Abstract 19105: Basis for Biochemical Discordance Between Activated Partial Thromboplastin Time and Anti-factor Xa in Patients with Continuous Flow Left Ventricular Assist Device on Unfractionated Heparin Infusion

Introduction: Unfractionated Heparin (UFH) has been the mainstay of therapy for bridging and treatment of suspected device thrombosis/hemolysis in Continuous Flow Left Ventricular Assist Device (CF-LVAD), however the optimal monitoring test has not been prospectively evaluated. We previously reported that that Activated Partial Thromboplastin Time (aPTT) and anti-Xa levels measured simultaneously are frequently discordant in these patients. Hypothesis: Warfarin administration and hemolysis might be the biochemical basis for discordance between aPTT and anti-Xa in patients with CF-LVAD requiring UFH. Methods: A prospective observational study consisting of 38 patients with HeartMateII, consecutively admitted for UFH therapy with simultaneous measurements of aPTT and anti-factor Xa levels. Patients were stratified based on requirement of UFH for either sub-therapeutic INR or suspected device thrombosis. Patients were grouped according to whether the paired values fell within or outside the concordant therapeutic range, when discordant thromboelastography and factor analysis were performed. Results: Anti-Xa and aPTT were concordant 41.9% of the time in those getting treated for sub-therapeutic INR and only 18.8% in the group that getting treated for hemolysis/ device thrombosis. Data pairs with a supratherapeutic aPTT values were most likely to be associated with an INR ≥1.5, (p<0.001) (figure). On logistic regression analysis, high LDH was found to be a significant predictor of discordance (95% CI: 1.47-3.84). There was no consistent relationship between thromboelastography and factor analysis in the incidence of discordance. Conclusions: The relationship between aPTT and anti-factor Xa is not consistent in patients with CF-LVAD and the most common pattern was a supra-therapeutic aPTT relative to anti-factor Xa . Elevated LDH which is the sign for hemolysis and warfarin administration might contribute to an increased incidence of discordance.