Correlation of Point-of-Care ecarin clotting time versus activated clotting time with bivalirudin concentrations

Abstract

To rapidly and specifically monitor the anticoagulant effect of direct thrombin inhibitors, a thrombin inhibitor management (TIM) point-of-care test was developed (PharmaNetics, Inc., Morrisville, North Carolina), based upon the ecarin clotting time (ECT). This method utilizes the enzyme ecarin (from the venom of Echis carinatus) to convert prothrombin to meizothrombin. Meizothrombin catalyzes the conversion of fibrinogen to fibrin and is rapidly inhibited by direct thrombin inhibitors, such as bivalirudin. This assay has the particular advantage of being relatively specific for the effect of direct thrombin inhibitors, because heparins are poor inhibitors of meizothrombin. 1,2 The TIM-ECT test card may provide a more accurate measurement of direct thrombin inhibitor activity than current point-of-care assays. The purpose of this study was to compare the TIM-ECT test and 2 available activated clotting time (ACT) methods with a central laboratory anti-Factor IIa assay for monitoring bivalirudin-mediated anticoagulation. ••• Consecutive patients who underwent non-emergency percutaneous coronary intervention (PCI) with bivalirudin at The Cleveland Clinic Foundation were enrolled into the study. The protocol was approved by the institutional review board, and all patients gave written informed consent. Patients were not allowed to receive lepirudin, argatroban, abciximab, epti fibatide, or tirofiban 72 hours before PCI. All unfractionated heparin was discontinued 12 hours before PCI and all fractionated heparins 24 hours before PCI. All patients received preprocedural aspirin. Information regarding patient demographics, laboratory data, procedural details, and serial postprocedural creatine kinase (CK, CK-MB) was prospectively collected. Clinical outcomes were assessed to 30-day follow-up. Arterial blood samples were collected at baseline (sample 1), after bivalirudin bolus and infusion initiation (sample 2), after glycoprotein IIb/IIIa inhibitor bolus and infusion initiation (sample 3), during the procedure (sample 4), and before sheath removal (sample 5). Samples were procured from a nonheparinized arterial sheath and were placed into a noncitrated tube (3 ml) and a 3.2% sodium citrate tube (2.7 ml). Immediately at collection, the noncitrated whole blood samples were tested with the Hemochron ACT (International Technidyne, Edison, New Jersey), CoaguChek Pro/DM ACT (Roche Diagnostics, Indianapolis, Indiana), and the TIM-ECT. After this, the citrated whole blood was tested with the TIM-ECT. The remaining citrated blood was promptly centrifuged, and the plasma was aliquoted into cryovials and frozen at 70°C for the bivalirudin concentration assay. The ACT measures the time for whole blood to clot in the presence of an activating substance. 3,4 The Hemochron tube-based system uses a magnet in a rotating glass specimen tube that contains diatomaceous earth.5 As the blood clots, the magnet is displaced from the tube’ s bottom, thereby activating a proximity switch. Hemochron ACT values were truncated at a maximum of 999 seconds. The Pro/DM ACT is a cartridge-based system that uses tissue factor and sulfatides as activating substances. 6 The blood sample is drawn by capillary action into the reagent chamber, where it mixes with the chemical activators. The time from application of blood to cessation of flow within the chamber is detected by an optical system and converted to an ACT equivalent. Pro/DM clotting times were truncated at a maximum of 500 seconds.