Increased short-term risk of thrombo-embolism or death after interruption of warfarin treatment in patients with atrial fibrillation

Aims It is presently unknown whether patients with atrial fibrillation (AF) are at increased risk of thrombo- embolicadverse events after interruptionof warfarin treatment. The purpose of this study was to assess the risk and timing of thrombo- embolismafter warfarin treatment interruption. Methods and results A retrospective, nationwide cohort study of all patients in Denmark treated with warfarin after a first hospitalization with AF in the period 1997–2008. Incidence rate ratios (IRRs) of thrombo- embolicevents and all-cause mortality were calculated using the Poisson regressionanalyses. In total, 48 989 AF patients receiving warfarin treatment were included. Of these, 35 396 patients had at least one episode of warfarin treatment interruption. In all, 8255 deaths or thrombo- embolicevents occurred during treatment interruptionshowing an initial clustering of events with 2717, 835, 500, and 427 events occurring during 0–90, 91–180, 181–270, and 271–360 days after treatment interruption, respectively. Correspondingly, the crude incidence rates were 31.6, 17.7, 12.3, and 11.4 events per 100 patient-years. In a multivariable analysis, the first 90-day interval of treatment interruptionwas associated with a markedly higher risk of death or thrombo- embolism(IRR 2.5; 95% confidence interval 2.3–2.8) vs. the interval of 271–360 days. Conclusion In patients with AF, an interruptionof warfarin treatment is associated with a significantly increased short-term risk of death or thrombo- embolicevents within the first 90 days of treatment interruption.