Distal Vein Patch Bypass for Limb Salvage: An Option When No Vein is Available

Background 

As the population ages, an increasing number of patients are in need of lower extremity revascularization. Improvements in surgical, anesthetic, and endovascular techniques provide an increasingly aggressive approach to limb salvage that can be offered to these older and often sicker patients. There is little question that the autologous saphenous vein is the ideal conduit for surgical revascularization, especially to a tibial artery. However, the lack of adequate vein can present a major challenge in the care of these patients. Because of its utility in peripheral and coronary arterial beds, the saphenous vein has become a valuable commodity that is often in short supply. In those patients needing primary revascularization of the lower extremity, as many as 30% lack a suitable autogenous vein. This number increases to 50% in those patients requiring a secondary bypass procedure.¹ Although the use of duplex ultrasound has been implemented to locate veins that may not be readily apparent, there remains a significant number of patients in whom an adequate vein cannot be found. The most common reasons for this lack of vein include previous vein harvest for coronary revascularization or another peripheral bypass, excision of varicose veins or a vein that is unsuitable due to small size or post-phlebitic changes.

PTFE for Tibial Artery Bypass Grafts

Alternative conduits have not resulted in equivalent results when used for distal bypass to tibial arteries.^2-5 Polytetrafluoroethylene (PTFE) is recognized as a useful prosthetic conduit for lower extremity revascularization. However, tibial artery bypass with PTFE has not consistently led to successful revascularization. A prospective, multicenter, randomized trial compared saphenous vein and PTFE for infrainguinal arterial revascularization.⁶ Patency differences became apparent within one month of operation, and differences increased progressively thereafter. At the four-year interval, primary patency for vein bypasses was 49% as compared to a 12% patency rate for those randomized to PTFE. This well-known study supported previous suspicions of the inferior results for PTFE bypass grafts to tibial arteries. Because of these poor results, primary amputation is often considered in certain patient subgroups without a vein.⁷ To deal with this problem, several authors have reported on the use of venous cuffs, collars and boots to improve the results of prosthetic grafts in these challenging patients.^8–10 These techniques have been proposed as an option for open revascularization in patients without an adequate saphenous vein to obtain limb salvage.

Vein Cuffs and Boots

In 1979, Siegman proposed using a vein cuff to ease the technical challenges of a difficult anastomosis to heavily calcified small arteries.¹¹ Subsequently, Miller proposed a variant of this vein cuff to overcome the technical difficulties of the anastomosis and to improve graft patency by influencing the elastic properties of the prosthetic graft and the target artery. The Miller vein cuff involved the longitudinal opening of a small piece of vein and a running suture to secure the edge of the vein to the arteriotomy. The two cut ends of the vein were then sutured together in order to construct an oval venous cuff. The prosthetic graft was then sutured directly to the oval vein cuff. Miller reported the initial experience of 114 infrainguinal procedures using this cuff technique.¹² The patient cohort included only 21 tibial artery bypass grafts. A patency rate of 72% was noted at 18 months. Since that initial report, several other authors have reported on their experience with the Miller cuff configuration.¹³ However, several potential disadvantages have been recognized in association with the Miller vein cuff technique. Significant turbulence has been noted due to the deep anastomotic reservoir and the difficulty of achieving a proper angle between the graft and recipient artery. This results in increased turbulence and shear stress at the distal anastomosis. These hemodynamic factors may help to explain the immediate and early graft failures reported in Miller’s initial series.¹⁴ Additionally, we have noticed that the oval formation of the Miller cuff is difficult to maintain in tight anatomic spaces, such as very distal bypasses to the dorsalis pedis artery of the forefoot and the plantaris pedis branches of the posterior tibial artery. The Taylor vein patch attempted to address several of these concerns. Taylor’s technique required a longer arteriotomy (3–4 cm), with a U-shaped slit on the underside of the graft to produce minimal angulation and ensure that the PTFE lay almost parallel to the artery. The heel of the graft was then sutured directly to the proximal arteriotomy with the suture line continued directly along the artery. The anterior surface of the PTFE was then incised parallel to the arteriotomy proximal to the heel of the anastomosis. A vein patch varying from 5–6 cm was harvested to close this elliptical defect. The patch was begun distally on the tibial artery with interrupted sutures and completed proximally onto the PTFE with a running suture. Taylor reported on 256 grafts (83 to tibial arteries) with 1-, 3-, and 5-year patency rates of 74%, 58%, and 54%, respectively.¹⁵ Taylor hypothesized that improved graft patency was due to a reduction in the compliance mismatch between the PTFE material and the tibial artery wall, or to the inherent properties of the vein endothelium located across the anastomosis. Recognizing that the anastomotic reservoir of the Miller cuff theoretically increased turbulence and shear stress at the distal anastomosis, Taylor felt the vein patch led to a more tapered funnel shape and theoretically, decreased turbulence. However, there are theoretical and practical disadvantages to the Taylor patch technique. The tibial artery intima is directly exposed to PTFE graft material for the proximal half of the distal anastomosis, thereby losing the advantage of the venous endothelium for half the anastomosis. Additionally, a significant length of vein must be available to accomplish the anastomosis using the Taylor patch technique. Tyrell and Wolfe tried to reproduce these results. The group reported a 1-year patency rate of 74% with use of PTFE and the Taylor patch, as compared to 47% with use of the Miller cuff technique. This experience led to the development of the St. Mary’s boot.¹⁶ The St. Mary’s boot technique utilizes a similar arteriotomy and venous harvest as the Miller cuff. However, the corner of the venous sheet is sutured to the apex of the arteriotomy to form the anastomotic toe. The remainder of the venous-arterial anastomosis is formed in a similar fashion to the Miller cuff, except that the redundant vein is excised obliquely and sutured to the longitudinal edge. The St. Mary’s boot maintains a fully compliant venous collar, avoids any direct contact between artery and PTFE, and maintains the hemodynamic advantages of the Taylor patch. Its main drawback is the technical difficulty of its construction.

The Distal Vein Patch

Stimulated by a large volume of patients in need of revascularization without an autogenous vein, we utilized both the Miller and Taylor configurations. This experience confirmed the theoretical disadvantages of both techniques, most notably, the large anastomotic reservoir of the Miller cuff that increased turbulence, and the need for direct suturing of the PTFE graft to the tibial artery. Therefore, we developed our own vein cuff configuration, combining a standard vascular technique (the Linton patch) with a PTFE bypass. This distal vein patch bypass (DVP) utilizes a technique familiar to all vascular surgeons and requires a shorter arteriotomy, thereby decreasing the amount of venous tissue required for the procedure. A 2–3 cm segment of tissue for the patch is suitable, and can include saphenous vein remnants, an arm vein harvested under local anesthesia, a superficial femoral vein, or a segment of occluded superficial femoral artery that is opened and endarterectomized. However, a segment of a vein can usually be located. The segment is gently irrigated with prepared vein solution and opened longitudinally in preparation for the patch. Valves are excised and the vein segment is briefly stored in the vein solution. A 2–3 cm arteriotomy is then performed in the artery chosen for the distal anastomosis. The venous segment is cut to the appropriate length and width in preparation for the patch. In most cases, the width is left unaltered to allow for a generous patch in order to permit bulging of the patch under arterial flow, with a functional result similar to that of a vein cuff. After the patch is sewn in place, a longitudinal venotomy is made in the proximal two-thirds of the patch. An externally-reinforced, 6-mm, thin-walled e-PTFE graft is then sutured to the vein patch using 6-0 Prolene monofilament suture. The anastomosis is constructed in order to maintain a rim of venous tissue interposed between the PTFE graft and the entire circumference of the arterial wall. Because the venotomy is made in the proximal two-thirds of the patch, more venous tissue is left interposed at the toe of the anastomosis than the heel of the anastomosis. A heparin infusion is started four to six hours postoperatively, with coumadin administered on the first postoperative day. Long-term anticoagulation with coumadin is continued with an INR of 2.0 as the goal.¹⁷ The initial data using this DVP technique included 79 patients with no autogenous vein available as conduit for a bypass.¹⁸ In each patient who received a DVP graft, the ipsilateral and contralateral greater saphenous veins were either not present, having been used for previous revascularization procedures, or were unsuitable due to inadequate length or quality. With follow-up ranging from 30 days to 4 years, 80 bypasses were performed in the 79 patients. During this time interval, the DVP group represented 16% of the total tibial bypass experience. Patient demographics were similar to other series with 39 males, 40 females and a mean age of 67 years. Risk factor analysis revealed 53% of patients with diabetes mellitus, 20% with renal failure, and 60% with increased perioperative cardiac risk, as assessed by Eagle’s criteria. The indication for revascularization was limb-threatening ischemia in all patients, with rest pain in 49% of limbs, and gangrene or non-healing ulceration present in 51%. Reasons for the lack of adequate saphenous vein included previous failed lower extremity bypass at an outside institution in 47 patients (59%), previous coronary bypass in 21 (26%), unsuitable vein quality due to size or thrombosis in 8 (10%), and absence of vein due to varicose vein stripping in 4 (5%). A fairly high percentage of grafts originated from the external iliac artery (43%) in order to avoid hostile, scarred groins from previous bypass attempts at outside institutions. Occasionally, the superficial femoral artery was a suitable source of inflow (8%), with the remainder of the grafts originating at the common femoral artery. Recipient arteries included the peroneal artery in 35 cases (44%), the posterior tibial artery in 28 cases (35%), and the anterior tibial artery in 17 cases (21%). Two of the posterior tibial bypasses were to inframalleolar plantar branches. Primary graft patency was 90% at 6 months, and 82%, 78%, 69%, and 62% at respective 12-month intervals up to 48 months. At the time of this analysis, six grafts remained at patent beyond 48 months. Since that report, the DVP technique has been used to perform an additional 149 cases for a total of 229 DVP bypass grafts. This number represents 27% of the total tibial experience (841 cases) at our institution during the study period.

Why Does the Interposed Vein Segment Help?

Bypass graft failure occurs for several reasons. In the early postoperative period, technical difficulty is the most common cause of graft failure. This includes a poor choice of the inflow or outflow artery, difficulty performing the anastomosis, and lack of appropriate conduit for the bypass. Graft stenosis due to myointimal hyperplasia becomes the leading cause of graft failure 6 to 24 months after the perioperative period. Beyond the two-year postoperative period, progression of atherosclerosis proximal or distal to the graft is the most likely cause of graft failure. Myointimal hyperplasia at the anastomosis is particularly important in the failure of prosthetic bypass grafts.¹⁹ The hyperplastic lesion is thought to originate from the proliferation of vascular smooth muscle cells in the arterial media with subsequent cellular migration into the “injured” intimal layer of the arterial wall at the anastomotic site. Possible stimuli for the cascade of events that result in this hyperplastic response include endothelial injury, abnormal hemodynamic patterns and a stimulation of a variety of peptide growth factors.²⁰ The study of this hyperplastic response remains an area of active clinical interest, as well as basic research, and is beyond the scope of this paper. The interposition of venous tissue between a PTFE graft and the recipient tibial artery may improve results in several ways. These bypasses are technically demanding, requiring an anastomosis between a small, diseased tibial artery and a fairly noncompliant prosthetic material. The interposed venous tissue may simply make the bypass less technically demanding by suturing vein to the tibial artery. There may also be an effect on the thrombogenicity that may play a role at the interface between the high resistance outflow artery and larger prosthetic graft.²¹ Other benefits of the venous segment include a beneficial alteration of hemodynamic factors such as compliance and shear stress. Additionally, mechanical considerations, such as anastomotic surface area and the angle of the cuffed anastomosis, are altered by the venous tissue, possibly contributing to improved graft function and patency. Finally, the venous tissue may create a “biologic buffer zone,” thereby reducing the stimulation of factors that lead to the hyperplastic myointimal response.

Should We Add a Distal Arteriovenous Fistula as Well?

The addition of an arteriovenous fistula at the distal anastomosis has been attempted as another measure to improve graft patency, even with the use of saphenous vein as the conduit. A prospective randomized trial by Hamsho compared distal prosthetic bypasses using PTFE with a Miller vein cuff both with and without a concomitant arteriovenous fistula.²² This series indicated that the fistula conferred no benefit, but did not stratify patients based on arterial runoff. We have added an arteriovenous fistula to the distal anastomosis of a distal vein patch bypass in several patients with severely disadvantaged arterial runoff on the preoperative arteriogram. This “patch-ula” modification involves opening the target tibial artery longitudinally with a venotomy in the corresponding tibial vein. The vein patch is then sutured to the common ostium created by this fistulous connection. An anastomosis is then constructed between the vein patch and the PTFE, as described in the DVP bypass configuration. The initial group of patients has included several who would not have been offered an attempt at a bypass due to the lack of a target artery with suitable runoff that would support a reasonable chance of success. The AV fistula was added to the DVP in the hopes of decreasing outflow resistance in those patients with a severely diseased arterial runoff bed. This initial patient series includes 15 patients with tissue loss and/or gangrene as the indication for revascularization. The “patchula” was performed due to the appearance of the preoperative arteriogram that showed an isolated tibial segment or a diminutive tibial artery as the recipient artery for the bypass. These patients are at various stages of follow-up from one to 18 months, with one graft thrombosis and subsequent amputation in this patient cohort (publication of full data pending). Additional patient numbers and more complete follow-up are needed prior to any conclusions, but the initial results are promising in this very challenging group of patients with threatened limbs and the combination of lack of autogenous conduit and severely diseased distal runoff.

Summary

In those patients requiring tibial bypass for revascularization in an attempt at limb salvage, despite the lack of autogenous conduit, acceptable long-term patency can be achieved using PTFE with a distal vein patch. The results presented above suggest that the addition of venous tissue at the outflow anastomosis somehow alters the thrombotic and hyperplastic response, thereby improving patency of prosthetic bypasses to tibial arteries. However, this issue would best be answered by a randomized trial of obligatory prosthetic bypasses in patients with an unavailable autogenous vein requiring infrapopliteal bypass. In our practice, PTFE with a DVP is preferred to both PTFE bypass alone or composite grafts constructed with PTFE and longer segments of saphenous vein. We will offer the patient without adequate vein the Distal Vein Patch bypass for limb salvage.

Commentary

Together with carotid revascularization and treatment of aortic aneurysms, lower extremity revascularization ranks amongst the most frequent and significant endeavors for vascular surgeons and vascular specialists in general. Despite current advances with endovascular techniques, distal bypass grafting to infrapopliteal arteries continues to represent an often-needed treatment option for limb salvage on patients presenting with critical ischemia secondary to multi-level extensive arterial occlusive disease. This article by Neville et al. succinctly and clearly delineates some of the most significant issues surrounding this subject. The techniques they describe are interesting and potentially attractive. It may well deserve a place in our armamentarium. Frank J. Criado, MD frank.criado@medstar.net