Introduction In atrial fibrillation (AF) dose-adjusted warfarin reduces the risk of stroke by almost 2/3, but patients with better therapeutic international normalised ratio (INR) derive most benefit. The new NICE guidance from August 2014 for non-valvular AF recommended consideration of novel oral anticoagulants (NOAC) if time in therapeutic range (TTR) with warfarin <65%.

We investigated the success of anticoagulation in our patients with AF with reference to the NICE guidance, and compared it with the published literature, and our cohort of patients with mechanical valves.

Materials and Methods Through the anticoagulation clinic we identified all patients on warfarin for the entire duration of 2012 who had taken warfarin for >6 months before 01/01/2012. We identified 2737 patients on warfarin for AF and 58 patients for prosthetic heart valve (PHV) in the aortic or mitral position. We excluded patients with elective/emergency hospital admissions not relating to anticoagulation and analysed TTR for 51 patients with PHV and a randomly selected a sample of 102 patients with AF. The target INR was 2.5 for AF and 3.5 for all PHV. Using the Rosendaal method we calculated the TTR in the two groups for all 365 days in 2012.

Results The results are shown in Table 1. Patients with AF had a better mean TTR (76%) than patients with PHV (61%) which could be explained by the difference in INR targets in the two groups. The patients with AF had an average of 11.9 INR tests per year while the patients with PHV had an average of 26.2 INR tests per year.

Discusion Our AF patients had the same therapeutic target as the published NOAC trials i.e. INR target 2.5; yet our cohort showed significantly higher TTR (76%) than the NOAC studies (55–65%) and was comparable to the Swedish registry as shown in Table 2. Patients with PHV showed an inferior TTR (61.4%) and required more INR tests (26.2 vs 11.9), however a different anticoagulation target meant that the two groups could not be directly compared.

Conclusion We conclude that in our AF population a target INR=2 is safely achieved with very good mean TTR (76%) and relatively few INR tests (<1 per month). This compares very favourably with the TTR seen in the NOAC trials, suggesting that the degree of benefit seen with NOACs in the published trials might not be expected in our cohort of patients with AF, making thus the choice of NOACs potentially less cost effective for routine use in our region.

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