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trial fibrillation (AF) is the most common chronic arrhythmia seen in clinical practice and is associated with a high risk of systemic thromboembolism and heart failure. [1][2][3] Chronic AF causes atrial enlargement and impairs ventricular function through loss of coordinative atrial contraction. 2,4,5 Cardiac structural and functional changes caused by chronic AF can be reversed when the sinus rhythm is restored and maintained. [6][7][8][9] Electrical cardioversion (CV) is the most commonly used method among the several treatment modalities to restore sinus rhythm (SR). Although the immediate success rate of CV has been reported to be up to 70-95%, the rate of long term SR maintenance is only approximately 50-60%. [10][11][12][13][14] In addition to AF duration and the left atrial dimension, the left atrial appendage (LAA) mechanical function has been suggested as an important factor for successful CV of AF and the maintenance of SR. [15][16][17][18][19][20] After electrical CV, atrial mechanical stunning develops, which presents as diminished LAA flow velocities. 18,21 This atrial stunning can be reversed by isoproterenol infusion. 22,23 The LAA is a distinct structure from the left atrium proper, although it lies adjacent to the left atrium. Its function has not been fully elucidated and a valid evaluation method has not been determined in cardioverted AF. In this study, we investigated a valid method for the evaluation of LAA mechanical reserve in cardioverted AF and demonstrated that increases in the LAA emptying velocity (LAAEV) and in the LAA filling velocity (LAAFV) with isoproterenol infusion after CV of AF can predict the long-term maintenance of SR. Methods Study PopulationSixty-seven consecutive chronic AF patients who had been successfully cardioverted to SR by direct current electrical CV between 2004 and 2005 were included in this study. Of them, 14 were excluded because of unsuitable echocardiographic image quality or follow-up loss, and a total of 53 patients were finally assessed. The mean age of the patients was 59±3 years (range, 40-76 years) and 40 were male (M/F =40/13). The mean duration of AF was 24±4 months (range, 1-72 months). Associated diseases were hypertension in 26 patients, diabetes mellitus in 3 patients, ischemic heart disease in 1 patient, and cerebrovascular disease in 4 patients. All patients gave written informed consent to participate in the study and the study protocol was approved by the institutional ethic committee for clinical trials. This study aimed to demonstrate the long-term prognostic implication of left atrial appendage (LAA) mechanical reserve determined after electrical cardioversion (CV) of atrial fibrillation (AF). Methods and Results 53 successfully cardioverted chronic AF patients were studied (M/F =40/13, mean age =59±3). LAA emptying velocity (LAAEV) and filling velocity (LAAFV) were measured using transesophageal echocardiography (TEE) before cardioversion, immediately after CV, and with isoproterenol infusion. TEE was done at baseline, 1 month, 3-6 ...

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