History

In 1964 in Leningrad, Kolesov performed the first coronary artery bypass (CAB) graft, and at the same time he was the first to use the left internal thoracic artery (ITA), while working without cardiopulmonary bypass.¹ Favaloro in Cleveland initiated the first CAB program in 1967,² and in 1968 Green and colleagues began using the left ITA in New York.³ Although the saphenous vein (SV) ultimately became the most frequently used conduit, 100 bilateral ITA grafts were reported in 1974.⁴ Survival benefit for a single ITA compared with the SV was not demonstrated until 1986, and then a survival benefit for two ITAs compared with one ITA was shown in 1998, both by surgeons at the Cleveland Clinic.^5,⁶

Along the way, other arterial conduits (radial artery, right gastroepiploic artery, and inferior epigastric artery) were introduced, but none performed as well as the left ITA grafted to the left anterior descending artery, which remains the gold standard for CAB grafts.

Conduit Options

Although the SV is the most frequently used conduit, most patients, with few exceptions (e.g., emergency or salvage operations, left subclavian artery occlusion, high-dose chest wall radiation), receive the left ITA grafted to the left anterior descending coronary artery.⁷^–⁹

Other arterial conduits are appropriate for patients 70 to 75 of age or younger, but they are also acceptable for older patients when the SV is lacking. CAB with the SV is appropriate for those with reduced life expectancy because of comorbidities (renal failure or dialysis, impaired left ventricular function with ejection fraction less than 30%, malignancy, debilitating cerebrovascular disease, severe pulmonary insufficiency). Arterial conduits can also be used to save the SV in patients with lower extremity vascular disease.

VENOUS CONDUITS

Greater Saphenous Vein

The greater SV extends from its junction with the femoral vein to the anterior medial malleolus. It lies in the subcutaneous tissue but is occasionally attached to the skin or deep fascia and may be duplicated for short distances. It is larger and has a thicker wall proximally, and it has multiple valves and branches.

The media is composed of smooth muscle and few elastic fibers, and it has an internal elastic lamina. Wall thickness is too great for transluminal nourishment, so when the vasa vasorum are deprived of inflow, much of the smooth muscle dies and is replaced by fibrous tissue, and the vein then becomes a rigid tube without vasomotion or the ability to remodel in response to flow change.¹⁰ The endothelium can be damaged or lost despite careful harvesting, but it can regenerate.¹¹ Native endothelial production of nitric oxide (NO) is less than that of arterial conduits, and it is further reduced in regenerated vein endothelium after grafting.^12,¹³ Whether this is a factor in the neointimal hyperplasia that occurs after grafting and later atherosclerosis is unknown, although the role of NO in inhibiting adherence of platelets and neutrophils and proliferation of smooth muscle cells is well known. It is likely that the neointimal hyperplasia that occurs in all arterialized veins is a precursor to the accelerated (compared with native arteries or arterial conduits) atherosclerosis found microscopically by 2 years after surgery and found grossly in 70% to 80% of vein grafts at 10 years after operation. The venous drainage function of the SV is assumed by the deep venous system, but if the latter is obstructed by thrombotic disease, the SV should not be harvested.

Harvesting

After a single incision, or preferably multiple small incisions made over the course of the vein, sharp and blunt dissection can be used to expose the vein and its branches, which are divided between ligatures or clips. Care is taken to not place the clip too close to the vein wall, which could pinch the adventitia and distort or injure the wall directly. Likewise, the vein wall should not be handled by forceps, which should grasp only the adventitia. Endoscopic vein harvest has become popular in the past decade, with several small studies indicating a reduction in wound complications and good graft patency.^14,¹⁵ However, a large randomized study of the use of edifoligide to reduce neointimal hyperplasia revealed a reduction in graft patency at 1 year in endoscopically harvested veins as opposed to veins obtained by open harvest. This report indicates a need to reassess endoscopic harvest, which is probably more traumatic than realized.¹⁶ Incisions are closed after vein harvest with or without drainage.

The distal end of the vein is cannulated, and heparinized saline, balanced salt solution, or blood is used to flush the vein and dilate it with physiologic pressure to overcome harvest spasm and identify uncontrolled branches or traumatic leaks, which may be sutured with 7-0 polypropylene. Marking the vein with ink while in situ or when it is pressurized will avoid later axial torsion. Storage in heparinized dilating solution at room temperature is appropriate, and although studies suggest that blood may be less injurious to the endothelium, no clear advantage has been proved, probably because harvesting and arterial pressure also damage the endothelium.

Pharmacology

Because spasm rarely recurs after hydrostatic dilation, pharmacologic prophylaxis is unnecessary. This may be because smooth muscle ischemic injury is not responsive to vasoconstrictors.

Grafting Strategy

Traditionally, one vein is used per target vessel, but patency for 1.5-mm or smaller coronary vessels is reduced,¹⁷ so sequential grafting, with smaller vessels receiving side-to-side anastomosis, gives better patency.^18,¹⁹ Optimally, the distal anastomosis is to a 2.0-mm artery, but this may require using one vein to graft two coronary territories, which is appropriate. If vein length is limited, Y-grafting, as well as sequential grafting, is commonly performed and may also include proximal anastomosis to an arterial graft. A “snake graft” for the entire heart may be appropriate when the vein is limited, although in most patients the left ITA is grafted to the left anterior descending artery.

Patency

A 1-year patency of 81% to 93% reflects a poor-quality vein, technical problems, or low flow leading to layering of thrombus, which progresses to occlusion (Table 89-1). In the 1970s, more aggressive neointimal hyperplasia was seen, and it could result in stenosis and occasionally occlusion by 6 to 8 weeks postoperatively. This extreme response is rarely seen today because of improved harvesting techniques and vein management. However, a recent multisite randomized clinical trial with 3000 patients reported 1-year patency of 74%,¹⁶ which is less than the historic data and may represent a more realistic assessment than reports from single institutions (see Table 89-1).^20,²¹ A 10-year patency of 60% to 70% falls to 32% to 50% at 15 years (see Table 89-1) because of progressive SV atherosclerosis—the Achilles heel of the SV graft.

Table 89–1 Bypass Conduit Patencies

Excellent (90%) 8.5-year SV patency has been achieved by harvesting the vein with a pedicle of fat.²² The vein is left in situ until it is used, but control veins were removed after mobilization and distended with saline at 300 mm Hg for 1 minute, which is known to damage the endothelium and media.²²^–²⁴ This approach needs confirmation.

Lesser Saphenous Vein

The lesser SV is a subcutaneous vein that extends from posterior to the lateral malleolus to the mid popliteal fossa, where it joins the popliteal vein. It is similar to the greater SV in most respects, except it is usually smaller, but it is not critical for venous drainage.

It is most easily harvested with the patient in a prone position or supine by flexing the hip and rotating the hip internally. This requires an assistant to hold the leg. One or several incisions may be used.

As described for the greater SV, pharmacologic prophylaxis is unnecessary.

Creating aortic anastomoses with the lesser SV can be more difficult than with the greater SV. It is best employed as a Y-graft attached to the body or the aortic hood of the greater SV. Short-term patencies for the lesser SV and the greater SV are comparable, but there are no long-term data.²⁵

Cephalic Vein

The cephalic vein ascends from the “snuff box” along the radial aspect of the forearm to the lateral bicipital furrow, and it pierces the deltopectoral triangle to join the axillary vein. The vein is smaller and has a thinner wall than the leg vein, but microscopically they are similar.

To harvest the cephalic vein, one or two incisions are made over the vein in the upper arm. If needed, a forearm vein may be harvested through several incisions, leaving a skin bridge over the antecubital fossa.

As described for the leg vein, pharmacologic prophylaxis is unnecessary.

Grafting strategy for the cephalic vein is similar to that used for the SV, but the proximal anastomosis should be to the SV or artery conduit because of the small size and fragility of the cephalic vein. Our experience in using this vein as a conduit was in the first 10 to 15 years of coronary surgery, before experience showed that multiple arterial conduits and complex grafting with them was better. Poor patency makes the cephalic vein a last choice.

ARTERIAL CONDUITS

Left Internal Thoracic Artery

The left ITA arises from the left subclavian artery opposite the vertebral artery origin and passes through the thoracic inlet, crossing dorsal to the subclavian vein with the phrenic nerve before passing deep to the endothoracic fascia just lateral to the sternal edge, which it follows to the sixth intercostal space. There it divides into the musculophrenic artery, having a lateral course, and the superior epigastric artery, which enters the rectus sheath.

The ITA is unique among the arterial conduits in that its muscular media has 6 to 12 elastic lamellae. The subintima lies on the prominent internal elastic lamina, which has few and small fenestrations in contrast to other small arteries, where more and larger fenestrations may allow entry of smooth muscle cells to the subintima and initiate plaque formation.²⁶ The reduced smooth muscle mass results in less- vigorous contraction when exposed to agonists than is seen with the other arterial conduits. The ITA supplies flow to the anterior chest wall and sternum, which are also supplied by the intercostals, assisted by a vascular anterior sternal periosteum.

Patency

In terms of patency, a graft from the left ITA to the left anterior descending artery is the gold standard for all conduits and target vessels. It is more than 95% at 1 year, 85% to 95% at 10 years, and 88% at 15 years (see Table 89-1). There is no loss of patency for sequential anastomoses in parallel, but there is a 10% decrease for crossing (diamond) anastomoses.³¹ Patency is unchanged for proximal circumflex branches (ramus intermedius, first obtuse marginal) and decreases 10% to 15% for distal circumflex branches.³¹ In contrast to the situation with other arterial conduits, the effect of decreasing stenosis (more competitive coronary flow) on graft patency is mild for the left anterior descending artery and slightly greater for other target vessels, and without a break point for decreasing stenosis.³²