Left ventricular end-systolic elastance was calculated by using the single-beat method. These echocardiographic scans display the evaluation of ejection fraction (left image) and preejection and ejection time (right image) using aortic Doppler waveforms. Normalized ventricular elastance at arterial end-diastole (End) was measured according to the following formula:where ai values are 0.35695, -7.2266, 74.249, -307.39, 684.54. -856.92, 571.95 and -159.1 for i = 1 to i = 7, respectively. The value tNd value was determined by the ratio of pre-ejection period (R-wave to flow onset) to total systolic period (R-wave to end-flow), with the time of onset and termination of flow-defined Doppler. Systolic blood pressure and diastolic blood pressure were measured invasively. The single-beat method used to calculate left ventricular end-systolic elastance was previously validated by Chen et al. .