(1178) Anti-Factor Xa Monitoring of Heparin for the Treatment of Pulmonary Embolism Managed by a PERT Team

Introduction: The mainstay of treatment for acute pulmonary embolism (PE) is anticoagulation, often with intravenous unfractionated heparin (UFH). The ability to achieve a therapeutic activated partial thromboplastin time (aPTT) in a timely fashion remains limited to biological factors leading to variability in UFH dosing. The anti-factor Xa (antiXA) assay is a more reliable marker of UFH activity and may be preferred in critically ill patients. The objective of this study is to determine the time to therapeutic antiXa for adult patients with an acute PE after activation of the PE response team (PERT) at a large academic medical center.

Methods: We conducted a retrospective cohort study of patients with a confirmed PE based on computed tomography (CT) with at least 2 antiXa levels when initiated on IV UFH. The primary endpoint was the time to a therapeutic antiXa of 0.3-0.7 units/mL. Secondary outcomes included descriptions of recurrent thromboembolism, major bleeding and PE-associated mortality within 3 months.

Results: A total of 330 patients with a PERT consult were identified, with 192 patients included in the study. The majority of the PEs were classified as sub-massive (64.6%) with 87% of patients receiving a bolus dose of UFH of 80 units/kg prior to a continuous infusion of 18 units/kg/hr. The median time to the first therapeutic antiXa was 9.13 hours with 93% of the cohort sustaining therapeutic anticoagulation at 48 hours. Recurrent thromboembolism, bleeding and mortality occurred in 1%, 5%, and 6.2%, respectively. Upon univariate analysis, an antiXa < 0.3 units/mL was associated with an increased risk of mortality [27.8% (5/18) vs 8% (14/174), p = 0.021].

Conclusions: We observed a low incidence of recurrent thromboembolism or PE-associated mortality utilizing an antiXa titrated UFH protocol. We believe antiXa is the preferred laboratory assay for measuring heparin’s effectiveness when treating PE. Larger studies are warranted to further confirm these findings.