LEFT ATRIAL APPENDAGE CONTRACTILE FUNCTION IN ATRIAL-FIBRILLATION - INFLUENCE OF HEART-RATE AND CARDIOVERSION TO SINUS RHYTHM

Background: A high incidence of embolic phenomena is associated with a trial fibrillation (AF) and the left atrial appendage (LAA) is frequen tly the source of the emboli. Thrombus formation may be due to stasis within the fibrillating and inadequately emptying LAA. Because LAA emp tying in AF may be the result of mechanical compression by the adjacen t left ventricle, it is possible that left ventricular diastolic filli ng duration will importantly influence passive emptying of the LAA. We hypothesized that the magnitude of emptying of the LAA in AF is relat ed to the duration of left ventricular diastolic filling which is dete rmined by the ventricular response rate in AF. Objective: The objectiv e of our study was to determine the relationship of ventricular respon se rate in AF to LAA emptying and to assess the influence of sinus rhy thm and heart rate on LAA emptying immediately after direct current ca rdioversion to sinus rhythm. Methods: To study this, we used transesop hageal echocardiography to measure LAA ejection fraction ([LAAmax-LAAm in]/LAAmaxX100%) and evaluated its relationship to left ventricular re sponse rate (VRR) in 26 patients with AF (mean age, 65 +/- 7 [1 SD] ye ars). Results: There was a strong inverse relationship between LAA eje ction fraction and VRR in AF (r=-0.73; p<0.001). LAA ejection fraction during AF was 26 +/- 10%, and immediately after successful cardiovers ion, it increased to 46 +/- 12% (p<0.001). However, during sinus rhyth m there was no relationship between LAA ejection fraction and VRR (r=0 .06; p=NS) in the subgroup of patients who were successfully converted to sinus rhythm. There were poor relationships between LAA. ejection fraction and peak transmitral flow velocity (r=-0.41; p=NS) or pulmona ry venous flow velocity (r=-0.03; p=NS) in AF. Conclusion: These resul ts indicate that the magnitude of LAA emptying in AF is strongly and i nversely influenced by ventricular rate. Direct current cardioversion to sinus rhythm is associated with an increase in the magnitude of LAA emptying that is not influenced by heart rate. The magnitude of LAA e mptying may be an important factor in the formation of thromboemboli i n AF. The extent to which controlling the VRR in chronic AF will preve nt stasis and LAA thrombus formation remains to be determined.