<h3>Objectives:</h3> The usefulness of the implantable loop recorder (ILR) with improved atrial fibrillation (AF) detection capability (Reveal XT) and the factors associated with AF in the setting of unexplained stroke were investigated. <h3>Methods:</h3> A cohort study is reported of 51 patients in whom ILRs were implanted for the investigation of ischemic stroke for which no cause had been found (cryptogenic) following appropriate vascular and cardiac imaging and at least 24 hours of cardiac rhythm monitoring. <h3>Results:</h3> The patients were aged from 17 to 73 (median 52) years. Of the 30 patients with a shunt investigation, 22 had a patent foramen ovale (73.3%; 95% confidence interval [CI] 56.5%–90.1%). AF was identified in 13 (25.5%; 95% CI 13.1%–37.9%) cases. AF was associated with increasing age (<i>p</i> = 0.018), interatrial conduction block (<i>p</i> = 0.02), left atrial volume (<i>p</i> = 0.025), and the occurrence of atrial premature contractions on preceding external monitoring (<i>p</i> = 0.004). The median (range) of monitoring prior to AF detection was 48 (0–154) days. <h3>Conclusion:</h3> In patients with unexplained stroke, AF was detected by ILR in 25.5%. Predictors of AF were identified, which may help to target investigations. ILRs may have a central role in the future in the investigation of patients with unexplained stroke.

Incidence of atrial fibrillation detected by implantable loop recorders in unexplained stroke