4.1 Patients Undergoing Elective Cardioversion of AF 4.1.1 Cardioversion of AF of More Than 48 h or Unknown Duration: Evidence favoring the ef cacy of pericardioversion anticoagulation is based on observational studies in mostly patients undergoing electrical rather than pharmacologic cardioversion. There is moderate-quality evidence from a system- atic review of 18 observational studies suggesting that the risk of stroke or thromboembolism is sub- stantially lower in patients receiving pericardiover- sion anticoagulation than in those who receive no anticoagulation (0.3% vs 2.0%), translating to a rela- tive risk of 0.16 (95% CI, 0.05-0.48) in favor of anti- coagulation.139 No data regarding major hemorrhagic events were reported in this systematic review. The conventional duration of a minimum of 3 weeks therapeutic anticoagulation before cardioversion and a minimum 4 weeks afterward is based on indirect pathophysiologic data and evidence from observa- tional studies and remains arbitrary. Observational data showing that thromboembolism was signi - cantly more common at an INR of 1.5 to 2.4 before 3.4 Patients With AF Managed by a Rhythm Control Strategy Some patients with AF will be managed with anti- arrhythmic drugs (AADs) to achieve and maintain normal sinus rhythm. Increasingly, patients with AF are also receiving catheter radiofrequency abla- tion procedures (pulmonary vein isolation) to main- tain normal sinus rhythm. In the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) trial, in which many patients in the rhythm control arm did not receive anticoagulation, patients in a rhythm control strategy had a similar risk of stroke compared with patients in a rate control strategy (see also section 4.1.1).125 There are several RCTs of catheter ablation vs AAD therapy in patients with AF, typically those who have failed rst-line therapy with AADs.126-132 All trials found a signi cant reduction in AF recurrence at 1 year of follow-up. 