66 CHAPTER 5 METHODS Data from the Julius General Practitioners’ Network (JGPN) were used for this study. The JGPN database contains pseudo-anonymous routine healthcare data from structured fields in electronic medical records of a large, ongoing, dynamic cohort consisting of all patients of the approximately 160 affiliated general practitioners (GPs) in the city of Utrecht and its vicinity in the Netherlands. The JGPN population is representative of the Dutch community with regard to sex and age and consisted of approximately 385,000 patients in 2017.14 Data extraction Patients with AF were identified in the JGPN database by using the International Classification of Primary Care (ICPC) code K78 (AF or atrial flutter), from 1 January 2008 to 31 December 2017.15 The following variables were extracted: sex, age, medical history using ICPC codes (see Supplementary File S1) and cardiovascular medication prescriptions (see Supplementary File S2). Medication prescriptions were classified according to the Anatomical Therapeutic Chemical classification system. Antithrombotic therapy was divided into three categories: VKA, NOAC and platelet inhibitor therapy. Medication prescription was not necessarily initiated by the GP but may have been started by a hospital specialist and continued by the GP. Statistical analyses Baseline characteristics of AF patients are reported for 2008 (if AF was first recorded in or before 2008) or for the year AF was first recorded (if this was after 2008 and before 2018). They are presented as count and percentage for categorical variables and as median with interquartile range (IQR) for continuous variables. The prevalence of reported AF was calculated for each year of the entire study period, whereby the whole JGPN population was placed in the denominator. In addition, the prevalence of AF was stratified by sex and by age (<55 years, 55–64 years, 65–74 years, 75–84 years and ≥85 years). The percentages of all AF patients who were prescribed VKA monotherapy, NOAC monotherapy, platelet inhibitor monotherapy, a combination of these antithrombotic treatments or no antithrombotic medication were calculated for each year of the entire study period. In addition, for the group of patients with a diagnostic code for AF and with a CHA2DS2-VASc score ≥2, the percentage of patients who were not prescribed OAC therapy (i.e. platelet inhibitor monotherapy or no antithrombotic therapy at all) was calculated for each year of the study period, to investigate possible changes over time in the percentage of patients who did not receive OAC therapy while this was considered necessary.
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