Anticoagulation Monitoring Shouldn’t We Validate? Mark T. Lucas, MPS, CCP, PBMT Chief of Perfusion Denver Cardiovascular Perfusionists Educational meetings should educate. They should also make you question what you do and ask if you are doing enough, the right thing or if you can do better.

“It’s not until you know better that you can do better.” To solve a problem, you need to understand all of the variables. Peter V Schiro 1926- 1997

“first law of hemostasis and thrombosis.” “The more thrombin the less bleeding but the more thrombosis” “The less thrombin the less thrombosis but the more bleeding” H. Coenraad Hemker, Raed Al Dieri and Suzette Béguin, Thrombin generation assays: accruing clinical relevance Curr Opin Hematol 11:170–175.

Current and Future Medical Practice Trend towards evidenced based coagulation and anticoagulation management POCT has typically been performed with less than the stringent regard for accuracy and precision than in the laboratory Goal directed anticoagulation is the future

Goal Directed Anticoagulation Focused purpose to inhibit thrombin potential Maximizing anticoagulation at specific time points for different patient categories Defined anticoagulant management program individualized for each patient receiving anticoagulant Use of multiple specific anticoagulants Unfractionated heparin Direct thrombin inhibitors

Verification and Validation ..are independent procedures that are used together for checking that a product, service, or system meets requirements and specifications and that it fulfills its intended purpose. Brian Bull ACT 480 seconds 1975 (visible clot) John Young ACT >400 seconds 1978 (fibrin monomer)

Anticoagulation Effectiveness Goal of anticoagulation is to suppress thrombin. How effective is your anticoagulation protocol at suppressing thrombin? 100%, 90%, 80%, 70%...How do you know? Have you validated your anticoagulation protocol in your system?

DCP Anticoagulation Protocol Arterial blood sample for baseline ACT and HMS Heparin Dose Response (500 s) Administer unfractionated heparin via central venous catheter per HDR dose Arterial blood sample for ACT after 3–5 min Ensure ACT 3–4 times above baseline ACT (>400 s) before initiating CPB 10,000 IU unfractionated heparin in CPB prime solution Start continuous heparin infusion with initiation of bypass at 100 IU/kg/hr First on-bypass sample within ten minutes of initiation, then monitor ACT/HPT 30 min during CPB <35 degrees and 20 min >35 degrees Maintain HPT +/- one channel from target and ACT >400 s Reverse heparin with protamine per HPT value after separation from CPB. Dose ratio .8 mg protamine per 1000 IU of heparin Arterial blood sample for ACT/HPT 3–5 min post protamine

Variability in Dosing 74% empiric dosing 20% heparin dose response 5% fixed number 1% other

Variability in Maintenance ACT value ACT/Protamine Assay Set time intervals Continuous infusion

Variability in Testing Method 59% of monitoring by ACT alone 33% ACT and Protamine titration 2% Viscoelastic 6% Other

Variability in Testing Frequency Testing every 10 minutes to greater than 60 minutes between tests. Or no testing at all.

Variability of Minimum ACT 5% Other

Goals of Anticoagulation Target ACT Preserve Coagulation factors Inhibit visible clot 100% Thrombin inhibition Target protamine titration

Chromogenic Anti-Xa Test The factor Xa assay is really a drug level using chromogenic Xa inhibition as the methodology; as the reference range and standard curve vary with the drug tested. Chromophore-linked substrate of factor Xa. Upon cleavage of the substrate by the active enzyme (factor Xa), a colored compound is released

How Xa Assay Works Known amounts of factor Xa and antithrombin added to the sample Heparin forms an inhibitory complex with antithrombin and inactivates factor Xa Excess amount of factor Xa remaining in the sample is inversely proportional to the amount of heparin Results are then compared to a standard curve and are provided in concentration of anti–factor Xa (units/mL).

Thrombin Generation Testing 20 patients – 5 CABG, 5 Valve, 5 DM, 5 HR Samples for analysis concordantly with Heparin protocol: Pre-bypass (baseline) Post heparin bolus (non-stimulated) 10” post bypass (stimulated) 10” post x-cl removal (stimulated) Post protamine dose (stimulated)

Validation Testing Goal Determine amount of thrombin produced for time points during procedure known for minimal and maximal thrombin stimulus Pre-surgery Post heparin bolus Post initiation bypass Post cross clamp removal Post heparin reversal with protamine

Thrombin Generation Assay (Currently for research use only) Calibrated Automated Thrombogram (CAT) Whole blood samples Flurigenic substrate Tissue factor stimulus Measures initiation of thrombin, fibrin formation, phase down and inactivation All forms of anti-coagulant therapies such as heparin therapy, direct thrombin inhibitors or oral anti-coagulants can be monitored TECHNOTHROMBIN® TGA is based on monitoring the fluorescence generated by thrombin cleavage of a fluorigenic substrate over time upon activation of the coagulation cascade by different concentrations of tissue factor (RA, RB, RC Low, RC High and RD*) and negatively charged phospholipids in plasma. From the changes in fluorescence over time, the concentration of thrombin (nM) in the sample can be calculated using the respective thrombin calibration curve (only one calibration has to be done for each lot). The rate of increase in thrombin concentration over time then allows to calculate generation of thrombin in the sample per minute and to plot this value over time for the whole coagulation process. This then results in the visualization of the different phases of clot formation.

Balance Balance between anticoagulation for cardiopulmonary bypass (CPB) and hemostasis after CPB. Too much heparin – bleeding Too little heparin – clot/bleeding

Summary Thrombin inhibition is the primary goal Considerable variability in anticoagulation practice and performance Technology affords us new opportunities Validation of anticoagulation effectivenesss is necessary for consistency and improved outcomes in CV surgery globally