Dr. Michael C. Dalsing
It is true that severe bleeding was not increased (intracranial hemorrhage, or hemodynamic compromise: 1 vs 2.7%, P = NS) but moderate bleeding (transfusion required: 0.7 vs 3.7%, P = .012) and mild bleeding (5.4 vs 12.1%, P = .004) was increased when this agent was used especially in vein graft surgery. This risk of bleeding was present even when clopidogrel was begun 2 or more days after surgery.1
To complicate this decision, a Cochrane review did not consider subgroup analysis as statistically valid and so the authors considered infrainguinal graft patency as not improved with clopidogrel but bleeding risk was increased. One might even question the use of acetylsalicylic acid (ASA) for vein graft bypasses based on the results of this metanalysis.2 Carotid endarterectomy is a common vascular surgery procedure in which antiplatelet use has been evaluated in the real-world situation and with large cohorts. As is always the case when dealing with patient issues, the addition of one agent does not tell the entire story and patient demographics can have a significant influence on the outcome. A report from the Vascular Quality Initiative (VQI) database controlled for patient differences by propensity matching with more than 4,500 patients in each of the two groups; ASA vs. ASA + clopidogrel; demonstrated that major bleeding, defined as return to the OR for bleeding, was statistically more common with dual therapy (1.3% vs. 0.7%, P = .004).3
The addition of clopidogrel did statistically decrease the risk of ipsilateral TIA or stroke (0.8% vs. 1.2%, P = .02) but not the risk of death (0.2% vs. 0.3%, P = .3) or postoperative MI (1% vs. 0.8%, P = .4). Reoperation for bleeding is not inconsequential since in patients requiring this intervention, there is a significantly worse outcome in regard to stroke (3.7% vs. 0.8%, P = .001), MI (6.2% vs. 0.8%, P = .001), and death (2.5% vs. 0.2%,P = .001). Further drill down involving propensity score–matched analysis stratified by symptom status (asymptomatic vs. symptomatic) was quite interesting in that in only asymptomatic patients did the addition of clopidogrel actually demonstrate a statistically significant reduction in TIA or stroke, any stroke, or composite stroke/death. Symptomatic patients taking dual therapy demonstrated a slight reduction in TIA or stroke (1.4% vs. 1.7%, P = .6), any stroke (1.1% vs. 1.2%, P = .9) and composite stroke/death (1.2% vs. 1.5%, P = .5) but in no instance was statistical significance reached. The use of protamine did help to decrease the risk of bleeding.
Regarding the use of dual therapy during open aortic operations, an earlier report of the VQI database demonstrated no significant difference in bleeding risk statistically, but if one delves deeper the data indicate something different. In the majority of cases, vascular surgeons do not feel comfortable preforming this extensive dissection on dual therapy. Of the cases reported, 1,074 were preformed either free of either drug or only on ASA while 42 were on dual therapy and only 12 on clopidogrel only. In fact, in the conclusions, the authors note that they do not believe that conclusions regarding clopidogrel use in patient undergoing open abdominal aortic aneurysm repair can be drawn based on their results since the potential for a type II error was too great.4
It may be that our current level of sophistication is not sufficiently mature to determine the actual effect that clopidogrel is having on our patients. Clopidogrel, a thienopyridine, inhibits platelet activation by blocking the ADP-binding site for the P2Y12 receptor. Over 85% of ingested drug is metabolized into inactive metabolites while 15% is metabolized by the liver via a two-step oxidative process into the active thiol metabolite. Inter-individual variability in the antiplatelet response to thienopyridines is noted and partially caused by genetic mutations in the CP isoenzymes. Platelet reactivity testing is possible but most of the work has been conducted for those patients requiring coronary artery revascularization. Results of tailoring intervention to maximize therapeutic benefit and decrease the risk of bleeding have been inconsistent but, in some studies, appear to be promising.5 This approach may ultimately be found superior to determining how effective clopidogrel actually is in a particular case with some insight into the bleeding risk as well. With this determination, whether or not to hold clopidogrel perioperatively can be made with some science behind the decision.
Clearly, a blanket statement that the risk of bleeding should be accepted or ignored because of the demonstrated benefits of clopidogrel in patients requiring vascular surgery is not accurate. In some cases, there is no clear benefit, so eliminating the bleeding risk may well be the appropriate decision. The astute vascular surgeon understands the details of the written word in order to make an educated decision and understands that new information such as determining platelet reactivity may provide more clarity to such decisions in the future.