Value of the Hemobahn/Viabahn Endoprosthesis in the Treatment of Long Chronic Lesions of the Superficial Femoral Artery:6 Years of Experience

PURPOSE

To evaluate the long-term efficacy of Hemobahn/Viabahn endoprostheses (HVE) in patients with femoral arterial occlusive disease.

METHODS

During a 6-year period, 57 patients (46 men; mean age 62.7+/-9.3 years, range 44-82) were treated with 82 Hemobahn or Viabahn endoprostheses for stenoses (13%) or occlusions (87%) of the superficial femoral artery (SFA) in 60 limbs. The average length of the treated lesions was 10.7 cm (range 3-34), and the mean length of the HVE was 15.9 cm (3-33). Patients had chronic limb ischemia in Rutherford stages 2/3 (92%), 4 (2%), and 5 (7%). The crossover method was used to deploy the stent-graft in 31 cases and the ipsilateral technique in 29.

RESULTS

Endoprosthesis deployment was technically successful in 59 (98%) of 60 limbs. In 2 cases, major complications (1 deployment failure and 1 thromboembolism) required additional surgery. Early thrombosis (within 30 days) occurred in 6 (10%) femoral arteries. The mean follow-up was 55 months (8-78). Late thrombosis or reocclusion was observed in 22 (37%) arteries up to 5 years after prosthesis placement (14 in the first year). Primary/ secondary patency rates were 90%/95% at 30 days (n=59), 67%/81% at 1 year (n=58), 57%/ 80% after 3 years (n=49), and 45%/69% after 5 years (n=32). In a subgroup analysis of 48 patients with "optimal" conditions for implantation (no heavy calcifications, popliteal obstruction, or complete superficial femoral artery occlusion; minimum 1-vessel runoff; and adequate antiplatelet therapy or anticoagulation), the primary/secondary patency rates were 80%/91% after the first year (n=46), 71%/89% after 3 years (n=38), and 62%/90% after 5 years (n=21).

CONCLUSION

HVE seems to be suitable for femoral arterial occlusive disease so long as ideal indications and prophylaxis against secondary thrombosis are strictly observed.

Histopathologic evaluation of an expanded polytetrafluoroethylene-nitinol stent endoprosthesis in canine iliofemoral arteries

PURPOSE

The authors assess a new ePTFE-nitinol stent for its long-term patency, healing, and properties of endothelialization.

MATERIALS AND METHODS

Adult greyhounds (n = 18) underwent bilateral iliofemoral placement of an endoprosthesis (Hemobahn) consisting of a nitinol stent lined with an ultrathin expanded polytetrafluoroethylene (ePTFE) material. Histologic and quantitative morphometric analyses were performed on devices explanted at 2 weeks and 1, 3, 6, and 12 months. The source of endothelialization was examined in four additional devices modified by sealing either the proximal and distal ends or the entire graft with poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP), a nonporous laminate to prevent potential transgraft endothelial cell migration.

RESULTS

Device patency assessed with both intravascular ultrasound and histologic study showed minimal arterial stenosis, irrespective of implant duration. The neointima at less than 3 months consisted of fibrin and inflammatory infiltrate; at later time points, it was composed of mostly smooth muscle cells. Flow surfaces were more than 75% endothelialized by 3 months, which was nearly complete by 6 months. Modified endoprostheses entirely enveloped with FEP resulted in endothelialization of only the proximal and distal ends; the middle regions showed nonocclusive thrombi. Conversely, devices wrapped proximally and distally showed nearly complete endothelialization.

CONCLUSIONS

This ePTFE-nitinol endoprosthesis demonstrated long-term patency at up to 1 year after implantation and showed early and nearly complete endothelialization by 6 months. The design promoted rapid endothelialization of flow surfaces, particularly in the midregion of the device possibly by transgraft migration.

Suppression by antithrombotic agents of pseudointimal hyperplasia of polytetrafluoroethylene graft implanted into venous system

The lumen of the polytetrafluoroethylene graft (PTFE) implanted into a rabbit inferior vena cava (IVC) was markedly narrowed by 4 weeks after grafting. This was due to initial thrombosis on the luminal surface of the graft, which was followed by pseudointimal hyperplasia (PIH). To elucidate the role of the initial thrombosis in subsequent PIH, the effect of ticlopidine (T) and/or warfarin (W) on PIH was studied in an animal model. A PTFE tube graft was implanted into a rabbit IVC. Twenty eight rabbits were randomly assigned to the following experimental groups. Eight rabbits without antithrombotic agents were observed for 2 weeks (A, n = 4) and 4 weeks (B, n = 4) after grafting. T (100 mg/kg/day) and W (0.33 mg/kg/day) were orally administered for 4 weeks to group C (n = 4) and group D (n = 4), respectively. A combination of a half dose of T and W ((T + W)/2) was given for 2 weeks (E, n = 4) and 4 weeks (F, n = 4) after grafting. Four rabbits in group G received the combination of T and W for the first 2 weeks and were observed for an additional 2 weeks without medication. All the grafts were patent at time of harvest. The dry weight of the intraluminal deposit (DW) was determined as an indicator of PIH (A:35 +/- 1 mg/graft, B:40 +/- 8, C:22 +/- 3, D:22 +/- 3, E:14 +/- 2, F:15 +/- 3, G:23 +/- 2). Administration of T or W was equally effective in reducing DW and (T+W)/2 was more effective than a single agent.(ABSTRACT TRUNCATED AT 250 WORDS)

The pathology of vascular grafts

In order to analyse the incorporation pattern of synthetic prosthesis made of Teflon and Dacron in the arterial system, 21 prostheses removed surgically and seven prostheses obtained from autopsies were examined; the duration of the implantation periods ranged from 30 min up to 10 years. Essentially the early phase of prosthetic incorporation (phase I) includes exudative inflammatory reactions as part of acute inflammatory processes. The degree of order within the tissue architecture and the mutual influence of matrix and cells in the reaction appeared to be slight. The cellular infiltrate found on the outer prosthetic surface is of local origin whereas the inner prosthetic lining contains cells of haematogenous origin. The organisation phase (phase II), which is comparable to the reparative-proliferative phase of an inflammatory reaction, showed activation of the reticulo-endothelial system together with the start of phagocytosis and a thinning of the prosthetic structures. Collagen type I and type III and fibronectin served both as a guidance and a growth tract for the cells during the cellular permeation of the prosthesis. Fibronectin and collagen type III have a special "catalytic" function. Collagen type I causes the firm anchoring of the vascular prosthesis in the periprosthetic tissue. The loss of stability of the prosthesis due to phagocytosis of fibres is balanced by the newly formed connective tissue within the wall of the vessel. The fibroblasts involved in the organisation must be derived from the flowing blood and from local mesenchymal cells. A chronic inflammatory reaction persisted during the late phase. In some cases increased proliferation of the inner mesenchymal lining of the prosthesis was observed together with regressive changes. The lack of a continuous surrounding stromal architecture on the luminal side of the vessel can be regarded as the main reason for this proliferation. Transformation of haematogenous cells into angioblasts or endothelial cells was not seen. Small endothelialised areas were only seen in the vicinity of anastomoses and following transprosthetic permeation by capillaries.

An artificial blood vessel with an endothelial-cell monolayer

An artificial blood vessel with an endothelial-cell monolayer was used as an arterial substitute in rats. Endothelial cells were isolated from the aorta of a Wistar rat by the digestion method. The cell identification was established by the cobblestone appearance of a confluent cell monolayer, by an expression of factor VIII-related antigen, and by the presence of Weibel-Palade bodies. The luminal surface of the thin-walled polytetrafluoroethylene (PTFE) graft (4 mm in diameter and 10 mm in length) was coated with an endothelial-cell monolayer for 7 days in vitro. An interpositional graft was placed using the endothelial cell-coated PTFE prosthesis on the right common carotid artery in seven rats. A total of 10 rats received an interpositional graft with the noncoated PTFE prosthesis as a control. The patency rate at 1 month after implantation was significantly higher in the coated group than in the control group. The vascular prosthesis with an endothelial-cell monolayer is a promising technique to inhibit the development of thrombosis.

Ultrastructural analysis of pseudo-intimal hyperplasia of polytetrafluoroethylene prostheses implanted into the venous and arterial systems

To evaluate and compare the pathogenesis of pseudo-intimal hyperplasia (PH) of venous and arterial prostheses, a segment of the inferior vena cava (n = 16) or abdominal aorta (n = 16) was substituted by a 3 mm internal diameter polytetrafluoroethylene tube graft (PTFE, 3 cm long, 30 microns in nodal distance) in albino rabbits. At designated time intervals (3-28 days) after the replacement, graft patency was examined and the dry weights of the intraluminal deposits measured as an indicator of the degree of PH. The harvested grafts were then subjected to an ultrastructural analysis by means of light microscopy (LM), and scanning electron and transmission electron microscopy (SEM, TEM). All the grafts remained patent during the entire observation period. The PH judged by the dry weight was significantly more extensive in the venous than in the arterial prostheses. The PH on day 28, observed by light microscopes was apparently most extensive in the mid-portion of venous prostheses but in the arteria prostheses it was mostly seen at the anastomotic sites. The lining of the intraluminal surface of the prostheses with endothelial-like cells observed by SEM was faster and more extensive in venous than in arterial prostheses. The process of PH in venous prostheses observed by TEM may be divided into the following steps: early thrombosis, phagocytosis of the thrombus, appearance of fibroblasts, growth of endothelial-like cells, appearance of smooth muscle cells, and pseudointimal thickening and proliferation of fibroblasts producing collagen fibrils. The process in arterial prostheses was essentially identical to that in venous prostheses but was much slower and less extensive. From these observations, it was concluded that the formation of PH occurs much faster in venous than in arterial prostheses, although the mechanism of PH is mostly identical in venous and arterial prostheses.

The chick chorioallantoic membrane as test system for biocompatible materials

Biologic and non-biologic materials clinically used as hemostyptica, as vascular prostheses, or as temporary skin substitutes were implanted to the chick chorioallantoic membrane (CAM) during days 9-14 of incubation. The histological study revealed an intact CAM after application of cellulose gauze (Tabotamp). The fibrin tissue adhesive (Tissucol), the collagen sponge (Tachotop), or the gelatin sponge (Gelfoam) induced different amounts of connective tissue. Some fibroblasts were about to grow into the fibrin adhesive. Fibroblasts and capillaries filled the interstices of the collagen sponge poorly, and in the case of the gelatin sponge markedly. Neutrophils and giant cells of the foreign body type occurred more often in the gelatin sponge than in the collagen sponge. With regard to the non-biologic materials, expanded polytetrafluorethylene induced squamous metaplasia of the chorionic epithelium. Dacron caused ulceration with the onset of connective tissue ingrowth, based on a reaction of giant cells of the foreign body type. Polyurethane foam (SYSpur-derm) showed bleeding into the implant due to spikes of the material. Eosinophilic granulocytes were absent in all materials studied. The results are related to different clinical findings. The correlation allows consideration of the CAM as an in vivo model in screening materials for their biocompatibility and their connective tissue reaction.

The use of long synthetic microvascular grafts to vascularise free flaps in rabbits

A 5 cm length of 2 mm internal diameter (i.d.) synthetic, expanded polytetrafluoroethylene (PTFE, or Gore-Tex) vascular graft was used to connect 25 rabbit inferior epigastric flaps to the contralateral femoral vessels. In 15 animals an expanded PTFE graft connected the opposite femoral artery to the flap while the ipsilateral venous drainage remained intact. In the remaining 10 animals an expanded PTFE graft was used to replace the venous drainage of the flap and connected to the opposite femoral vein while the ipsilateral femoral artery supplied the flap. Flap survival and graft patency were evaluated over 3 weeks. Ten of 15 flaps with intra-arterial grafts survived at 3 weeks (67%). Only 27% (4/15) of their supplying grafts remained patent for 3 weeks, although 67% (10/15) were patent at 10 days. All 10 flaps, where expanded PTFE grafts replaced venous outflow, failed within 36 hours. At exploration these grafts were thrombosed or collapsed. In conclusion, currently available 2 mm (i.d.) expanded PTFE vascular graft cannot maintain patency in a low blood flow circulation supplying an isolated free flap.