Comparison of fondaparinux, low molecular-weight heparin and unfractionated heparin in preventing thrombus formation on mechanical heart valves: Results of an in-vitro study

Background and aim of the study: The study aim was to investigate the efficacy of three different anticoagulants in preventing thrombus formation on mechanical heart valves, using an in-vitro system. Methods: Blood samples (470 ml) were taken from young and healthy male volunteers and anticoagulated with unfractionated heparin (UFH; n = 18), low molecular-weight heparin (LMWH; n = 18) or fondaparinux (n = 16). Bileaflet mechanical heart valves were placed in a new device - the 'Thrombosis Tester' - and exposed in a continuous circulation at a rate of 80 beats per min to the anticoagulated blood samples for a total exposure time of 60 min. Results for thrombus weight were skewed distributed and presented as log-transformed values. Results: The weight of each valve was measured before and after 1 h of perfusion; subsequent mean (SD) thrombus weights were 0.739 +/- 0.573 g for UFH, 0.789 +/- 0.099 g for LMWH, and 0.934 +/- 0.145 g for fondaparinux (p = 0.397 for comparison of all groups by ANOVA). Electron microscopy showed concordant results with regard to thrombus formation on heart valve surfaces. Conclusion: Fondaparinux and LMWH were as effective as UFH in preventing thrombus formation on mechanical heart valves in vitro. The 'Thrombosis Tester' proved to be a new, unique instrument for investigating the ability of anticoagulants to prevent valve thrombosis on mechanical heart valves under in-vitro conditions.