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Medical Therapy - Anti-Platalet Agents

Antiplatelet agents are commonly used in the treatment of coronary artery disease. Unfortunately, the ACC/AHA guidelines did not reference the two largest studies pertaining to the protective effects of aspirin during the perioperative period.

The ACE(21) trial was a randomized controlled trial of varied doses of ASA given preoperatively to 2849 patients having elective carotid endarterectomy. Low dose aspirin (less than 325 mg/day) reduced the incidence of stroke, MI or death by 54%.

The other major trial was the pulmonary embolism prevention (PEP) trial (22). This was a RCT in emergency or elective hip and knee surgery comparing 162 mg ASA perioperatively to placebo. This trial found that there was a 36% reduction in thromboembolic events with this low dose of aspirin. Both trials assessed MI although it was not a primary outcome. Neither trial found a reduction in MI but they did not use troponin as a biomarker of MI. However, these trials did show that the practice of continuing low dose aspirin was safe as neither study found increased surgical bleeding or a need for blood transfusion. Of interest, in both the ACE and PEP trials there was a suggestion that the anti-platelet effect was diminished if this dose was combined with preoperative NSAIDS. Although there is limited information on combinations of NSAIDS and ASA, the combination does not appear to offer cardioprotection and may increase the risk of a cardiac event.

As noted earlier, in patients who have previously undergone PCI and DES insertion and are currently taking ASA and Plavix, consultations between the cardiologist, surgeon and anesthesiologist are imperative in order to individually optimize the patient’s management. In a recent review, Dalal et al (43) developed an algorithm for the perioperative management of these patients. (The reader is referred to this article which can be found in the CJA,vol 53(12); Dec 2006, pp 1230-43). The salient points are that all elective surgery should be delayed for at least 6 months. After 6 months, following consultation with cardiologist and surgeon, the patient’s medication is modified according to the risk of bleeding. If the risk is low, both medications should be continued perioperatively. Alternatively, if the risk of bleeding is intermediate or high, then management may require discontinuation of one or both of the medications. Factors that can affect this decision and need to be taken into account include those that increase the likelihood of stent thrombosis such as poor LV ejection fraction, renal failure, diabetes and vessel characteristics such as the size of the stented vessel or stents placed at bifurcations. For the most part, ASA can be continued perioperatively, except for cases with the potential for significant morbidity from surgical bleeding. When discontinuation of Plavix is deemed necessary, it should be stopped at least 5 days preoperatively. In some cases, admission to hospital may be required during withdrawal of the antiplatelet medications in order to monitor for ischemia and stent thrombosis. (43) In the event of life threatening emergency surgery, platelet transfusions may be required to treat excess clinical bleeding.

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