Population
We identified adult patients (aged 18 or over) with AF from January 1,
2013, to December 31, 2017. AF was detected by searching for the
International Classification of Diseases, 9th Revision
(ICD-9) codes 427.3, 427.31 or 427.32, or the International
Classification of Diseases, 10th Revision (ICD-10)
code I48.29,30 The first instance of AF coding was
used to determine eligibility. The cohort was subsequently restricted to
patients who filled a new prescription for rivaroxaban (15 mg or 20 mg
once daily), apixaban (2.5 or 5.0 mg twice daily) or warfarin within a
year of AF diagnosis. Few patients had a new prescription of either
dabigatran or edoxaban and so were not included in our analysis. The
date of the first OAC claim was defined as the date of cohort entry. New
OAC users were defined as those not exposed to any OACs in the year
prior to the claim index date. Patients were also required to have had
pharmacy coverage for at least 12 months and enrolment in a drug health
insurance plan for at least one year before cohort entry.
We also excluded patients with a code for any condition or procedure
that might have impacted the choice of OAC and duration of treatment at
discharge: cardiac valve replacement or valve procedures in the five
years before cohort entry; end-stage CKD (meaning being on dialysis),
kidney transplant, dialysis or coagulation deficiency in the three years
before cohort entry; medical procedures (including cardiac
catheterization, stent, coronary artery bypass grafting, cerebrovascular
or defibrillator) in the three months before cohort entry; deep vein
thrombosis or orthopedic surgery in the six months before cohort entry.
Lastly, the cohort was restricted to patients with stage III CKD, as
defined by a composite variable covering the ICD code, drug use, and
consultations with a nephrologist (as identified in the administrative
databases). This composite variable has been validated, with reference
to medical chart reviews of older adults with CKD (the algorithm used
for estimated glomerular filtration rate (eGFR) definition had a
positive predictive value ranging from 94.5% to
97.7%).31