Use of oral anticoagulants in atrial fibrillation is highly variable and only weakly associated with estimated stroke risk: Cross-sectional population database study

Abstract

Background: Current international guidelines promote the use of stroke risk stratification tools to inform decision making about oral anticoagulant (OAC) use in atrial fibrillation (AF).

Objectives: To examine (a) differences between CHADS₂ and CHA₂DS₂VASc in classifying stroke risk in a primary care population of AF patients; (b) patterns of use of antithrombotics by stroke risk; and (c) patient and practice characteristics associated with use of oral anticoagulants in patients with AF.

Methods: Cross-sectional multilevel modelling study of all patients with AF and without rheumatic heart disease or valve replacement (n = 21 564) from 315 Scottish General Practices.

Results: (a) CHADS₂ characterized 30.3% in the intermediate and 53.8% in the high-risk category, compared to CHA₂DS₂VASC only 9.7% intermediate and 85.1% high-risk. (b) Of included patients, 17.8% were currently not prescribed any antithrombotic and 43.3% were on OAC. OAC use was only weakly related to stroke risk. (c) Patients with paroxysmal AF and those with dementia and previous peptic ulcer (adjusted ORs 0.26, 0.25 and 0.79) were less likely to be prescribed OAC. OAC use varied over five-fold between practices after adjustment for patient case mix, with remote and non-training practices and those with high levels of high-risk prescribing being more likely to prescribe OAC.

Conclusion: Evidence was found of both underuse and overuse of OAC in patients with AF. Promoting instruments for stroke risk assessment in AF is a plausible but untested strategy to improve decision making in AF, and its impact on OAC prescribing and patient outcomes should be evaluated in pragmatic trials.

Keywords::

• atrial fibrillation
• family practice
• quality of health care
• stroke risk
• antithrombotics

ACKNOWLEDGEMENTS

The authors would like to thank the practices who contributed data to the SPICE-PC programme and allowed the anonymised data to be used for research; the Primary Care Clinical Information Unit at University of Aberdeen who carried out the initial data extraction and management, particularly Katie Wilde and Fiona Chaloner; and project advisory group members Colin Simpson, Colin McCowan, Lorna Scahill and Mairi Scott.

FUNDING

This work was supported by NHS quality improvement Scotland (better measures project grant supporting KB) and Scottish government health directorates chief scientist office applied research programme grant 07/02 supporting TD. Study design, data analysis, interpretation and publication were the responsibility of the research team who had sole access to the data.

ETHICS

Analysis used fully anonymised data compliant with the PCCIU research governance process, and NHS research ethics service review was, therefore, not required.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.