Abstract Number: PB0297
Meeting: ISTH 2020 Congress
Background: Pulmonary endarterectomy (PEA) is curative for suitable chronic thromboembolic pulmonary hypertension (CTEPH) patients. Careful anticoagulation prevents postoperative bleeding and thromboembolic recurrence. Post-operative heparin monitoring is usually guided by aPTT which may be shortened by postoperative elevation in Factor VIII – an acute phase reactant. Anti-Xa-guided anticoagulation on the other hand is not affected by elevated Factor VIII.
Aims: We investigated the correlation between aPTT and Anti-Xa for monitoring unfractionated heparin after PEA and the impact of coagulation factors.
Methods: 55 paired perioperative aPTT and Anti-Xa samples from 14 PEA patients were analyzed. aPTT monitoring was used for postoperative unfractionated heparin titration. Samples were considered concordant if aPTT (target 45-65 sec) and Anti-Xa (target 0.3-0.5 IU/ml) were in the same category of subtherapeutic, therapeutic or supratherapeutic as defined by our local aPTT and Anti-Xa nomograms for monitoring heparin. Antithrombin activity, Factor VIII and fibrinogen were concomitantly measured. Single-cell RNA sequencing of PEA specimens (n=5) was used to screen for coagulation factor transcription.
Results: aPTT and Anti-Xa were concordant in 64% of the postoperative sample pairs. Most common discordant pattern was subtherapeutic aPTT with therapeutic (15.6%) or supratherapeutic (11.1%) Anti-Xa. Compared to pre-operative levels, plasma Factor VIII increased on day 1 (p=0.04) and day 3 (p=0.0003), and fibrinogen on day 3 after PEA (p=0.008). Discordant aPTT and Anti-Xa samples had higher antithrombin (p< 0.0001), Factor VIII (p=0.0001) and fibrinogen (p=0.0002) levels than concordant samples. Single-cell RNA sequencing showed endothelial Factor VIII transcription in the PEA specimen.
Conclusions: aPTT monitoring underestimates anticoagulation after PEA compared to Anti-Xa and is possibly influenced by elevated postoperative Factor VIII levels. Local Factor VIII production by thrombus endothelium may contribute to CTEPH pathogenesis.
To cite this abstract in AMA style:Nykanen A, Selby R, McRae K, Zhao Y, Donahoe L, Granton J, DePerrot M. Postoperative Heparin Monitoring by Anti-Xa Is More Accurate Than by aPTT After Pulmonary Endarterectomy – Role of Increased Systemic and Endothelial Production of Factor VIII [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/postoperative-heparin-monitoring-by-anti-xa-is-more-accurate-than-by-aptt-after-pulmonary-endarterectomy-role-of-increased-systemic-and-endothelial-production-of-factor-viii/. Accessed October 1, 2023.
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