Low molecular weight heparin after mechanical heart valve replacement

Background-Patients with mechanical heart valves require life-long anticoag ulation. We report here the first large and comparative series of consecuti ve patients anticoagulated with low molecular weight heparin (LMWH) after m echanical heart valve replacement. Methods and Results-In this comparative, nonrandomized study, 208 consecuti ve patients who underwent a single or double heart valve replacement with m echanical prostheses were anticoagulated subcutaneously with unfractionated heparin (UH) in the first period (n=106) and LMWH in the second phase (n=1 02) of the study. Baseline characteristics were similar in the 2 groups. Th e mean durations of UH and, LMWH treatments were 13.6 +/- 0.5 and 14.1 +/- 0.6 days, respectively (not significant). On the second day of treatment, 8 7% of patients treated with LMWH had an anti-Xa activity:within the range o f efficacy (0.5 to 1 IU/mL), but only 9% of UH-treated patients had an acti vated partial-thromboplastin time value within the therapeutic range (1.5 t o 25 times control, P<0.0001 between the 2 groups). On the last day of pres cription, all LMWH-treated patients had anti-Xa activity above 0.5 IU/mL, b ut 19% were above 1 IU/mL. In the UH group, 27% of patients had an activate d partial-thromboplastin time above 1.5 times control, but 62% were overant icoagulated. Two major bleedings occurred in each group, and one stroke occ urred in the UH group. Conclusions-In this first comparative study, anticoagulation with LMWHs aft er mechanical heart valve replacement appears feasible, provides adequate b iological anticoagulation,: and compares favorably with UH anticoagulation. Randomized studies are now needed to further evaluate this new therapeutic approach.