Preoperative Vein Mapping
Kathleen D. Gibson
Aaron Ebert
Endovascular approaches for the treatment of infrainguinal arterial disease (angioplasty, stenting, and atherectomy) are increasingly being offered as initial procedures for patients with lower extremity ischemia.1 Bypass grafting, however, remains the gold standard to which all other treatments are compared. The BASIL trial randomized 452 patients with critical limb ischemia to a “surgery first” or “angioplasty first” revascularization. That study demonstrated the superiority of bypass surgery over angioplasty for overall long-term survival and a trend toward decreased rates of amputation in patients with critical limb ischemia who survived for at least 2 years after randomization.2 Both prosthetic grafts and autogenous veins are used as bypass conduits, but in most series, long-term patency rates for autogenous veins are superior.3,4 This is particularly true when the distal anastomosis is below the knee.5 While a multitude of studies have documented superior patency for autogenous vein grafts, it is also clear that a prosthetic graft is better than a poor-quality vein in terms of patency. As such, preoperative vein mapping is an important part of surgical planning for finding adequate vein to use as a conduit, both in diameter and in quality. In addition, vein mapping with skin marking can be an invaluable aid to the surgeon for planning incisions and identifying branches that will require ligation.
AUTOGENOUS CONDUITS: REVERSED VEIN, IN SITU VEIN, AND ALTERNATIVE VEIN
The two main techniques for utilizing autogenous conduit for infrainguinal arterial revascularization involve either removing and reversing the vein graft (taken from the same lower limb, the opposite lower limb, or the upper extremities) or leaving the vein graft in situ. The most common autogenous conduit used for bypass grafting is the great saphenous vein (GSV). Its proximity to arterial target vessels as well as its size and length make it the ideal conduit for lower extremity bypass. In the absence of an adequate GSV, the small saphenous vein (SSV), or arm veins (cephalic or basilic), can be used as alternative conduits.
The GSV can be dissected out and removed entirely from its normal anatomic location, reversed, and then tunneled along the anatomic course of the native arterial circulation. With a reversed vein graft, the proximal to distal reversal is necessary to allow blood to flow through the graft in the proper direction relative to the valves within the vein. Alternatively, the vein can be left in its anatomic position (an in situ graft). In this procedure, the saphenofemoral junction (SFJ) is divided, and the hood of the SFJ is used to create the proximal arterial anastomosis. The distal end of the vein is then mobilized and swung over to the target artery to create the distal anastomosis. Because the normal valves would prohibit flow in the arterial direction through the in situ graft, the valve leaflets must be lysed with a device inserted into the vein called a valvulotome. Additionally, to prevent arteriovenous fistulae, all major venous side branches must be ligated.
Long-term patency rates of in situ vein grafts and reversed vein grafts are similar,6,7 and the choice of bypass technique is largely dependent on the distal bypass target and surgeon’s preference. In situ bypass grafts offer the advantages of fewer or shorter incisions, avoidance of the need for tunneling the vein anatomically, and better vein-to-artery size match for distal (tibial artery) anastomoses. Graft patency versus occlusion is readily apparent with in situ bypass grafts on physical examination, as the graft pulse is usually easily palpable in the thigh and calf. The superficial location of in situ bypass grafts also facilitates Doppler evaluation and duplex graft surveillance (see Chapter 17). In some cases, however, the SFJ is too low to allow an in situ bypass, as the vein simply will not reach the intended proximal anastomotic site. Reversed vein grafts avoid the need for valve lysis and allow visual examination of the entire vein at the time of surgery. The bypass graft is also less likely to become exposed if there is a wound problem as it is tunneled anatomically in the deeper tissue planes.
In the absence of an adequate GSV, alternative autogenous conduits can be used for infrainguinal bypasses. Arm veins (basilic or cephalic), the SSV, and spliced vein segments from various sources (a composite graft) can be used. Although patency and limb salvage rates are acceptable using alternative autogenous conduits, they are significantly inferior to bypasses utilizing a single segment of GSV.8
VEIN MAPPING
Vein mapping is an integral part of preoperative planning for infrainguinal arterial revascularization. It serves three important functions:
Identifying adequate venous conduit for bypass in terms of diameter, length, and vein quality
Locating major vein branches
Characterizing any anatomic anomalies along the course of the vein
Mapping is valuable even if the patient has a previous history of vein harvest or stripping, as dual saphenous trunks do occur, and it is possible that there will still be a GSV segment or a usable tributary vein present. Identifying adequate venous conduit includes assessing the diameter of the vein as well as identifying any vein segments that are abnormal. Despite having an adequate diameter, veins that show thickening and
phlebosclerosis make poor conduits. In general, veins must be a minimum of 2.0 mm in diameter to be adequate for use as a bypass conduit. Recent data have shown that veins less than 3.0 mm in diameter have more than double the risk of early failure compared to veins greater than 3.0 mm in diameter.9
phlebosclerosis make poor conduits. In general, veins must be a minimum of 2.0 mm in diameter to be adequate for use as a bypass conduit. Recent data have shown that veins less than 3.0 mm in diameter have more than double the risk of early failure compared to veins greater than 3.0 mm in diameter.9
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