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Cardiothoracic Surgery, The Regional Heart and Vascular Center, Yvonne Viens, SGM, Research Institute, St. Vincent Mercy Medical Center, 2222 Cherry St, MOB2, Suite 1250, Toledo, OH 43608
(Email: robert_habib{at}mhsnr.org).
We thank Dr Savage for his insightful comments [1], and indeed, we entertained a number of them during the formulation of our study [2].
In regards to the issue of target vessel stenosis and its impact on graft patency, it is increasingly apparent that radial artery graft patency is adversely affected by the decreasing severity of the proximal stenosis. This relationship has been established in the case of the radial artery by multiple authors [3]. Given this relationship, radial artery grafts were necessarily placed to target vessels with high-grade lesions to optimize long-term graft patency.
We understand Dr Savage's concern that such an approach to using the radial artery may have led to a disproportionate number of vein grafts used to bypass lower-grade lesions (<75%) which may have exaggerated their true relative failure rates. However, competitive flow-mediated graft failure is a complex phenomenon influenced by the coronary system grafted, target vessel size, graft size, conduit type, and target vessel stenosis. In case of saphenous vein grafts, we believe the following points should be considered.
First, Sabik and colleagues [4], and more recently Desai and colleagues [5], have shown that unlike internal thoracic artery [4] or radial artery [5] grafts, saphenous veins do not exhibit competitive flow-mediated graft failure regardless of coronary system grafted along a wide range of target stenosis between 40% up to 100%.
The second point relates to the evaluation of long-term durability of grafts in patients requiring an endarterectomy, which is the central element of our study [2]. Specifically, the differences in radial vs vein graft patency results that we report (see Table 4) reflect a late (>1 year) rather than early variance in failure, as is illustrated in Figure 2 (middle panel). Arterial vs venous graft failure related to competitive flow issues almost certainly is an early postoperative phenomenon. Our data indicate that the graft patency of radial and venous grafts is essentially equivalent in the immediate postoperative period and it is only in the long-term that a patency benefit of radial conduits is realized.
The issue of pharmacologic postoperative management of coronary endarterectomy patients aimed at minimizing adverse thrombotic events impacting graft patency evolved from the early use of warfarin to the later use of clopidogrel. Dr Savage correctly points out that this shift was coincident with a progressively increasingly frequent utilization of radial arteries, and indeed, this may have added an element of bias to our conclusions. On the other hand, we are unaware of any comparative data of warfarin vs clopidogrel on coronary graft patency with or without endarterectomy. The switch to clopidogrel was motivated by the favorable experience with clopidogrel in the era of stenting in interventional cardiology, with the thrombotic burden of an endarterectomized vessel being akin to that of coronary stents.
Regardless of the lack of data on the efficacy of these two regimens, it is imperative to emphasize that both approaches were used for only several weeks postoperatively and our results focus on long-term graft durability. Any alleged differences between these regimens should have been detectable in the early (<1 year) graft patency data, a fact that we were unable to document. The patency differences become only apparent later and persisted for the duration of the study follow-up period.
The distribution of coronary artery bypass grafting/coronary endarterectomy among the 5 surgeons was highly uneven, with about 70% performed by a single surgeon. In contradistinction, radial artery utilization rates were similar for all surgeons in the practice. This should mitigate Dr Savage's concern on surgeon graft choice variations in this series.
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