Embolic Stroke of Undetermined Source and Detection of Atrial Fibrillation on Follow-Up: How Much Causality Is There?

Background: There is increasing debate whether atrial fibrillation (AF) episodes during follow-up in patients with embolic stroke of undetermined source (ESUS) are causally associated with the event. AF-related strokes are more severe than strokes of other etiologies. In this context, we aimed to compare stroke severity between ESUS patients diagnosed with AF during follow-up and those who were not. We hypothesized that, if AF episodes detected during follow-up are indeed causally associated with the index event, stroke severity in the AF group should be higher than the non-AF group. Methods: Dataset was derived from the Athens Stroke Registry. ESUS was defined by the Cryptogenic Stroke/ESUS International-Working-Group criteria. Stroke severity was assessed by the National Institutes of Health Stroke Scale (NIHSS) score. Cumulative probabilities of recurrent stroke or peripheral embolism in the AF and non-AF ESUS groups were estimated by Kaplan-Meier analyses. Results: Among 275 ESUS patients, AF was detected during follow-up in 80 (29.1%), either during repeated electrocardiogram monitoring (18.2%) or during hospitalization for stroke recurrence (10.9%). NIHSS score was similar between the two groups (5 [2-13] versus 5 [2-14], P = .998). More recurrent strokes or peripheral embolisms occurred in the AF group compared with the non-AF group (42.5% versus 13.3%, P = .001). Conclusions: Stroke severity is similar between ESUS patients who were diagnosed with AF during follow-up and those who were not. Given that AF-related strokes are more severe than strokes of other etiologies, this finding challenges the assumption that the association between ESUS and AF detected during follow-up is as frequently causal as regarded.