Atrial flutter and the risk of thromboembolism: a systematic review and meta-analysis.

PURPOSE We conducted a systematic review and meta-analysis of observational studies to assess the risk of thromboembolism associated with atrial flutter. METHODS MEDLINE, EMBASE, bibliographies, and consultation with clinical experts were used to identify studies that report the risk of thromboembolism associated with attempted cardioversion and longer-term risk in chronic atrial flutter. The review process and data extraction were performed by two reviewers. Study event rates were assessed graphically, and a chi-squared test was used to assess heterogeneity across studies. Meta-regression with weighted logistic regression was used to assess the association between study-level clinical factors and reported thromboembolic event rates. RESULTS We found 13 studies that reported the risk of thromboembolism associated with cardioversion of atrial flutter. Short-term event rates ranged from 0% to 7.3%. A chi-squared test for heterogeneity was significant (P < 0.001), so results were not pooled. Instead, a meta-regression analysis was performed, which partly explained the heterogeneity across studies. Studies were more likely to report high event rates when they included patients with a prior history of thromboembolism, and to report lower event rates when at least some patients were anticoagulated or if patients underwent echocardiography before cardioversion. Four studies reported the longer-term risk of thromboembolism, and these suggest a yearly event rate of approximately 3% with sustained atrial flutter. CONCLUSION These findings suggest that atrial flutter is indeed associated with an increased risk of thromboembolism, and that clinical factors account for the low event rates reported in some studies.