LEFT ATRIAL APPENDAGE THROMBUS IS NOT UNCOMMON IN PATIENTS WITH ACUTEATRIAL-FIBRILLATION AND A RECENT EMBOLIC EVENT - A TRANSESOPHAGEAL ECHOCARDIOGRAPHIC STUDY

Objectives. The objective of this study was to determine the frequency of left atrial thrombus in patients with acute atrial fibrillation. B ackground. It is commonly assumed but unproved that left atrial thromb us in patients with atrial fibrillation begins to form after the onset of atrial fibrillation and that it requires greater than or equal to 3 days to form. Thus, patients with acute atrial fibrillation (i.e., < 3 days) frequently undergo cardioversion without anticoagulation proph ylasis. Methods. Three hundred seventeen patients (250 men, 67 women; mean [+/-SD] age 64 +/- 12 years) with acute (n = 143) or chronic (n = 174) atrial fibrillation were studied by two-dimensional transesophag eal echocardiography. Results. Left atrial appendage thrombus was pres ent in 20 patients (14%) with acute and 47 patients (27%, p < 0.01) wi th chronic atrial fibrillation. In patients with a recent embolic even t, the frequency of left atrial appendage thrombus did not differ betw een those with acute (5 [21%] of 24) and those with chronic (12 [23%] of 52, p = NS) atrial fibrillation. Patients with acute versus chronic atrial fibrillation, respectively, did not differ (p = NS) in mean ag e (64 +/- 13 vs. 65 +/- 11 years), frequency of concentric left ventri cular hypertrophy (32% vs. 26%), hypertension (32% vs. 41%), coronary artery disease (35% vs. 39%), congestive heart failure (43% vs. 48%), mitral stenosis (4% vs, 7%) or mitral valve replacement (1.4% vs. 6%). The minimally detectable difference in proportions between patients,v ith acute and chronic atrial fibrillation based on a power of 0.80 and base proportion of 0.20 was 14%. Conclusions. Left atrial thrombus do es occur in patients with acute atrial fibrillation <3 days in duratio n. The frequency of left atrial thrombus in patients with recent embol i is comparable between those with acute and chronic atrial fibrillati on. These data suggest that patients with acute atrial fibrillation fo r <3 days require anticoagulation prophylaxis or evaluation by transes ophageal echocardiography before cardioversion and should not be assum ed to be free of left atrial thrombus.