In Cryptogenic Stroke and Underlying Atrial Fibrillation [CRYSTAL AF], 441 patients randomly assigned to prolonged ambulatory cardiac monitoring with a subcutaneous implantable loop recorder or to a control group with conventional follow- up, detected more AF in the monitored group while in a 30-Day Cardiac Event Monitor Belt for Recording Atrial Fibrillation After a Cerebral Ischemic Event: A Randomized Controlled Trial [EMBRACE], 572 patients randomly assigned to additional ambulatory monitoring with a 30-day external loop recorder (intervention group) or a 24-h Holter monitor (control group) found more AF in the intervention group (16.1% vs 3.2% in the control group; In a systematic review and meta-analysis, Sposato described a much higher rate of AF detection after multi-phase sequential cardiac monitoring, at 23.7% (Table 10). 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. 