TEE has limited application during positive-pressure ventilation because the image can shift out of the region of interest. This is why we analyzed only high-quality images after two independent observers using accepted criteria reviewed them. The overall percentage of good-quality images in our study is nevertheless comparable to other studies in which the ABD technique has been used to assess the ventricular area. Still, issues of the rotational artifact of the LV cavity relative to the TEE, induced by positive-pressure breaths, need to be addressed. This rotational artifact can be either lateral or vertical to the plane of the 2D image. In both instances, the area measured by the ABD method may not reflect LV area at the same anatomic location seen during apnea. Lateral movement was clearly seen in several breaths in some of our subjects. In these examples, the ABD measurement moved off the region of interest borders, and these data were rejected. No data with lateral rotational artifacts were used in our analysis. Rotational artifacts were not the only cause for rejecting data. Despite the fact that the TEE probe was not moved during the data acquisition, upward and downward cardiac movement could have been missed because the esophageal position allows for no reference point within the thorax. However, Smith et al addressed this issue previously. They moved the TEE probe 2 cm in and out (4 cm total distance) in the transgastric position from a midpapillary short-axis vein. so
When they compared measures of EDA and ESA from these three vertical positions, they saw no difference. Because it is highly unlikely that vertical movement of the mediastinal block (including esophagus and heart) exceeded 2 cm during a positive-pressure breath, vertical rotational artifacts likely had little influence on our measured values. Furthermore, in two patients in open chest condition, we were able to validate our measurements further by using the electromagnetic flow probe on the aorta. Close correlation was observed between TEE SA and flow probe-derived stroke volume during both ventilation and inferior vena caval occlusion maneuvers.