Since the first coronary artery bypass grafting procedure in 1963, saphenous vein has been the mainstay conduit used in this country and worldwide. Because vein grafts often become diseased and occluded, arterial grafts have become more popular, particularly, the internal thoracic artery. Other arterial conduits have recently been introduced because of improvements in technical skill, pharmacologic modification of vascular reactivity and improvements in harvesting techniques. Its the purpose of this review to give our groups priority of graft conduit utilization for coronary artery bypass grafting and to justify those opinions.
Internal Thoracic Artery
Since the first reports of large numbers of patients in the mid 80s, the internal thoracic artery has been the mainstay for coronary artery bypass grafting, principally to the left anterior descending artery. This graft would be our first choice of a conduit and would be performed as a pedical graft to the LAD with an occasional sequential anastomosis to an intermediate or diagonal branch. We perform this graft on virtually every patient despite advanced age or comorbidity. The right internal thoracic artery is often harvested in younger patients, particularly those without diabetes or chronic obstructive pulmonary disease. The right internal thoracic artery can be used as a free graft and based either off the aorta or the side of the left pedical graft. Because of sternal complications, bilateral mammary artery grafting is performed only in younger patients in our institution and is specifically avoided in patients with diabetes, obesity and/or COPD.
Radial Artery
Since the radial artery was re-introduced as a conduit in the early portions of this decade, it has become the clear second choice in our institution as a bypass conduit. It can be based off the side of the pedical ITA graft or from the aorta. Sequential anastomoses are easily performed. The radial artery should not be harvested from a patient with a positive Allen test. And if that rule is followed, the postoperative results in terms of hand function are excellent. Several groups are now using bilateral radial artery harvesting without untoward effect. It is has been shown that the radial artery has greater reactivity to pharmacological stimuli than the internal thoracic artery and thus pharmacologic vasodilatation with a calcium channel blocker is preferred for a few weeks or months. It has also been shown that the endothelial function of the radial artery is similar to that of the internal mammary artery, thus suggesting long-term patency rates will be equivalent.
Right Gastroepiploic Artery
The right gastroepiploic artery is often used in our institution as a secondary arterial conduit in patients with internal thoracic artery grafts. It can be used as a pedical graft to the posterior descending coronary artery or distal right branches and is a free graft to virtually any vessel. It is important during harvesting to remove the graft at its origin to provide enough length and a graft of sufficient size to permit long-term patency. In addition, older patients with peripheral vascular disease often have stenoses of either the celiac axes or hepatic artery, thus rendering a pedical graft unsatisfactory. The incision into the abdomen often increases operative morbidity, but probably not mortality.
Inferior Epigastric Artery
The inferior epigastric artery has not been extensively studied, but has been used in some centers as an additional arterial graft. It requires a separate abdominal paramedian incision which increases the operative morbidity, and the graft is often not long enough to permit an aortic
anastomosis. Nevertheless, it can be a side branch from a pedical graft or radial artery graft to increase the number of arterial anastomoses. The vascular reactivity of the inferior epigastric artery is similar to that of the radial artery.
Saphenous Vein
It has been known for sometime that a saphenous vein often has a limited life expectancy resulting in 60-70 percent of grafts being stenotic or occluded at ten years. The graft is very useful in elderly patients and can be used for single or multiple sequential anastomoses. The principle indication for saphenous vein grafts in our institution is elderly patients and patients without sufficient arterial conduits. Modification of certain risk factors is very important in increasing postoperative patency rates in saphenous veins. Complete avoidance of smoking is of paramount importance as well as careful control of any plasma lipid elevations. Preparation of the vein is also of great importance in improving long-term patency. Venous valves should be avoided, if possible, particularly if the sinus of the valve is significantly larger then the diameter of the vein itself. An attempt should be made to incise stenotic valves in that they have been shown to produce early occlusion. We feel that it is important to avoid overdistention of the vein and we use heparinized blood as a venous preservative between harvesting and implantation.
Other Conduits
The use of other conduit material is controversial and low patency rates can be expected. Arm vein is a conduit of last resort, which is also true for cryo-preserved saphenous vein. Bovine internal mammary grafts and prosthetic material are to be avoided because of exceedingly low patency.
References
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