Vitamin K Antagonist Treatment in Patients With Atrial Fibrillation and Time in Therapeutic Range in Four European Countries

Purpose

Patients with atrial fibrillation are at increased risk for stroke and thus require anticoagulant prophylaxis with vitamin K antagonists. However, many such patients fail to achieve target coagulation status. The objective of this study was to evaluate time in the therapeutic range and its relationship to clinical outcomes in patients with nonvalvular atrial fibrillation prescribed a vitamin K antagonist in everyday clinical practice in 4 European countries (France, Germany, Italy and the United Kingdom).

Methods

Data were extracted from the European electronic primary care database, the Longitudinal Patient Database. Included in the analysis were 6250 adult patients for whom data on monitoring of coagulation time and international normalized ratio were available. The time within the therapeutic range was estimated by using the Rosendaal method. Patients spending >70% of time within the therapeutic range were considered to have well-controlled treatment. Data on stroke and bleeding events occurring during the study period were taken from patient records. Stroke risk was calculated by using the CHA₂DS₂-VASc score (i.e. 2 points for a history of stroke or TIA and age >75years, and 1 point for age between 65 and 74 years, hypertension, diabetes mellitus, a recent cardiac failure, vascular disease and female sex).

Findings

The proportion of patients with poorly controlled treatment varied from 34.6% in the United Kingdom to 55.8% in Germany. The incidence of stroke was 0.5/100 person-years in well-controlled patients, compared with 1.0/100 in poorly controlled patients. After adjustment for stroke risk factors, the odds ratio was 1.38 (95% CI, 0.93–2.06; P = 0.110). The incidence of hemorrhage was 1.1 and 1.3 events/100 person-years, respectively (odds ratio, 0.91 [95% CI, 0.72–1.16]).

Implications

Many patients receiving prophylaxis with vitamin K antagonists in everyday community care have poorly controlled anticoagulation treatment with vitamin K antagonists. Their international normalized ratio is frequently outside the therapeutic range, and they are thus exposed to an unnecessary risk of stroke or bleeding complications.