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Royse et al. Vessel Plus 2020;4:5 I http://dx.doi.org/10.20517/2574-1209.2019.34 Page 17 of 22

The effects of competitive flow are subject to some popular misconceptions:
1. Reduced arterial graft patency with reduced degree of coronary stenosis is not a “binary” phenomenon.
Surgeons often assume that patency will be 100% when grafted to coronary lesions of more than a particular
value (e.g., 80% or 90% stenosis) - and, conversely, they assume the patency will be 0% when grafted to
lesions of less than this value. This is incorrect and exaggerated. The patency progressively diminishes as
the degree of coronary stenosis decreases, and there is no specific cut-off value whereby patency falls to
zero [71,109-112] . In our as yet unpublished experience, the patency of all conduits exceeds 50% at angiography
when grafted to coronary lesions of ≥ 50%.
2. Use of SVG is resistant to the effects of competitive flow and can be used without adverse consequence
for mild or moderate lesions. Our data indicate that even single SVG is associated with long-term
adverse survival implications and we would advise avoidance of grafting with any conduit under these
circumstances.
3. Early arterial graft failure from competitive flow is still a failure. From the clinical perspective, this is
not true. The lack of a flow limiting coronary lesion (at rest) results in a minimal blood pressure drop
distal to the lesion, and therefore a minimal pressure gradient driving flow across the conduit. The lack of
conduit flow presumably leads to conduit ischemia, although the precise mechanism of arterial graft failure
is unknown. Late histology of a string sign reveals a viable media and adventitia; however, the lumen is
mostly obliterated with intimal hyperplasia. Because the target myocardium remains well supplied by blood
at rest, there is no ischemic consequence to this graft failure.
4. A “string sign” (an angiographic appearance of severe and diffuse narrowing of an arterial conduit lumen,
which does not fill the native coronary artery via the graft) is thought to be a reversible state. Many would
believe that this is caused by spasm of the conduit (rather than the intimal hyperplasia seen at histology)
and that relaxation of the conduit wall will reverse patency. We have never documented a case of reversal of
string sign and consider it permanently occluded.

FINAL WORD: BUYING INTO THE LEFT MAIN CORONARY STENOSIS PCI VS. CABG DEBATE
Head et al. [113] performed a patient level pooled analysis of 11 RCT examining PCI vs. CABG. The findings
were of five-year all-cause mortality benefit for CABG (HR = 1.20, 95%CI: 1.06-1.37, P = 0.004). However,
the benefit was confined entirely to multivessel and complex coronary disease and in diabetic patients (HR
= 1.28, 95%CI: 1.09-1.49, P = 0.002). Non-diabetics and those with left main stenosis had no significant
difference.

In late 2019, the five-year data for the EXCEL [114] and NOBLE [115] trials examining left main coronary
stenosis of low and intermediate complexity were released. Great controversy surrounding the definition
used for myocardial infarction (alleged to favour PCI) was ongoing at the time of this manuscript
preparation. Nevertheless, these two trials reported apposing analyses using composite endpoints. The
EXCEL trial reported no significant difference (HR = 1.19, 95%CI: 0.95-1.50, P = 0.13). The NOBLE trial
reported superiority for CABG (HR = 1.58, 95%CI: 1.24-2.01, P < 0.001).

The key relevance to this manuscript is that none of the CABG vs. PCI trials accurately describe the
revascularisation techniques of the CABG arm. Since the vast majority of patients are from North American
or European centres, it is left to the reader to assume that the technique of CABG would closely reflect
“routine” clinical practice in these regions. Specifically, it is therefore likely that the vast majority of patients
undergoing CABG in these trials would have received a single arterial graft and supplementary SVG. What
this suggests, is that the superiority of CABG over PCI in these trials - may be further magnified by a factor
of at least 1.22 - if all of the CABG arm were to have received total arterial revascularisation.

It is therefore a matter of speculation as to whether PCI vs. CABG that is comprised entirely of total arterial