LEFT ATRIAL APPENDAGE STUNNING AFTER ELECTRICAL CARDIOVERSION OF ATRIAL-FLUTTER - AN ATTENUATED RESPONSE COMPARED WITH ATRIAL-FIBRILLATION AS THE MECHANISM FOR LOWER SUSCEPTIBILITY TO THROMBOEMBOLIC EVENTS

Objectives. This study sought to determine whether left atrial appenda ge stunning occurs in patients with atrial flutter and to compare left atrial appendage function in the pericardioversion period with that i n patients with atrial fibrillation. Background. Left atrial appendage stunning has recently been proposed as a key mechanistic phenomenon i n the etiology of postcardioversion thromboembolic events in atrial fi brillation. Atrial flutter is thought to be associated with a negligib le risk of thromboembolic events; therefore, anticoagulation is common ly withheld before and after cardioversion in these patients. Methods. Sixty-three patients with atrial flutter (n = 19) or atrial fibrillat ion (n = 44) underwent transesophageal echocardiography immediately be fore and after electrical cardioversion. In addition to assessing the presence of thrombus and spontaneous echo contrast, we measured left a trial appendage emptying velocity and calculated shear rates by pulsed wave Doppler and two-dimensional echocardiography. Results. Patients with atrial flutter exhibited greater left atrial appendage flow veloc ities before cardioversion than those with atrial fibrillation (42 +/- 19 vs. 28 +/- 15 cm/s [mean +/- SD], p < 0.001), Left atrial appendag e shear rates were also higher in patients with atrial flutter (103 +/ - 82 vs. 59 +/- 37 s(-1), p < 0.001), After cardioversion, left atrial appendage flow velocities decreased compared with precardioversion va lues in patients with atrial fibrillation (28 +/- 15 before to 15 +/- 14 cm/s after cardioversion, p < 0.001) and atrial flutter (32 +/- 19 to 27 +/- 18 cm/s, respectively, p < 0.001), Shear rates decreased fro m 59 +/- 37 before cardioversion to 30 +/- 31 s(-1) after cardioversio n in atrial fibrillation (p < 0.001), and from 103 +/- 82 s to 65 +/- 52 s(-1), respectively (p < 0.001), in atrial flutter, This decrease i n flow velocity from before to after cardioversion occurred in 36 (82% ) of 44 patients with atrial fibrillation and 14 (74%) of 19 with atri al flutter, The impaired left atrial appendage function after cardiove rsion was less pronounced in the group with atrial flutter (27 +/- 18 cm/s for atrial flutter vs. 15 +/- 14 cm/s for atrial fibrillation, p < 0.001). New or increased spontaneous echo contrast occurred in 22 (5 0%) of 44 patients with atrial fibrillation versus 4 (21%) of 19 with atrial flutter (p < 0.05). Conclusions. Left atrial appendage stunning also occurs in patients with atrial flutter, although to a lesser deg ree than in those with atrial fibrillation. These data suggest that pa tients with atrial flutter are at risk for thromboembolic events after cardioversion, although this risk is most likely lower than that in p atients with atrial fibrillation because of better preserved left atri al appendage function. (C) 1997 by tbe American College of Cardiology.