Background
The evaluation of the submitral apparatus is challenging from the conventional transesophageal approach. The aim of this study was to test the feasibility of using three-dimensional (3D) transesophageal echocardiographic (TEE) imaging from the transgastric approach to visualize the submitral apparatus and quantify the lengths of the chordae tendineae by using multiplanar reconstruction analysis.
Methods
Twenty-two patients who had transgastric full-volume 3D TEE data sets before mitral valve surgery underwent surgical measurement of chordal length. A short-axis plane at the chordal level was extracted from the 3D data set to identify leaflet segments and the corresponding primary chords. Then, for each chord, the optimal plane was selected to visualize and measure the entire chordal length from its origin at the leaflet margin to the papillary muscle tips. Measurements were performed at the phase of the cardiac cycle when chordal length reached its maximum. Measured values were compared with surgical measurements using linear regression and Bland-Altman analyses.
Result
One hundred forty-six primary chords were measured intraoperatively. Three-dimensional TEE imaging was able to measure the lengths of all these chords. The surgical and 3D TEE measurements (mean, 1.96 ± 0.56 vs 1.93 ± 0.50 cm, respectively) correlated highly ( r = 0.93, P < .0001), with a minimal bias of 0.03 cm and narrow limits of agreement from −0.39 to 0.45 cm.
Conclusion
Transgastric 3D TEE imaging of the submitral apparatus allows visualization and accurate measurement of chordae tendineae lengths, which may be useful for planning mitral valve repair, including percutaneous transcatheter procedures.
Three-dimensional (3D) transesophageal echocardiographic (TEE) imaging is a useful tool for the detailed evaluation of mitral valve anatomy and is essential for decision making regarding surgical strategy for mitral valve repair and assessment of postoperative results. Although 3D TEE imaging can accurately depict mitral valve leaflet morphology, visualization of the submitral apparatus is challenging from the conventional midesophageal approach. In degenerative mitral valve disease, superiority of repair over replacement in terms of improved outcomes is well established, and the strategy for mitral valve repair has recently focused on the restoration of leaflet coaptation and annular stabilization using neochord insertion without the need for leaflet resection. In patients with severely tethered leaflets and functional mitral regurgitation, it has been reported that the implantation of an undersized annuloplasty ring alone without additional surgical interventions is frequently not durable, and additional submitral surgery is required, including chordal cutting, papillary muscle approximation, and/or suspension. In these clinical scenarios, in addition to the recently established volumetric quantification of the mitral valve leaflets, the ability to visualize and measure mitral chords would be of surgical benefit because it would enhance the understanding of the in vivo dynamic subvalvular apparatus, as well as potentially facilitate the use of new technology, such as transapical and percutaneous mitral valve repair techniques.
In this study, we hypothesized that the use of 3D TEE imaging from the transgastric approach would allow visualization of the submitral apparatus and, by the use of two-dimensional multiplanar reconstruction (MPR) images, accurate measurement of chordal lengths. Accordingly, we designed a study to test the feasibility of using 3D TEE imaging from the transgastric approach to measure chordae tendineae lengths and compare the results to intraoperative measurements.
Methods
Patient Selection
Twenty-two consecutive patients who underwent 3D TEE imaging from the transgastric approach in the operating room before mitral valve surgery were included in this study. These patients had intraoperative measurements of chordae tendineae performed by the surgeon, including seven women (32%) and 15 men (68%) (mean age, 63 ± 11 years; range, 35–88 years). Patients with mitral stenosis, endocarditis, and functional mitral regurgitation were excluded, while atrial fibrillation was not an exclusion criterion. Of the 22 patients, 18 underwent sternotomy and four underwent endoscopic robotic surgery for mitral repair. In the cases of median sternotomy, neochord loops were prepared and replaced. In the robotic surgery cases, papillary muscles were sutured and sutures passed through the leaflet margins and tied after adjusting the length using a saline injection test.
Three-Dimensional TEE Imaging from the Transgastric Approach
After the induction of anesthesia and endotracheal intubation, and before cardiopulmonary bypass, electrocardiographically gated full-volume data sets were acquired over four consecutive cardiac cycles, using an iE33 echocardiographic imaging system with a TEE matrix-array transducer (model X72t; Philips Medical Systems, Andover, MA). The tip of the transducer was positioned in the fundus of the stomach with the transducer array at 0° to obtain short-axis views of the left ventricle. Short-axis views at the papillary muscle level were optimized by anteflexion and/or slight withdrawal of the transducer tip. Then, the multiplane angle was rotated to 90° to visualize both the anterolateral papillary muscle and posteromedial papillary muscle (PPM) in the mitral bicommissural view. By monitoring the biplane image, lateral and elevation angles were adjusted for the volume data set to contain the entire mitral annulus and the tip of both the anterolateral papillary muscle and the PPM. The lateral and elevation angles of the volume data set were minimized to maximize volume rates. When it was not feasible to capture all structures of interest in a single scan volume simultaneously, additional 3D data sets were acquired from different windows to include the missing structures. The ventilator was suspended during image acquisition to avoid stitch artifacts. In patients with frequent premature contractions or atrial fibrillation, efforts were made to acquire data sets with relatively regular R-R intervals.
Measurement of Primary Chords Using 3D TEE Imaging
Image Analysis by MPR
Offline analysis of the stored images was performed by an experienced echocardiographer blinded to surgical measurements using Philips QLAB software (version 9.0 with the 3DQ plug-in; Philips Medical Systems) as shown in Figure 1 . From the transgastric mitral bicommissural MPR plane, a reference line (blue line) was oriented to obtain a short-axis plane at the papillary muscle level, while a second reference line (red line) was selected as the long-axis plane orthogonal to the mitral bicommissural plane. The short-axis view allowed visualization of the papillary muscles, commissures, coaptation line, and aortic valve by changing the level of this blue plane along the long axis.
Identification of the Chords
Figure 2 shows how the short-axis plane at the chordal level just proximal to the papillary muscle tip was used to identify the chordal distribution, including primary, secondary, and tertiary chords. Primary (marginal) chords were defined as the chords that connect to the free margin of the leaflet; secondary (intermediate) chords connect to the ventricular side of the leaflet and tertiary (basal) chords extend from the papillary muscle or directly from the ventricular wall and are attached to the base of the posterior and commissural leaflets or to the annulus. Chords located at both ends of the “mouth” were identified as the chords for the lateral and medial commissural segments ( Figure 2 , right). The chords originating from the midsection of the “upper and lower lips” were identified as the chords for the mid anterior and posterior (A2 and P2) segments, respectively. The chords between the commissures and A2 and P2 segments were recognized as A1 and P1 and A3 and P3, respectively ( Figure 2 , right).
Selection of the Optimal Image to Measure Primary Chords
Figure 3 shows the methodology used to measure chordal length. Each chord identified on the short-axis view was visualized on the mitral bicommissural and long-axis planes. The long-axis view allowed identification of the coaptation point and separation of primary from secondary or tertiary chords ( Figure 3 , middle). On the long-axis plane, the reference line was precisely oriented along the primary chord ( Figure 3 , middle) to visualize its entire length from the leaflet margin to the papillary muscle tip on the mitral bicommissural plane. Measurements were performed on the mitral bicommissural plane where chordal lengths reached their maximum ( Figure 3 , right).
