73 TRENDS IN PREVALENCE AND ANTITHROMBOTIC PRESCRIPTIONS IN AF In the international GARFIELD-AF registry (study period 2009–2016), 38.0% of new-onset AF patients with an indication for OAC therapy did not receive any anticoagulation.21 Since the percentages of undertreatment cannot be fully explained by patients with a contraindication for anticoagulants (around 2.2%),22 all three studies (GLORIA-AF registry,20 GARFIELD-AF registry,21 and our study) clearly emphasise that antithrombotic treatment in AF patients still leaves room for improvement and undertreatment remains a point of attention for both patients and physicians.23,24 Identifying subgroups at risk of stroke due to inappropriate treatment should be the focus of new research. However, as a first step, we performed additional descriptive analyses, stratified by CHA2DS2-VASc score, to explore the characteristics of all AF patients who were prescribed a platelet inhibitor or no antithrombotic therapy at all in 2017 (see Supplementary File S3). It seemed, among other things, that physicians regard platelet inhibitors as a reasonable alternative for OAC therapy or they do not consider initiating OAC therapy in AF patients with pre-existing vascular disease, such as coronary artery disease or peripheral vascular disease, perhaps because these patients are already prescribed a platelet inhibitor. Strengths and limitations A major strength of our study is that we used uniformly registered, routine clinical practice data on trends in AF in primary care spanning a decade. Two limitations, which are inherent to using data derived from structured fields in electronic health records, are: 1) lack of specific granular information (e.g. no differentiation based on AF subtype (paroxysmal, persistent, permanent) and inability to differentiate between primary versus secondary AF and between AF versus atrial flutter); and 2) risks of misclassification in predictor values used in the CHA2DS2-VASc model, misclassification in diagnosis and - to a lesser extent when using data from the JGPN database - misclassification in treatment. However, the JGPN consists of a dedicated group of GPs who have been trained in accurately coding diseases using ICPC codes. Moreover, van Doorn et al. have demonstrated that the risk of substantial misclassification in individual predictors of the CHA2DS2-VASc model is relatively small in multivariable analyses, albeit present.25 Clinical implications The clinical implications of this study are multiple. Firstly, the large increase in reported AF prevalence over time was far greater than previously expected.17 This can lead to an increase in AF care, in particular care aimed at stroke prevention, which could, for example, be realised to a large extent through integrated management of AF in primary care.26 5
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