In patients implanted with CIEDs for conventional indications, AHREs, with a short duration, ranging from 3 atrial premature complexes to 15 to 20 s, are currently considered of no speci c clinical signi cance since this type of AHRE was found not to be signi cantly 1178 Evidence-Based Medicine [ 1 5 4 # 5 C H E S T N O V E M B E R 2 0 1 8 ] associated with episodes of longer duration, or with an increased risk of stroke or systemic For this reason, most of the interest in patients with CIEDs is focused on AHRE with a duration $ 5 to 6 min, a nding associated with a substantial risk of subsequently presenting clinical AF (HR, 5.5-6.0), initially reported by the ancillary Atrial Diagnostics Ancillary Study of the Mode Selection Trial and then by the ASSERT study,371 where CIED-detected AHREs > 6 min were followed by clinical AF detected by a surface ECG in approximately 16% of patients at 2.5 years of follow-up (e-Table 21). The association between CIED-detected atrial tachyarrhythmias of variable durations and stroke or systemic thromboembolism has been evaluated by several studies that overall collected data on > 22,000 patients, taking into account the maximum duration of AHRE episode, or the maximum daily AF burden (ie, the maximum time spent in adjudicated AF in 1 day of the follow-up period).371,379-387 The studies show that AHRE burden with a duration $ 5 to 6 min are signi cantly associated with an increase in the risk of stroke or systemic thromboembolism (HR, 2-9). 