Anti-Xa Versus aPTT Monitoring of Continuous Heparin Infusions in CTEPH Patients Post-PTE

Introduction: Chronic thromboembolic pulmonary hypertension (CTEPH) is a pulmonary vascular disease caused by chronic obstruction of major pulmonary arteries that can be treated with a pulmonary thromboendarterectomy (PTE). Post-operatively, it is common for patients to receive intravenous (IV) unfractionated heparin (UFH) prior to bridging to long-term anticoagulant (AC) therapy with warfarin. Traditional activated partial thromboplastin time (aPTT) monitoring of IV UFH has its limitations. Anti-activated factor X (anti-Xa) activity is a pharmacokinetic test that directly evaluates Xa inhibition by anticoagulants and is not impacted by external factors.


Methods: This retrospective, pre- and post-intervention, observational study compared the incidence of major and minor bleeding events with anti-Xa versus aPTT monitoring in CTEPH patients on IV UFH post PTE. A total of 101 patients, 36 in the aPTT cohort and 65 in the anti-Xa cohort, who received IV UFH for a minimum of 24 hours, were included. Major bleed was defined as meeting one of the following criteria: withholding of AC >24 hours, transfusion of one or more units of blood, or greater than one administration of reversal agent protamine. Minor bleed criterion was defined as withholding AC >12 hours or administration of reversal agent protamine once. The secondary outcomes were the comparison of all-cause mortality and time in therapeutic aPTT and anti-Xa range while on IV UFH measured in hours between the two cohorts.


Results: 13.8% in the anti-Xa group and 18.4% in the aPTT group experienced major bleeding (P=0.28). 22.2% in the anti-Xa group and 18.4% in the aPTT group experienced minor bleeding (P=0.65). There was one death in the aPTT group and none in the anti-Xa group. Among time in range outcomes, the anti-Xa group had fewer levels drawn before the first in-range and remained in therapeutic range for 5.5 more hours than the aPTT group. The aPTT reached the first in-range level 2.63 hours earlier than the anti-Xa group.


Conclusions: In CTEPH patients post-PTE on IV UFH, there were no statistically significant differences in the incidence of major and minor bleeding, all-cause mortality, or time in therapeutic range between the anti-Xa and aPTT monitoring groups.