title: Anti-factor Xa and activated partial thromboplastin time measurements for heparin monitoring in mechanical circulatory support.
abstract: OBJECTIVE
  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 253 samples (74.4%), with a high degree of variability in aPTT for any given anti-FXa level (r(2) = 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.
authors.affiliation: Department of Medicine, Cardiology Division, University of Minnesota, Minneapolis, Minnesota. Electronic address: snadatya@umn.edu.
authors.forename: Sirtaz
authors.initials: S
authors.lastname: Adatya
authors.affiliation: Department of Medicine, Cardiology Division, University of Chicago, Chicago, Illinois.
authors.forename: Nir
authors.initials: N
authors.lastname: Uriel
authors.affiliation: Department of Medicine, Cardiology Division, University of Minnesota, Minneapolis, Minnesota.
authors.forename: Hirad
authors.initials: H
authors.lastname: Yarmohammadi
authors.affiliation: Department of Medicine, Cardiology Division, University of Minnesota, Minneapolis, Minnesota.
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Holley
authors.affiliation: Department of Medicine, Cardiology Division, University of Minnesota, Minneapolis, Minnesota.
authors.forename: Amy
authors.initials: A
authors.lastname: Feng
authors.affiliation: Department of Medicine, Cardiology Division, University of Minnesota, Minneapolis, Minnesota.
authors.forename: Samit S
authors.initials: SS
authors.lastname: Roy
authors.affiliation: Department of Medicine, Division of Hematology, Oncology and Transplantation, University of Minnesota, Minneapolis, Minnesota.
authors.forename: Mark T
authors.initials: MT
authors.lastname: Reding
authors.affiliation: Department of Medicine, Cardiology Division, University of Minnesota, Minneapolis, Minnesota.
authors.forename: Ranjit
authors.initials: R
authors.lastname: John
authors.affiliation: Department of Medicine, Cardiology Division, University of Minnesota, Minneapolis, Minnesota.
authors.forename: Peter
authors.initials: P
authors.lastname: Eckman
authors.affiliation: Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, Minnesota.
authors.forename: Nicole D
authors.initials: ND
authors.lastname: Zantek
mesh_terms: D000925:Anticoagulants / Q000008:administration & dosage*; D004334:Drug Administration Schedule; D065427:Factor Xa Inhibitors / Q000378:metabolism*; D005260:Female; D006471:Gastrointestinal Hemorrhage / Q000517:prevention & control; D006333:Heart Failure / Q000628:therapy*; D006353:Heart-Assist Devices / Q000009:adverse effects*; D006461:Hemolysis / Q000502:physiology; D006493:Heparin / Q000008:administration & dosage*; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D008875:Middle Aged; D010314:Partial Thromboplastin Time / Q000379:methods; D011446:Prospective Studies; D011475:Prosthesis Failure / Q000009:adverse effects; D013923:Thromboembolism / Q000517:prevention & control; D016896:Treatment Outcome; D014859:Warfarin / Q000009:adverse effects
chemical_list: D000925:Anticoagulants; D065427:Factor Xa Inhibitors; D014859:Warfarin; D006493:Heparin
keywords: activated partial thromboplastin time; anti-factor Xa; continuous-flow left ventricular assist device; intravenous unfractionated heparin; monitoring