Coronary Artery Bypass Graft Surgery

Objectives

In this chapter, you will learn:

ACCESSING THE HEART

To access the heart, the surgeon makes an incision down the middle of the chest (midline sternotomy). The sternum itself must be cut using a saw, and retractors are used to spread the chest open to visualize the chest cavity. As described in Chapter 4, the patient is placed on cardiopulmonary bypass, and the heart is stopped using a concentrated electrolyte (cardioplegia) solution. The lungs are deflated in most cases to allow more room for the surgeon to work.

THE BYPASS CONDUITS

A vessel chosen as a bypass conduit needs to meet certain criteria. Removing it from the body should not impair circulation, it should be long enough to reach from the aorta to the coronary artery, and it must be the right size to attach to a coronary artery. The greater saphenous vein has been the traditional choice of conduit for CABG surgery. An artery used as a conduit has the advantage of lasting longer without reocclusion than a saphenous vein. The two most commonly used arteries are the internal mammary artery (IMA) and the radial artery.

Saphenous Vein

The saphenous vein is usually harvested endoscopically (using a small camera inserted into small incisions) or using a skip incision (a series of small incisions separated by intact skin). This is chosen over an open harvest to decrease pain, decrease leg edema, and speed wound healing. However, patients for whom these techniques are not possible will have their vein harvested using an open incision. The saphenous vein, like all veins, has valves that serve to keep blood flowing toward the heart. When a saphenous vein is used as a bypass conduit, the valves must be removed or it must be turned backward so that they do not obstruct the flow of blood in the bypass graft. When using a saphenous vein graft (SVG), the surgeon sews one end to the aorta and the other end to a coronary artery distal to the occlusion.

Internal Mammary Artery

The IMAs run from the subclavian artery to the right and left sides of the chest wall. Either IMA makes for a long-lasting bypass graft. The left internal mammary artery (LIMA) is most commonly used to bypass occlusions in the left anterior descending artery (LAD). The right internal mammary artery (RIMA) may be used to bypass occlusions in the right coronary artery (RCA). To use an IMA, the surgeon carefully dissects the distal end of the artery away from the chest wall and sews it into a coronary artery beyond the occlusion (Figure 5.1). There is minimal manipulation of the artery, so chances of spasm are minimized.

FIGURE 5.1    Bypass grafts. The saphenous vein or radial artery graft in this drawing is sewn proximally into the aorta and distally into the right coronary artery (RCA) below the occlusion. The left internal mammary artery (LIMA) in this drawing remains attached to the subclavian artery at the proximal end and the distal end is sewn into the left anterior descending artery (LAD).

Radial Artery

The radial artery is harvested from either the right or left wrist. Before removing the artery, an Allen test is performed to make sure the ulnar artery is patent and will perfuse the hand with blood (Table 5.1). If it is determined that blood flow to the hand will be inadequate if the radial artery is removed, another bypass conduit will be sought. The radial artery is typically harvested from the nondominant arm, but the artery in the dominant arm may be used if needed.

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