Anti–Factor Xa and aPTT Measurements for Heparin Monitoring in Mechanical Circulatory Support | Journal Scan

Study Questions:

What are the relationships between anti-Factor Xa (anti-FXa) and activated partial thromboplastin time (aPTT) for monitoring intravenous unfractionated heparin (UFH) in patients with continuous-flow left ventricular assist devices (CF-LVADs)?


A prospective single-center cohort study of consecutive patients with CF-LVAD implantation was conducted between 2012 and 2014. Paired blood samples were compared for concordance between anti-FXA and aPTT levels based on subtherapeutic, therapeutic, and supratherapeutic ranges. Clinical heparin dosing was performed using anti-FXA levels in this population.


A total of 340 paired lab samples from 38 patients with CF-LVADs were evaluated. Anti-FXA and aPTT results were discordant in 253 samples (74.4%) with high aPTT variability at each anti-FXA level (R2 = 0.57). Discordant results were also seen in 104/163 (63.9%) samples from 24 patients undergoing heparin bridging therapy for a subtherapeutic international normalized ratio (INR) without device obstruction (R2 = 0.48), and 149/177 (84.2%) samples in patients with device obstruction and/or hemolysis (R2 = 0.49). Discordance was more prevalent in device obstruction/hemolysis samples as compared to bridging samples (p < 0.001). The most common discordant result pattern was a supratherapeutic aPTT value despite a therapeutic anti-FXA level (49.1% for bridging vs. 75.8% for device obstruction/hemolysis).


The authors concluded that aPTT levels were significantly discordant from anti-FXA levels in CF-LVAD patients. They noted that this discordance was particularly common among patients with device obstruction/hemolysis, where aPTT may be falsely elevated and lead to overestimation of heparin concentration and under-anticoagulation.


This single-center, prospective study of CF-LVAD patients demonstrates the divergent results seen between anti-FXa and aPTT results in patients treated with intravenous UFH. This study adds to the mounting literature highlighting the challenges of titrating UFH using aPTT levels. For many centers, anti-FXa is becoming the gold standard for intravenous UFH dose titration. Of interest, these authors demonstrated that the divergent anti-FXa and aPTT levels were more prominent in the setting of device obstruction or hemolysis. Use of anti-FXa levels requires system-wide efforts around education and staff training, but might be related to better clinical outcomes in patients treated with intravenous UFH.

Clinical Topics: Anticoagulation Management, Cardiac Surgery, Dyslipidemia, Heart Failure and Cardiomyopathies, Cardiac Surgery and Heart Failure, Lipid Metabolism, Novel Agents, Acute Heart Failure, Mechanical Circulatory Support

Keywords: Anticoagulants, Blood Coagulation, Factor Xa, Heart-Assist Devices, Hemolysis, Heparin, International Normalized Ratio, Partial Thromboplastin Time, Prospective Studies, Cohort Studies, Heart Failure

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