Discussion
Exceptional results of the NT SVGs have been demonstrated when used in
on-pump CABG 3-5 . To our knowledge, no randomized
study on patency rates of NT SVGs in off-pump CABG has been reported.
This is a sub-study of a large international randomized multicenter
trial 9 that was designed to compare the clinical
outcomes in high risk patients operated with either on- or off-pump
CABG. Graft patency of the conduits was not investigated in this study.
As we routinely use NT SVGs at our department, all of our patients
included in this trial received one or two NT SVGs in addition to the
LITA graft. Thus, the aim of this study was to evaluate the patency of
the NT SVGs in both on- and off-pump CABG.
There was no superiority of on-pump CABG in terms of graft patency,
91.3% vs 84.7% for on- and off-pump respectively, p=0.35. The patency
was excellent at five years for both the LITA and NT SV grafts when used
to bypass the LAD territory, 29/30 (96.7%) for the LITA vs 32/32
(100%) for NT SVGs independent of the surgical technique used. This is
in agreement with our previous results 13. On the
other hand, the patency rates of NT SVGs to the right coronary targets
were clearly less favorable, 80% in on-pump vs 62.5% in off-pump
surgery. Further analysis showed that 24.7% of the PDAs in this study
had a diameter around 1 mm, potentially jeopardizing the patency of SVGs
attached to these vessels. These results differed from earlier results
of a randomized trial with on-pump CABG in which the patency rate of NT
SVGs anastomosed to the PDA at 1.5, 8.5 and 16 years were 100%, 95%
and 94% respectively 3-5.
The ROOBY and DOORS trials 14, 15 reported similar
results with lower patency of grafts used to bypass the right coronary
region in off-pump CABG. ROOBY showed 75.6% patency at one year while
DOORS reported 72% patency at six months postoperatively. This was also
true for both SV and arterial grafts used in a composite formation to
bypass the right coronary artery (RCA). Hwang et al. reported lower
patency of SV and arterial grafts to the RCA at one year
postoperatively, although the patency was similar between the different
conduits, 84.9% vs 82.9 for SV and arterial grafts respectively16. There are several possible explanations for this
discrepancy in the patency rates of grafts anastomosed to different
coronary territories between on- and off-pump CABG. Difficulties in
surgical access, a demanding technique requiring more surgical
experience and smaller target vessels could be the most acceptable
justifications.
Kim et al. reported improved NT SVG patency in off-pump CABG in the
context of composite grafts one year postoperatively17. The patency rate in the NT group was significantly
higher than the minimal manipulation SVG group before and after
propensity score matching, before, 97.4% vs 92.4%, p = 0.024;
after, 97.3% vs 92.6%, p = 0.051. Hence, the NT SVG may improve
the results and simplify a complex off-pump procedure especially when it
comes to sequential grafts where the surrounding tissue in NT SVGs
remains intact and acts as a biological, external stent protecting the
long sequential grafts from kinking and reducing the potential for
technical error. The number of grafts and distal anastomoses was higher
in on-pump than in the off-pump group (3.8 vs 3.1). This corresponds
with several previous studies 18 19.
Although previous studies have shown no differences in graft patency
between hand-sewn proximal anastomoses with the clamp-less Heartstring
device vs partial clamp 20, we chose to use the
clamp-less technique avoiding excessive manipulation of the aorta.
The NT SVG was used to substitute the LITA in low-grade stenosis, in
cases where the LITA was surgically damaged, and in patients with
multiple co-morbidities. This is in accordance with a previous study on
a similar group of patients. Hence, the patency rate of NT SVGs to the
LAD was 98% at a meantime of six years 13. The
patients who received a planned SVG to the LAD were older, hade a lower
left ventricular ejection fraction, higher risk scores, a low grade
stenosis in the LAD and underwent concomitant procedures. The obvious
limitation of our study is the small number of patients. Being a
sub-study, the power estimation was not calculated to investigate the
current issue.