Comment
The present study demonstrated 3 main findings. First, the early
postoperative occlusion rate of the SV was 1.7% in patients who had
received the NT SV conduit as a composite graft based on the in situ
left ITA. The occlusion rate tended to be lower in patients who had
received the NT SV conduit with pedicle tissue than in patients who had
received the NT SV conduit without pedicle tissue. Second, more than
25% of the occluded SV conduit anastomoses seen in early postoperative
angiograms were patent in the 1-year angiograms. The reopening rates
tended to be higher in patients who had received the NT SV conduit with
pedicle tissue than in patients who had received the NT SV conduit
without pedicle tissue. Third, the reopening of the SV conduits took
place irrespective of the reversibility of perfusion impairment in the
preoperative SPECT results or the progression of native target coronary
artery disease in the 1-year angiograms.
Arterial conduits have the advantage of superior long-term patency in
CABG compared with vein grafts [7, 8]; however, development of
perioperative spasm in the arterial conduits has been indicated as a
drawback that might cause graft failure [9]. Of the arterial
conduits used in CABG, observation of a patent free radial artery
conduit that was occluded immediately after the operation provided the
momentum for revival of use of the radial artery in CABG [10]. In
another study which included 976 patients who received right
gastroepiploic artery (RGEA) conduits in CABG, 9 of 23 patients who had
RGEA conduit occlusions at early angiography showed patent RGEA conduits
(7 composite and 2 in situ grafts) at 1 year [11].
The pathogenesis of SV conduit occlusion forms a continuum between early
thrombosis within the first postoperative month, followed by intimal
hyperplasia between 1 month and 1 year, and subsequent atherosclerotic
change [12]. Platelet inhibitor therapy has been suggested to be of
significant benefit on an early postoperative phase of platelet
thrombotic occlusion and a late phase of occlusion toward the end of the
first postoperative year, in which the intimal hyperplasia is
superimposed by platelet thrombi [13]. One previous study documented
spontaneous late canalization of aortocoronary SV conduits that were
found to be occluded on 4-year postoperative angiogram but were patent
on 10-year angiogram [14]. Although the mechanism of recanalization
of aortocoronary SV conduits was unknown, the possibility of medical
treatment was raised [14].
To the best of our knowledge, however, the reopening of occluded SV
composite grafts has not been documented previously. In the present
study, the SV was harvested using the NT technique with or without
pedicle tissue to preserve the endothelial integrity and function of the
SV [15-17]. The reversed SV was then anastomosed to the in situ left
ITA to construct a composite graft, continuously exposing the SV to
endothelium-protective substances, such as NO released from the left ITA
[5,15]. In addition, it has been suggested that the NT SV composite
grafts based on the ITA go through a process of advantageous negative
remodeling because the SV showed decreased lumen diameter but a similar
ratio of intima-media thickness to that of the left ITA during the first
postoperative year [18]. In the present study, the occlusion rates
were lower and reopening rates of occluded SV conduits were higher in
patients who received the NT SV with pedicle tissue than in patients who
received the NT SV without pedicle tissue, although the statistical
significance was marginal. The current study failed to demonstrate any
correlation between the preoperative reversibility score or progression
of native target coronary artery disease and the conduit reopening at
the territory of SV occlusion. A further effort to preserve the
endothelial integrity of the NT SV and using the NT SV as a composite
graft based on the ITA might have resulted in the lower early occlusion
and higher reopening rates of the SV conduits. We suggest that the early
occlusion of the SV conduits can be presumed to be the result of
thrombotic occlusion at the anastomosis site and resolved by the
revascularization strategy using the NT SV composite graft based on the
in situ ITA, in combination with postoperative dual antiplatelet
therapy.
This study has limitations that must be recognized. First, this was a
retrospective observational study from a single institution and the
number of the study patients was relatively small. Second, 7 patients
(13.2%) who had shown occluded SV anastomoses but were not re-evaluated
by 1-year postoperative angiography were excluded in the present study.
Third, although the NT SV composite graft with pedicle tissue was
suggested to be related with the reopening of the SV in the 1-year
postoperative angiograms, the statistical significance was marginal for
drawing a definite conclusion, probably due to the small sample size and
the low incidence of the event.