About coronary bypass graft surgery

Does the surgeon remove my blockages?
Is my artery replaced by the vein graft?
How many grafts can be placed?
How long is the operation good for?
What is the benefit of using the internal mammary
    artery for a bypass graft?

Atherosclerotic blockages can be present anywhere in the system, in small, medium, or large vessels, as identified by coronary angiography. By carefully studying an angiogram, a surgeon can determine the arteries that can be bypass grafted. The surgeon does not remove any of the blockages nor replace any of the arteries. The surgeon procures a piece of saphenous vein 6-8 inches in length from the patient’s leg. One end of this vein graft is then anastamosed to the aorta, and the other end to the coronary artery distal to the blockage. Through this newly constructed route, blood will freely flow to the coronary artery bypassing the blockage; hence the name aortocoronary saphenous vein bypass graft, as shown in Fig 16 A.

Figure 16 A: Anatomy of a bypass graft Aortocoronary saphenous vein bypass graft AO – aorta overdrawn into the angiogram. RCA – right coronary artery. VG – vein graft. Black arrow – the ostia of the right coronary artery.

There is no absolute limit for the number of blockages that can be bypass grafted. I knew one patient who had nine bypass grafts—the maximum I have seen. There are three major vessels in the coronary system (the left anterior descending artery, the circumflex artery, and the right coronary artery) that most often are subjected to bypass grafting. Several branches of these vessels, such as diagonals, marginals, posterior descending, etc., are also often grafted. However, a surgeon cannot graft all the blockages in some patients due to diffuse disease, and the small caliber or heavy calcification of the vessels. Generally, a coronary artery less than 1 mm in diameter is almost impossible to be grafted. In essence, even after multivessel bypass grafting, there could be several more small vessels with blockages ungrafted due to technical reasons. That is the reason why some patients, even after bypass graft surgery, could have residual symptoms or demonstrable ischemia.

Coronary bypass using the internal mammary artery

The left internal mammary artery (LIMA) originates from the proximal left subclavian artery and is meant to supply the left anterior chest wall. This arterial supply is not an absolute must for the chest wall. Therefore, this artery can be liberated from the chest wall, and can be directly grafted to the left anterior artery of the heart, thereby establishing a direct arterial conduit to the coronary artery. This graft lasts for several decades and is somewhat immune to atherosclerosis. Nowadays, the surgeons make every effort to put a LIMA graft in favor of its longevity (Fig 16 B).

Vein grafts have a tendency to undergo dilatation, thrombosis, intimal hyperplasia, degeneration, atherosclerosis, and occlusion in a somewhat predictable way. The leg veins are very thin-walled conduits, meant to carry blood to the heart under very low pressure of 3-5 mmHg. When these tubes are placed into high-pressured arterial systems (120-222 mmHg or more, depending on the blood pressure of the patient), they undergo the above-mentioned changes very quickly.

Figure 16 B: Internal mammary artery anastamosis to the left anterior descending artery AO – aorta. LAD – left anterior descending artery. LIMA – left internal mammary artery. Black arrow – total blockages of the proximal LAD.

Figure 16 B is an angiogram of a 78-year-old man with history of hypertension, hypercholesterolemia, and prior history of cigarette smoking. He had multivessel bypass graft surgery in 1989 with insertion of LIMA to the LAD, and aortocoronary saphenous vein bypass graft to the first marginal, second marginal, and the right coronary artery.

The angiogram done in August 2000 showed that all vein grafts are diffusely diseased or occluded. However, the LIMA was widely patent perfusing the LAD system. The LIMA looks pristine with no evidence of stenosis or atherosclerosis. This patient is dependent on this single graft.