Quality of Warfarin Anticoagulation for Atrial Fibrillation in Indigenous and Non-Indigenous Australians

Abstract

Background: Atrial fibrillation (AF) is a leading cause of preventable stroke. Suboptimal anticoagulation therapy affects a significant percentage of patients with AF. Currently, there is little data on the quality of warfarin anticoagulation therapy from Australia, and to the best of our knowledge, none in Indigenous Australians. Purpose: To characterise the quality of warfarin anticoagulation therapy and predictors of time in therapeutic range (TTR) in Indigenous and non-Indigenous Australians with AF. Methods: 512 patients with AF on warfarin therapy from a large tertiary centre were included (88 Indigenous and 424 non-Indigenous). Administrative, clinical, prescriptive and laboratory data were linked. TTR was calculated as a proportion of daily international normalised ratio (INR) values between 2-3 for non-valvular AF and 2.5-3.5 for valvular AF. INR values between tests were imputed using the Rosendaal technique. Linear regression models were employed to characterise predictors of TTR. Results: TTR was significantly less in Indigenous compared to non-Indigenous Australians (40 ± 29 vs 50 ± 31%, p = 0.006). Univariate predictors of better TTR included increasing age, non-Indigenous status, heart failure, chronic obstructive pulmonary disease, valvular heart disease, diuretic use and amiodarone use (p < 0.05 for all). Multivariate analyses suggested that TTR discrepancy between Indigenous and non-Indigenous Australians was mediated by differences in age, comorbidities (such as valvular heart disease) and greater diuretic use in Indigenous Australians. Conclusions: Warfarin anticoagulation therapy, as determined by TTR, is suboptimal in Indigenous Australians compared to their non-Indigenous counterparts.