Observational Study to Evaluate the Effectiveness of DOACS for Secondary Thrombosis Prevention in Low-risk Thrombotic APS Patients

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by the occurrence of arterial, venous, or small-vessel thrombosis in the presence of persistent antiphospholipid antibodies. Patients with thrombotic APS have a high risk of recurrent thrombosis and require long-term anticoagulation. Vitamin K antagonists (VKAs) have traditionally been the treatment of choice in this population. Direct oral anticoagulants (DOACs) have demonstrated efficacy and safety in other clinical settings, such as venous thromboembolism and non-valvular atrial fibrillation. However, their use in APS remains controversial following randomized clinical trials that showed an increased risk of arterial thrombotic events, particularly in patients with high-risk serological profiles. Current clinical guidelines suggest that DOACs may be considered in selected patients with low-risk thrombotic APS, defined by venous thrombosis and the absence of triple antiphospholipid antibody positivity. Nevertheless, evidence supporting their use in this specific subgroup is limited. This observational, analytical, ambispective (retrospective and prospective) study aims to evaluate the effectiveness and safety of DOACs compared with VKAs in patients with low-risk thrombotic APS under routine clinical practice conditions. Adult patients with a diagnosis of low-risk thrombotic APS who are receiving treatment with DOACs or VKAs at the time of inclusion will be eligible. Anticoagulant therapy will be prescribed at the discretion of the treating physician, with no intervention by the study protocol. The primary objective is to assess a combined effectiveness and safety endpoint, including thrombotic recurrence and major or clinically relevant bleeding. Secondary objectives include all-cause mortality, cardiovascular mortality, and treatment-related quality of life assessed using the Anti-Clot Treatment Scale (ACTS). The study will be conducted in Internal Medicine units across Spain and is expected to provide relevant real-world evidence to support clinical decision-making in the anticoagulant management of patients with low-risk thrombotic antiphospholipid syndrome.