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31. Aspirin resistance provokes early graft failure in veins with poor endothelial integrity after off-pump coronary artery bypass
Robert S Poston, Jr., Junyan Gu, Charles White, Marc Gibber, Jeffrey Manchio, Eric Christenson, Bartley P Griffith; Baltimore, MD

Objective: OPCAB may be associated with an increased incidence of early vein graft failure compared to on-pump CAB. We have found that postoperative aspirin resistance and endothelial disruption of the venous conduit after harvest are common findings in OPCAB patients. The goal of this study was to define their role in early graft failure after OPCAB.
Methods: A prospective cohort study was performed in 125 OPCAB patients treated with aspirin as the sole antiplatelet agent during the study. Arterial grafts were used in each patient but were not included in the analysis. Veins (n=259) were harvested endoscopically (89%) and prepared for grafting using standard techniques. Surplus vein segments were procured for analysis of endothelial integrity by image analysis of percent CD31 staining using immunohistochemistry (IHC); poor integrity was defined as CD31 positivity <25% of luminal circumference. Aspirin resistance was determined at baseline, immediately after surgery, and on postoperative days 1 and 3 according to platelet responsiveness on modified thrombelastograpy (using arachidonic acid), whole blood aggregometry (using low vs. high dose collagen), and flow cytometry and by a postoperative increase in 11-dehydro TXB2 levels, a prostaglandin metabolite that is typically suppressed by aspirin. Early graft patency was assessed in patients with creatinine <2.0mg/dl (n=115) on POD5 using multichannel CT angiography (CTA).
Results: Early graft failure was demonstrated in 10 out of 227 evaluated vein grafts (4.5%). Failed grafts demonstrated significantly less endothelial integrity than patent grafts (10.75±17.56 vs. 51.45±36.29%, p<0.01). By POD3, the definition of postoperative aspirin resistance was met according to at least 3 of the 4 assays in 41% of patients. Failed grafts were detected in 14% of patients with aspirin resistance vs. 4% of those maintaining aspirin sensitivity on these assays (p<0.05). The combination of aspirin resistance and poor endothelial integrity in the vein had a synergistic effect on early failure (see figure).
Conclusions: Postoperative aspirin resistance and endothelial disruption in the vein conduit are common findings after OPCAB that appear to synergistically influence early graft failure. These findings suggest that the advantages demostrated by the use of conduits with improved endothelial integrity (i.e. IMA) and alternate antiplatelet agents (i.e. clopidogrel) may be enhanced after OPCAB.

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