Abstract 18219: Monitoring of Anti-Xa in Pregnant Patients with Mechanical Prosthetic Valves Receiving Low Molecular Weight Heparin: Peak or Trough Levels?
Introduction: Low molecular weight heparin (LMWH) is often used for anticoagulation in pregnant women with mechanical prosthetic heart valves (PHV). Recent AHA/ACC guidelines recommend the measurement of plasma Anti-Xa levels in pregnant women with PHV, 4–6 hours after the morning LMWH injection (peak levels) and adjusting the dose to achieve levels between 0.7–1.2 u/ml. In spite of these recommendations cases of PHV thrombosis during pregnancy on LMWH therapy continue to occur.
Hypothesis: Recommended peak Anti-Xa levels with adjusted dose LMWH given every 12 hours are associated with sub-therapeutic trough levels of anticoagulation.
Methods and Results: We studied 26 pregnant patients receiving anticoagulation with adjusted dose subcutaneous enoxaparin given q12 hours who had measurements of both trough (predose) and peak (4–6 hours) Anti-Xa levels throughout pregnancy for a total of 177 paired determinations. Peak Anti-Xa levels between 0.7–1.2 u/ml were observed in 93 (53%) of the measurements, out of these 47 (51%) measurements were found to be subterapeutic (Anti-Xa level <0.6 u/ml). Subterapeutic trough levels were found in 7/9 (78%) measurements with peak Anti-Xa levels of 0.7–0.79 u/ml, 13/16 (81%) of 0.8–0.89 u/ml, 18/26 (69%) of 0.9–0.99 u/ml, 13/24 (54%) of 1.0–1.09 u/ml, 4/17 (24%) of 1.1–1.19 u/ml and 1/11 (9%) of 1.2 u/ml. There were 51 measurements of peak Anti-Xa > 1.2 u/ml with only 5 (10%) showing subterapeutic trough levels. Trough levels of anti-Xa > 0.6 u/ml were found in 73 measurements, with peak levels > 1.5 u/ml in only 7 (6%) and 6 of these had trough levels > 0.8 u/ml.
Conclusions: Anticoagulation with adjusted does LMWH aimed to achieve guidelines recommended peak levels of anti-Xa at 0.7–1.2 units/ml is commonly (> 50%) associated with subterapeutic trough levels which may result in reported thromboembolic
- © 2010 by American Heart Association, Inc.