FUNCTIONAL PLATELET AND HEPARIN ACTIVITY ASSAYS APPLIED TO OVINES

Abstract

Objective: Bleeding and thrombosis are common complications with ventricular assist device (VAD) support. We adapted several assays to evaluate functional platelet and heparin activity in ovines for use during preclinical evaluation of VADs. Methods: Functional thrombosis was assessed by Thrombelastograph (TEG), Platelet Function Analyzer 100 (PFA-100), and platelet aggregometry measurements. An anti-FXa assay quantified plasma heparin activity. TEG and PFA-100 measurements were conducted according to manufacturer directions. ADP, thrombin, platelet activating factor (PAF), collagen, ristocetin, and arachidonic acid (AA) were used as agonists for platelet aggregometry. Ovine blood was collected 1:10 in sodium citrate, discarding the first 5 mL. Results: The TEG produced consistent, repeatable results and normal ovine values for TEG parameters were determined (R=3.2±0.8 min, K=1.5±0.8 min., α=70.3±6.7°, MA=67.3±6.1 mm; N=9). The PFA-100 often produced out of range results, particularly the collagen/epinephrine test. Three agonists proved useful for aggregometry testing: ADP, thrombin, and PAF, while ristocetin and AA produced no response and collagen generated inconsistent effects. The anti-FXa assay yielded repeatable results within a limited range, 0–0.8 U/mL. Sample dilution with pooled plasma was required to generate accurate results for higher plasma heparin activity levels. Conclusion: The application of these assays to ovine studies may provide better understanding and monitoring of thrombotic disturbances encountered during preclinical testing of cardiovascular devices.