Dunn and Turpie1 provide a comprehensive review of studies that have evaluated various approaches to perioperative anticoagulation when warfarin sodium therapy needs to be interrupted to perform surgery. In their review, they consider the risks and benefits of using perioperative intravenous heparin or subcutaneous therapeutic-dose low-molecular-weight heparin (LMWH) as "bridging therapy," while patients are not orally anticoagulated. They conclude by recommending such bridging therapy for patients with mechanical mitral valves and for those with atrial fibrillation with a history of thromboembolic stroke. This recommendation assumes that, similar to warfarin therapy, intravenous heparin and therapeutic-dose LMWH reduce the risk of cardioembolism by about 75%. We made the same assumptions in a previous risk-benefit analysis of bridging therapy using intravenous heparin2; however, randomized trials have since disproved this assumption in patients with atrial fibrillation.3 Most notably, within 2 weeks of acute stroke, therapeutic-dose LMWH has been shown to be no more effective than aspirin at preventing recurrent ischemic stroke (odds ratio of 1.1 in favor of aspirin [95% confidence interval, 0.6-2.2]). The efficacy of unfractionated heparin and LMWH therapy is also uncertain in patients with mechanical heart valves; in pregnant patients, indirect comparisons suggest that both are less effective than warfarin therapy.4 Therefore, it should not be assumed that heparin or LMWH is as effective as warfarin therapy for preventing systemic embolism in patients with atrial fibrillation or a prosthetic heart valve.
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