Internal Mammary Arteries Unlike SVGs, IMAs usually are patent for many years postoperatively (10-year patency 90%)89,95,102,108 117 be- cause of the fact that 4% of IMAs develop atherosclerosis, and only 1% have atherosclerotic stenoses of hemodynamic significance.118 120 This resistance to the development of atherosclerosis is presumably due to 1) the nearly continuous internal elastic lamina that prevents smooth muscle cell migration and 2) the release of prostacyclin and nitric oxide, potent vasodilators and inhibitors of platelet function, by the endothelium of IMAs.119,121,122 The disadvantage of using the IMA is that it may spasm and eventually atrophy if used to bypass a coronary artery without a flow-limiting stenosis.89,95,118,123 130 Observational studies suggest an improved survival rate in patients under- going CABG when the LIMA (rather than an SVG) is used to graft the LAD artery86 88; this survival benefit is independent of the patient s sex, age, extent of CAD, and LV systolic function.87,88 Apart from improving survival rate, LIMA grafting of the LAD artery reduces the incidence of late MI, hospitalization for cardiac events, need for reoperation, and recurrence of angina.86,88 The LIMA should be used to bypass the LAD artery provided that a contraindication to its use (eg, emergency surgery, poor LIMA blood flow, subclavian artery stenosis, radiation injury, atherosclerosis) is not present. Because of the beneficial influence on morbidity and mortality rates of using the IMA for grafting, several centers have advocated bilateral IMA grafting in hopes of further improving CABG results.90,91,94 In fact, numerous observa- tional studies have demonstrated improved morbidity and mortality rates when both IMAs are used. On the other hand, bilateral IMA grafting appears to be associated with an increased incidence of sternal wound infections in patients with diabetes mellitus and those who are obese (body mass ). 2.1.4.3. 