Despite this, one recent analysis only found that 2.6% and 9.7% of stroke patients had ambulatory ECG monitoring in the 7 days and 12 months poststroke, leading to underdiagnosis.359 Unsurprisingly, AF is more likely to be detected in elderly patients with more prolonged monitoring, especially if there is evidence of prior embolic cortical or cerebellar In a retrospective analysis, newly detected atrial tachycardia or AF (atrial tachycardia/AF > 5 min on any day) was identi ed in 30% patients with implantable cardiac rhythm devices and $ 1 stroke risk factors during a follow-up of 1.1 years.362 The presence of atrial tachycardia/AF > 6 h on $ 1 day increased signi cantly with increased CHADS2 scores. Similarly, the Prevalence of Sub-Clinical Atrial Fibrillation Using an Implantable Cardiac Monitor in Patient With Cardiovascular Risk Factors [ASSERT-II] study reported that subclinical AF lasting $ 5 min was present in 34.4% per year, in a prospective cohort of elderly patients with risk factors but no prior stroke.363 Of note, data from the Athens Stroke Registry show that the CHADS2 and CHA2DS2-VASc scores are independently associated with the risk of ischemic stroke/TIA recurrence and death in ESUS patients, with the risk of stroke recurrence and death in patients with a CHA2DS2-VASc score $ 2 being approximately threefold and 15-fold higher compared with that in patients with a score of 0, respectively.364 If ESUS is phenotypically different from AF-associated stroke, we should see differences in stroke severity and outcomes; however, no difference in National Institutes of Health Stroke Scale score was evident in ESUS where AF was detected on follow-up, compared with where no AF was Nevertheless, it remains possible that within ESUS there is a spectrum of underlying proximal embolic sources, suggested by the strong effect of age on recurrence risk and mortality.366 Current guidelines recommend use of antiplatelet agents including aspirin in ESUS patients316 unless AF is detected (often requiring prolonged workup, as above), when such patients would be managed with oral anticoagulation. 