2.1 Sample cohort assembly and drug exposure
We identified patients diagnosed with atrial fibrillation (AF) without
any prior haemorrhagic and/or thromboembolic events for at least three
months before the first OAC exposure in an inpatient or outpatient
setting. These patients were followed for at least six months from the
date of first OAC exposure. Patients were included in the final cohort
if they had at least one OAC dispensing record per 90-day period in the
six months following index exposure in an inpatient or outpatient
setting i.e. a minimum of two drug dispensing records within a six-month
period. For patients on warfarin, the presence of an International
Normalised Ratio (INR; Concept ID: 3022217) measurement was used as an
additional surrogate to ascertain continued warfarin exposure. These
patients were followed up for the occurrence of haemorrhagic or
thromboembolic events at any time after the first exposure to
anticoagulants. Figure 3 outlines the protocol and definitions applied
in this study.
The OACs included for analysis were warfarin (Concept ID: 1310149),
rivaroxaban (40241331), apixaban (43013024), and dabigatran (45775372).
The diagnosis codes for AF included ‘Atrial Flutter’ (Concept ID:
314665), ‘Atrial Fibrillation’ (313217), ‘Atrial Arrhythmia’ (4068155),
and ‘Atrial Fibrillation and Flutter’ (4108832). The concept IDs for
both thromboembolic and bleeding events are as shown in the
Supplementary Table 1.