Dabigatran and warfarin for secondary prevention of stroke in atrial fibrillation patients: a nationwide cohort study.

BACKGROUND This register-based observational study compares dabigatran to warfarin for secondary stroke prevention in atrial fibrillation patients among both "new starters" on dabigatran and "switchers" to dabigatran from warfarin. METHODS We identified, in nationwide Danish registries, 2398 patients with atrial fibrillation and a history of stroke/transient ischemic attack, making a first-time purchase of dabigatran 110 mg twice a day (bid; D110) and 150 mg bid (D150). Patients were categorized as either vitamin K antagonist (VKA) naive or experienced. Warfarin controls were identified using a complete (for VKA-naive dabigatran patients) or matched sampling approach (for VKA-experienced dabigatran patients). Subjects were followed for an average of 12.6 months for stroke and transient ischemic attacks. Confounder-adjusted Cox regression models were used to compare event rates between treatments. RESULTS Among patients with a history of stroke/transient ischemic attack and prior VKA experience, switching to dabigatran was associated with an increased stroke/transient ischemic attack rate for both dabigatran doses compared with continuing on warfarin (D110 hazard ratio [HR] 1.99; 95% confidence interval [CI], 1.42-2.78; D150 HR 2.34; 95% CI, 1.60-3.41). Among prior stroke/transient ischemic attack patients who were new starters on dabigatran or warfarin, the rate of stroke/transient ischemic attack for both doses of dabigatran was similar to or lower than warfarin (D110 HR 0.64; 95% CI, 0.50-0.80; D150 HR 0.92l; 95% CI, 0.73-1.15). CONCLUSIONS In this register-based study, VKA-experienced patients with a history of stroke or transient ischemic attack who switched to dabigatran therapy had an increased rate of stroke compared with patients persisting with warfarin therapy.