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.