Discussion
The analyses of this large and nationally representative data suggest changing practice trends in the rate and type of OAC prescribing over the last ten years. The proportion of patients with moderate to high stroke risk who were prescribed an OAC increased steadily by one-third from 2009-2018. This increase in the proportion patients with moderate to high stroke risk who were prescribed an OAC was significantly higher from 2013 onwards, corresponding with the PBS listing of DOACs for Australian government subsidisation (rivaroxaban in August 2013, and apixaban and dabigatran in September 2013) (Drug Utilisation Sub-Committee (DUSC), June 2016). In 2010, the European Society of Cardiology (ESC) guidelines recommended prescribing of an OAC for all AF patients at moderate-high risk of stroke (i.e., CHA2DS2-VASc score ≥1) instead of antiplatelet therapy (Camm et al., 2010). This was followed by the 2012 ESC’s updated recommendation to avoid prescribing of aspirin in low-stroke risk patients (Camm et al., 2012). These changes may also explain the surge in OAC prescribing during the study period (Camm et al., 2012). Similar trends of an increase in OAC use, with a slow initial uptake after the introduction of DOACs, have been reported by studies from the United Kingdom and Denmark (Gadsboll et al., 2017; Loo, Dell’Aniello, Huiart & Renoux, 2017).
In 2018, just over half of the high-risk patients were prescribed an OAC. This rate is low compared with the rates reported from previous studies. The Tasmanian AF study found 63% of high-risk patients were prescribed an OAC. However, that study involved hospitalised patients who might have been more comorbid than general practice patients and it excluded patients with known OAC contraindications. A study in the UK using general practice data found that over three-quarters of high-risk patients with AF were prescribed an OAC (Adderley, Ryan, Nirantharakumar & Marshall, 2018). Another study from Denmark found that two-thirds of patients were prescribed an OAC (Gadsboll et al., 2017).
Despite an overall increase in OAC prescribing over the study period, there remained wide gaps between the highest- and lowest-performing practices in both appropriate (for moderate to high stroke risk) and potentially inappropriate (for low stroke risk) prescribing, which increased over time. One possible reason for the observed gaps in the appropriate use of an OAC might be the absence of regular reassessment of CHA2DS2-VASc scores. A study by Yoon et al. (Yoon et al., 2018) found that 46.6% of low-risk and 72% of moderate-risk patients at baseline were reclassified as being at high stroke risk within 10 years of follow-up. Increasing general practitioners’ awareness of the need for annual stroke risk assessment may improve OAC prescribing.