Left ventricular outflow tract mean systolic acceleration as a surrogatefor the slope of the left ventricular end-systolic pressure-volume relationship

Objectives The goal of this study was to analyze left ventricular outflow tract systolic acceleration (LVOTAcc) during alterations in left ventricular (LV) contractility and LV filling. Background Most indexes described to quantify LV systolic function, such as LV ejection fraction and cardiac output, are dependent on loading conditions. Methods In 18 sheep (4 normal, 6 with aortic regurgitation, and 8 with old myocardial infarction), blood flow velocities through the LVOT were recorded using conventional pulsed Doppler. The LVOTAcc was calculated as the aortic peak velocity divided by the time to peak flow; LVOTAcc was compared with LV maximal elastance (Em) acquired by conductance catheter under different loading conditions, including volume and pressure overload during an acute coronary occlusion (n = 10). In addition, a clinically validated lumped-parameter numerical model of the cardiovascular system was used to support our findings. Results Left ventricular Em and LVOTAcc decreased during ischemia (1.67 ± 0.67 mm Hg·ml−1 before vs. 0.93 ± 0.41 mm Hg·ml−1 during acute coronary occlusion [p < 0.05] and 7.9 ± 3.1 m·s−2 before vs. 4.4 ± 1.0 m·s−2 during coronary occlusion [p < 0.05], respectively). Left ventricular outflow tract systolic acceleration showed a strong linear correlation with LV Em (y = 3.84x + 1.87, R = 0.85, p < 0.001). Similar findings were obtained with the numerical modeling, which demonstrated a strong correlation between predicted and actual LV Em (predicted = 0.98 [actual] −0.01, R = 0.86). By analysis of variance, there was no statistically significant difference in LVOTAcc under different loading conditions. Conclusions For a variety of hemodynamic conditions, LVOTAcc was linearly related to the LV contractility index LV Em and was independent of loading conditions. These findings were consistent with numerical modeling. Thus, this Doppler index may serve as a good noninvasive index of LV contractility.