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| Arterial grafts are channels used to replace or bypass diseased arteries. Grafts fall under three main categories, vein grafts, synthetic grafts and preserved grafts of human or animal origin. The choice of graft depends on several factors. The most important of these is the site of distal anastomosis (the far end of the bypass). Whilst bypassing offers an excellent treatment for occluded or severely diseased arteries, it is not without its problems. The most obvious of these is graft durability. Unlike natural normal arteries, vein grafts have valves inside them. These valves either have to be destroyed or rendered ineffective by reversing the vein before it can be used as a graft. Synthetic grafts lack the natural smooth lining that normally prevents the blood from clotting inside vessels and offer very little resistance to infection. These are only a few examples as to why arterial bypasses may not last for long periods of time.
When available, veins from the same patient offer the best possible arterial bypass grafts. Extensive research has shown that these grafts, when appropriately used, are much more likely to last than any other form of grafts. As veins normally carry blood as well, they are best suited for this purpose. Veins are less likely to induce blood clotting as they are lined by a thin smooth lining very similar to that of arteries. Also, vein grafts offer much better resistance to infection when compared with synthetic grafts. Despite these advantages, vein grafts have their own problems. In addition to the presence of valves, veins are not always available from a patient. When available, veins may be too small or too short to be of use. The process of removing and preparing a vein for grafting, known as "harvesting" remains time consuming and fraught with technical difficulties.
The need for synthetic grafts became apparent when vascular surgeons began treating aneurysms of large arteries. In these situations, large grafts are usually needed and since none of the veins in the human body is either large enough or strong enough for this purpose, synthetic grafts were introduced. These grafts are made of materials that do not cause irritation or allergy to the surrounding tissues and are strong enough to withstand the high pressure in big arteries. The two main materials used to make these grafts are Dacron and Teflon. Dacron is a type of synthetic cloth that was originally used for clothing. It was found to posses qualities that make it suitable for use as a graft material. Dacron grafts can come in fairly large sizes and are therefore the grafts of choice for aortic surgery. The second common graft material is Teflon. This is an extremely inert material (has very little interaction with the surrounding environment) that can be shaped into tubular grafts. These grafts are quite smooth and pliable and best suited for long bypasses.
This group includes grafts of human or animal origin that has been especially preserved for use in humans. Such grafts include veins from human umbilical cords or legs, and arteries or ureters from certain farm animals. The use of these grafts is very limited and is only indicated when all other types of grafts are not available or suitable. We rarely use these grafts at St Richard's Hospital. |
A vein graft is being harvested and prepared to use as a bypass graft. The most commonly used vein for this purpose is the "long saphenous" from the leg. Arm veins can also be used.
An aortic graft made of "Dacron". Dacron is a synthetic material that poses certain criteria that make it suitable for large arterial grafting. |
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