Infrainguinal revascularisation in the era of vein-graft surveillance--do clinical factors influence long-term outcome?

Gene Therapy for the Extension of Vein Graft Patency: A Review

The mainstay of treatment for long-segment small-vessel chronic occlusive disease not amenable to endovascular intervention remains surgical bypass grafting using autologous vein. The procedure is largely successful and the immediate operative results almost always favorable. However, the lifespan of a given vein graft is highly variable, and less than 50% will remain primarily patent after 5 years. The slow process of graft malfunction is a result of the vein's chronic maladaptive response to the systemic arterial environment, its primary component being the uncontrolled proliferation of vascular smooth muscle cells (SMCs). It has recently been suggested that this response might be attenuated through pre-implantation genetic modification of the vein, so-called gene therapy for the extension of vein graft patency. Gene therapy seems particularly well suited for the prevention or postponement of vein graft failure since: (1) the stimulation of SMC proliferation appears to largely be an early and transient process, matching the kinetics of current gene transfer technology; (2) most veins are relatively normal and free of disease at the time of bypass allowing for effective gene transfer using a variety of systems; and (3) the target tissue is directly accessible during operation because manipulation and irrigation of the vein is part of the normal workflow of the surgical procedure. This review briefly summarizes the current knowledge of the incidence and basic mechanisms of vein graft failure, the vector systems and molecular targets that have been proposed as possible pre-treatments, the results of experimental genetic modification of vein grafts, and the few available clinical studies of gene therapy for vascular proliferative disorders.

The role of established and emerging risk factors in peripheral vascular graft occlusion

Several studies have evaluated the association between established as well as emerging vascular risk factors with peripheral graft occlusion. There is evidence for a link between the risk for graft occlusion and total serum cholesterol, low-density lipoprotein cholesterol and triglyceride levels. The overall effect of smoking shows a 2.35-fold increase in risk of graft failure. Studies involving diabetic patients undergoing peripheral bypass may have failed to detect higher occlusion rates, possibly due to increased morbidity and mortality as well as higher amputation rates even if the graft is patent. Both antiplatelet agents and anticoagulation seem to be effective in the prevention of graft occlusion. Unconvincing data have been published with regards to the effect of hypertension on graft patency. Emerging factors such as fibrinogen, lipoprotein (a), C-reactive protein and homocysteine levels should also be considered when assessing the risk of graft occlusion. More research is needed to prevent graft occlusion due to the obvious clinical relevance, quality of life and cost issues.

Homocysteine Levels, Haemostatic Risk Factors and Patency Rates After Endovascular Treatment of the Common Iliac Arteries

OBJECTIVES

To investigate the impact of clinical risk factors, plasma homocysteine and haemostatic variables on the results after endovascular treatment of symptomatic atherosclerosis of the common iliac artery.

DESIGN

Prospective observational study.

SETTING

University hospital.

PATIENTS AND METHOD

The study included 139 technically successful interventions in 103 patients. Technical success was defined as < or = 30% residual stenosis as seen on the post treatment angiogram. Blood samples for analyses of fasting plasma values of homocysteine, fibrinogen, D-dimer, activated protein C resistance were drawn upon admission. Median follow-up for all procedures was 22 months (range 0-55 months). Patency was defined as freedom from > or = 50% restenosis or reocclusion.

RESULTS

The technical success rate for all procedures was 93%. The 1-year cumulative primary patency rate based on intention to treat was 85%. Multivariate analysis revealed a significant independent association between patency rates and levels of fibrinogen and homocysteine and the nature of the lesion treated (stenosis vs. occlusion).

CONCLUSION

The aetiology of restenoses and reocclusions is probably multifactorial. Procoagulant activity, the nature of the lesion treated and homocysteine levels within and above the upper range of normal limits are important risk factors for failure after endovascular treatment of the common iliac arteries.

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.

Biologic degeneration of vein grafts after thrombotic occlusion: thrombectomy within 3 days results in better indices of viability

OBJECTIVES

To clarify the mechanism for poor patency of vein grafts after thrombectomy and the time limit for successful salvage operation, we investigated the time course of biologic degenerative changes in thrombosed vein grafts. Materials and methods The right femoral artery was replaced with a femoral vein graft in 25 mongrel dogs. After 3 months, grafts were explanted in 5 dogs (control grafts), and the remaining 20 dogs underwent femoral artery ligation to create a thrombosed graft. Of the 20 grafts, 5 were explanted at 3 days after ligation (group I-3) and 5 were explanted at 5 days after ligation (group I-5). Of the remaining 10 grafts, 5 underwent thrombectomy at 3 days after ligation (group II-3) and 5 underwent thrombectomy at 5 days after ligation, and were reimplanted into the left femoral artery, then explanted 28 days after reimplantation. The grafts were assessed with immunohistochemistry and prostaglandin (PG) I(2) assay (6-keto-PGI(1alpha)).

RESULTS

Of the 25 grafts, occlusion recurred in 3 in group II-5 within 28 days after reimplantation. There were significant differences between group I-5 and group I-3 or control grafts for percentage of areas positive for alpha-actin, total number of cells per field, and proliferating cell nuclear antigen (PCNA)-positive cells in layer of thickened intima and atrophied media (I/M), and for total cell and PCNA- positive cell numbers per field in the adventitia. Mean 6-ketoPGF(1alpha) was 40 +/- 14.1 pg/mg/min in control dogs, 84 +/- 18.9 pg/mg/min in group I-3, and 15.4 +/- 7.7 pg/mg/min in group I-5, demonstrating a significant reduction in group I-5 (P =.009).

CONCLUSION

Graft wall cell viability and PGI(2) production in thrombosed vein grafts are well preserved for up to 3 days. Therefore graft salvage operations no later than 3 days after thrombotic occlusion may provide acceptable long-term patency of salvaged grafts.

Infrainguinal bypass graft patency and limb salvage rates in critical limb ischemia: influence of the mode of presentation

Rest pain, ulceration, and gangrene are often considered together in studies describing outcomes in patients with critical limb ischemia. A retrospective analysis of prospectively collected data of 152 infrainguinal bypass grafts performed on 128 patients with chronic critical limb ischemia over a 6-year period was carried out. Grafts were classified according to the mode of presentation and were followed up by regular clinical and duplex examinations. Mean follow-up period was 29 months (range 12 to 60 months). Patients' demographics, risk factors, and graft characteristics were not statistically different between the groups. The 5-year cumulative primary patency rates were 33%, 52%, and 51% for gangrene, ulceration, and rest pain, respectively (p = 0.04). The 5-year cumulative primary assisted patency rates were 46%, 70%, and 72% for gangrene, ulceration, and rest pain, respectively (p = 0.01). The 5-year cumulative secondary patency rates were 48%, 76%, and 75% for gangrene, ulceration, and rest pain, respectively (p = 0.003). The 5-year cumulative limb salvage rates were 59%, 87%, and 83%, for gangrene, ulceration, and rest pain, respectively (p = 0.01). Gangrene is a distinct subcategory of critical limb ischemia with a worse prognosis than ulceration and rest pain and should be classified as such when reporting results of infrainguinal bypass grafts.

Conduit choice for above-knee femoropopliteal bypass grafting in patients with limb-threatening ischemia

Many surgeons consider PTFE to be the conduit of choice for above-knee femoropopliteal bypass grafting, since PTFE is relatively easy to implant and spares autogenous saphenous vein (ASV) for subsequent peripheral or coronary artery bypass grafting (CABG). This practice has recently been challenged, as some studies have suggested that ASV may exhibit superior patency in certain patient subgroups. The purpose of this retrospective study was to examine the contemporary outcome of above-knee femoropopliteal bypass grafting in patients with limb-threatening ischemia. Between January 1995 and December 2000, 159 above-knee femoropopliteal bypass grafts were created for limb-threatening ischemia (rest pain or tissue loss). There was a high incidence of comorbid illness, including open foot wounds at the time of operation (62%), hypertension (58%), coronary artery disease (53%), diabetes mellitus (36%), cerebrovascular disease (23%), prior contralateral bypass or amputation (21%), disadvantaged or "blind" outflow (19%), prior ipsilateral bypass (14%), prior CABG (11%) end-stage renal failure (7%). The use of PTFE predominated (n = 11), with a minority of grafts comprising single-segment ipsilateral or contralateral ASV (n = 18). Although the small number of patients undergoing ASV grafting limited the statistical power of comparison, our results suggest that above-knee ASV performs better than PTFE in patients with limb-threatening ischemia.

The hemodynamics of vein grafts: measurement and meaning

The long-term patency of infrainguinal vein grafts appears to depend primarily on the size and quality of the venous conduit. Therefore, those quantities which directly relate to the conduit's ability to act as a transporter of blood, namely internal diameter and longitudinal impedance (Z(L)), have predictive value for patency. Autologous grafts of good quality frequently remain patent even with compromised outflow. Therefore, those quantities that are outflow dependent, including deltaP, flow, velocity, shear stress, and resistance, carry less predictive value for long-term performance.

Effective hemodynamic diameter: an intrinsic property of vein grafts with predictive value for patency

INTRODUCTION

Conduit size and quality are major determinants of the long-term success of infrainguinal autologous vein grafting. However, accurate measurement of the internal diameter of vein grafts is difficult given their variable wall thickness and taper. The purpose of this study was to define the "effective" internal diameter of a vein graft according to its hemodynamic properties and to determine its significance for graft patency.

METHODS

Sixty infrainguinal bypass grafts performed on 57 patients were evaluated intraoperatively. Proximal and distal graft pressure and blood flow (Q(meas)) were measured with fluid-filled catheter transduction and ultrasonic transit-time flowimetry, respectively, after unclamping. Waveforms were recorded digitally at 200 Hz under baseline conditions and after stimulation with 60 mg of papaverine. According to Fourier transformation of the measured pressure gradient (DeltaP), the Womersley solution for fluid flow in a straight rigid tube was used to calculate theoretical flow waveforms (Q(calc)) for a range of graft diameters. The theoretical waveforms were then compared with the measured flow waveforms and the best-fit diameter chosen as the "effective hemodynamic diameter" (EHD). Only grafts in which the correlation coefficient of Q(calc) versus Q(meas) was more than 0.90 were accepted (n = 47) to assure validity of the hemodynamic model. After a mean follow-up of 12.5 months (range, 0.1-43.9 months), patency was determined by the life table method. Hemodynamic and clinical variables were tabulated, and their effect on patency determined the use of univariate and multivariate Cox regression.

RESULTS

Mean EHD was 4.1 +/- 0.1 mm with a range of 2.5 to 5.7 mm. Administration of papaverine caused profound changes in DeltaP (+78% +/- 17%) and Q(meas) (+71% +/- 12%) as expected, but had no effect on EHD (+0.05% +/- 0.1%). Univariate regression identified five variables associated with decreased secondary patency (P <.10): low EHD, conduit source other than the greater saphenous vein, high baseline DeltaP(mean), female sex, and redo operation. Of these, only low EHD was significant after multivariate analysis (P =.03). Patency of small diameter grafts (EHD < 3.6 mm; n = 11) was compared with patency of larger grafts (EHD > 3.6 mm; n = 36) to test a frequently espoused clinical guideline. Grafts with an EHD less than 3.6 mm exhibited significantly lower secondary patency compared with larger grafts (P =.0001). The positive and negative predictive values for an EHD less than 3.6 mm for secondary graft failure for grafts with at least 1 year follow-up were 86% and 88%, respectively.

CONCLUSION

An EHD is a unique parameter that quantifies conduit size and has a significant impact on vein graft patency. An EHD less than 3.6 mm portends graft failure.