**3. Histology of saphenous vein**

Carpentier in 1971 and fell into disrepute shortly after its introduction because of high failure rates but was revisited as many of these original grafts appeared widely patent at 6 years. [12, 13] Initially used as a free graft in a fashion similar to that of the saphenous vein graft, more recently the RA has been used as a T or Y graft from the left IMA (LIMA) or an extension graft from the distal right IMA (RIMA). On the basis of superior long-term outcomes of arterial conduits compared with vein grafts, other arteries have been used in CABG such as the gastroepiploic artery (GEA), the inferior epigastric artery (IEA), the splenic artery, the subscapular artery, the inferior mesenteric artery, the descending branch of the lateral femoral circumflex artery, and the ulnar artery. However none of these arteries have shown similar

*Surgical revascularization in the current era -* A number of studies and trials have consistently shown the benefit of CABG in select patient populations. Indisputable, surgical revasculari‐ zation which in most cases is performed utilizing the saphenous vein for bypassing non LADlesions and arterial bypass grafts for LAD lesions, has dramatically changed the management of patients with ischemic heart disease. Currently, over 300,000 patients undergo CABG in the United States each year. [14] Although the short-term outcomes of CABG are generally excellent, patients remain at risk for future cardiac events due to progression of native coronary disease and/or coronary bypass graft failure. [15-18] To illustrate, over half of saphenous vein grafts (SVG) are occluded at 10 years post CABG and an additional 25% show significant stenosis at angiographic follow-up. [19] Additionally, diseased grafts represent an increasing proportion of culprit lesions and acute graft occlusion may cause acute coronary syndromes (ACS). [20] In the next paragraphs we will describe in further detail the pathophysiologic mechanisms that lead to coronary artery bypass graft failure, and elude to management

**2. Pathophysiology of coronary artery bypass graft failure**

burden, the majority of CABG procedures continue to use SVG. [21]

The use of the SVG, arterial grafts or both during CABG is largely depending on the site of anatomic obstruction, the availability of good quality conduits, patient preferences, and the clinical condition of the patient. Adequate arterial conduits are not always available, in contrast SVG are usually of good quality and calibre and are easily harvested, and are thus commonly used as conduits. However, there is an increasing interest for the use of arterial conduits as coronary artery bypass grafts, especially for bypassing the left coronary artery. Although, the choice to use arterial conduits partly depends on the coronary run-off, the long-term patency of arterial grafts is superior for CABG compared to SVG. As more than half of SVG are occluded at 10 years post CABG and an additional 25% show significant stenosis at angiographic followup. [19] SVG failure is the main cause of repeat intervention either by redo CABG or PCI and is even more common than the progression of native coronary artery disease in patients whom underwent CABG. In spite the fact that SVG failure remains a significant clinical and economic

patency rates as the internal mammary artery.

strategies.

194 Artery Bypass

The saphenous vein consists of three layers: the intima, media, and adventitia. The intima is composed of a continuous layer of endothelial cells on the luminal surface of the vessel. Beneath lies the fenestrated basement membrane embedded with a fragmented internal elastic lamina. The media comprises of smooth muscle cells (SMC) arranged in an inner longitudinal and an outer circumferential pattern with loose connective tissue and elastic fibers interlaced. The middle muscle layer is most extensive at the insertion points of the valves and leaflets. The adventitia forms the outer layer and consists of longitudinally arranged SMC, collagen fibers and a network of elastin fibers, in addition to vascular and nerve supplies to the vessel.The great saphenous vein is the most frequently used conduit for myocardial revascu‐ larization but other venous conduits such the short saphenous vein or upper extremity veins (cephalic and basilica) can be used as well.
