In the study of Chan et al concerning the use of warfarin in outpatients with atrial fibrillation (AF), among the 9,113 outpatients with nonvalvular AF who were at moderate to high risk for stroke and would be optimally treated with warfarin, only 5,018 received warfarin (55.1%). Interestingly, there was substantial variation in treatment, ranging from 25% to 80%.

In a systematic review of 54 studies that reported stroke risk levels in subjects with AF and the percentage of patients treated, most showed underuse of oral anticoagulants for high-risk patients. Additionally, among 29 studies of patients with previous stroke or transient ischemic attack, who should receive oral anticoagulation, 25 studies reported undertreatment, with 21 of 29 studies reporting oral anticoagulation treatment levels <60%. In patients with CHADS ₂ scores ≥2, 7 of 9 studies reported treatment levels <70%.

In light of these data, warfarin is largely underused in patients with AF and unquestionable medical indications for anticoagulation. However, the problem of thromboembolic prophylaxis is not limited to the underuse of anticoagulants. In a study that included 3,287 patients with AF (mean age 71.9 ± 10.1 years, 52.3% men), although >2/3 of patients had CHADS ₂ scores ≥2, about 1/3 of them were not receiving anticoagulation. In contrast, nearly 52% of patients with CHADS ₂ scores of 1 were anticoagulated, and furthermore, almost half of patients with CHADS ₂ scores of 0 were taking anticoagulants.

Therefore, the problem is not only that anticoagulation is underused in high-risk patients but worrying overall incorrect therapeutic management. Nevertheless, this may change in the coming years with the use of the CHA ₂ DS ₂ -VASc score, recently proposed in European guidelines, which may clarify and expand the indications for anticoagulation in nonvalvular AF. With respect to anticoagulant medications, although warfarin has proved highly effective for decreasing thromboembolic episodes in patients with AF, its narrow therapeutic window and its well-known frequent interactions markedly limit its common use. It is likely that the introduction of newer oral anticoagulant drugs will facilitate the correct anticoagulation of those patients it in whom the therapy is indicated.

To date, the prevention of thromboembolic events in patients with AF is not correctly performed by physicians: anticoagulation is underused in some patients and overused in others. Therefore, it is necessary to implement more continuing medical education programs to improve the clinical management of these patients.