Stability of High‐Quality Warfarin Anticoagulation in a Community‐Based Atrial Fibrillation Cohort: The Anticoagulation and Risk Factors in Atrial Fibrillation (ATRIA) Study

BACKGROUND: Warfarin reduces ischemic stroke risk in atrial fibrillation (AF) but increases bleeding risk. Novel anticoagulants challenge warfarin as stroke‐preventive therapy for AF. They are available at fixed doses but are more costly. Warfarin anticoagulation at a time in therapeutic range (TTR) ≥70% is similarly as effective and safe as novel anticoagulants. It is unclear whether AF patients with TTR ≥70% will remain stably anticoagulated and avoid the need to switch to a novel anticoagulant. We assessed stability of warfarin anticoagulation in AF patients with an initial TTR ≥70%. METHODS AND RESULTS: Within the community‐based Anticoagulation and Risk Factors in AF (ATRIA) cohort followed from 1996 to 2003, we identified 2841 new warfarin users who continued warfarin over 9 months. We excluded months 1 to 3 to achieve a stable dose. For the 987 patients with TTR ≥70% in an initial 6‐month period (TTR (1); months 4–9), we described the distribution of TTR (2) (months 10–15) and assessed multivariable correlates of persistent TTR ≥70%. Of patients with TTR (1) ≥70%, 57% persisted with TTR (2) ≥70% and 16% deteriorated to TTR (2) <50%. Only initial TTR (1) ≥90% (adjusted odds ratio 1.47, 95% CI 1.07–2.01) independently predicted TTR (2) ≥70%. Heart failure was moderately associated with marked deterioration (TTR (2) <50%); adjusted odds ratio 1.45, 95% CI 1.00–2.10. CONCLUSIONS: Nearly 60% of AF patients with high‐quality TTR(1) on warfarin maintained TTR ≥70% over the next 6 months. A minority deteriorated to very poor TTR. Patient features did not strongly predict TTR in the second 6‐month period. Our analyses support watchful waiting for AF patients with initial high‐quality warfarin anticoagulation before considering alternative anticoagulants.