Chapter 49: Thromboembolic Disorders – Anticoagulant Therapy

The physiological basis of clot formation is explored through Virchow’s triad—venous stasis, vascular injury, and hypercoagulability—and the intricacies of the clotting cascade, emphasizing the roles of activated factors like IIa (thrombin) and Xa, and the natural regulatory mechanisms provided by antithrombin III and Proteins C/S. Diagnosis relies on risk stratification using tools like the Wells and CHA2DS2-VASc scores, alongside objective testing measures such as D-dimer and compression ultrasonography. The core of treatment involves antithrombotic agents, categorized into parenteral anticoagulants like unfractionated heparin (UFH) and low-molecular-weight heparins (LMWHs), the vitamin K antagonist (VKA) warfarin, and direct-acting oral anticoagulants (DOACs), including direct thrombin inhibitors (dabigatran) and Factor Xa inhibitors (rivaroxaban, apixaban, edoxaban). Key considerations for agent selection include the specific indication (VTE treatment versus stroke prevention in AF), renal function, bleeding risk assessment (HAS-BLED, VTE-BLEED scores), and potential drug-drug/drug-food interactions, particularly with warfarin. Finally, the chapter outlines the critical protocols for monitoring anticoagulation (INR for warfarin, aPTT for UFH) and managing major bleeding events, including the use of specific reversal agents such as 4F-PCCs for VKAs and idarucizumab or andexanet alpha for certain DOACs.