ABSTRACT

Pathology of SVG Failure Within one year following CABG, most SVG have developed some degree of concentric intimal proliferation similar to the smooth muscle cell proliferative response observed after vascular injury induced by percutaneous coronary intervention (PCI). The development of intimal hyperplasia in “arterialized” veins is a ubiquitous process commencing approximately four weeks after implantation. While this proliferative response often results in mild luminal narrowing throughout the SVG, it may be of sufficient magnitude to obstruct blood flow. The etiology of this pathologic response probably involves endothelial cell damage or denudation occurring during harvesting, vascular ischemia when vasa vasorum are severed, and barotrauma resulting from exposure of the vein to arterial pressure. This proliferative response is often most exuberant at anastomotic sites suggesting greater injury at these loci. Even if intimal hyperplasia does not result in ischemia within the first year following CABG, its presence may provide the substrate for accelerated SVG atherosclerosis (5). Canˇos et al. compared the clinical, angiographic, and intravascular ultrasound (IVUS) characteristics of early (mean SVG age 6 months) and late (mean SVG age 105 months) SVG failure. Early SVG failures were more likely to be ostial (37.5% vs. 17.5%, p < 0.001), and had smaller pretreatment reference diameters (2.47 0.86 vs. 3.26 0.83, p < 0.001), smaller minimum lumen diameters (MLD) (0.80 0.64 vs. 1.08 0.64, p < 0.001), and greater pretreatment diameter stenosis (71.6 19% vs. 66.7 17.7%, p < 0.017). Additionally, early SVG failure was associated with lower thrombolysis in myocardial infarction (TIMI) flow rates and SVG that failed late were more likely to have degenerated, diffuse atheroma. IVUS analysis suggested that SVG that fail early are diffusely diseased conduits without positive remodeling, resulting in smaller lumen size (7). While it is controversial as to whether SVG undergo positive remodeling, the lack of positive remodeling may contribute to early graft failure.