Comparison between activated clotting time and anti-activated factor X activity for the monitoring of unfractionated heparin therapy in patients with aortic aneurysm undergoing an endovascular procedure

J Vasc Surg. 2018 Aug;68(2):400-407. doi: 10.1016/j.jvs.2017.11.079. Epub 2018 Mar 20.


Objective: Current guidelines recommend administration of unfractionated heparin (UFH) and measurement of activated clotting time (ACT) during endovascular procedures. The aim of this study was to compare ACT and anti-activated factor X (anti-Xa) measurements for monitoring of UFH therapy during an aortic endograft procedure and to assess the association of peak ACT and peak anti-Xa activity with periprocedural bleeding.

Methods: We retrospectively studied 104 patients with aortic aneurysm undergoing endovascular procedures with repeated coagulation measurements. After a UFH bolus, further UFH doses were given according to ACT (target range, ≥250 seconds) in clinical routine, and in parallel to each ACT (Hemochron; Accriva Diagnostics, Newport Beach, Calif) measurement, we determined anti-Xa activity (HemosIL Liquid anti-Xa; Instrumentation Laboratory, Bedford, Mass). UFH redosing was solely based on the ACT measurements. We defined periprocedural bleeding as a drop in hemoglobin level ≥3 g/dL or red blood cell transfusion within 24 hours.

Results: After the initial UFH bolus (median, 67 IU/kg body weight), ACT and anti-Xa measurements showed a weak correlation (rs, 0.46; P < .001). Median ACT was 233 seconds (range, 127-374 seconds; interquartile range [IQR], 204-257 seconds); median anti-Xa activity was 1.0 IU/mL (range, 0.5-2.0 IU/mL; IQR, 0.9-1.2 IU/mL). Only 31% of the patients had an ACT value ≥250 seconds, whereas all patients had an anti-Xa activity ≥0.5 IU/mL. Accordingly, ACT triggered redosing of UFH frequently. Consequently, we saw a median total UFH use of 90 IU/kg during the procedure, a median peak ACT of 255 seconds (IQR, 234-273 seconds), and a median peak anti-Xa activity of 1.2 IU/mL (IQR, 1.0-1.4 IU/mL). Periprocedural bleeding occurred in 40 (38%) patients. Peak ACT ≥250 seconds was not associated with bleeding (odds ratio, 1.05; 95% confidence interval, 0.41-2.70; P = .952), whereas peak anti-Xa activity ≥1.2 IU/mL was independently associated with bleeding (odds ratio, 4.95; 95% confidence interval, 1.82-13.48; P = .002). Moreover, no periprocedural thromboembolic event occurred.

Conclusions: In this retrospective study of patients with aortic aneurysm undergoing an endovascular procedure, ACT and anti-Xa measurements showed poor correlation; only increased peak anti-Xa activity was independently associated with periprocedural bleeding, not increased ACT. Our findings also suggest that monitoring of UFH therapy with anti-Xa during aortic endograft procedures may reduce total UFH use. We further speculate that this approach could reduce periprocedural bleeding.

Publication types

  • Comparative Study

MeSH terms

  • Aged
  • Anticoagulants / administration & dosage*
  • Anticoagulants / adverse effects
  • Aortic Aneurysm / blood
  • Aortic Aneurysm / diagnostic imaging
  • Aortic Aneurysm / surgery*
  • Blood Coagulation / drug effects*
  • Blood Loss, Surgical / prevention & control
  • Blood Vessel Prosthesis Implantation* / adverse effects
  • Chi-Square Distribution
  • Drug Monitoring / methods*
  • Endovascular Procedures* / adverse effects
  • Erythrocyte Transfusion
  • Factor Xa / metabolism*
  • Factor Xa Inhibitors / blood*
  • Female
  • Heparin / administration & dosage*
  • Heparin / adverse effects
  • Humans
  • Logistic Models
  • Male
  • Monitoring, Intraoperative / methods*
  • Multivariate Analysis
  • Odds Ratio
  • Postoperative Hemorrhage / chemically induced
  • Postoperative Hemorrhage / therapy
  • Predictive Value of Tests
  • Reproducibility of Results
  • Retrospective Studies
  • Risk Factors
  • Time Factors
  • Treatment Outcome
  • Whole Blood Coagulation Time*


  • Anticoagulants
  • Factor Xa Inhibitors
  • Heparin
  • Factor Xa