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Question:
How often do bypass grafts fail and how is the patient then treated? submitted by Shirley, from New York, 1/12/09
Answer:
by Texas Heart Institute cardiovascular surgeon, William E. Cohn, MD 
Bypass grafts are veins or arteries harvested from elsewhere in the body, where they are not needed, and used as plumbing to bypass a blocked coronary artery on the heart. Free grafts, like a vein from the inner part of the thigh or lower leg, or an artery from the forearm, have to be attached at one end to the aorta just above the heart, the largest blood vessel in the body, and at the other end to the coronary artery beyond the blockage. Blood from the aorta can then flow down the graft into the artery, 'bypassing' the obstruction. Other grafts, like the left and right mammary arteries, don't have to be attached to the aorta because they already have brisk arterial blood flowing down them. They are divided distally and peeled from the back of the chest wall and sewn to the coronary artery beyond the obstruction. The other end is left attached to the chest wall, and does not have to be divided and attached to the aorta.
The frequency with which grafts become occluded after a bypass operation is dependant on many things. We know, for example that the larger the coronary artery is beyond the obstruction, both in diameter and distribution, the higher the flow will be through the graft and the more likely the graft is to stay open. Conversely, coronary arteries that are small or have multiple blockages along their length are less likely to stay open. Furthermore, we know that grafts that are constructed from the left internal mammary artery (LIMA) have a better chance of staying open for a long time than do vein grafts. There are several studies that show a LIMA graft to the artery that runs down the front of the heart (the LAD… generally a big artery) has a 90%-95% chance of continued function ten years after bypass surgery. In contrast, we know that 10%-20% of vein grafts become blocked in the first year after bypass. Most of these occlude because the coronary arteries they are used to bypass are small or badly diseased or the vein used for the bypass graft was of poor quality. Occasionally vein grafts to large arteries occlude in the first year for unknown reasons. Vein grafts that are working at one year generally do fairly well for the next 3-4 years. After that, they begin to develop blockages very similar to the ones that caused the coronaries to be obstructed in the first place, but at an accelerated pace. As a result, 5%-10% of grafts occlude each year so that 10 years after bypass surgery, half of the vein grafts are occluded and another quarter or so have significant blockages in them.
When a graft becomes blocked, the best course of action depends on the importance of the graft. Occasionally a graft occlusion will trigger severe symptoms such as angina, or rarely, a heart attack. These events require urgent attention and may require angioplasty and stenting of the bypassed artery, or even a repeat operation. Sometimes a blocked graft can be reopened in the catheterization laboratory if it has only recently occluded. Generally however, graft occlusion is a silent event and is only discovered when a stress test and subsequent angiogram or multi-slice CT is performed. If symptoms occur, frequently they can be managed medically. Often, angioplasty and stenting is useful to treat the narrowing in the bypassed coronary artery. If the occluded grafts supply large or otherwise important coronary arteries that are poorly suited for angioplasty, a repeat bypass may be considered. Although technically more difficult, results after repeat coronary artery bypass are very acceptable.
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Updated January 2009
