Preoperative examination of bilateral IMAs
Each patient was examined in the supine position with a Philips EPIQ7 Ultrasound Machine (United States) with L12-3 frequency of 3–12 MHz, connected to electrocardiography. To examine the left IMA, the probe was placed on the fourth intercostal space on the left side of the sternum and moved to the left to search for IMA. Luminal diameter was measured in the two-dimensional image. The angle between the sound beam and the blood flow was adjusted to <60°. Spectral Doppler ultrasound was used to measure the peak systolic velocity (PSV), peak diastolic velocity (PDV), systolic velocity–time integral (sVTI, integrating instantaneous speed with time to obtain distance of systolic blood flow), and diastolic velocity–time integral (dVTI, integrating instantaneous speed with time to obtain distance of diastolic blood flow) and to calculate resistance index (RI=PSV/PDV) and diastolic velocity–time integral fraction [dVTIF = dVTI/(dVTI + sVTI)]. The mean values of three cardiac cycles were then used for analysis. Examination of the right IMA was performed using the same method as in the left IMA.