In the ASSERT study, subclinical atrial tachyarrhythmias with at least 6 min duration were detected within 3 months in approximately 10% of patients implanted with a CIED.371 During a follow-up period of 2.5 years, additional subclinical atrial tachyarrhythmias occurred in approximately 25% of patients, and around 16% of those who had subclinical atrial tachyarrhythmias developed symptomatic AF.371 Considering these ndings, as well as data from the literature reported in e-Table 20, there is evidence that AHREs with a duration > 5 to 6 min are common in patients implanted with CIEDs. 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). 