Transgastric LV 2-chamber views for mitral apparatus (Figure 5)
Mitral apparatus evaluation is the key to both surgical and transcatheter mitral valve repair. Severity of leaflet tethering by infarcted myocardium determines the success of mitral repair. During chordal length determination for artificial chordae implantation, it is important to have the papillary muscle, measured chordae tendineae and the edge of mitral valve all be clearly identified simultaneously on a two-dimensional plane in a systolic phase. Such evaluations could be performed on the transgastric LV bi-commissural view, which can be derived from planar rotation from the transgastric LV short axis view at papillary muscle level (Figure 5). On CT simulation, we can start with a mid-esophageal foreshortened 4-chamber view, and then move the MPR crosshairs into the gastric cardia. Next, we simulate anteflex at the sagittal MPR plane to obtain a short axis view at papillary muscle level. Finally, we rotate the axial MPR line on the coronal MPR plane to obtain the transgastric view for mitral apparatus.
Transgastric views for LV outflow tract (LVOT) to ascending aorta (AsAo) (Deep transgastric 5-chamber view and transgastric long axis view) (Figure 6)
This is the ideal view to obtain a parallel alignment of Doppler signal to the LV outflow jet. When there are aortic or mitral prostheses or calcification, this is the only view to investigate aortic valve cusps without acoustic shadowing. After transcatheter aortic valve replacement, this view is the optimal to evaluate paravalvular leakage; and it is also crucial to estimate the pressure gradient at LVOT and aortic valve after procedures, such as, mitral valve-in-valve and transcatheter aortic/mitral valve replacement. More often than not, there are configural differences between pre-operative CT and intra-operative TEE images on the aorto-mitral structure. On CT simulation, we firstly move the MPR crosshairs into the gastric fundus and then rotate the axial MPR line clockwise toward the aortic valve (step1). Next, we adjust the sagittal MPR line to cross the aortic valve on the axial MPR plane (step2). Lastly, we rotate the axial MPR line on the coronal MPR plane to check the relationship between mitral structure/device and LVOT (step3).
During the TEE manipulation, an important tip to acquire the transgastric LVOT-AsAo view is to add some “flex to the left.” The in vitro motion of TEE probe during “flex to the left” deviates somewhat for there is to the certain extent “anteflex” and it becomes, instead, more like a “turn to the left” (i.e., counterclockwise rotation of the TEE probe, Figure 4). However, due to the resistance of the esophageal tract and accumulated torque at esophagogastric junction (EGJ), there will be an in vivo disproportional loss of rotation at the TEE probe to that added by imager. As a result, the “flex to the left” will be a more suitable method to control the TEE probe in the gastric fundus to achieve better contact and a more predictable and controllable rotation. In patients with dilated LV chamber or horizontal AsAo, it is more difficult to acquire the deep transgastric 5-chamber view because the scanning sector cannot simultaneously include the LVOT and LV chamber even with the “flex to the left.” In that case, the transgastric long axis view may catch the LVOT-AsAo structure in the right side. If the axial MPR plane cannot produce the ideal deep transgastric 5-chamber view after the step 2 mentioned earlier, (i.e., only AsAo and atria but limited LV chamber), the transgastric long axis view may become a more suitable intraoperative choice (Figure 4). As a result, CT simulation can provide with a quick check for the difficulty in TEE acquisition.