Stroke Prevention in Atrial Fibrillation

SEE PAGE 141 T he prevention of stroke due to atrial fibrillation (AF) is one of the great successes of evidence-based medicine (1,2). Although initial randomized trials demonstrated that warfarin substantially reduced stroke, its uptake into clinical practice was not commensurate with its efficacy (3)—the result of challenges with warfarin management, persistence with therapy, and the fears and realities of bleeding complications. More recently, direct oral anticoagulants (DOACs) have been evaluated in high-quality randomized trials, which enrolled over 75,000 individuals. Compared with warfarin, DOACs convincingly demonstrated a further reduction in stroke, bleeding, or both, and were also associated with a 10% reduction in all-cause mortality (4). However, demonstrating efficacy in randomized trials is only 1 step toward improving the health of a population. In some cases, an efficacious treatment may have negative consequences when introduced outside of a carefully defined trial setting into general clinical practice (5). For this reason, observational data are highly desirable following the introduction of a new therapy, to ensure that patient selection and dosing are in accordance with the criteria in the seminal trials; to monitor large numbers of individuals for rare and unexpected adverse effects, and to confirm that the main benefits and risks of treatment are similar in magnitude to what would be expected based on the results of randomized trials. By contrast, observational studies have limited ability