In subgroup analyses stratified by anticoagulation status at hospital discharge, patients with a history of AF who received LAA occlusion without postoperative anticoagulation had a significantly lower thrombo- embolism rate than those who received neither LAA occlusion nor anticoagulation. There also was no signif- icant difference in the risk of thromboembolism among patients with a history of AF discharged with antico- agulation therapy, whether they received surgical LAA occlusion or not. These data support a role for antico- agulation in patients with a history of AF, particularly in patients not receiving LAA occlusion. A propensity-matched analysis of prophylactic surgi- cal LAA occlusion in patients undergoing cardiac sur- gery did not demonstrate an association between LAA occlusion and long-term thromboembolic events.S4.4.2-2 The propensity-matched LAA occlusion and non LAA occlusion groups were relatively small (461 patients per group), and fewer than half the patients in each group had a history of AF. The study did show that surgical LAA occlusion, which often was incomplete, was asso- ciated with increased risk of early postoperative AF, but it did not influence the risk of stroke or death. There are several important limitations to these stud- ies, and future RCTs may be valuable. 6. RHYTHM CONTROL 6.1. Electrical and Pharmacological Cardioversion of AF and Atrial Flutter 6.1.1. Prevention of Thromboembolism Recommendations for Prevention of Thromboembolism Referenced studies that support modified recommendations are summarized in Online Data Supplement 6. 