The problem with this approach is the presence of left atrial thrombus on TEE in up to 14% of patients with AF of short duration in observational studies.264,265 In addition, the high prevalence of asymptomatic AF makes determining the exact duration of AF dif cult.266 If there is uncertainty about precise time of AF onset, then such patients should be managed as if AF > 48 h. A recent Finnish observational study of 5,116 successful cardioversions in 2,481 patients with acute (< 48 h) AF showed low incidence of stroke/thromboembolism during the 30 days following cardioversion, even without perioperative anticoagulation (0.7%).267 These results concur with low rates of stroke/thromboembolism in observational studies (Table 8).234,267-272 However, there is lower incidence of stroke/thromboembolism with cardioversions performed during anticoagulation (0.1% vs 0.7%; P .001), and with anticoagulation vs no anticoagulation in patients with a CHA2DS2-VASc score of $ 2 (0.2% vs 1.1%; P .001). It should also be noted that there is a high risk of recurrence of the composite of cardioversion failure and recurrence of AF within Overall, the evidence suggests that peri-cardioversion anticoagulation is bene cial and that the decision regarding peri- and post-cardioversion anticoagulation should be based on risk of stroke/thromboembolism,267 even if an individual is presenting for the rst time with AF. Recommendations *15. For patients with AF of documented duration of 48 h or less undergoing elective cardioversion (electrical or pharmacologic), we suggest starting anticoagulation at presentation (low-molecular- weight heparin or unfractionated heparin at full venous thromboembolism treatment doses) and proceeding to cardioversion rather than delaying cardioversion for 3 weeks of therapeutic anticoagulation or a TEE-guided approach (Weak recommendation, low quality evidence). *16. 