title: Relations between left atrial appendage blood flow velocity, spontaneous echocardiographic contrast and thromboembolic risk in vivo.
abstract: OBJECTIVE
  The aim of this study was to determine the relations between spontaneous echo contrast, left atrial appendage blood flow velocity and thromboembolism.
  
  
  BACKGROUND
  Left atrial thrombus and spontaneous echo contrast, a putative marker of thromboembolic risk, are frequently located in the left atrial appendage. Measurement of left atrial appendage outflow Doppler velocity by transesophageal echocardiography is a recent technique for assessment of left atrial appendage function, which may be important in thrombus formation.
  
  
  METHODS
  Transthoracic and transesophageal echocardiographic studies were performed in 140 patients with atrial fibrillation (chronic in 80 patients, paroxysmal in 50 patients, first episode < 2 weeks in 10 patients). The left atrium and appendage were inspected for thrombus and spontaneous echo contrast, which was graded from 0 (none) to 4+ (severe). Outflow velocity profiles were obtained by pulsed wave Doppler at the orifice of the left atrial appendage.
  
  
  RESULTS
  Left atrial spontaneous echo contrast was present in 78 patients (56%). In multivariate logistic regression analysis, spontaneous echo contrast was the only significant correlate of left atrial thrombus and was present in 14 (93%) of 15 patients. Spontaneous echo contrast and age were associated positively, and anticoagulant therapy was associated negatively, with previous thromboembolic events. Increasing grades of spontaneous echo contrast were associated with decreasing left atrial appendage blood velocity. The velocity in patients with thrombus was not significantly different from that in patients with 4+ spontaneous echo contrast. In multivariate linear regression analysis, the grade of spontaneous echo contrast was significantly and negatively associated with left atrial appendage velocity (p = -0.0001) and mitral regurgitation (p = -0.0002) and significantly and positively associated with left atrial area (p = 0.0005). The odds ratio for spontaneous echo contrast was 28:1 for low left atrial appendage blood flow velocity (< 35 cm/s) and 96:1 for low velocity and the absence of mitral regurgitation.
  
  
  CONCLUSIONS
  Spontaneous echo contrast is the cardiac factor most strongly associated with left atrial appendage thrombus and embolic events. Spontaneous echo contrast formation is promoted by reduced blood flow velocity and increased left atrial size but is diminished by mitral regurgitation.
authors.affiliation: Cardiology Department, St. Vincent's Hospital, Sydney, New South Wales, Australia.
authors.forename: D
authors.initials: D
authors.lastname: Fatkin
authors.forename: R P
authors.initials: RP
authors.lastname: Kelly
authors.forename: M P
authors.initials: MP
authors.lastname: Feneley
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001281:Atrial Fibrillation / Q000150:complications / Q000000981:diagnostic imaging* / Q000503:physiopathology; D016279:Atrial Function, Left; D001783:Blood Flow Velocity; D017548:Echocardiography, Transesophageal; D005260:Female; D006325:Heart Atria / Q000000981:diagnostic imaging* / Q000503:physiopathology; D006331:Heart Diseases / Q000150:complications / Q000000981:diagnostic imaging / Q000503:physiopathology; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D013923:Thromboembolism / Q000453:epidemiology / Q000209:etiology*; D013927:Thrombosis / Q000150:complications / Q000000981:diagnostic imaging* / Q000503:physiopathology