Is treatment of atrial fibrillation in primary care based on thromboembolic risk assessment?

Antithrombotic treatment in atrial fibrillation should be guided by the risk of thromboembolic events. Although practice studies have shown underutilization of antithrombotics, it is not clear whether physicians make use of thromboembolic risk stratification in their treatment decisions, as recommended in current guidelines.

The aim of the present study was to assess which clinical determinants influence coumarin and aspirin prescription in patients with atrial fibrillation in primary care.

In a cross-sectional study of 15 computerized general practices covering 38 000 patients in The Netherlands, we identified patients with atrial fibrillation using several search algorithms. Determinants of antithrombotic therapy were assessed using polytomous logistic regression analysis.

A total of 247 patients with atrial fibrillation were identified among 10 335 patients aged 55 years or over (prevalence 2.4%). Mean age was 77 years (range 55-95); 51% were male. Overall, 52% of the patients used coumarin and 27% used aspirin. About 50% of patients were also treated by a cardiologist. Referred patients were prescribed coumarin more often (63% versus 35%, P < 0.001). Prior stroke/transient ischaemic attack or systemic embolism [adjusted odds ratio (OR) 5.3, 95% confidence interval (CI) 1.1-24.8], and chronic heart failure (adjusted OR 2.1, 95% CI 0.8-5.1) were independent determinants for coumarin prescription. These associations were less strong for aspirin prescription. However, other established risk factors for future thromboembolic events, such as hypertension and diabetes mellitus, did not lead to higher prescription rates. In contrast, several factors not associated with thromboembolic events, such as chronic (versus paroxysmal) atrial fibrillation (adjusted OR 3.7, 95% CI 1.7-8.2) and longstanding (versus recent) diagnosis (adjusted OR 2.2, 95% CI 1.1-4.5), were also associated with higher coumarin prescription.

These results illustrate that physicians' decisions about initiating antithrombotic therapy in atrial fibrillation are not evidence based. They are guided partly by thromboembolic risk stratification, but also by factors insignificant for thromboembolic risk.