Transesophageal Echocardiographic Examination
Two-dimensional (2D) TEE signals were acquired by an echocardiographic automated border detector ([ABD]; Sonos 1500; Hewlett Packard Systems; Andover, CA). This methodology has been described and validated previously for this type of patient population. Briefly, an automated-edge border-detec-tion algorithm is superimposed on the 2D echocardiographic image and displayed in real time on the video monitor as a red line that follows the endocardial contour (Fig 1). If the endocardial contours are still unclear, lateral or total gain control is adjusted to improve image resolution. The tracing of a region of interest is then drawn manually. Within this region of interest, integration of the edge-detected area occurs, which allows measurements of instantaneous area-time relation of the blood-pool area in square centimeters. From these data, stroke area (SA), which is the difference between the maximum end-diastolic area (EDA) and minimum end-systolic area (ESA), is calculated. SA, EDA, and ESA were taken to reflect stroke volume, end-diastolic volume, and end-systolic volume, respectively. The images analyzed from the TEE-ABD were obtained from a transgastric, midventricular, short-axis view by using the LV midpapillary level as an anatomic landmark. The area signal was calibrated at zero on both the ABD and the computer workstation with a predetermined area. These measurements and calculations, along with the pressure measures, were displayed on-line and stored on computer disk for subsequent analysis. An example of the recorded signal is shown in Figure 2. antibiotics buy
The TEE technique using this border-detection algorithm has been previously validated by us and others, and it has demonstrated a good correlation between LV stroke volume and LV SA in both animal and human studies when different modes were used to measure LV volume and when offline tracing was compared with manual planimetry tracing. To further validate the findings of the TEE, two additional patients were subsequently studied separately.
Figure 1. A transgastric, midventricular, short-axis view obtained from TEE with ABD. The LV endocardial blood/tissue interface is shown in red. The region of interest encircles the LV and represents the area analyzed continuously. Shown below the echocardiographic image is the ECG and the LV area signal displayed over time.
Figure 2. ECG, arterial pressure (Pa), right atrial pressure (Pra), pulmonary artery pressure (Ppa), LV area (LVA), and airway pressure (Paw) recorded over time following apnea in a patient after cardiac bypass surgery during the closed chest condition.