Echocardiography
A comprehensive transthoracic echocardiography (TTE), which included two-dimensional, M-mode, Doppler echocardiography was performed according to the recommendation of the American Society of Echocardiography.14 TTE examinations were performed using a Vivid 7 Ultrasound System (GE Healthcare, Horten, Norway). From the parasternal long axis view, we recorded the LV end-diastolic and end-systolic diameters. The LV end-diastolic volume (EDV), LV end-systolic volume (ESV) and LVEF were calculated using the biplane method of the disk summation. The stroke volume was calculated using the outflow tract diameter measured at the base of the aortic leaflet in the parasternal long axis view and the pulsed Doppler velocity integral obtained at the same level in the five-chamber or apical long axis view.
LDSE was performed before surgery. Dobutamine was infused intravenously in 10-min stages at incremental doses of 5 and 10 g/kg/min while monitoring a single-lead electrocardiogram and blood pressure. EDV, ESV, LVEF and stroke volume were obtained at each stage.