cNo statistically signi cant effect, and CIs are very wide. Trial was not suf ciently large to demonstrate comparable safety between conventional and TEE-based strategies. dMost of these were GI bleeds. www.chestpubs.org CHEST / 141 / 2 / FEBRUARY, 2012 SUPPLEMENT e567S recommendations for long-term antithrombotic therapy in section 2.1. 4.1.2 Cardioversion of AF of 48 h Duration or Less: There is uncertainty over the precise duration of AF necessary for thrombus to develop and, hence, the threshold of AF duration below which precar- dioversion anticoagulation can be safely avoided. For AF of short duration (eg, 48 h), a common practice is to cardiovert without a TEE or prolonged precardioversion anticoagulation. However, observa- tional studies have found left atrial thrombus on TEE in as many as 14% of patients with acute AF of short duration.158,159 Moreover, because many indi- viduals develop AF asymptomatically, it is often dif cult to accurately determine a patient s dura- tion of AF, making the 48-h rule dif cult to apply.160 No RCTs have compared different anticoagulation strategies in patients with AF of documented dura- tion of 48 h. Observational data suggest that the risk of stroke or thromboembolism in these patients is similar to those who have received conventional anticoagulation for a minimum of 3 weeks before Recommendation 4.1.2. For patients with AF of documented duration of 48 h or less undergoing elective cardioversion (electrical or pharmacologic), we suggest starting anticoagulation at presenta- tion (low-molecular-weight heparin or unfrac- tionated heparin at full venous thromboembolism treatment doses) and proceeding to cardiover- sion rather than delaying cardioversion for 3 weeks of therapeutic anticoagulation or a TEE-guided approach (Grade 2C). 