title: Efficacy and safety of low molecular weight heparin in patients with mechanical heart valves: systematic review and meta-analysis.
abstract: BACKGROUND
  Low molecular weight heparins (LMWHs) are not approved for patients with mechanical heart valves (MHVs). However, in several guidelines, temporary LMWH off-label use in this clinical setting is considered to be a valid treatment option. Therefore, we reviewed the efficacy and safety of LMWHs in patients with MHVs.
  
  
  METHODS
  MEDLINE and CENTRAL databases were searched from inception to June 2013. Review articles and references were also searched. We included experimental and observational studies that compared LMWHs with unfractionated heparin (UFH) or vitamin K antagonists (VKAs). Data were analyzed and pooled to estimate odds ratios (ORs) with 95% confidence intervals (CIs) for thromboembolic and major bleeding events. Statistical heterogeneity was evaluated with the I(2) -test.
  
  
  RESULTS
  Nine studies were included: one randomized controlled trial (RCT) and eight observational studies, with a total of 1042 patients. No differences were found between LMWHs and UFH/VKAs in the risk of thromboembolic events (OR 0.67; 95% CI 0.27-1.68; I(2) = 9%) or major bleeding events (OR 0.66; 95% CI 0.36-1.19; I(2) = 0%).
  
  
  CONCLUSIONS
  The best evidence available might support the temporary use of LMWHs as a prophylactic treatment option in patients with MHVs. However, conclusions are mostly based on observational data (with large CIs), and an adequately powered RCT is urgently needed in this clinical setting.
authors.affiliation: Clinical Pharmacology Unit, Instituto de Medicina Molecular, Lisbon, Portugal; Laboratory of Clinical Pharmacology and Therapeutics, Faculty of Medicine, University of Lisbon, Lisbon, Portugal.
authors.forename: D
authors.initials: D
authors.lastname: Caldeira
authors.forename: C
authors.initials: C
authors.lastname: David
authors.forename: A T
authors.initials: AT
authors.lastname: Santos
authors.forename: J
authors.initials: J
authors.lastname: Costa
authors.forename: F J
authors.initials: FJ
authors.lastname: Pinto
authors.forename: J J
authors.initials: JJ
authors.lastname: Ferreira
mesh_terms: D000925:Anticoagulants / Q000009:adverse effects / Q000627:therapeutic use; D006349:Heart Valve Diseases / Q000150:complications / Q000628:therapy; D006350:Heart Valve Prosthesis; D006351:Heart Valves / Q000187:drug effects; D006470:Hemorrhage / Q000517:prevention & control; D006495:Heparin, Low-Molecular-Weight / Q000009:adverse effects / Q000627:therapeutic use*; D006801:Humans; D064887:Observational Studies as Topic; D016017:Odds Ratio; D016032:Randomized Controlled Trials as Topic; D015203:Reproducibility of Results; D013923:Thromboembolism / Q000150:complications / Q000188:drug therapy / Q000517:prevention & control; D014859:Warfarin / Q000009:adverse effects / Q000627:therapeutic use*
chemical_list: D000925:Anticoagulants; D006495:Heparin, Low-Molecular-Weight; D014859:Warfarin
keywords: coumarins; heart valve prosthesis; heparin; heparin, low-molecular-weight; warfarin