**4. Patency of RIMA versus LIMA**

procedures performed, 92.4% of patients had at least one IMA graft, and the frequency of LIMA usage by each hospital ranged from 48.0% to 100% with a median of 94% [3]. The presence of an IMA graft has also been identified as an independent predictor of survival and confers significantly better long-term survival rates than the use of saphenous vein grafts alone [2].

While anatomically identical to the LIMA, the RIMA is rarely used in CABG procedures, and is almost always used as part of bilateral internal mammary artery (BIMA) grafts when it is utilized. Despite several studies showing that BIMA use confers significantly improved clinical outcomes [4-6], between 2003 and 2005 the frequency of BIMA use was only 4% [3]. Reasons for not using the RIMA include increased operative time and perceived technical difficulty associated with the harvest, concern for perioperative morbidity and mortality, the possibility of reoperations for bleeding, sternal wound infection, and uncertainty as to whether there is

Despite its low prevalence of use, many studies have shown that RIMA use in conjunction with the LIMA can confer significantly better clinical outcomes when compared to conven‐

Several observational, retrospective studies have found that there are significantly greater long-term survival benefits in patients who received BIMA grafting compared to SIMA grafting. Lytle *et al.* studied 10,124 elective CABG patients receiving either SIMA or BIMA grafts with or without any additional vein grafts in a retrospective, non-randomized study with a mean follow-up of 10 post-operative years. Hospital mortality rates were identical for the SIMA and BIMA groups (0.7%). However, over 12 years of post-operative follow up, survival rates for BIMA patients were significantly better than for SIMA patients (79.1% versus 71.6% respectively, p < 0.001) [9]. In a follow-up to the original study, which extended the mean post-operative follow up to 16.5 years, survival rates for BIMA and SIMA patients at 20 years were 50% versus 37% respectively (p < 0.0001), demonstrating a significant long-term survival advantage for patients receiving two internal mammary grafts compared to just one [10].

Nasso *et al.* aimed to determine whether or not there were significant benefits to using two arterial conduits rather than just a single arterial conduit. 815 patients were randomized to one of four revascularization strategies: *in situ* LIMA to LAD plus isolated RIMA Y graft, *in situ* RIMA to LAD plus *in situ* LIMA, *in situ* LIMA to LAD plus free radial artery, and *in situ* LIMA to LAD with saphenous vein grafts as a control. All revascularization groups received saphenous vein grafts to bypass the remaining coronary occlusions, if needed. Although the authors found no significant overall survival advantage between any of their revascularization groups over a follow-up period of two years, there was a significant difference in survival when considering cardiac event-free survival. Patients in groups receiving two arterial grafts had significantly better cardiac event-free survival rates when compared to patients who only

tional CABG procedures with the LIMA and saphenous vein grafts.

**Survival benefits of BIMA versus Single Internal Mammary Artery (SIMA)**

a significant benefit with BIMA grafting [7, 8]

**3. Outcomes of BIMA in CABG**

120 Artery Bypass

Patency is the most important determinant in long-term prognosis [7]. Due to the extremely low prevalence of use for the RIMA, there have been few studies evaluating its patency compared to the LIMA. However, the studies that have been performed suggest that the RIMA has similar early and even long-term patency rates as the LIMA, especially when grafted to similar coronary territories [17].

Fukui *et al.* reviewed the angiographic records of 705 patients undergoing BIMA CABG procedures. Early angiography and 1-year angiographic results for RIMA patency are good, with an overall patency of 98.8% at early angiography and 94.3% at 1-year postoperative follow-up compared to 99.1% and 97.0% for the LIMA at the same follow-up times (p = 0.7732 and p = 0.1288, respectively). In terms of grafting technique, at both early and 1-year angio‐ graphic follow up, there were no significant differences in the patencies of *in situ* versus free RIMA grafts. For free RIMA grafts, there were also no significant differences in patency rates between sites of proximal anastomoses (composite versus aorta). However, for the *in situ* RIMA, patency rates were significantly better when anastomosed to the anterior coronary territory when compared to other grafting methods (p < 0.0001)[16].

While Burfeind *et al.* found no significant difference in 15-year mortality rates for pa‐ tients receiving single IMA grafts or multiple (bilateral) IMA grafts, they did find signifi‐ cant differences in the rates of MI and CABG reoperation. However, these rates differ based on the definition of what constitutes a patient receiving multiple IMA grafts. In their study 1,067 patients that had undergone isolated CABG procedures were analyzed by three different methods. In the first analysis (analysis I), patients were analyzed based on the initial surgical strategy for revascularization – SIMA or BIMA grafts. However, not all patients who were designated to receive BIMA grafts were able to be revascular‐ ized with multiple IMAs, and likewise some patients designated to receive SIMA grafts ultimately received BIMA grafts. Analyses II and III were therefore performed based on the surgery the patient ultimately received and not the initial surgical strategy. Analysis II defined "multiple IMA grafts" based on the number of distal anastomoses performed. Therefore, in analysis II, multiple coronary systems anastomosed with multiple IMA grafts were considered "multiple IMA grafts" as well as a single coronary system se‐ quentially anastomosed with a single IMA graft. In analysis III only multiple coronary systems anastomosed with multiple IMA grafts were considered to be "multiple IMA grafts." In both analyses II and III, Burfeind *et al.* found that there were significantly re‐ duced rates of CABG reoperation in patients receiving multiple IMA grafts when com‐ pared to patients only receiving a single IMA graft (analysis II: 9.7% reop SIMA, 4.5% BIMA p = 0.0095; analysis III: 9.7% reop SIMA, 3.4% BIMA, p = 0.0026). However, in analysis III there was also a significantly reduced rate of MI in BIMA patients when com‐ pared with SIMA patients (17.4% versus 11.6% for SIMA and BIMA patients, respective‐

Total Arterial Revascularization in Coronary Artery Bypass Grafting Surgery

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In their original retrospective study on BIMA versus SIMA grafting in elective CABG patients, Lytle *et al.* also found that patients receiving BIMA grafts had significantly greater reoperationfree survival rates after 12 post-operative years than patients receiving only SIMA grafts with or without any additional vein grafts. BIMA patients had a reoperation-free survival of 76.8%

As previously mentioned, Nasso *et al.* found that patients receiving two arterial grafts had significantly better long-term, cardiac-event free survival outcomes than patients who just received a single arterial graft with or without additional saphenous vein grafts. As expected, adverse cardiac events occurred significantly less frequently in the groups receiving two arterial grafts versus the group receiving just one. There was no significant difference in the occurrence of adverse cardiac events between the three groups receiving two arterial grafts. Cerebrovascular complications occurred more frequently in the SIMA group, however this difference was not significant. The authors note that this increased incidence of cerebrovas‐ cular complications may be due to the more extensive manipulation of the ascending aorta

needed in the SIMA group due to the greater number of proximal anastomoses [11].

Damgaard *et al.* performed a study to assess the health-related quality of life improvements in patients undergoing traditional CABG procedures versus patients undergoing TAR CABG procedures. 331 patients were randomized between the two revascularization techniques and over 90% of patients responded to the questionnaire at the specified time points. Preopera‐

compared to the 62.4% reoperation-free survival rate of SIMA patients [9].

ly, p = 0.0181) [6].

Tatoulis *et al.* evaluated the results of 991 consecutive RIMA postoperative CABG angiograms taking place between 1986 and 2008. The main focus was graft patency, with grafts considered non-patent if they had a greater than 80% stenosis, string sign, or total occlusion. When com‐ pared to the LIMA for identical grafting territories, there was no significant difference in RIMA and LIMA patency. For the LAD, overall LIMA patency was 96.9% while overall RIMA patency was 94.6% (p = 0.74). When grafted to the circumflex, LIMA patency was 90.7% versus RIMA pa‐ tency of 91.9% (p = 0.85). Long-term patency results for the RIMA were favorable as well, with 92% of 352 RIMA grafts in place for greater than 10 years being patent. RIMA patencies were al‐ ways better than radial artery or saphenous vein graft patencies. At 15 years, RIMA patency was 79% compared to 50.7% for saphenous vein grafts (p < 0.001). 15-year data were not available for the radial artery; 10-year patency was 78% (p < 0.01 when compared to RIMA 10-year patency). However, the authors noted that data for radial artery patency is limited [17].

There are a variety of grafting techniques for BIMA, such as *in situ* grafting versus Y/T-grafts that may have an impact on patency rates. In a study by Glineur *et al*., 304 patients receiving BIMA grafts were randomized to receive either an *in situ* RIMA graft or a Y-graft with the RIMA anastomosed proximally to the *in situ* LIMA as an end-to-side graft. Follow-up angiog‐ raphy was performed at 6 months and the RIMA patency rate in both groups was 97% (p = 0.99) [18]. In a similar but slightly larger study, Calafiore *et al.* also found no significant differences in patency rates between *in situ* and Y-graft RIMA grafts at both early (13 days) and long-term (17 months) angiographic follow up [19]. A longer study by Hwang *et al.* studied 5-year angiographic patency results of BIMA grafting configurations. At 1 year of follow-up, *in situ* RIMA patency rates were not significantly different than Y-graft RIMA patency rates (92.5% versus 95.7%, respectively, p = 0.138). Similarly at 5 years of follow up, there were also no significant differences in patency rates (92.5% *in situ* versus 92.4% Y-graft, p = 0.978) [20].
