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PART 3 — PERIPHERAL ARTERIAL
materials. Prosthetic (synthetic) bypass grafts are made of various manufactured materials including polytetrafluoroethylene (PTFE) and woven com- posites such as Dacron. The preferred bypass graft material is autogenous vein, and this chapter will focus primarily on this type of graft. The great saphe- nous vein, small saphenous vein, cephalic vein, and basilic vein can all be used as bypass conduit. Vein grafts have better long-term patency than synthetic grafts by being less thrombogenic than their synthet- ic counterparts.3–7 Although vein grafts are the pre- ferred bypass of choice, they have the potential for early failure and early surveillance is recommended.8 PTFE grafts have a low potential for early technical failure and ultrasound-detected abnormalities. How- ever, these PTFE grafts have a distinctly worse long- term success rate due to progressive stenoses usually at the inflow or outflow arteries, which will be de- tectable on ultrasound usually later in the grafts’ his- tory. Another type of bypass graft is a cryopreserved human allograft. This type of material is not com- monly used for lower extremity bypasses; however, ultrasound evaluation of these graft types would be similar to those outlined in this chapter.
IN SITU BYPASS GRAFTS
Because bypass grafts using an autogenous vein can be constructed using various surgical techniques, these grafts are further described based on the sur- gery employed. An in situ bypass graft is performed using the great saphenous vein left in place or in situ within its natural tissue bed. Branches of the vein are ligated and the valves within the vein are lyzed. This allows a downward flow of blood with- out the need to reverse the vein bypass and allows the larger end of the great saphenous to be anas- tomosed to the larger artery proximally and the smaller end of the vein to be anastomosed distally, usually to a smaller artery such as a tibial artery. This provides a conduit where one end can then be sutured to an artery proximal to the site of disease (the inflow artery), and the other end of the vein conduit is sutured to an artery distal to the distal (the outflow artery). There is often a preference for this type of orientation when the proximal and dis- tal vein sizes match more closely the size of the ar- teries at the anastomotic sites.
ORTHOGRADE AND RETROGRADE BYPASS GRAFTS
The great saphenous vein and other autogenous veins can also be used as a free vein graft where the vein is completely dissected free from its natural position in the body. This conduit can be placed in
an orthograde position where the proximal portion of the vein is used for the proximal anastomosis and the distal portion of the vein is used at the distal anastomosis. In this position, the valves with the vein will need to be lyzed so that blood can flow freely. A free vein graft can also be placed in a ret- rograde (reversed) position where the vein now has the smaller distal end of the vein anastomosed to the inflow artery and the larger proximal end of the vein is anastomosed to the outflow artery. Essentially, the vein is flipped or reversed so the valve leaflets do not need to be removed and there is no barrier to blood flow.
BYPASS GRAFT PLACEMENT
The actual position of a bypass is determined by the level of arterial disease. The proximal anastomosis is commonly performed using the common femoral or superficial femoral artery as the inflow artery source (Fig. 11-1). Less commonly, the profunda femoral, superficial femoral, or popliteal can be used as the inflow artery. The distal anastomosis is generally constructed below the level of the most distal site of arterial disease. Thus, the outflow artery can be the popliteal artery (either the above knee or below
Bypass graft
Superficial femoral artery
Popliteal artery
Figure 11-1 Types of vein bypass grafts. The figure on the left illustrates a common femoral to popliteal bypass, whereas on the right, the bypass is from the common femoral artery to the tibioperoneal trunk.