"Stunning" of the left atrium after spontaneous conversion of atrial fibrillation to sinus rhythm - Demonstration by transesophageal Doppler techniques in a canine model

Objectives. This study compared left atrial and left atrial appendage contr action velocities in sinus rhythm before and after a brief period of atrial fibrillation in a canine model. Background. In patients, left atrial appendage contraction velocities measu red during sinus rhythm after cardioversion from atrial fibrillation are de pressed relative to left atrial appendage emptying velocities measured duri ng atrial fibrillation, suggesting that the left atrial appendage is mechan ically "stunned." Methods. This phenomenon was studied in a canine model of acute (60 min) pa cing-induced atrial fibrillation followed by spontaneous reversion to sinus rhythm using epicardial and transesophageal pulsed wave Doppler. Unique fe atures of the model include: 1) comparison of left atrial function postconv ersion to baseline sinus rhythm rather than to measurements during atrial f ibrillation, 2) control of the duration of atrial fibrillation and 3) elimi nation of the extraneous influences of direct current shock and antiarrhyth mic agents, which may independently depress left atrial function. Results. Hemodynamic conditions (heart rate, mean arterial pressure, cardia c output, mean pulmonary artery pressure, mean right atrial pressure and me an left atrial pressure) at baseline, during 60 min of atrial fibrillation and after reversion to sinus rhythm were constant throughout the study peri od. Peak left atrial contraction velocities (measured from the transmitral how velocity profile) were significantly (p < 0.02) reduced to 64 a 22% of baseline values upon spontaneous conversion of atrial fibrillation to sinus rhythm and recovered to basal values by 20 min after resumption of sinus r hythm. Peak left atrial appendage contraction velocities were significantly (p < 0.001) reduced to 49 +/- 24% of baseline values upon spontaneous conv ersion of atrial fibrillation to sinus rhythm and recovered to basal values by 40 min after reversion to sinus rhythm. Conclusions. Even brief (60 min) periods of atrial fibrillation in normal c anine hearts result in marked depression of global left atrial systolic fun ction and regional left atrial (left atrial appendage) systolic function up on resumption of sinus rhythm. This "mechanical stunning" of left atrial sy stolic function appears to be more profound and of longer duration for the left atrial appendage compared with the left atrium as a whole, which may p redispose the appendage to blood stasis and thrombus formation. Chronic mod els of atrial fibrillation need to be developed to examine the impact of lo nger periods of atrial fibrillation upon the magnitude and duration of post conversion left atrial "stunning." (J Am Coil Cardiol 1998;32:2081-6) (C) 1 998 by the American College of Cardiology.