Previous studies have shown regional differences in atrial distensibility. We studied 12 open-chest dogs to test the hypothesis that left atrial compliance is decreased after removal of the left atrial appendage and to determine the effect of altered atrial compliance on atrial reservoir and conduit function. Sonomicrometer crystal pairs were used to measure the long- and short-axis diameters of the left atrium over a wide range of intracardiac pressures and volumes obtained by intravenous hetastarch infusion both before and after suture ligation of the left atrial appendage (appendectomy). Pulmonary venous flow was measured with an ultrasonic flowmeter, and transmitral flow velocities were measured with transesophageal Doppler echocardiography. After appendectomy, the diastolic pressure-volume relation was shifted upward and to the left in six of seven dogs. The mean dynamic stiffness constant of the left atrial diastolic pressure-volume relation was significantly greater after appendectomy than before (0.20 +/- 0.11 [mean +/- SD] versus 0.14 +/- 0.08 ml-1, p < 0.01); the mean y intercept was slightly, but significantly, less after appendectomy (0.6 +/- 0.3 versus 1.3 +/- 0.6 mm Hg, p < 0.05). The left atrial reservoir volume (maximum minus minimum left atrial volume) was significantly less after appendectomy at matched left atrial pressures. The systolic to diastolic flow integral ratio of pulmonary venous flow (JFTI/KFTI), an index of the relative reservoir to conduit functions of the left atrium, increased significantly with volume infusion only before appendectomy; at matched left atrial pressure, JFTI/KFTI was significantly less afterwards.(ABSTRACT TRUNCATED AT 250 WORDS)
We conclude that (1) in the intact heart, LA contraction may be approximated by time-varying elastance with time-dependent changes in E(t) and that (2) LA systolic P-V relations using either the nonisochronal maximum P-to-V ratio or end systole may be useful as an estimate of Emax, are highly linear and sensitive to calcium-induced changes in inotropic state, and may be useful in identifying LA chamber adaptation to chronic hemodynamic loads.
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.
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