Subtherapeutic INR Levels in Patients With AVK: Incidence, Associated Factors, Prognosis and Control Strategies

Inclusion Criteria: * Patients aged ≥ 18 years. * Patients with a diagnosis of nonvalvular atrial fibrillation according to the criteria of the Spanish Agency of Medicines and Medical Devices (AEMPS) (2013) who are treated in cardiology practices. * Patients about to start treatment with a vitamin K antagonist or who are in the first two months of treatment. * Patients for whom access to at least 80% of INR tests performed during treatment with vitamin K antagonists is expected to be available. * Patients with the mental and physical capacity to complete the study questionnaires and give their informed consent to participate in the study. Exclusion Criteria: * Patients with mitral stenosis or another significant valve disease for which specific treatment is scheduled or has already been performed (prosthesis or valvuloplasty). * Patients hospitalised at the time of inclusion in the study. * Patients with a life expectancy of less than 13 months. * Patients who are participating in a clinical trial. * Patients receiving double antiplatelet therapy.