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The presence of spontaneous echo contrast (SEC) in the left atrium has been reported to be an independent predictor of thromboembolic risk in patients with atrial fibrillation (AF). Dabigatran was associated with lower rates of stroke and systemic embolism as compared with warfarin when administered at a higher dose. Between July 2011 and October 2015, nonvalvular AF patients treated with warfarin or dabigatran who had transesophageal echocardiography prior to ablation therapy for AF were enrolled. The intensity of SEC was classified into four grades, from 0 to 3. Univariate and multivariate analysis was performed to analyze factors associated with SEC. Sixty-five patients were on dabigatran and 65 were on warfarin, with the prothrombin time in therapeutic range. There were no significant differences in the age, CHADS2 score, left atrial dimension, and left atrial appendage flow between the two groups. However, there were more grade 2 or higher patients with left atrial SEC in the warfarin group (n = 20) than in the dabigatran group (n = 2) (p < 0.001). When multivariate regression analysis was performed, grade 2 or higher left atrial SEC was independently associated with no dabigatran usage in addition to high brain natriuretic peptide level and high incidence of diabetes mellitus or persistent AF. Thus, dabigatran exhibited low intensity of left atrial SEC in nonvalvular AF patients as compared with warfarin.

Patients with persistent atrial fibrillation (AF) and a large left atrium are at a high risk for thromboembolisms. Recently, direct oral anticoagulants (DOACs) have mainly been used for the prevention of cardiac embolisms caused by AF. Transesophageal echocardiography (TEE) is performed in order to exclude any left atrial appendage (LAA) thrombi. We herein report two cases of persistent AF, both of which were treated with rivaroxaban for more than two years. Since TEE identified mobile LAA thrombi with this treatment, we switched from rivaroxaban to the direct thrombin inhibitor dabigatran. Dabigatran resolved the LAA thrombi that had been refractory to rivaroxaban.