jamanetwork.com/journals/ja...
“Despite the impressive reduction of risk of stroke and death in patients with atrial fibrillation (AF) conferred by anticoagulation with warfarin or non–vitamin K antagonist oral anticoagulants,1,2 there is still an appreciable stroke risk during anticoagulant treatment, approximating 1.7% per year for warfarin and 1.4% per year for non–vitamin K antagonist oral anticoagulants at 2.2 years’ follow-up.2 This residual stroke rate is often regarded as treatment failure, but, to our knowledge, it has not been compared with a matched control population and could instead reflect the stroke rate in people of a comparable baseline risk without AF”]
“We conclude that residual stroke risk in anticoagulant-treated patients with AF is more likely to reflect the population-associated risk of noncardioembolic strokes in patients of similar age, sex, and comorbidity without AF rather than anticoagulant treatment failure”
I think they are saying that anticoagulants may stop AF related strokes completely, and that a small number of AF patients on anticoagulants may have a stroke for other reasons. This was 2016. This theory may have been disproved since then?