Antiplatelet and anticoagulation for patients with prosthetic heart valves

BACKGROUND: Patients with prosthetic heart valves are at increased risk for valve thrombosis and arterial thromboembolism. Oral anticoagulation alone, or the addition of antiplatelet drugs, has been used to minimize this risk. An important issue is the effectiveness and safety of the latter strategy.

OBJECTIVES: To compare the effectiveness and safety of adding antiplatelet therapy to standard oral anticoagulation among patients with prosthetic heart valves.

SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (Cochrane Library Issue 2, 2003), MEDLINE (January 1966 to August 2002), EMBASE (January 1988 to July 2001) and reference lists of individual reports, review articles, meta-analyses, and consensus statements.

SELECTION CRITERIA: All reports of randomised controlled trials comparing standard dose oral anticoagulation to standard dose oral anticoagulation and antiplatelet therapy in patients with one or more prosthetic heart valves. We included reports published in any language or in abstract form.

DATA COLLECTION AND ANALYSIS: Two reviewers independently performed the search strategy, assessed trials for inclusion criteria, study quality, and extracted data. Adverse effects information was collected from the trials.

MAIN RESULTS: Eleven studies involving 2,428 subjects met the inclusion criteria. Year of publication ranged from 1971 to 2000. Compared with anticoagulation alone, the addition of an antiplatelet agent reduced the risk of thromboembolic events (odds ratio 0.39 (95% confidence interval 0.28 to 0.56; p<0.00001)) and total mortality (odds ratio 0.55 (95% confidence interval 0.40 to 0.77; p=0.0003)). Aspirin and dipyridamole reduced these events similarly. The risk of major bleeding was increased when antiplatelet agents were added to oral anticoagulants (odds ratio 1.66 (95% confidence interval 1.18 to 2.34; p=0.003)). For major bleeding, there was no evidence of heterogeneity between aspirin and dipyridamole and in the comparison of trials performed before and after 1990, around the time when anticoagulation standardization with the international normalized ratio was being implemented.

REVIEWER'S CONCLUSIONS: Adding antiplatelet therapy, either dipyridamole or low-dose aspirin, to oral anticoagulation decreases the risk of systemic embolism or death among patients with prosthetic heart valves. The risk of major bleeding is increased with antiplatelet therapy. These results apply to patients with mechanical prosthetic valves or those with biological valves and indicators of high risk such as atrial fibrillation or prior thromboembolic events. The effectiveness and safety of low dose aspirin (100 mg daily) appears to be similar to higher dose aspirin and dipyridamole.