ALTERED LEFT ATRIAL COMPLIANCE AFTER ATRIAL APPENDECTOMY - INFLUENCE ON LEFT ATRIAL AND VENTRICULAR FILLING

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 How (J(FTI)/K(FTI)), 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, J(FTI)/K(FTI) was significantly less afterwards. Similarly, the early diastolic transmitral velocity increased with volume infusion but was less at each level of left atrial pressure after appendectomy. We conclude that left atrial compliance decreases after appendectomy and is characterized by decreased relative reservoir to conduit function of the left atrium and decreased early left ventricular filling rate.