The protective efficacy of
warfarin for cardiogenic
cerebral embolism has been established. However,
warfarin is generally administered to only approximately 35% of the
atrial fibrillation patients who required
warfarin therapy. It has been reported that international normalized ratio (INR) control was carried out appropriately in < 50% of such patients. Therefore, from the viewpoint of prevention of the onset and recurrence of
embolism, the maintenance of a stable
anticoagulant level is necessary. In
warfarin therapy, in addition to INR control, time in therapeutic range (TTR) also markedly affects the efficacy of
warfarin therapy. Therefore, we classified patients into two groups on the basis of the cutoff TTR ≥ 65% at which the inhibitory effect of
warfarin on
stroke has been observed. We aimed to examine the association between INR and TTR with the correction of the therapeutic efficacy of
warfarin by analyzing the factors leading to poor TTR control. The most valuable finding of this study is that marked fluctuations of
brain natriuretic peptide levels in patients with complication of
heart failure was a risk factor for poor TTR control. Identification of the factors leading to the poor TTR control is useful for making the decision to switch to other
anticoagulants, such as
dabigatran or
apixaban, or to continue
warfarin by correcting risk factors in
atrial fibrillation patients receiving long-term
warfarin therapy.