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.