Coagulation factor abnormalities related to discordance between anti-factor Xa and activated partial thromboplastin time in patients supported with continuous-flow left ventricular assist devices

Background High levels of discordance between activated partial thromboplastin time (aPTT) and anti-factor Xa (anti-FXa) have been reported in patients with continuous-flow left ventricular assist devices (CF-LVADs). We sought to determine the biochemical basis for discordance by simultaneous measurement of coagulation factors with aPTT and anti-FXa. Methods Consecutive CF-LVAD patients admitted for intravenous unfractionated heparin (IV-UFH) therapy were studied. IV-UFH was monitored based on an anti-FXa. APTT, INR, lactate dehydrogenase (LDH), and coagulation factors II, V, VII, VIII, IX, X, XI, and XII were measured simultaneously with anti-FXa. Results Discordance rate between anti-FXa and aPTT was 74.7% overall (568/760 samples from 62 patients). In samples in which coagulation factors were simultaneously measured the discordance rate was 66% (49/74 samples from 52 patients). In patients with INR≤1.0 the discordance level was 31.8% versus 82.7% with INR>1.8. No difference was observed in the rate of discordance between samples with low versus normal vitamin K-dependent factors (65.9% vs. 64.7%, p =0.99). Low factor XII was found in 15%; of these, 90.9% exhibited anti-FXa/aPTT discordance. Low factor V was found in 8.2%, and all were discordant. Factor VIII was elevated in 97% of samples; 65.7% were discordant. Conclusions In addition to the effects of warfarin administration on aPTT, the influence of other factors such as low factor XII or V may contribute to the discordance between aPTT values and anti-FXa. Coagulation factor levels may assist in individualization of anticoagulation targets while on IV-UFH in patients implanted with CF-LVADs.