|Commonly Asked Questions|
"How long does CABG last?"We have over thirty years of experience with coronary artery bypass graft surgery since its introduction in 1967. Bypassing a coronary blockage by insertion of a graft (bypass graft operation) is accomplished by two types of conduits: the arteries or the veins. An arterial conduit employing the internal mammary artery lasts the longest. At the end of 10 years, over 90% of the LIMA grafts are patent. In fact, we have seen many patients with an internal mammary graft surviving well over a quarter of a century, with no evidence of atherosclerotic buildup.
On the contrary, the vein graft conduits do degenerate faster with atherosclerotic changes, resulting in thrombosis and occlusion. In general, at the end of the first year after the operation 10-15% of the vein grafts are occluded; at the end of fifth year 40% of the vein grafts are occluded; however, by the tenth year nearly 75% of the vein grafts are occluded. Approximately 50% of the people will need a second revascularization process, either by bypass graft surgery or by angioplasty by the tenth postoperative year.
Arterial conduits last longer because they are designed to handle high-pressure arterial circulation, whereas veins are genetically meant to carry venous blood, which has very low luminal pressure. These thin-walled vein grafts when interposed in a relatively high-pressured arterial circulation, such as in coronary artery bypass graft surgery, undergo degenerative changes, dilatation, thrombosis, intimal hyperplasia, and atherosclerosis. That is the reason why these days more arterial conduits are being used by cardiac surgeons for coronary artery bypass graft surgery. The commonly used arterial conduits are the internal mammary arteries, radial arteries, and gastroepiploic arteries.
Even in patients with the worst cardiac risk factors, atherosclerosis in the venous system (not harvested) producing blockages is virtually unheard of. However, when they are removed and grafted into a high-pressure system, they undergo quite significant changes, as we had discussed earlier. Whereas all other cardiac risk factors remain the same, pretty much the only difference this harvested vein graft experiences is the high intraluminal pressure because of its interposition in the arterial system. In my opinion, hypertension is the worst atherosclerotic risk factor for vein grafts. (This is not confirmed or disputed by any studies.)
In my practice, I have seen only two cases (both postmortem) where some significant atherosclerosis of 40-50% was observed in the pulmonary arteries. Pulmonary arteries, in fact, are extensions of the bodys venous system carrying impure blood from the heart to the lungs for purification. The pulmonary arterial wall is thicker than the systemic veins, but much thinner than similar sized systemic arteries. Their luminal pressure is also somewhat in between (25-35 mmHg) venous and arterial pressures. The two cases I mentioned had severe pulmonary hypertension of 70-80 mmHg. This rise in pressure, I believe, is the sole reason for the development of atherosclerotic blockages in pulmonary arteries in these patients.
I have given great emphasis to keep the blood pressure to the bare bottom level of 120 mmHg in everybody, particularly those after a bypass graft surgery. Remember, by the tenth postoperative year, well over 75% of the vein grafts will be either totally occluded or significantly diseased. Using aspirin from the second postoperative day onwards has shown significant benefit in reducing vein graft occlusions.
In essence, the two venous conduits are totally dysfunctional. However, the arterial conduit (IMAFG) looked pristine, as a normal smooth conduit without any of the degenerative changes that happened to the venous system. Dr. David Cheeran, a senior cardiothoracic surgeon at Rochester General Hospital had the following comments on the subject. Of course, internal mammary artery is the best conduit when it is directly anastamosed to the coronary artery. IMA or any other arterial conduits such as a the radial artery, when used as a free graft, fares much better than the saphenous vein grafts, but not as good as direct anastamosis of the internal mammary artery. The saphenous veins in some, particularly obese patients, are very large at the time of harvest, such vein grafts may degenerate much quicker particularly in a hypertensive.
Although the saphenous vein grafts degenerate in a predictable fashion, it certainly is not a universal phenomenon. I have seen several vein grafts, fifteen or twenty years after the bypass graft, working quite well with no evidence of degenerative changes. It is my feeling that CABG using medium-sized healthy vein grafts in subjects without hypertension or diabetes, and who do not smoke, last longer than the rest.
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