2.3 Three-Dimensional transesophageal echocardiography
Real-time 3D TEE was performed for all patients during TMVI, using an iE33 ultrasound system equipped with a fully sampled matrix-array TEE transducer (X7-2t). 3D images of the MV were acquired with live 3D zoom mode or one beat full volume mode. All images were digitally stored for offline analysis.
Using commercially available software (GI3DQ, QLAB, Philips), the 3D relationship between aortic valve and MV was assessed. First, the end-systolic frame was defined as the last frame during the aortic valve opening. Then, using the 2 orthogonal MV long-axis planes, the MV short-axis cut plane was determined to include the planes of the prosthesis sewing ring, the annuloplasty ring, or the projected native mitral annulus including the posterior saddle-shaped top and the lateral and medial commissures (Figure 1, A-C). The aortic valve long-axis cut plane (Figure 1D, green line; and Figure 1E) was determined to cross both the bottom of the right-coronary cusp and the aortic valve commissure between left- and non-coronary cusps. Aortic annular plane was then obtained as the line that connected mitral anterior leaflet insertion point with the bottom of the right-coronary cusp. In patients with aortic valve replacement, the aortic annular plane was carefully determined as the plane perpendicular to the long-axis of the prosthetic valve. 3D derived AM angle was measured as the obtuse angle between the aortic annulus and the MV short-axis (Figure 1F). Post-procedural AM angle, defined as the obtuse angle between the aortic annulus and the transcatheter heart valve short-axis, was also measured following the same steps as above, in which the short-axis cut plane of the transcatheter heart valve was determined to include the plane of the stent valve edge in LA. Notably, the larger the AM angle, the more parallel the LVOT and MV inflow will be and the smaller the angle, the more likely that the MV inflow is directed toward the LVOT and upper septum. We also collected the data of the AM angle measured by MDCT in 26 patients from the medical record, with which the accuracy of the AM angle by 3D TEE was evaluated.
Using commercially available software (3DQ, QLAB, Philips), the LVOT cross sectional area after stent valve implantation was evaluated from one-beat full volume images including MV and basal LV. The LV long-axis plane in late-systole was determined by following the same process as the determination of the AM angle. A short-axis cut plane (red dotted lines; Figure 2A), perpendicular to the LV long-axis plane, was then moved manually up and down with rotation to search for the smallest area at each level: the level of the valve stent distal edge defined as the most distal portion of the mitral valve stent that was closest to the LV apex and the level of the middle portion of the valve stent (Figure 2, B and C). At both levels, LVOT areas were measured as the area surrounded by the contour of the basal LV wall and the tangent line of the valve stent or the mitral anterior leaflet. Further, the aortic annular area was measured at the level of lowest aortic cusp hinge point (Figure 2D). LVOT dimensions were also measured at each level using LV long-axis cut plane (Figure 2A). In a patient with systolic anterior motion of the anterior mitral leaflet (SAM), LVOT area and dimension at the valve stent distal edge were altered to those at the level of MV leaflet tip (Figure 2, E-H).
2.4 Observer variability
To evaluate reliability of measurements, we randomly selected 6 patients. Two independent observers repeated the measurements of the 3D derived pre- and post-procedure AM angle (total 12 variables) and post-procedure LVOT area at valve stent distal edge, middle portion, and aortic annulus (total 18 variables). One observer repeated the measurements at least 1 month later. The intraobserver and interobserver variability was calculated as the absolute differences between the corresponding 2 measurements in the percentage of their mean (±standard deviation) and interclass correlation.