Left Atrial Relaxation and Left Ventricular Systolic Function Determine Left Atrial Reservoir Function

Background —Determinants of left atrial (LA) reservoir function and its influence on left ventricular (LV) function have not been quantified. Methods and Results —In an open-pericardium, paced (70 and 90 bpm) pig model of LV regional ischemia (left anterior descending coronary constriction), with high-fidelity LV, LA, and RV pressure recordings, we obtained the LA area with 2D automated border detection echocardiography, LA pressure-area loops, and Doppler transmitral flow. We calculated LV τ, LA relaxation (a−x pressure difference divided by time, normalized by a pressure), and stiffness (slope between x and v pressure points of v loop). Determinants of total LA reservoir (maximum−minimum area, cm 2 ) were identified by multiple regression analysis. Different mean rates of LA area increase identified 2 consecutive (early rapid and late slow) reservoir phases. During ischemia, LV long-axis shortening (LAS, LV base systolic descent) and LA reservoir area change decreased (7.3±0.3 [SEM] versus 5.6±0.3 cm 2 , P <0.001) and LA stiffness increased (1.6±0.3 versus 3.1±0.3 mm Hg/cm 2 , P =0.009). Early reservoir area change depended on LA mean ejection rate (LA area at ECG P wave minus minimum area divided by time; multiple regression coefficient=0.9; P <0.001) and relaxation (coefficient=4.9 cm 2 ×ms/s; P <0.001). Late reservoir area change depended on LAS (coefficient=8 cm/s; P <0.001). Total reservoir filling depended on LA stiffness (coefficient=−0.31 cm 4 /mm Hg; P =0.001) and cardiac output (coefficient=0.001 cm 2 ×min/L; P =0.002). The strongest predictor of cardiac output was LA reservoir filling (coefficient=301 L/min×cm 2 ; P <0.001). The v loop area was determined by cardiac output, LV ejection time, τ, and early transmitral flow. Conclusions —Two (early and late) reservoir phases are determined by LA contraction and relaxation and LV base descent. Acute LV regional ischemia increases LA stiffness and impairs LA reservoir function by reducing LV base descent.