Atrial fibrillation (AF) is an important risk factor for stroke, cardiovascular disease and all-cause mortality with high prevalence, and appropriate anticoagulant therapy is the core of preventing AF-related stroke. Warfarin is still the main anticoagulant at present, but the therapeutic window of warfarin is narrow, fixed dose of warfarin can easily lead to excessive coagulation or insufficient anticoagulation at the initial stage of treatment. There are few previous clinical studies on overanticoagulation of warfarin.

To analyze the epidemiological and clinical characteristics of overanticoagulation in patients with AF at the initial stage of warfarin anticoagulation therapy, and explore the influencing factors of overanticoagulation.

The study was a single-center retrospective cohort study. A total of 552 patients with AF treated with warfarin 2.5 mg/d admitted to Linyi City's Hospital from January 2017 to December 2022 were included as the study subjects. The clinical data of patients were collected, including age, gender, body mass, type of AF (non-valvular/valvular), comorbidities (hypertension, diabetes, hypoproteinemia, transaminase abnormalities, heart failure), combined medication (number of combined drugs, combined antibiotics, combined amiodarone), the laboratory test results before treatment were also collected, including serum albumin (Alb), serum creatinine (Scr), serum alanine aminotransferase (ALT) and serum aspartate aminotransferase (AST) levels, as well as international normalized ratio (INR) before treatment and INR after 7 days of treatment. Patients were divided into the overanticoagulation group (INR>3.0, n=122) and non-overanticoagulation group (INR≤3.0, n=430) according to whether INR>3.0 after 7 days of warfarin therapy. The data of patients between the two groups were compared, univariate and multivariate Logistic regression analysis was used to explore the influencing factors of overanticoagulation in the initial stage of warfarin anticoagulation therapy.

The age, proportion of female, valvular atrial fibrillation, hypoproteinemia, transaminase abnormalities, number of combined drugs, proportion of combined amiodarone and AST of patients in the overanticoagulation group were higher than those in the non-overanticoagulation group, and the body mass, hypertension, diabetes, Alb and ALT were lower than those in the non-overanticoagulation group (P<0.05). Multivariate Logistic regression analysis showed age≥65 years (OR=1.954, 95%CI=1.243-3.073, P=0.004), body mass≤63 kg (OR=2.967, 95%CI=1.841-4.783, P<0.001), number of combined drugs>5 (OR=1.976, 95%CI=1.175-3.323, P=0.010), and Scr≥91 μmol/L (OR=2.087, 95%CI=1.222-3.561, P=0.007) were independent risk factors for overanticoagulation at the initial stage of warfarin anticoagulation in patients with AF, while diabetes (OR=0.424, 95%CI=0.191-0.939, P=0.034) was a protective factor for overanticoagulation at the initial stage of warfarin anticoagulation therapy in patients with AF.

Age≥65 years, body mass≤63 kg, number of combined drugs>5, Scr≥91 μmol/L may be risk factors for overanticoagulation at the initial stage of warfarin anticoagulation therapy in patients with AF, while diabetes may be a protective factor at the initial stage of warfarin anticoagulation therapy in patients with AF. INR should be closely monitored in patients on warfarin anticoagulation with advanced age, low body mass, multiple drug combinations and elevated Scr level.