Anti-Factor Xa and Activated Partial Thromboplastin Time Measurements for Heparin Monitoring in Mechanical Circulatory Support

Sirtaz Adatya, Nir Uriel, Hirad Yarmohammadi, Christopher T. Holley, Amy Feng, Samit S. Roy, Mark T. Reding, Ranjit John, Peter Eckman, Nicole D. Zantek

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


Objectives: This study investigated the relationship between anti-factor Xa (anti-FXa) and activated partial thromboplastin time (aPTT) for monitoring intravenous unfractionated heparin (IV-UFH) in patients with continuous-flow left ventricular assist devices (CF-LVADs). Background: CF-LVADs have become mainstream therapy for patients with advanced heart failure. Thromboembolic events, device thrombosis, and bleeding continue to be a challenge with this technology. Adequate anticoagulation is required to prevent these adverse events. Methods: A prospective study of consecutive patients implanted with a CF-LVAD was conducted. Paired samples were considered concordant if aPTT values fell into expected ranges for subtherapeutic, therapeutic, and supratherapeutic anti-FXa levels. Heparin dosing was on the basis of anti-Xa levels. Results: A total of 340 paired values from 38 patients were evaluated. Anti-FXa and aPTT were discordant in 253samples (74.4%), with a high degree of variability in aPTT for any given anti-FXa level (r2= 0.57). Results were discordant in 104 samples (63.8%) from patients undergoing bridging therapy with warfarin and in 149 samples (84.2%) from patients with device obstruction and/or hemolysis (p< 0.001). The most common pattern of discordance was a supratherapeutic aPTT value despite a therapeutic anti-FXa level (49.1% for bridging vs. 75.8% for device obstruction and/or hemolysis; p< 0.001). Conclusions: Levels of aPTT were disproportionately prolonged relative to the corresponding anti-FXa levels in CF-LVAD patients, particularly those with device obstruction. Hemolysis and warfarin administration may falsely elevate aPTT, resulting in overestimation of heparin concentration and under-anticoagulation. Use of aPTT and anti-FXa to guide heparin therapy may lead to different estimates of heparin concentration in the same patient.

Original languageEnglish (US)
Pages (from-to)314-322
Number of pages9
JournalJACC: Heart Failure
Issue number4
StatePublished - Apr 1 2015

Bibliographical note

Publisher Copyright:
© 2015 American College of Cardiology Foundation.


  • APTT
  • Activated partial thromboplastin time
  • Anti-FXa
  • Anti-factor Xa
  • Continuous-flow left ventricular assist device
  • INR
  • IV-UFH
  • Intravenous unfractionated heparin
  • LDH
  • Monitoring


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