The fate of polytetrafluoroethylene grafts in lower limb bypass surgery: a six year follow-up

An Update on Endovascular Therapy of the Lower Extremities

Considerable advances have been made over the last decade in percutaneous technology for treatment of atherosclerotic diseases in the iliac, femoropopliteal, and distal tibioperoneal arteries. While treatment strategies are well defined in the iliofemoral segment, where angioplasty and stenting perform well in appropriately selected lesions, the search for a durable transcatheter therapy for femoropopliteal and distal occlusive disease continues. The spectrum of treatment alternatives to angioplasty ranges from transcatheter plaque excision to laser ablation, rotational atherectomy, cryoplasty, brachytherapy, and stenting. We review in this article the status of percutaneous endovascular techniques for the treatment of lower extremity vascular occlusive disease.

Long-term Results with the Palmaz Stent in the Superficial Femoral Artery

Purpose:

Femoral stenting has demonstrated inconsistent and often disappointing long-term results. To compare our experience, we retrospectively analyzed a series of patients who had Palmaz balloon-expandable stents placed exclusively for superficial femoral artery (SFA) lesions.

Methods:

From January 1990 to November 1993, 39 patients were evaluated for claudication (79%) or critical ischemia in 42 limbs. The culprit lesions were confined to the SFA: 24 (57%) occlusions and 18 (43%) stenoses, including 3 restenotic lesions. Stenting was elective in 12 (29%) cases: the 3 restenoses and 9 chronic, calcified occlusions. The remaining stents were applied for postangioplasty residual stenosis or angioscopic findings of thrombogenic luminal irregularities. A total of 55 prostheses were successfully implanted. All patients were maintained on ticlopidine and followed by routine duplex scanning. Follow-up angiography was performed in 28 (72%) patients between 4 and 45 months.

Results:

In the postprocedural period, two acute thromboses (4.8%) occurred within 48 hours in patients who had long occlusions and poor runoff; no other major complications were encountered, for a clinical success rate of 95%. Follow-up evaluation ranged from 4 months to 4 years with a mean of 25 months. The restenosis rate was 19% (34% in occlusions; 10% in stenotic lesions, p = NS). At 24 months, cumulative primary patency was 77% and secondary patency 89%.

Conclusions:

Palmaz stents performed well in the SFA, demonstrating a low acute thrombosis rate and good long-term patency. The incidence of restenosis is likely to be greater in occlusions than in stenoses.

Mesenchymal stem cell-based tissue engineering of small-diameter blood vessels

The aim of the study was to construct small-diameter vascular grafts using canine mesenchymal stem cells (cMSCs) and a pulsatile flow bioreactor. cMSCs were isolated from canine bone marrow and expanded ex vivo. cMSCs were then seeded onto the luminal surface of decellularized arterial matrices, which were further cultured in a pulsatile flow bioreactor for four days. Immunohistochemical staining and scanning electron microscopy was performed to characterize the tissue-engineered blood vessels. cMSCs were successfully seeded onto the luminal surface of porcine decellularized matrices. After four-day culture in the pulsatile flow bioreactor, the cells were highly elongated and oriented to the flow direction. Immunohistochemistry demonstrated that the cells cultured under pulsatile flow expressed Von Willebrand factor, an endothelial cell marker. In conclusion, cMSCs seeded onto decellularized arterial matrices could differentiate into endothelial lineage after culturing in a pulsatile flow bioreactor, which provides a novel approach for tissue engineering of small-diameter blood vessels.

Development of the novel biotube inserting technique for acceleration of thick-walled autologous tissue-engineered vascular grafts fabrication

To accelerate the fabrication of thick-walled autologous tissue-engineered vascular grafts (TEVGs), a novel biotube inserting technique was developed. After 2 weeks of subcutaneous embedding in rabbits, silicone rods (diameter, 3 mm; length, 35 mm) became encapsulated in connective tissues. Single-layered biotubes were obtained after removing the silicone rods. One silicone rod encapsulated in tissues was inserted into a single-layered biotube to form two layers of autologous tubular tissues. Three layers of autologous tubular tissues were also obtained by applying the same technique. Following a 2-week re-embedding procedure, two layers or three layers of autologous tubular tissues were integrated to form two-layered or three-layered TEVGs. Both wall thickness and burst pressure of three-layered TEVGs were significantly higher than those of two-layered and single-layered TEVGs (P < 0.05). The two-layered TEVGs could be applied as small-caliber vascular grafts, and three-layered TEVGs could be applied as medium- or large-caliber vascular grafts.

An update on endovascular therapy of the lower extremities

Considerable advances have been made over the last decade in percutaneous technology for treatment of atherosclerotic diseases in the iliac, femoropopliteal, and distal tibioperoneal arteries. While treatment strategies are well defined in the iliofemoral segment, where angioplasty and stenting perform well in appropriately selected lesions, the search for a durable transcatheter therapy for femoropopliteal and distal occlusive disease continues. The spectrum of treatment alternatives to angioplasty ranges from transcatheter plaque excision to laser ablation, rotational atherectomy, cryoplasty, brachytherapy, and stenting. We review in this article the status of percutaneous endovascular techniques for the treatment of lower extremity vascular occlusive disease.

Optical Transillumination Tomography for Imaging of Tissue-Engineered Blood Vessels

Recent progress in tissue engineering led to the development of completely biological human vessels grown from the patient's own cells. Those tissue-engineered blood vessels (TEBV) are grown on an individual basis at high costs per item, and therefore require close growth monitoring and quality control. We designed and tested an optical transillumination tomography system using red laser light to image weakly scattering specimens, such as TEBV. Fixated TEBV were imaged and the results compared to optical coherence tomography. This preliminary scanner prototype had an in-plane resolution of 50 microm and allowedto see small inhomogeneities and defects in the samples. Tissue attenuation was found to be 70 cm(-1). Main advantages of the transillumination tomography scanner over optical coherence tomography were the inexpensive instrumentation and the potential to rapidly acquire complete 3D sections with a CCD camera. The prototype presented in this study provides a basis to further improve image quality and acquisition speed.

Preparation of porcine carotid arteries for vascular tissue engineering applications

Biomaterials derived from tissue continue to offer viable alternatives to synthetic materials when autologous materials are unavailable for transplantation due to their unique chemical and mechanical properties. Tissue processing aims to stabilize the material against host degradation and render it immunologically inert by removing cellular material and crosslinking the structural proteins. It is clear that different approaches taken to achieve these goals have very different chemical and mechanical effects on the material. We describe herein the development of a tissue processing methodology to generate acellular scaffolds for tissue engineering small-diameter vascular grafts. Carotid arteries were isolated from Great White pigs and exposed to various solvent treatments, xylene, butanol, and ethanol to determine optimal parameters for the extraction of host lipids. The tissue was then exposed to a limited proteolysis with trypsin to disrupt cellular protein. This resulted in a controlled digestion that disrupted porcine nuclear DNA and cleared bulk cellular protein, leaving the more resistant structural proteins largely intact and retaining the bulk mechanical properties of the matrix. Histological analysis and scanning electron microscopy illustrated the complete removal of intact cells and nuclear material. The decellularized graft was stabilized by crosslinking with the photooxidative dye methylene green in the presence of 30,000 LUX of broad-band light energy. High-performance liquid chromatography analysis showed that the crosslinked tissue yielded 78.6% less hydroxyproline, compared with control tissue, after 20 h incubation with pepsin. Analysis of the crosslinked vessels' burst-pressure and stress-strain characteristics have shown comparable mechanical properties to those of control vessels. Assessment of in vitro cell adhesion and compatibility was conducted by seeding primary human umbilical vein endothelial cells and adult human vascular smooth muscle cells onto the lumenal and ablumenal surfaces, respectively; these cells were shown to adhere and proliferate under traditional static culture conditions.

Limb salvage after infrainguinal bypass graft failure

OBJECTIVE

The purpose of this study was to examine the outcome of patients in whom an infrainguinal bypass graft failed.

METHODS

This was a retrospective analysis of consecutive patients undergoing infrainguinal bypass grafting in a single institution over 8 years.

RESULTS

Six hundred thirty-one infrainguinal bypass grafts were placed in 578 limbs in 503 patients during the study period. The indication for surgery was limb-threatening ischemia in 533 patients (85%); nonautologous conduits were used in 259 patients (41%), and 144 (23%) were repeat operations. After a mean follow-up of 28 +/- 1 months (median, 23 months; range, 0-99 months), 167 grafts (26%) had failed secondarily. The rate of limb salvage in patients with graft failure was poor, only 50% +/- 5% at 2 years after failure. The 2-year limb salvage rate depended on the initial indication for bypass grafting: 100% in patients with claudication (n = 16), 55% +/- 8% in patients with rest pain (n = 49), and 34% +/- 6% in patients with tissue loss (n = 73; P <.001). The prospect for limb salvage also depended on the duration that the graft remained patent. Early graft failure (<30 days; n = 25) carried a poor prognosis, with 2-year limb salvage of only 25% +/- 10%; limb salvage was 53% +/- 5% after intermediate graft failure (<2 years, n = 110) and 79% +/- 10% after late failure (>2 years, n = 15; P =.04). Multivariate analysis revealed shorter patency interval before failure (P =.006), use of warfarin sodium (Coumadin) postoperatively (P =.006), and infrapopliteal distal anastomosis (P =.01) as significant predictors for ultimate limb loss.

CONCLUSION

The overall prognosis for limb salvage in patients with failed infrainguinal bypass grafts is poor, particularly in patients with grafts placed because of tissue loss and those with early graft failure.

A comparative evaluation of polytetrafluoroethylene, umbilical vein, and saphenous vein bypass grafts for femoral-popliteal above-knee revascularization: a prospective randomized Department of Veterans Affairs cooperative study

PURPOSE

Currently, the choice of a vascular prosthesis for a femoral-popliteal above-knee arterial bypass graft is left to the surgeon's preference, because the available information on comparative evaluations is inconclusive. The Department of Veterans Affairs (VA) Cooperative Study 141 was established to identify whether improved patency exists with different bypass graft materials for patients with femoral-popliteal above-knee bypass grafts.

METHODS

Between June 1983 and June 1988, 752 patients at 20 VA medical centers were randomized to receive either an externally supported polytetrafluoroethylene (PTFE; N = 265), human umbilical vein (HUV; N = 261), or saphenous vein (SV; N = 226) for an above-knee femoral-popliteal bypass graft. The indication for the bypass grafting operation was limb salvage in 67.5% of the patients. Patients were observed every 3 months for the first year and every 6 months thereafter. All patients were instructed to take aspirin (650 mg) daily for the duration of the study.Doppler-derived ankle-brachial indices (ABIs) were determined preoperatively and serially postoperatively. A bypass graft was considered to be patent when the Doppler-derived postoperative ABI remained significantly improved (more than 0.15 units higher than their preoperative value) and additional objective information, such as angiograms or operations, did not contradict these observations. Patency failure also included bypass grafts that were removed because of an infection or aneurysmal degeneration. Patency rates were compared by using the Kaplan-Meier life table analysis.

RESULTS

The cumulative assisted primary patency rates were statistically similar among the different conduit types at 2 years (SV, 81%; HUV, 70%; PTFE, 69%). After 5 years, above-knee SV bypass grafts had a significantly (P </=.01) better patency rate (73%) than HUV bypass grafts (53%), which had a significantly (P </=.01) better patency rate than PTFE bypass grafts (39%). Limb salvage was slightly worse with PTFE conduits. The number of bypass graft thromboses and major amputations within the first 30 days was highest in the HUV group.

CONCLUSION

The overall results of this prospective randomized study suggest that the SV should be considered as the bypass graft of choice for femoral-popliteal above-knee reconstruction and that, when a prosthetic bypass graft is used, an HUV should also be considered as an alternative choice to PTFE.

Prospective randomised trial of distal arteriovenous fistula as an adjunct to femoro-infrapopliteal PTFE bypass

OBJECTIVES

To compare graft patency and limb salvage rate following femoro-infrapopliteal bypass using ePTFE grafts with and without the addition of adjuvant arterio-venous fistula.

DESIGN

A prospectively randomised controlled trial.

MATERIALS

Patients referred to two teaching hospital vascular surgery units in the U.K. for the treatment of critical limb ischaemia.

METHODS

Eighty-seven patients (M:F; 2.3:1) undergoing 89 femoro-intrapopliteal bypass operations with ePTFE grafts for critical limb ischaemia were randomly allocated to have AVF included in the operative procedure (n = 48) or to a control group without AVF (n = 41). An interposition vein-cuff was incorporated at the distal anastomosis in all patients.

RESULTS

The cumulative rates of primary patency and limb salvage at 1-year after operation for patients with AVF were 55.2% and 54.1% compared to 53.4% and 43.2%, respectively, for the control group. The differences between the AVF and control groups did not reach statistical significance, in terms of either graft patency or limb salvage, at any stage after operation (Log-Rank test).

CONCLUSIONS

AVF confers no additional significant clinical advantage over interposition vein cuff in patients having femoro-infrapopliteal bypass with ePTFE grants for critical limb ischaemia.

Below-knee popliteal and distal bypass with PTFE and vein cuff

OBJECTIVES

To determine the value of PTFE grafts with a distal vein cuff as a conduit for below-knee (BK) popliteal and distal bypass in the absence of autologous vein.

DESIGN

Retrospective study.

MATERIALS AND METHODS

Forty below BK popliteal and distal bypass procedures in 39 patients with PTFE and distal vein cuff (Miller cuff n = 31, Wolfe cuff and adjuvant arteriovenous fistula n = 9). Nineteen primary and 21 secondary reconstruction procedures.

RESULTS

The primary patency rate was 62.5% at 1 year falling to 50% at 2 years. The secondary patency rates were very similar owing to poor outcome of thrombectomy. Ten cases (25%) resulted in major amputation postoperatively. There was a tendency towards better outcome for primary procedures compared to secondary/redo procedures.

CONCLUSIONS

BK popliteal and distal bypass with PTFE and distal vein cuff is a worthwhile procedure in the absence of autologous vein. The value of thrombectomy following thrombosis of a secondary bypass procedure with PTFE and distal vein cuff is questionable.

A completely biological tissue-engineered human blood vessel

Mechanically challenged tissue-engineered organs, such as blood vessels, traditionally relied on synthetic or modified biological materials for structural support. In this report, we present a novel approach to tissue-engineered blood vessel (TEBV) production that is based exclusively on the use of cultured human cells, i.e., without any synthetic or exogenous biomaterials. Human vascular smooth muscle cells (SMC) cultured with ascorbic acid produced a cohesive cellular sheet. This sheet was placed around a tubular support to produce the media of the vessel. A similar sheet of human fibroblasts was wrapped around the media to provide the adventitia. After maturation, the tubular support was removed and endothelial cells were seeded in the lumen. This TEBV featured a well-defined, three-layered organization and numerous extracellular matrix proteins, including elastin. In this environment, SMC reexpressed desmin, a differentiation marker known to be lost under standard culture conditions. The endothelium expressed von Willebrand factor, incorporated acetylated LDL, produced PGI2, and strongly inhibited platelet adhesion in vitro. The complete vessel had a burst strength over 2000 mmHg. This is the first completely biological TEBV to display a burst strength comparable to that of human vessels. Short-term grafting experiment in a canine model demonstrated good handling and suturability characteristics. Taken together, these results suggest that this novel technique can produce completely biological vessels fulfilling the fundamental requirements for grafting: high burst strength, positive surgical handling, and a functional endothelium.

Prospective randomized study of carbon-impregnated polytetrafluoroethylene grafts for below-knee popliteal and distal bypass: results at 2 years. The Association Universitaire de Recherche en Chirurgie

The purpose of this prospective randomized multicenter study is to compare patency for a new carbon-impregnated polytetrafluoroethylene (PTFE) graft and standard PTFE grafts. One hundred and sixty patients presenting severe chronic ischemia of the lower extremity were recruited at 17 centers of the French Association Universitaire de Recherche en Chirurgie. Eighty-one carbon-impregnated graft and 79 standard grafts were implanted. The procedure consisted of below-knee femoropopliteal bypass in 83 cases and femorodistal bypass in 77 cases. The minimum duration of the follow-up period was 2 years. Twenty-four patients died during the study. The actuarial primary patency rate, actuarial secondary patency rate, and limb salvage rate were 45%, 53%, and 57% respectively in the carbon-impregnated PTFE group and 35%, 36%, and 47% respectively in the standard PTFE group. The carbon-impregnated graft appeared to achieve better patency than the standard graft but the difference was not statistically significant. Since there was no difference up to 12 months, the study will be continued to determine if further follow-up confirms these findings. In this study we also assessed factors contributing to patency of below-knee prosthetic bypass grafts. Only two factors had a significant influence on patency, i.e., ankle/arm pressure difference greater than 0.25 as opposed to ankle/arm pressure difference less than 0.25 (p < 0.01) and below-knee femoropopliteal bypass as opposed to femorodistal bypass (p < 0.001).

Incorporation of nitric oxide-releasing crosslinked polyethyleneimine microspheres into vascular grafts

Over the years, many attempts have been made to increase the patency of small- to medium-sized prosthetic vascular grafts. However, none of them has greatly affected long-term rates. Recently, nitric oxide (NO) has been shown to inhibit thrombus formation in such grafts, suggesting that local delivery of NO may help to increase graft patency. This study describes the site-specific delivery of NO by entrapping NO-releasing microspheres in the pores of a vascular graft. NO-releasing polyethyleneimine microspheres (PEIX) were developed using a novel water-in-oil emulsion technique involving chemical crosslinking with a bis-epoxide. The PEIX microspheres were then derivatized with NO forming the [N(O)NO]- moiety of the diazeniumdiolates formerly known as NONOates. These polymeric NO-releasing particles were found to spontaneously release 194 nmol NO/mg with a half-life of over 66 h under physiologic conditions. Fluorescein isothiocyanate-labeled microspheres were then embedded into the pores of a 60-micron nonreinforced Gore-tex vascular graft using a simple evacuation technique and evaluated for microsphere placement and NO release. Scanning electron microscopic analysis showed the microspheres entrapped in the pores of the vascular graft releasing 10 nmol NO/mg with a half-life of 51 h. The microspheres remained entrapped in the graft even after immersion and NO release, as confirmed by fluorescence of the medium. These results suggest that NO-releasing particles can be incorporated into the pores of a vascular graft to deliver therapeutic amounts of NO for the prevention of thrombosis in small-diameter prosthetic grafts.

Analysis of 274 Omniflow Vascular Prostheses implanted over an eight-year period

BACKGROUND

Polytetrafluoroethylene (PTFE), dacron, and, more recently, collagen prostheses are finding increasing use for femoropopliteal reconstruction when a suitable vein is not available. The main factors to be considered when choosing a prosthesis are patency, susceptibility to infection and formation of aneurysms.

METHODS

Sheep collagen prostheses were implanted on 274 occasions in the femoropopliteal or crural regions.

RESULTS

The patency rate for supragenual bypass after 3 years was 61.9% with good vascular periphery and 44% with poor vascular periphery. If the prosthesis extended below the knee, the patency rate was 55.4% with good and 35.3% with unfavourable vascular periphery. Patency for the femorocrural bypass was 28.7% after 2 years. The rate of infection was 0% and an aneurysm occurred in three patients (1.1%).

CONCLUSIONS

With this low infection rate and very slight danger of aneurysm, the long-term results suggest that the ovine collagen prosthesis can be recommended for use when no suitable vein is available.

The effect of a surveillance programme on the patency of synthetic infrainguinal bypass grafts

OBJECTIVES

Vein graft surveillance is widely acknowledged to be of benefit in improving graft patency at least in the first year after arterial bypass surgery. The aim of this study was to examine the effect of a surveillance programme on the patency of synthetic infrainguinal bypass grafts.

DESIGN

A prospective study of 69 consecutive prosthetic bypass grafts was undertaken over a 3 year period.

METHODS

Patients were seen at 3 monthly intervals after surgery and underwent measurement of ankle brachial pressure indices and a colour Duplex scan of the graft.

RESULTS

The surveillance programme was able to detect treatable lesions in five grafts and in the run-off vessels of two other grafts prior to occlusion. However 14 grafts failed after the first 30 days, 12 of which were not predicted by the surveillance programme.

CONCLUSIONS

Surveillance appears to be of limited benefit in the maintenance of patency of synthetic infrainguinal bypass grafts.

Femoropopliteal bypass revisited: an analysis of 138 cases

Femoropopliteal bypass is utilized for infrainguinal arterial reconstruction in patients with claudication, rest pain, non-healing ulcers and gangrene. Reported patency and limb salvage rates have varied considerably and controversy exists concerning conduit choice. The purpose of this study was to review the authors' results with femoropopliteal bypass to determine factors which may influence outcome in a contemporary series of patients. Between 1986 and 1991, 138 femoropopliteal bypasses were performed in 120 patients. Mean follow-up was 28 (range 1-66) months. Autogenous vein was used in 59% and polytetrafluoroethylene (PTFE) in the remainder. Above-knee anastomoses were performed in 34% and below-knee in 66%. The secondary patency for autogenous vein grafts (95% at 4 years) was significantly better than for PTFE grafts (69% at 4 years; P<0.01). Secondary patency for below-knee autogenous vein grafts also was better than that for below-knee PTFE grafts (95% versus 50% at 4 years; P<0.02). Limb salavage rates were worse for below-knee PTFE grafts than all other groups (P<0.01). Eight of 15 failed above-knee PTFE grafts were salvaged with below-knee autogenous vein grafts and did well. In the present series, autogenous vein femoropopliteal grafts demonstrated better overall patency and limb salvage. Below-knee PTFE bypasses should be reserved for limb salvage cases in patients without adequate autogenous conduits. Failed PTFE grafts can be salvaged by autogenous bypasses, yet an advantage to this approach was not seen.

Preferential use of vein for above-knee femoropopliteal grafts

OBJECTIVES

Many centres preferentially use polytetrafluoroethylene (PTFE) for above-knee femoropopliteal bypass as surgery is simplified and patency rates are comparable to vein, which is preserved for subsequent revisions or for distal disease progression. In this Unit, vein remains first choice graft material. The aim of this study was to audit our results with respect to above-knee bypass to establish the demand for vein for secondary reconstruction and to document the ultimate fate of the limb.

PATIENTS

Between 1983 and 1992, 112 above-knee reconstructions were performed on 109 patients (89 vein and 23 PTFE grafts). PTFE was used where vein was absent or inadequate. Life table analysis of primary graft patency, limb salvage and patient survival up to 36 months follow-up concurs with previously reported series.

RESULTS

Twenty-eight vein grafts (31%) and 11 PTFE grafts (48%) occluded during a median follow-up of 64 months (8-116 months). In only four cases was vein required for secondary procedures. The remainder were salvaged by thrombectomy and local procedures for technical problems. Amputation rates following graft occlusion were 12% in the vein group (20% of these being above-knee) as against 26% in the PTFE group (80% above knee).

CONCLUSIONS

The demand for vein for secondary procedures is low. Amputation rates when vein grafts do occlude are half those of PTFE and amputation level is significantly influenced by graft type. We advocate preferential use of vein in above-knee femoropopliteal bypass.

The current status of prosthetic-vein composite grafts for lower extremity revascularization

When infrageniculate lower extremity vascular reconstructions are required in the face of inadequate or insufficient autogenous vein, prosthetic-vein composite grafts remain a viable alternative. Graft patency and limb salvage for composite grafts are intermediate between those of completely autogenous and prosthetic bypasses alone. The sequential technique may offer superior patency in patients with the appropriate anatomy. The addition of adjunctive techniques such as a distal arteriovenous fistula and/or anticoagulation may further improve results. An algorithm illustrating the proper role of composite grafts for distal lower extremity reconstructions is shown in Figure 6. Any significant interval of patency is important in this group of patients in whom limb salvage can often be achieved by healing ischemic lesions and in whom overall life expectancy is limited.

Long-term results with the Palmaz stent in the superficial femoral artery

PURPOSE

Femoral stenting has demonstrated inconsistent and often disappointing long-term results. To compare out experience, we retrospectively analyzed a series of patients who had Palmaz balloon-expandable stents placed exclusively for superficial femoral artery (SFA) lesions.

METHODS

From January 1990 to November 1993, 39 patients were evaluated for claudication (79%) or critical ischemia in 42 limbs. The culprit lesions were confined to the SFA: 24 (57%) occlusions and 18 (43%) stenoses, including 3 restenotic lesions. Stenting was elective in 12 (29%) cases: the 3 restenoses and 9 chronic, calcified occlusions. The remaining stents were applied for postangioplasty residual stenosis or angioscopic findings of thrombogenic luminal irregularities. A total of 55 prostheses were successfully implanted. All patients were maintained on ticlopidine and followed by routine duplex scanning. Follow-up angiography was performed in 28 (72%) patients between 4 and 45 months.

RESULTS

In the postprocedural period, two acute thromboses (4.8%) occurred within 48 hours in patients who had long occlusions and poor runoff; no other major complications were encountered, for a clinical success rate of 95%. Follow-up evaluation ranged from 4 months to 4 years with a mean of 25 months. The restenosis rate was 19% (34% in occlusions; 10% in stenotic lesions, p = NS). At 24 months, cumulative primary patency was 77% and secondary patency 89%.

CONCLUSIONS

Palmaz stents performed will in the SFA, demonstrating a low acute thrombosis rate and good long-term patency. The incidence of restenosis is likely to be greater in occlusions than in stenoses.

Cryopreserved saphenous vein allografts for below-knee lower extremity revascularization

OBJECTIVE

Cryopreserved saphenous vein allografts have been offered as an alternative conduit for bypass in ischemic limbs. The authors examined the efficacy of this conduit for arterial bypass to the distal popliteal and tibial arteries in patients in whom autogenous vein was not available.

SUMMARY BACKGROUND DATA

Previous experience with arterial and venous allografts has been unsatisfactory because of aneurysmal degeneration and poor patency. Endothelial loss and host rejection have been suggested as mechanisms of graft failure. Cryopreservation by modern techniques with rate controlled freezing, dimethyl sulfoxide (DMSO), and other cryopreservants, has addressed these issues and rekindled interest in vein allografts.

METHODS

Over a period of more than 5 years, 115 cryopreserved vein allografts were implanted in 87 limbs to the distal popliteal (14) or tibial (101) arteries. The indication for surgery was rest pain in 56 procedures (49%), gangrene in 36 (31%), claudication in 21 (18%), and replacement of aneurysmal allografts in 2. Follow-up was 1 to 61 months (mean 25 months).

RESULTS

There was no significant difference in patency related to site of proximal or distal anastomosis, patency of runoff vessels, use of anticoagulation, age, sex, diabetes, hypertension, smoking, indication, source of graft, or use of multiple segments. Revision was required in six grafts for aneurysmal dilatation. Histologic examination of explanted sections of allografts showed no immune response, and immunosuppressive drugs were not used.

CONCLUSIONS

Although limb salvage has been satisfactory, long-term patency rates for cryopreserved vein allografts are poor when compared with autogenous vein. The cost of cryopreserved allografts far exceeds that of prosthetic grafts, for which comparable and superior results have been reported. Use of cryopreserved vein allografts should be reserved for situations in which adequate lengths of autogenous vein do not exist and the risk of infection of prosthetic grafts is high.

ePTFE grafts for femoro-crural bypass--improved results with combined adjuvant venous cuff and arteriovenous fistula?

Patency rates for long prosthetic bypass grafts with standard anastomoses to single tibial or peroneal arteries are very poor. Adjuvant techniques employed with the aim of improving patency rates include arteriovenous fistula (AVF) at the distal anastomosis to accelerate blood flow above thrombotic threshold velocity (TTV) and a venous cuff (VC) or patch which may reduce or modify anastomotic myointimal hyperplasia within the recipient artery. In a consecutive series of 43 femoro-crural bypasses with ePTFE grafts, adjuvant AVF and VC procedures have been applied in combination. The results are compared with those of an antecedent series of 76 similar grafts with AVF alone and a contemporaneous series of 179 autologous vein grafts. All operations were undertaken for critical limb ischaemia with anastomosis to a single calf or pedal artery. The three groups were well matched for age, sex, diabetes, smoking history, previous surgery and the proportion with rest pain and tissue necrosis. The cumulative patency rate at 2 years for ePTFE grafts with combined AVF and VC was 62% compared to 28% for those with AVF alone and 68% for autologous vein grafts. The patency rate for prosthetic grafts with AVF and VC was significantly higher than AVF alone (p < 0.01) and did not differ significantly from vein grafts. Cumulative limb salvage rates for ePTFE grafts with AVF and VC were 68% at 1 year and 55% at 2 years compared to 38 and 35% for AVF alone and 78 and 69% for vein grafts.(ABSTRACT TRUNCATED AT 250 WORDS)

Femorocrural grafting and regrafting: does polytetrafluoroethylene have a role?

Between 1980 and 1988, 263 patients received 307 femorocrural bypass grafts. 180 were primary infrainguinal grafts, 106 secondary, 18 tertiary and three quaternary. Rest pain or tissue loss was the indication in 96% of cases. Outflow vessels were the tibioperoneal trunk (n = 34), posterior tibial artery (n = 115), peroneal artery (n = 89) and anterior tibial artery (n = 69). 88 primary vein grafts were completed. 201 polytetrafluoroethylene (PTFE) grafts were inserted (92 primary and 109 subsequent reconstructions). There were no direct PTFE to crural vessel anastomoses. A Miller cuff was used in the majority (n = 175). The three year primary patency for primary vein grafts (36%) was similar to primary PTFE grafts (29%), but significantly higher than subsequent PTFE grafts (20%) (p = 0.03). Three year foot salvage for primary vein grafts (65%) was similar to primary PTFE (64%), but significantly better than subsequent PTFE (42%) (p = 0.02). The results support both redo femorocrural grafting for critical ischaemia, as judged by foot salvage rates, and the use of PTFE with a distal vein cuff in primary and subsequent femorocrural reconstruction if autologous vein is not available.

Polytetrafluoroethylene in above-knee arterial bypass surgery for critical ischemia

Seventy-one consecutive above-knee polytetrafluoroethylene (PTFE) femoropopliteal arterial bypasses performed between 1981 and 1989 for critical ischemia were followed prospectively to determine graft patency and limb salvage. Cumulative graft patency and limb salvage rates were calculated by life table analysis. Graft patency was 80%, 68%, 55%, 39%, and 39%, and limb salvage 97%, 87%, 84%, 77%, and 77% at 1, 2, 3, 4, and 5 years, respectively. Twenty-nine grafts have occluded with re-emergence of critical ischemia in 14, treated by 5 amputations and 9 reconstructions using autogenous saphenous vein (ASV) in 6 and PTFE in 3. These favorable results are not as good in terms of primary patency as those reported with ASV, but good limb salvage, good early patency, ease of use, and preservation of the saphenous vein for use later have encouraged us toward primary use of PTFE in selected patients. This experience strongly questions the wisdom of an "all autogenous" policy for reconstruction at this level.

Improved technique for polytetrafluoroethylene bypass grafting: long-term results using anastomotic vein patches

Results of peripheral arterial bypass using polytetrafluoroethylene grafts have remained poor in comparison with those using saphenous vein grafts, particularly for anastomoses to tibial and peroneal vessels. A simple modification to the conventional operative technique, involving the incorporation of a vein patch into the distal anastomosis, has enabled considerable improvement. Five-year patency rates of 71 per cent for popliteal and 54 per cent for infrapopliteal grafts have been achieved in a series of 256 patients operated on between 1982 and 1989.

Infrainguinal polytetrafluoroethylene grafts: saved limbs or wasted effort? A report on ten years' experience

Two-hundred and twenty-four infrainguinal polytetrafluoroethylene reconstructions were performed for critical ischemia over a 10 year period: 48 to the above-knee popliteal artery, 113 to the below-knee popliteal artery, and 63 to the tibial vessels. The cumulative patency rates were 84 +/- 6% and 63 +/- 9% for above-knee popliteal, 53 +/- 5% and 35 +/- 7% for below-knee popliteal, 45 +/- 6% and 30 +/- 9% for tibial vessels at one and five years respectively. Limb salvage rates were 81 +/- 6% and 73 +/- 9% (above-knee popliteal), 69 +/- 5% and 57 +/- 9% (below-knee popliteal), 64 +/- 7% and 32 +/- 10% (tibial vessels) at one and five years respectively. Graft occlusion did not result in limb loss in 32 cases. Preoperatively, 54% of the patients had limited mobility while 43% were regarded as severely restricted. At follow-up, 57% of the patients were considered to be independent, 26% had limited mobility, and 17% were still severely restricted. Polytetrafluoroethylene provides good short-term limb salvage and improved mobility in patients with critical ischemia and poor life expectancy. Its use is well worth the effort.

Infrainguinal bypass surgery: factors determining late graft patency

The results of 373 infrainguinal bypass grafts, in a single centre, between 1980 and 1988 are reviewed. One hundred and thirty in situ vein (ISV), 47 reversed saphenous vein (RSV), 118 polytetrafluoroethylene (PTFE) and 78 human umbilical vein (HUV) grafts were used. The indications for surgery were disabling claudication in 25 per cent of patients and limb salvage in 75 per cent. In 36 per cent of operations the distal anastomosis was above the knee and in 64 per cent it was below the knee. Overall 5-year patency rates and limb salvage rates respectively were, for ISV (41 and 69 per cent), RSV (62 and 90 per cent), PTFE (31 and 67 per cent) and HUV (29 and 59 per cent). There was no significant difference in patency among these grafts at the above-knee level, but significant differences between vein and prosthetic grafts were evident below the knee (P less than 0.001). Using a proportional hazards model the three factors that consistently correlated with late graft patency were graft type (P less than 0.001), site of distal anastomosis (P less than 0.001) and distal run-off (P less than 0.001). Overall, the results suggest that prosthetic grafts are a suitable alternative to autogenous vein when the distal anastomosis is above the knee, but vein should always be used, if available, below the knee joint.

Current techniques for infrainguinal arterial reconstruction

Infrainguinal reconstruction for peripheral vascular occlusive disease comprises an increasingly complex array of interventions which provide unparalleled options for the salvage of threatened limbs. Conventional autogenous saphenous vein bypass remains the most durable revascularization with anticipated graft patency rates approaching 80 percent after five years and excellent long term limb salvage. These excellent results are equally applicable to vein grafts carried to infrapopliteal and even inframalleolar levels, possibly reflecting increased utilization of the in situ method. Although 20 per cent of grafts fail within five years, secondary intervention results in sustained limb salvage in the majority of patients. In the absence of autogenous vein, however, prosthetic material performs poorly such that new interventions consisting of percutaneous transluminal angioplasty, rotary atherectomy devices and laser systems are under aggressive development. Although initial results with these devices are encouraging, long term patency rates remain poor largely due to restenosis. Further progress seems to depend primarily on an increased understanding of the natural healing response of the injured artery.

Endothelial cell response to polyvinyl chloride-packaged GORETEX: effect of surface contamination

A Fourier transform infrared spectroscopic study of polyvinyl chloride packaged GORETEX vascular prostheses indicated that their internal and external surfaces were coated with an additive layer presumed to be derived from the polyvinyl chloride packaging. This layer was not removed by washing in phosphate buffered saline but was soluble in trimethyl pentane and hexane. Some other treatments of GORETEX and the packaging were shown to remove the contaminant from the surface and this correlated with an inferior in vitro aortic endothelial cell response. Analyses of materials extracted from both the polyvinyl chloride and the GORETEX surface indicated that the major surface component was a long chain aliphatic ester, either a plasticizer or a lubricant constituent.

The effect of distal anastomotic site on PTFE graft patency in lower extremity bypass

The site of distal anastomosis of polytetrafluorethylene (PTFE) lower extremity bypass grafts may significantly affect results. We examined patency in 144 cases; 45 femoro-popliteal above knee (AK), 55 femoro-popliteal below the knee (BK) and 44 femoro-distal (D) PTFE bypasses, the groups being comparable with regard to other risk factors studied. Cumulative graft patency at 3 years was 71.3% for AK, 36.7% for BK, 16.4% for D and overall 35%. The site of distal anastomosis is an important determinant, of PTFE lower extremity bypass patency. We have abandoned the use of PTFE for BK and D, but feel that AK PTFE is a suitable alternative to autogenous reversed saphenous vein.

Below-knee femoropopliteal bypass using externally supported polytetrafluoroethylene (PTFE) grafts

Twenty-seven externally supported polytetrafluoroethylene (PTFE) grafts were implanted in the femoropopliteal position crossing the knee joint. All patients underwent surgery because of limb threatening ischemia (rest pain or gangrene). There was one early graft failure (successful thrombectomy). No patient died postoperatively. The mean follow-up period was 17.32 months (range 3-44 months). Cumulative patency rate for this follow-up period was 73%. Absence of kinking when bending the knee joint was determined by ankle Doppler pressure measurements and arteriography. If an adequate saphenous vein is not available for knee-crossing femoropopliteal bypass, externally supported PTFE can be used, yielding short-term patency rates comparable to those obtained with autologous venous bypasses.

The non-reversed vein femoro-distal bypass graft: a modification of the standard in situ technique

The results of 85 in situ vein femoro-distal bypass grafts using a modified technique where the vein was completely mobilised but left "non-reversed" have been reviewed with particular regard to risk factors and complications. The distal anastomosis was to the infrageniculate popliteal artery in 55% and to the tibioperoneal trunk or a single calf vessel in the rest. Arteriographic run-off was by a single vessel in 42%. The primary failure rate at 1 month was 20% and the secondary failure rate 9%; the majority of early failures being due to missed technical errors despite the use of a pulse volume recorder. The cumulative secondary patency rate at 1 and 2 years was 77% and 72%; limb salvage 85% and 77%; and patient survival 89% and 83% respectively. The only significant risk factors were the level of the distal anastomosis and the run-off (P = 0.002 and 0.03 respectively). Complete mobilisation of the vein allows a tension free proximal anastomosis to the common femoral artery and avoids the risk of arteriovenous fistulae. A high vein utilisation rate of 93% was achieved by using a small 2.5 mm Hall valvulotome. Although there was a trend towards lower patency rates in veins with a minimum diameter less than 4 mm the results are still superior to PTFE. Compared to reversed vein the in situ technique has a better utilisation rate and the long-term patency rates are at least as good if not better. Improved methods of haemodynamic assessment during reconstruction to reduce technical errors may be the key to better early patency rates.

Choice of material for above-knee femoropopliteal bypass graft

Autogenous saphenous vein is generally considered to be the best material for arterial bypass grafts below the inguinal ligament. Recent results have suggested that the advantage of vein over prosthesis is more pronounced in a distal situation, but it is not immediately apparent whether the difference is sufficient to justify a policy of using prosthesis for the initial above-knee graft to preserve the vein in case later surgery is required. An attempt has been made to answer this question. The literature has been reviewed to obtain estimates of the patency rates for grafts in different situations and a mathematical model has been set up using these figures to predict the outcome of different treatment policies. The model can be used to predict the result of alteration or inaccuracy in the data or to make use of the results of newly reported studies. The model predicts that the use of prosthesis for an initial graft will reduce the overall patency and substantially increase the requirement for reoperation, even if the present data give a substantial overestimate of the advantages of vein above the knee.