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Royse et al. Vessel Plus 2020;4:5 I http://dx.doi.org/10.20517/2574-1209.2019.34 Page 7 of 22

Figure 4. Survival of propensity score matched radial artery Y graft versus left internal mammary artery and supplementary saphenous
vein graft patients, n = 332 pairs. Reproduced with permission, JACC 2018 [37] . LIMA-RA-Y: left internal mammary artery radial artery Y
graft; LIMA + SVG: left internal mammary artery and supplementary saphenous vein graft

survival outcomes compared to SVG [37,40,42-44] . Therefore, the study design of one versus two IMA, rather
than one versus two arterial grafts was confounded by RA being used. Additionally, there was a high cross-
over from the randomised allocation. For patients randomised to one IMA, RA was used in 22% and BIMA
used in 4% resulting in 26% receiving more than one arterial graft. Additionally, of patients randomised
to two IMA, 14% crossed over to a single IMA, resulting in a 40% crossover rate of one versus two arterial
grafts. It was not reported how many patients randomised to BIMA received additional RA grafts, which
could potentially further magnify the groups discrepancy. By contrast, the post-hoc (non-randomised)
dataset analysed all-cause mortality according to the use of 1 or ≥ 2 arterial grafts and found a significant
survival advantage for more arterial grafts (HR 0.81, 95%CI: 0.68-0.95). Criticism of post-hoc non-
randomised data is reasonable and valid.

However, this argument misses an even more important consideration of this dataset, which is that both
groups in either of these analyses include supplementary SVG. If SVG is the conduit known to progressively
fail and leads to ischemic events, of which some lead to death (see below), then the two groups remain
relatively similar because both groups still use SVG. Specifically, SVG is more important in the causation
of failure of CABG than the arterial grafts, in the long term. A further analysis of this dataset according to
TAR vs. ≥ 1 SVG has not been published.

“The chicken and the egg” dilemma
The obvious consequence of increasing use of arterial grafts is that there is a compensatory reduction in
the number of SVG being used. We conducted an analysis whereby the number of grafts was restricted and
[42]
then performed separate matching for all grafting combinations within each stratum [Figure 5]. For each
stratum, the increasing use of SVG (and reduction in the use of arterial grafts) resulted in an increasing
mortality hazard.