Clinical Evaluation of the Heparin Therapeutic Window Using Activated Clotting Time in Neurological Interventional Radiology at an Academic Medical Center.

Abstract

Context.—: Activated clotting time (ACT) is useful for monitoring heparin therapy in neurointerventional radiology (NIR). We previously used the Hemochron Signature Elite instrument for measuring ACT in NIR.

Objective.—: To evaluate the suitability of measuring ACT using i-STAT in NIR by comparing its performance with Hemochron and a laboratory-based anti-Xa (anti-factor Xa) assay.

Design.—: All ACT measurements were performed in duplicate, using 2 Hemochron and 2 i-STAT devices in 53 samples from 15 unique multidose heparin administrations in NIR procedures and 110 samples in cardiovascular procedures. Samples were tested simultaneously within 1 minute of each other.

Results.—: For 12 of the 15 procedures in NIR, anti-Xa was assessed at the beginning of the procedure and at the end of all procedural dosing. We also reviewed the patient's charts anonymously for any indication of postprocedural neurological bleeding. Interinstrument variability was much higher with Hemochron than with i-STAT. We also observed lower ACT values with i-STAT than with Hemochron. Therefore, the historical ACT range of 250 to 300 seconds for Hemochron was revised to 200 to 250 seconds for i-STAT devices. In the therapeutic window for anti-Xa, ACT results from both instruments exhibited a linear correlation. However, at supratherapeutic range for anti-Xa, ACT results from Hemochron exhibited more linear correlation, while i-STAT ACT demonstrated a plateau effect. No patient had any evidence of severe postprocedural neurological bleeding.

Conclusions.—: The i-STAT analyzers produce more reproducible ACT results, but the target range should be lowered to 200 to 250 seconds. This range appears to provide adequate and safe heparin therapy, confirmed by anti-Xa assay results and clinical outcome.