIS) patch is a biologic vascular patch derived from porcine small intestine. It is composed primarily of cell-free collagen and other extracellular matrix constituents that act as a scaffold for host cell deposition.

METHODS

In May 2001, we began an investigational trial of SIS patches in 76 patients undergoing patch angioplasty of the carotid artery after CEA.

RESULTS

No adverse events related to the patches were observed in the first 69 patients implanted with an SIS patch. However, in late 2002, seven patients were found to have asymptomatic pseudoaneurysms (PSA) by duplex imaging < or =10 weeks after their CEAs. The trial was immediately suspended. The PSAs were treated by surgical resection with vein grafting in two patients and placement of covered endoluminal stents in four patients. One patient is being followed as the PSA is small and has remained stable. Histopathologic examination of the SIS patch explanted from one of the surgically treated patients demonstrated the presence of actin-positive myofibroblasts or smooth muscle cells. Extensive mechanical testing of the SIS material from the two material lots associated with PSAs demonstrated thinner and more variable physical characteristics compared with control device lots.

CONCLUSIONS

Biologic patches that undergo active remodeling in the carotid artery require greater thickness than was anticipated to decrease wall stress and suture hole elongation. Patches exceeding this minimum thickness will be required to ensure the safety of new SIS patch designs for vascular operations.

Xenogeneic ossicular implants: an experimental study of heterotopic, demineralized, lyophilized, porcine implants in the guinea-pig

This study was done to compare the outcome of porcine ossicular implants in the middle ear and the subcutaneous dorsal region of the guinea-pig to those of allo-implants implanted in parallel in the dorsal region. The implants were heteropic, xenogeneic, demineralized (HCl), lyophilized and sterilized. The evaluation was histological (light microscopy and scanning electron microscopy) and immunological (immunofluorescence staining). Fifty-four guinea-pigs were implanted in the middle ear and 14 of them were also implanted subcutaneously in the dorsal region with xeno-implants and allo-implants. The middle ear implants were found to be constantly reossified and coated with normal mucosa with only a minimal immune reaction. In contrast, the dorsal xeno-implants were found to be the target of mononucleic infiltration, fibrous encapsulation and an influx of immunoglobulins resulting in segregation. The corresponding allo-implants were found to be partially reoccupied and reossified. These findings highlight the value of HCl demineralization in the induction of non-species-specific Bone Morphogenetic Protein and the failure of attempts at immuno-despecification. It appears that the fate of the implant depends less on its antigenic load than on the site of implantation. In this regard the middle ear is apparently very advantageous. The very good short-term tolerance and recovery observed in the middle ear xeno-implant suggest that these implants offer sufficiently good results to warrant clinical testing.

In vivo evaluation of four chemically processed biological grafts implanted as infrarenal arterial substitutes in dogs

Four chemically processed grafts implanted as arterial substitutes in dogs were evaluated as blood conduits in terms of patency rates, healing characteristics and biostability. Omniflow, Biopolymeric, Dardik-Biograft of the second generation and BIMA grafts were implanted as infrarenal aortic substitutes for 4, 24 and 48 h (short-term), 1, 2 and 4 wk (medium-term), 3 and 6 month (long-term), each type of graft being implanted for a complete series. The explanted grafts were evaluated macroscopically and processed for light and scanning electron microscopy. One Omniflow graft was occluded at 6 months and two Dardik-Biografts were thrombosed, one at 24 h and one at 1 month. All explanted grafts in the Biopolymeric series and in the BIMA were patent at the animals' death. Histological studies revealed frequent subintimal fibrosis in the Biopolymeric and Omniflow grafts. A peripheral inflammatory reaction was present in most grafts explanted. Scanning electron microscopy showed an aggravation of flow surface irregularities, after implantation of Omniflow, Biopolymeric and Dardik-Biograft, compared to virgin prostheses. These grafts presented an internal capsulae on the graft flow surface along the anastomoses. The capsulae slightly extended towards the centre of the graft after long-term implantation, (6 month) and corresponded to the pannus. Endothelial-like cells covered this pannus. The BIMA graft performed the most satisfactorily and retained its blood compatibility best, that is, the luminal surface was smooth with only minor thrombotic deposits and a thin pannus along the anastomotic lines.

The role of physical and chemical characteristics in assessing the performance of a new biological vascular graft

Information obtained from physical and chemical characterization of vascular grafts can prove valuable in obtaining a preliminary assessment of potential in vivo performance. The data presented illustrate the concept and show that the new biological graft made from bovine ureters has adequate performance characteristics for use as a potentially successful vascular graft.

Glutaraldehyde preparation of coronary artery bypass bioprostheses

A method for glutaraldehyde (GA) fixation of canine carotid arteries has been developed for the preparation of small caliber biologic prostheses for coronary artery bypass. The biologic grafts were preserved by a static inflation technique that proved to be more advantageous than the standard stenting method. The most suitable static inflation pressure was found to be 120 mm Hg. By means of colorimetric measurements the minimal tanning time and the amount of GA required for complete fixation for canine vascular tissue were established. Stabilization of the vessel collagen and confirmation of GA-collagen cross-linking were verified by evaluation of the elastic properties and shrinkage temperature of the grafts. Stress-strain measurements were evaluated to determine the number of cross-links introduced in the vascular tissue by GA. This number was shown to be proportional to the inflation pressure. Ethyl alcohol was chosen as the storage solution because it maintained the best physical, chemical, and histologic characteristics of the grafts. Biological evaluations were performed with carotid implants that were examined following acute low flow studies and implantations up to 112 days. All implantations have yielded 100% patencies.

Modification and morphology of human umbilical cord vein as canine arterial bypass grafts

Human umbilical cord veins treated with various concentrations of glutaraldehyde (GA) and ethanol (ET) were used to replace short segments of the infrarenal abdominal artery in 40 dogs. The patency rates were 62.5% (5/8) in Group I; tanned with 1% GA for 24 hours and preserved in the same solution 87.5% (7/8) in Group II; tanned with 1% GA for 24 hours and preserved in 50% ethanol, 100% (8/8) in Group III; tanned in the same manner as Group II, but preserved in 70% ET; 87.5% (7/8) in Group IV; tanned with 0.5% GA for 24 hours and preserved in 50% ET, and 87.5% (7/8) in Group V; tanned as in Group IV but preserved in 70% ET when examined 14 days to 6 months after implantation. Angiographically, most of the anastomotic lines gradually contracted with the lapse of time because of excessive proliferation of connective tissue into the intraluminal surfaces, although the structural integrity of the graft was well preserved. Microscopically, the irregular fibrin membrane covering the entire inner surface of the graft became smoother and thinner with the lapse of time. The pannus increased gradually both in thickness and width. Scanning electron-micrography of the graft revealed that no endothelial cells were found more than 5 mm from the suture lines even 6 months after implantation. Antigenicity of the graft using a complement-dependent cytotoxicity test was effectively suppressed with glutaraldehyde regardless of whether its concentration was 0.5% or 1.0%. Although human umbilical cord vein tanned with 0.5% glutaraldehyde and preserved in 50% ethanol until used was considered to be useful as an arterial substitute, final conclusion could not be drawn since six grafts followed for six months, the longest follow-up, were stenotic.

Successful arterial substitution with modified human umbilical vein

Human umbilical veins were prepared as vascular grafts by tanning with dialdehyde starch or gluteraldehyde and by structural re-inforcement with an outer polyester fiber mesh. These grafts were implanted in baboons in the aortoiliac position for periods of 3 days to 9 months. There was no aneurysm formation and there was an excellent maintenance of patency as well as function. Histologic evaluation of the graft materials showed a dense collagen layer within the encircling polyester fiber mesh. A multicellular subintimal layer formed a discrete inner capsule. The inflammatory response with the umbilical component was insignificant. There was no evidence of rejection. This study suggests that the modified umbilical vein can serve as a satisfactory blood conduit. Experience with three short-term clinical implants supports the applicability and potential for this new vascular graft.

Heterografts as aortocoronary bypass conduits in human beings

Clinical and necropsy observations are described in a man in whom two sheep carotid arterial heterografts were inserted as aortocoronary bypass conduits 30 months before death, and in whom a canine saphenous vein heterograft was inserted several hours before death. All three grafts failed. The lumens of the sheep carotid arterial heterografts had closed by the time of catheterization 6 months after operation; at necropsy both grafts were totally occluded at their coronary and aortic ends and their media and adventitia were infiltrated by granulomatous inflammatory cells. Little information is available regarding the use of heterografts as coronary bypass conduits. Examination of previous reports describing heterografts for vascular reconstruction or bypass in both man and experimental animals and observations in our patient suggest that heterografts are unsatisfactory as aortocoronary bypass conduits.