The importance of time in therapeutic range in switching from vitamin K antagonist to non-vitamin K antagonist oral anticoagulants in atrial fibrillation

Aims: Patients with non-valvular atrial fibrillation (NVAF) receiving vitamin K antagonists (VKAs) with time in therapeutic international normalized ratio (INR) range (TTR) <70%, despite good adherence, are by guidelines recommended to switch to non-VKA oral anticoagulants (NOACs). The aim was to assess if patients are switched from VKA to NOAC when TTR is <70% in a real-world setting.

Methods and results: Non-valvular atrial fibrillation patients receiving VKA (1 January 2010 to 31 December 2012) were identified in nationwide registries. Time in therapeutic range was calculated by the Rosendaal method by a minimum of three INR values. Time in therapeutic range of patients continuing VKA (non-switchers) were compared with patients switched from VKA to dabigatran or rivaroxaban (switchers), the only NOACs available at that time. Factors associated with switching were analysed in a multivariable logistic regression model. 7276 patients with NVAF receiving VKA were included; of these, 6437 (88.5%) patients continued VKA [57.9% male, median age 76.7 years (Q1-Q3 68.9-83.5)] and 839 (11.5%) switched to NOAC [54.0% male, median age 76.5 years (Q1-Q3 68.4-83.6)]. No significant differences in CHA2DS2-VASc and HAS-BLED scores were seen between the groups. The mean TTR for non-switchers was 64.0 [standard deviation (SD) 27.8] and 52.9 (SD 28.1) for switchers. Among non-switchers, 51% had a TTR <70% vs. 69% among switchers. 85% of patients with TTR <70%, were not switched contrary to recommendations. Time in therapeutic range <70% was associated with the switch [odds ratio 2.28, 95% confidence interval (1.92-2.72)].

Conclusion: A TTR below 70% was associated with switching from VKA to NOAC, yet by guidelines, most patients were still not switched.