Heart Associates     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.

Case Studies

The following two case studies demonstrating the differentials in the degree of dilatation and degeneration between a vein graft and an arterial graft used for aortocoronary bypass graft surgery.
    This 54-year-old man with history of cigarette smoking, hypertension, hypercholesterolemia, and overweight had three- vessel CABG in February 2000 for unstable angina. LIMA was inserted to the LAD, saphenous vein graft to the right coronary artery, and saphenous vein graft to the circumflex-marginal in sequence. The patient was readmitted with acute coronary syndrome five months after the surgery. The angiogram (Fig. 17A) now shows the saphenous vein graft to the right coronary artery is totally occluded, LIMA to the LAD is widely patent, saphenous vein graft to the circumflex-marginal system are patent. However, the vein graft as shown in the figure is quite markedly dilated with sluggish flow.
The saphenous vein with its very thin wall is not meant to function as an arterial conduit with very high intraluminal pressure (210/120 mmHg, as in this case). The vein graft then undergoes dilatation, tortuosity, thrombosis, intimal hyperplasia, atherosclerosis, and finally occlusion. When a vein graft is harvested from its natural habitat, the manipulation and disruption of its own native blood supply are all responsible cofactors. However, in my observation, patients harboring high blood pressure degenerate their vein grafts much quicker.

Fig17 A

Fig. 17 A: Aortocoronary bypass vein graft to the marginal system

AO – aorta. SVG – saphenous vein graft. Black bent arrows – proximal occlusion of the circumflex marginal system. White arrows – the marginal branches of the circumflex artery.

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 body’s 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.

Fig17 B

Fig. 17 B: Aortocoronary bypass graft. The saphenous vein graft is bypassed to the circumflex-marginal system. The internal mammary is used as a free graft from the aortic root to the mid LAD.

IMAFG – internal mammary artery free graft. SVG – saphenous vein graft. Thick arrows – 99% stenosis of the saphenous vein. Thin arrow – widely patent internal mammary artery used as a free graft. C - Catheter.

    This angiogram is from a 68-year-old patient weighing 258 pounds with history of hypertension, hypercholesterolemia, family history of coronary artery disease, and extensive peripheral vascular disease who had multivessel bypass graft surgery in 1995. His CABG consisted of a saphenous vein graft to the circumflex-marginal, saphenous vein graft to the distal right coronary artery, and internal mammary artery used as a free graft to the LAD. In the usual circumstances, the internal mammary artery is directly anastamosed to the coronary artery, such that the blood freely flows from the brachial artery to the coronary artery. In this case, the internal mammary artery is used as an aortocoronary conduit because this patient had atherosclerotic disease in the left proximal subclavian artery.

    At the time of this study in August 2000, the patient already had sustained a diaphragmatic myocardial infarction and had developed congestive heart failure with an ejection fraction of 45%. The saphenous vein graft to the right coronary artery was totally occluded. The saphenous vein graft to the circumflex-marginal system was dilated, tortuous, atherosclerotic, and critically stenosed with significant intraluminal load of thrombus.

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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