BACKGROUND: Atrial fibrillation (AF) patients on a vitamin K antagonist (VKA) with time in therapeutic range (TTR) ≥70% are not recommended to switch to a direct oral anticoagulant according to guidelines.

OBJECTIVES: This study sought to assess future TTR and risk of stroke/thromboembolism and major bleeding among AF patients on VKA with TTR ≥70%.

METHODS: The authors used Danish nationwide registries to identify AF patients on VKA from 1997 to 2011 with available international normalized ratio values. Patients were included 6 months after VKA initiation, divided according to TTR, and followed for 12 months after inclusion. Cox proportional hazard models estimated hazard ratios (HRs). TTR was examined both as a baseline variable and as a time-dependent covariate in the Cox models.

RESULTS: Of the 4,772 included AF patients still on VKA 6 months after initiation, 1,691 (35.4%) had a TTR ≥70%, and 3,081 (65.6%) had a TTR <70%. Among patients with prior TTR ≥70% still on treatment 12 months after inclusion, only 513 (55.7%) still had a TTR ≥70%. Compared with prior TTR ≥70%, prior TTR <70% was not associated with a higher risk of stroke/thromboembolism (HR: 1.14; 95% confidence interval [CI]: 0.77 to 1.70) or major bleeding (HR: 1.12; 95% CI: 0.84 to 1.49). When the authors estimated TTR time-dependently during follow-up, TTR <70% was associated with an increased risk of stroke/thromboembolism (HR: 1.91; 95% CI: 1.30 to 2.82) and major bleeding (HR: 1.34; 95% CI: 1.02 to 1.76).

CONCLUSIONS: Among AF patients on VKA, almost one-half of patients with prior TTR ≥70% had TTR <70% during the following year. Prior TTR ≥70% per se had limited long-term prognostic value.