Background: Patients with mechanical heart valves (MHV) have an increased risk of thromboembolic complications. Low molecular weight heparin (LMWH) and unfractionated heparin (UFH) are often recommended for bridging anticoagulation; however, it is not clear which strategy is more beneficial.
Methods: The PubMed, EMBASE, and Cochrane databases were searched from January 1960 to March 2019. Randomized controlled trials and observational studies were analyzed. The Newcastle-Ottawa Scale (NOS) was used to evaluate the quality of the studies. Stata 11.0 was used for the meta-analysis.
Results: A total of 6 publications were included; 1366 events were selected, involving 852 events with LMWH and 514 events with UFH. The thromboembolism risk of the LMWH group was lower than that of the UFH group (risk ratio [RR] = 0.34, 95% confidence interval [CI] 0.12-0.95, P = .039). The incidence of major bleeding was lower in the LMWH group than in the UFH group, albeit without statistical significance (RR = 0.94, 95% CI 0.68-1.30, P = .728), as was mortality (RR = 0.52, 95% CI 0.16-1.66, P = .271). Subgroup analysis showed that LMWH cardiac surgery patients had a higher risk of major bleeding compared with UFH cardiac surgery patients (RR = 1.17, 95% CI 0.72-1.90, P = .526); but among non-cardiac surgery patients, the LMWH group had a lower risk of major bleeding than the UFH group (RR = 0.79, 95% CI 0.51-1.22, P = .284), although the difference was not statistically significant.
Conclusion: Our meta-analysis suggests that LMWH not only reduces the risk of thromboembolism in patients with MHV but also does not increase the risk of major bleeding. LMWH may provide safer and more effective bridging anticoagulation than UFH in patients with MHV. It is still necessary to conduct future randomized studies to verify this conclusion.