Concordance between Anti-Factor Xa and Activated Partial Thromboplastin Time Measurements in Syncardia Total Artificial Heart Recipients Receiving Postoperative Anticoagulation with Unfractionated Heparin

Abstract

Activated Partial Thromboplastin Time has been the method of choice for anticoagulation monitoring in patients undergoing mechanical circulatory support with intravenous unfractionated heparin (IVUFH). However, aPTT assay is relatively susceptible to interference effects and is being progressively superseded by the anti-factor Xa (anti-FXa) method. The aim of this study was to identify the determinants of the concordance between aPPT and anti-FXa measurements in Syncardia Total Artificial Heart (TAH) recipients receiving post-operative anticoagulation with IVUH. A retrospective single centre analysis of 20 patients who underwent cardiectomy and TAH implantation from July 2014 to October 2018 entailed the comparison of simultaneous aPTT and anti-FXa measurements. Concordance was assessed analysing paired samples using a novel statistical approach based on the Bland-Altman method. In spite of a positive correlation between aPPT and anti-FXa measurements, normal target ranges were poorly aligned. At anti-Xa values of 0.2 and 0.4 U/mL predicted APTT values were = 51.1 and 64.3 seconds, respectively, slightly lower than expected for in range values of aPTT. APTT was affected by increase in the white cell count showing falsely decreased results when anti-FXa was within range. We describe a novel method to guide the transition from aPTT to anti-FXa for TAH recipients which generalizable to other forms of MCS. We conclude that low levels of anticoagulation were not associated with adverse sequalae because pro-haemorrhagic effects prevail over prothrombotic effects in TAH recipients. The influence of certain markers of infection and hepatic function on concordance provide falsely low aPTT values when anti-FXa is in range.