3.5 Patients With Atrial Flutter Many patients with persistent atrial utter have periods of atrial utter alternating with periods of AF.133,134 The prevalence of thrombus in the body of the atria and atrial appendage on TEE in patients with atrial utter ranges from 1% to 21%.135-138 There are few data from longitudinal studies assessing the risk of thromboembolism with well-documented sustained atrial utter. A study describing a series of 191 consecutive, unselected patients hospitalized for treatment of atrial utter reported thromboembo- lism in 7% of patients during a mean follow-up of 26 months.134 The role of anticoagulant therapy for patients with atrial utter has not been evaluated in e566S Antithrombotic Therapy for Atrial Fibrillation bolism. If no thrombus is seen, the patient proceeds immediately to cardioversion. A TEE-guided strategy requires an experienced echocardiographer because accurate visualization of thrombus may be operator dependent. The Assessment of Cardioversion Using Transesoph- ageal Echocardiography (ACUTE) RCT compared a TEE-guided strategy of abbreviated therapeutic anti- coagulation with IV unfractionated heparin (started 24 h before cardioversion) or warfarin (INR 2.0-3.0) (started 5 days before cardioversion) to a strategy of therapeutic anticoagulation for at least 3 weeks before cardioversion.145 The evidence is of low quality given the wide 95% CIs around the point estimates of effect on patient-important outcomes (Table 13). Thus, the results do not exclude with con dence the possibility of important bene t or harm with a TEE- guided approach compared with a conventional approach of 3 weeks anticoagulation precardioversion. Acknowledging these uncertainties, a TEE-guided approach may be best suited for patients who are very symptomatic while in AF because cardioversion can be done sooner if the TEE is negative for thrombus. It may also suit patients who would prefer to avoid prolonged oral anticoagulation before cardioversion and those at increased risk for bleeding. 