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Browne et al. Vessel Plus 2024;8:19 https://dx.doi.org/10.20517/2574-1209.2023.126 Page 5 of 18

Table 2. Comparison of clinical outcomes by CABG conduits used to supplement LIMA-LAD grafting
RA vs. Vein Vein vs. RIMA RA vs. RIMA
Outcome
HR (95%CI) P value HR (95%CI) P value HR (95%CI) P value
Gaudino et al., 2022 [29] (n = 10,256 patients)
All-cause mortality, MI, or stroke 0.78 (0.67-0.90) 0.04 0.96 (0.84-1.10) 0.66 0.75 (0.65-0.86) 0.02
All-cause mortality 0.62 (0.51-0.76) 0.003 0.94 (0.79-1.12) 0.59 0.59 (0.48-0.71) 0.001
Gaudino et al., 2018 [33] (n = 1,036 patients)
All-cause mortality, MI, or repeat revascularization 0.67 (0.49-0.90) 0.01
All-cause mortality 0.90 (0.59-1.41) 0.68
MI 0.72 (0.53-0.99) 0.04
Repeat revascularization 0.50 (0.40-0.63) < 0.001
HR: Hazard ratio; LIMA-to-LAD: left internal mammary artery to left anterior descending artery; MI: myocardial infarction; RA: radial artery;
RIMA: right internal mammary artery.

non-LAD targets, may be an important confounding factor to consider and therefore comparisons of the
CABG conduits within the same target vessel region may be preferable. We note that modern angiography
and clinical outcomes data reflect the expanded use of the radial artery and RIMA by an increasing number
of surgeons to more distal (non-LAD) target vessels of varying size and degree of stenosis. In this context,
the relatively high rates of RIMA failure, particularly to non-LAD targets, are concerning. Future
randomized controlled trials should assess the efficacy and safety of RIMA use using both graft imaging and
clinical outcome measures.

SUBOPTIMAL RATES OF CONTEMPORARY RIMA GRAFT FAILURE: POSSIBLE
EXPLANATIONS
The potential of the RIMA in facilitating multiple arterial grafting, and consequently improving patient
outcomes in CABG surgery, is widely recognized. However, the relative rate of RIMA graft failure has
recently come under scrutiny. Several contemporary studies published after 2018 (e.g., Gaudino et al.,
Yokoyama et al., Lamy et al., Alboom et al.) have reported failure rates that are often comparable to, or
worse than, those of saphenous veins [4,6,7,13,28] . Despite this, the optimal failure rates of the LIMA-to-LAD
graft and the biological equivalence of the RIMA and LIMA provide a priori evidence that the suboptimal
RIMA graft failure is likely not due to the inherent biology of the graft, but rather the specific circumstances
surrounding its use. Several factors may contribute to the overall suboptimal rates of RIMA graft failure
compared with the other conduits. Firstly, recent trials have shown selective improvements in vein graft
failure, which may diminish the true superiority of RIMA over saphenous veins. Secondly, RIMA is often
grafted to the left circumflex artery, where higher failure rates are expected due to less severe stenosis of
target vessels. Thirdly, skeletonized harvesting of RIMA conduits may result in higher failure rates
compared with the traditional pedicled harvesting technique [8,9,35] . Fourthly, in situ RIMA grafts may have
higher failure rates than free or composite proximal graft configurations [7,36] . Lastly, varying surgeon
experience may contribute to suboptimal RIMA failure rates as RIMA use adds technical complexity to
CABG surgery. These hypotheses will be explored in greater detail in the sections that follow.

Optimal rates of contemporary vein graft failure
Despite their historical suboptimal failure rate, saphenous vein grafts continue to be the most widely used
conduit for CABG surgery worldwide. Historically, failure rates were 20%-25% at 12-18 months in the large
PREVENT IV (2003) and ROOBY (2008) trials. However, a recent meta-analysis of individual patient
[37]
[18]
data that included 48 studies and 41,530 vein grafts has shown a downward trend in early vein graft failure
rates over time. In contemporary studies, which included patients enrolled after 2010, the estimated