INFLUENCE OF ACUTELY ALTERED LOADING CONDITIONS ON LEFT ATRIAL APPENDAGE FLOW VELOCITIES

Objectives. The purpose of this study was to identify the effects of altered loading conditions on left atrial appendage flow velocities. Background. Although studies have suggested that Doppler analysis of left atrial appendage blood how may have clinical utility, the hemodynamic and cardiac mechanical determinants of left atrial appendage flow are poorly understood. Methods. Transesophageal Doppler echocardiography was performed in eight atrially paced anesthetized dogs instrumented with sonomicrometers on the left atrial appendage and the left ventricular minor axis and with left atrial and left ventricular micromanometers. Left atrial appendage emptying and filling velocities corresponding to early and late ventricular diastole, respectively, were measured using volume expansion and phenylephrine infusion. Results. Volume infusion caused a significant decrease in the early to late emptying and filling ratios (mean +/- SD 0.85 +/- 0.24 vs. 0.46 +/- 0.17 and 0.80 +/- 0.50 vs. 0.40 +/- 0.20, both p < 0.05). By contrast, phenylephrine infusion did not significantly alter either filling or emptying ratio. The independent determinants of each flow wave were identified with multiple regression analysis: early emptying velocity-time constant of left ventricular relaxation, left ventricular end-systolic dimension and aortic pressure (r = 0.75, p < 0.001); late emptying velocity-left ventricular peak positive time derivative of left ventricular pressure (dP/dt) and fractional shortening (r = 0.74, p < 0.001); early filling velocity-left atrial appendage shortening fraction (r = 0.45, p = 0.01) and late filling velocity-left atrial appendage lengthening rate and left ventricular fractional shortening (r = 0.56, p < 0.01). Conclusions. These results indicate that 1) both the magnitude and the pattern of left atrial appendage emptying and filling velocities are dependent on loading conditions, and 2) left atrial appendage velocities are influenced to a greater extent by changes in left ventricular than in left atrial appendage function. These findings may have implications for the pathogenesis of left atrial appendage thrombi.