In-Situ Saphenous Vein Graft for Lower Extremity Occlusive Disease



In-Situ Saphenous Vein Graft for Lower Extremity Occlusive Disease



Dhiraj M. Shah, Benjamin B. Chang, R. Clement Darling, III, Philip S.K. Paty, Paul B. Kreienberg, Sean P. Roddy, Kathleen J. Ozsvath and Manish Mehta


Bypass to infrageniculate arteries for chronic limb-threatening ischemia continues to provide a most challenging aspect of arterial reconstruction confronting vascular surgeons today. Their length and low flow all too often exceed the functional limits of synthetic and often even of reversed vein grafts. However, the saphenous vein used in situ provides a viable, physiologically active, and, hence, antithrombotic endothelial flow surface that is ideally suited for such bypasses. In addition, its gradual distal taper contributes an optimal hemodynamic configuration and a size match to the arteries it connects. These attributes have allowed consistent use of small veins that were previously considered unsuitable when used as reversed vein grafts, as reflected by higher vein utilization rates for bypass to the tibial arteries. Of equal or greater importance is the ability to use limited outflow tracts, such as isolated tibial segments, with no significant reduction in patency rates.


There is no question that this method of using the saphenous vein is on occasion tedious, time consuming, and demanding, but the surgeon’s patience and persistence are rewarded with immediate in-situ bypass function in more 95% of patients with the most diffuse and advanced stages of atherosclerotic occlusive disease. In selecting patients to be recipients of this investment of time and effort, one should be certain the indications for it are secure. Such operations for intermittent claudication are done infrequently with the full understanding by the patient that it is for functional improvement only, and can prejudice long-term limb preservation, because all reconstructions have a rate of attrition of approximately 5% a year. Once this vein is used electively, it is not available should limb-threatening degrees of ischemia develop in the future.



Operative Technique


The crux of the issue of using the greater saphenous vein in situ, and the only valid reason for its excision and reversal for femoral or distal arterial bypass, is removal of valvular obstruction to arterial flow. All other considerations aside, leaving the saphenous vein in situ is consistently the most reliable method of endothelial preservation, provided the valves can be rendered incompetent without significant endothelial injury. Its use in situ entails interruption of the venous branches that can become arteriovenous fistulas and minimal mobilization of its ends for construction of proximal and distal anastomoses. The simplest, most expedient, and least traumatic method of rendering the bicuspid venous valve incompetent is to cut the leaflets in their major axes while they are held in the functionally closed position by arterial pressure from above. This is the essence of the valve incision technique.





Procedure


Following preparation and sterile draping of the entire extremity, warm (37°C) papaverine solution (60 mg/500 mL Plasmolyte or normal saline) is injected into the subcutaneous tissue adjacent to the saphenous vein below the knee. The proximal saphenous vein that lies immediately deep to the superficial fascia is then exposed, and papaverine solution is infiltrated into the surrounding tissue.


Although the common femoral artery has been considered the proper site for proximal anastomosis, there is evidence that the superficial femoral artery is equally satisfactory. In spite of its less accessible location, the deep femoral artery can provide the most satisfactory site for proximal anastomosis. If the common femoral artery is to be used as the inflow source, the saphenous bulb is completely dissected and its branches are ligated. If additional length is required to facilitate anastomosis to the common femoral artery, a portion of the anterior aspect of the common femoral vein is removed in continuity with the saphenous bulb. The valve leaflets at the saphenous femoral junction are excised, removing only the transparent portion. The second valve, invariably present 3 to 5 cm distal, can be incised before the vein is divided with a retrograde valvulotome through a side branch distal to the valve, or it may alternatively be cut either with scissors or an antegrade valvulotome through the open end of the vein. These valves are identified by gently distending the vein with dextran or heparinized blood.


The plane of closure of the valve cusps is invariably parallel to the skin. This dictates the orientation of all instruments with relation to the valve cusps. If the cutter is to be used, a 3- to 5-cm incision is made 5 mm posterior to the vein position marked on the skin, in order to identify a branch seen on the venogram to gain access to the lumen of the saphenous vein. A 3-Fr Fogarty catheter is introduced into this side branch and is passed proximally with the leg straightened to exit through the open end of the vein. The catheter is then divided at an acute angle at the 20- or 30-cm mark. The valve cutter is screwed onto the catheter and an 8-Fr catheter is secured to the cutter with a loop of a fine suture. The leading cylinder of the cutter is drawn into the vein, thus providing partial obstruction to venous flow while permitting visualization of the cutting blade and minimal resistance in torque; thus it allows precise orientation of the cutting edges at 90 degrees to the plane of closure of the valves. The catheter–cutter assembly is then drawn slowly distad while the dextran solution or blood is introduced through the catheter at 200 to 300 mm Hg. This pressurized fluid column snaps each successive valve to the closed position so that the cusps are efficiently engaged by the blades of the cutter.


A slight but definite resistance can be felt as the cutter encounters each valve and cuts the leaflets. Greater resistance than this should be managed by turning the cutter 45 degrees and making another attempt at advancement. If this does not produce the desired result, the cutter should be withdrawn and dismounted, and the area of impaction should be exposed. The cutter is advanced through a predetermined safe distance, generally to the knee, and is then withdrawn. The cutter is dismounted, and the catheter is removed from the saphenous vein. The proximal anastomosis is then performed, the clamps are removed, and the pulsatile impulse provided makes the next competent valve apparent.


Exposing the full length of the saphenous vein is only necessary if the cutter cannot be used and the combination of thick subcutaneous tissue, small vein, and reduced pulsation makes the valve sites difficult to determine. The remaining valves are incised by means of a retrograde valvulotome introduced through a side branch or the distal end of the vein. This instrument is designed to engage leaflets, center itself, and cut the leaflet in its longitudinal axis. It is then readvanced, carefully rotated through 180 degrees, and withdrawn, thus engaging the remaining leaflet. In passing the valvulotome intraluminally to and from a valve site, it is important that any pressure on the vein wall resulting from the curving path be exerted on the shaft of the instrument rather than on the projecting blade tip. This lessens the likelihood of the blade’s tip becoming lodged in a side branch and lacerating the vein wall. Before transecting and mobilizing the distal vein, the anticipated distal anastomotic site is exposed.


Bypasses to the popliteal artery are preferentially performed at or immediately proximal to the anterior tibial artery orifice. This medial below-knee exposure does not require division of the tendons. Anatomically, the ideal in-situ bypass is to the midcalf posterior tibial artery because of the proximity of vein and artery. However, of greater importance as an outflow tract is the peroneal artery, because it is the most commonly patent single tibial vessel and the most likely to be the least diseased. It can be readily exposed from the medial aspect by posterior displacement of the gastrocnemius muscle and separation of the underlying soleus from its tibial origin. In the lower half of the calf, the peroneal artery passes anterior to the flexor hallucis longus, which must be divided to gain access to the artery that lies adjacent to the medial edge of the fibula. Bypass routing to the anterior tibial artery depends on the level of anticipated anastomosis. In its proximal third, it is best passed through the popliteal fossa. In its middle third, it is best either tunneled subcutaneously anterior to the tibia or through the tibiofibular fascia posterior to the tibia and, in its distal third, simultaneously anterior to the tibia.


Following completion of the distal anastomosis, flow in the bypass is confirmed by the sterile Doppler ultrasound probe. A completion angiogram is then performed with radiopaque reference markers attached to the skin with adhesive strips to identify arteriovenous fistulas. Most branches of the saphenous vein are guarded by a competent valve, thus preventing flow away from the arterialized saphenous vein. Only valveless branches immediately become arteriovenous fistulas. However, these are usually small, and they generally undergo spontaneous thrombosis. This is signaled by development of a superficial phlebitis. Although occasionally a large area of induration results, it is self-limiting and invariably resolves. Even if such superficial veins remain patent, loss of distal arterial flow is generally small and does not threaten continued patency of a bypass.


As a general rule, only branches with flow sufficient to opacify the deep venous system on the completion angiogram need to be ligated. However, the intraoperative Doppler ultrasound readily identifies these fistulas and facilitates their control. An isolated region of a continuous high-pitched flow signal might represent a small fistula or a stenotic lesion, such as a missed valve leaflet, preexisting stenosis (rare), or stenosis caused by platelet deposition. Occlusion of the bypass immediately distal to this segment results in continued flow if a fistula is present or an occlusive signal if the cause is a stenosis.


Late postoperative fistulas can develop owing to failure of a previously competent valve or progressive enlargement of an original small side branch. These only become important when the resultant increased venous pressure leads to persistent limb swelling. These fistulas are readily ligated using local anesthesia, usually as an outpatient procedure. They can be detected and accurately localized by Doppler ultrasound examination. Only on rare occasions is arteriography required.

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Jul 15, 2018 | Posted by in CARDIOLOGY | Comments Off on In-Situ Saphenous Vein Graft for Lower Extremity Occlusive Disease

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