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Browne et al. Vessel Plus 2024;8:19 https://dx.doi.org/10.20517/2574-1209.2023.126 Page 11 of 18

Figure 2. Illustration of in situ, free, and composite grafting of the right internal mammary artery to the left circumflex artery during
[7]
coronary artery bypass grafting surgery. Adapted from Alboom et al. . LIMA: Left internal mammary artery; RIMA, right internal
thoracic artery.

trial of 304 isolated CABG patients assigned to receive in situ RIMA or Y-composite RIMA to supplement
LIMA-LAD grafting, rates of RIMA graft failure were similar with either configuration at 6 months (4.0%
[5/126] vs. 2.6% [7/267]) and 3 years (7% vs. 5.5%) . However, the risk of major adverse cardiovascular
[56]
[57]
and cerebrovascular events (i.e., a composite of all-cause mortality, myocardial infarction, stroke, or repeat
revascularization) at 7 years was lower with Y-composite compared with in situ RIMA grafting
(25% [38/152]) vs. 34% [51/152]). The main driver of the composite was a reduced risk of repeat
revascularization with Y-composite RIMA (7% [10/152] vs. 13% [20/152]). Similar risks of all-cause
mortality, myocardial infarction, and stroke were reported for both grafting configurations. The mean
number of anastomoses with in situ RIMA was 1.8 compared with 1.0 in the Y-composite RIMA group,
consistent with the need for an additional supplementary graft in the in-situ RIMA group.

Similar results were reported in a single-center retrospective observational study of 1,818 patients who
underwent BIMA grafting and received either in situ RIMA or Y-composite RIMA . Survival at 8 years
[58]
was similar in both groups (95.8% vs. 94.8%) and angiograms obtained in 88 (5%) patients at a mean follow-
up of 1.5 years revealed similar rates of graft failure in both in situ and Y-composite groups (0% [0/25] vs.
0.8% [2/63]). However, the very low participation in angiographic follow-up indicates the failure rates
should be interpreted with caution (i.e., they are likely underestimates due to attrition bias).

Observation evidence suggests that free RIMA may be preferable to in situ RIMA, with comparable results
between in situ and composite proximal RIMA grafting approaches. Failure rates are largely influenced by
distal target vessel location, where free or composite RIMA grafting may be preferred to reach more distant
target vessels in the left circumflex and right coronary artery territories. However, it is important to note
that these results should be considered hypothesis-generating due to the methodological limitations of the
studies. Most studies were retrospective or post hoc in nature, except for a single randomized controlled
trial. Additionally, there was high variability in the proportion of patients completing angiographic follow-
up (i.e., potential attrition bias) and timing of angiography, and potential selection bias may have been
introduced by symptom-driven rather than systematic postoperative angiography. Randomized controlled
trials are needed to determine the optimal proximal grafting configuration for RIMA grafting in CABG
surgery.