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Long-Term Patency of Internal Mammary Artery Bypass Grafts: Relationship With Preoperative Severity of the Native Coronary Artery Stenosis

Background—Internal mammary artery conduits (IMA) have an excellent long-term patency rate. Nevertheless, graft closure does occur and significantly limits future revascularization options. We sought to investigate the relationship between the long-term patency of IMA with clinical and angiographic parameters. Particularly, the preoperative degree of stenosis of the relevant bypassed coronary vessel was assessed to analyze the importance of chronic competitive flow on the arterial graft closure rate. Methods and Results—Consecutive patients in whom occlusion of at least 1 IMA had been documented at angiography (OCC group) were compared with a group of patients with patent IMA grafts (PAT group). The degree of stenosis in the native coronary artery on which the IMA was placed was analyzed by off-line quantitative coronary angiography. Multivariate stepwise logistic regression was used to identify independent clinical and angiographic predictors of occlusion. The OCC group comprised 96 patients (67±10 years) with 103 native bypassed arteries analyzed. The PAT group comprised 127 patients (69±8 years) with 170 native bypassed arteries analyzed. Both groups were similar except for gender (42% versus 32% female; P=0.04), height (166±8 versus 169±8 cm; P=0.006), minimum lumen diameter (0.76±0.7 versus 0.51±0.5; P=0.001), and diameter stenosis of the native artery (73±25% versus 84±16%; P<0.0001) in OCC versus PAT, respectively. In the multivariate analysis, only percent diameter stenosis was an independent and statistically significant predictor for graft patency. Among IMA placed on coronary arteries with a diameter of stenosis <50% (n=28), the occlusion rate was very high (79%). Conclusion—The degree of stenosis in the native vessel is a major predictor of internal mammary artery bypass graft patency. The association between nonsignificant stenosis of the native artery and high occlusion rate of the arterial bypass conduit raises concerns about the use of IMA in the treatment of native vessels with only mild or moderate stenosis.