Prophylactic Left Internal Mammary Artery Graft In Mildly-Stenosed Coronary Lesions. Still An Open Discussion.

Abstract

The main advantages of CABG with the left internal mammary artery (LIMA) have been well established since the 80s and can be enumerated as follows.1 Increased long-term patency, undoubtedly demonstrated; Atherosclerosis resistance based on the endothelial production of nitric oxide and prostacyclin; Contrary to the venous bypass, it has been used not only for pedicle grafts as well as for free grafts; Improved clinical outcomes (various studies have shown the influence of LIMA graft on the recurrence of angina, nonfatal myocardial infarction, and favorable survival, and; Less need for reoperations (a 2-fold lower incidence of reoperations has shown in patients without LIMA graft compared to the left anterior descending coronary artery (LAD). It has been well established that coronary venous grafts in arteries with moderate atherosclerotic lesions (<70%) had early occlusion mainly due to flow competition with the native coronary circulation. Otherwise, to graft a moderately stenosed coronary vessel with LIMA remains debatable, keeping the question by Hayward and colleagues open: Should all moderate coronary lesions be grafted during primary coronary bypass surgery?.2 However, controversy exists whether LIMAs should be used to bypass coronary arteries with noncritical stenoses.3 Left internal mammary flow Doubts about the quality of LIMA flow began to fade in the late 1970s. However, in the 1980s, numerous studies demonstrated the ability to LIMA to dilate or decrease its diameter according to the myocardial needs, demonstrating the dynamic nature of its luminal diameter. Excluding surgical problems (damage during harvesting and mobilization, spasm, inflammation, or a steal phenomenon arising from a large undivided proximal LIMA branches), LIMA graft failure in coronary artery bypass grafting (CABG) is mostly considered to be a result of competitive flow (CF) from the native coronary artery, limiting future revascularization options particularly in young patients. As time goes by, the controversies remain alive, emphasizing that experimental studies, concerning the prophylactic use of LIMA grafts for moderate coronary obstructions, demonstrate and keep controversial results. Results from acute experiments have indicated that competitive flow from a fully patent native artery did not abolish LIMA graft flow. The chronic experiments results demonstrate that even after 2 months of maximal chronic flow competition from a fully patent native artery, LIMA graft flow was maintained above in situ levels, and a recruitable flow reserve could be demonstrated when the native vessel was occluded. These data suggest that LIMA grafts are dynamic and may remain patent despite significant residual flow in the native vessel.4 LIMA graft patency decreases as coronary artery competitive flow increases. However, the effect of competitive flow on LIMA graft patency is mild, and no degree of proximal coronary stenosis led to declining LIMA patency. This finding suggests that LIMA should not be avoided when bypassing coronary arteries with moderate degrees of stenoses.3