Evaluation of the anticoagulant effect of vitamin K antagonists in patients with non-valvular atrial fibrilation

Background/Aim. Despite the introduction of new oral anticoagulants (dabigatran, rivoroxaban, apixaban), vitamin K antagonists (VKA), such as warfarin and acenocoumarol are still the most widely used oral anticoagulants for the treatment of non-valvular atrial fibrillation (NVAF). Time in therapeutic range (TTR) represents a measure of the quality of the anticoagulant effect of these drugs, and it is considered that the lower value of TTR is associated with the adverse effects of therapy. The study aim was to evaluate of the effectiveness of VKA therapy in patients with NVAF and to identify factors affecting the anticoagulation efficacy. Methods. A retrospective study was conducted on a population of 725 outpatients with NVAF, treated with VKA and followed in Blood Transfusion Institute of Nis from January to December 2017. Laboratory control of the INR was done from capillary blood of patients on Thrombotrack Solo (Axis Shield, Norway) and Thrombostat (Behnk Elektronik, Germany). Targeted therapeutic INR was between 2.0 and 3.0. For each patient we evaluated all available INR values to calculate the individual TTR according to the Rosendaal method. Results. The study included a total of 725 patients with NVAF which had 6105 INR measurements, what is 8.13±2.47 INR measurements per patient. The mean value of TTR and was 60.15±17.52%, but 49.72% of patients had a TTR less than 60%. Patients were at high risk of thrombosis in 6.15% of time (INR 4.5). The most significant independent factors affecting the quality of VKA therapy are gender, arterial hypertension, diabetes mellitus and the use of amiodarone and antiplatelet drugs (aspirin, clopidogrel). Conclusion. The TTR is undoubtedly useful indicator of the effectiveness of VKA treatment. The most important predictors of poorer efficacy of VKA therapy are arterial hypertension, diabetes mellitus, patints' gender and the use of amiodarone and antiplatelet (aspirin, clopidogrel) drugs. To improve the quality of VKA therapy, education of patient and better collaboration with them, as well as a successful teamwork with clinicians are also imperative. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 175061, Grant no. 43012 and Grant no. 41004]