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Page 2 of 22 Royse et al. Vessel Plus 2020;4:5 I http://dx.doi.org/10.20517/2574-1209.2019.34

THE WHY: ACHIEVING TOTAL ARTERIAL REVASCULARISATION
As of 2019, almost all cardiac surgeons perform 90%-95% of coronary bypass surgery (CABG) with the use
[1,2]
of saphenous vein graft (SVG) worldwide . Of the patients receiving total arterial revascularisation (TAR),
a proportion will have been performed without specific strategic intent to achieve TAR [e.g., a single or
double CABG using the internal mammary artery (IMA)]. Consequently, a deliberate strategy to achieve
TAR in every patient is uncommon.

Consider the following proposition: if SVG develops atherosclerosis and fails - and that failure, then leads
to the failure of the treatment of CABG - why is it that we count the number of arterial grafts?

The argument in favour of counting veins rather than arteries
“The LIMA-LAD is the only important graft in CABG”
[3-5]
The seminal publications of Lytle and Loop in the 1980s reported data acquired during the 1970s, the
period of IMA introduction. They found that use of left IMA (LIMA) significantly improved survival
compared to exclusive use of SVG. The popular interpretation of these data over the following decades
established the LIMA-LAD as somehow “sacrosanct”. It should be borne in mind that LIMA was almost
always the only arterial graft used, and the left anterior descending (LAD) almost always the only coronary
target. All other targets including branches of the LAD were grafted with SVG. As of 2019, it is almost
universally accepted that CABG is not of adequate quality if the LIMA-LAD is not used.

There are two apparent interpretations to the original papers by Lytle and Loop:
A. The IMA has “magical” properties which are impossible to define (not real, not scientific).
B. The observation arises from the difference between the late patency of an arterial graft compared to the
late patency of a venous graft [3,6-14] .

Interpretation B is not popular with surgeons or cardiologists [3,15,16] , whilst Interpretation A is inconsistent
with science or logic.

Modes of conduit failure
Progressive atherosclerosis of SVG is very widely documented with up to 50% of grafts occluding by about
10 years postoperative [8,17-19] . An angiographic classification was developed to categorise diseased SVG
[20]
(see the work by Fitzgibbon ). At durations longer than 10 years, the progressive decline in SVG patency
continues, although may be ameliorated with the widespread use of optimal medical therapies including
[21]
statins .
It is widely accepted that the LIMA has a small early graft failure rate, considered to reflect flow competition
from the native coronary circulation, and thereafter there is no clear evidence of any progressive conduit
atherosclerosis as is the case for SVG. A LIMA which survives the early postoperative period is considered
by most to be a “permanent graft” without prospects of progressive failure irrespective of the duration
[22]
postoperative. The angiographic evidence in the late period supports this contention . Indirectly, the
greater survival of patients who have received LIMA grafts also supports this contention [23,24] .

For the LIMA, and most likely any IMA, the late angiographic findings are of: (1) patency (Patent); and
(2) normal conduit lumen (Perfect Patency); or (3) Occluded/String sign. A string sign has not been
well documented in the literature as being capable of reversal and is considered occluded (permanently).
Thus, the angiographic findings are “binary” - Patent + Normal or occluded. Therefore, the Fitzgibbon
classification is not suited to the use for this arterial conduit. A subtlety of complex arterial reconstructions
is the variable diameter of an arterial conduit related to “autoregulation” of flow via changes to the diameter
of the conduit. For example, the proximal segment of the LIMA in a composite graft such as LIMA-RA-Y