Background
The strategy for mitral valve (MV) repair has recently focused on the restoration of the submitral apparatus. However, the relationship between geometric changes of the submitral apparatus and the mitral leaflets has not been systematically investigated. The aim of this study was to determine the relationships among chordal length (CL) and LV size and leaflet surface area (LSA) in normal subjects, patients with primary (degenerative) mitral regurgitation (PMR), and patients with functional (secondary) mitral regurgitation (FMR).
Methods
A total of 72 patients who underwent three-dimensional transesophageal echocardiography, including: 27 with PMR with isolated P2 flail leaflet, 25 with FMR with greater than mild mitral regurgitation, and 20 with normal mitral valves. LSA was quantified at midsystole from full-volume midesophageal views. CL was calculated by averaging the lengths of eight primary chords from transgastric full-volume data sets using multiplanar reconstruction.
Results
Both CL and LSA in the PMR group were significantly longer compared with the FMR and normal control groups. No difference in CL was noted between patients with FMR and normal subjects. In all three groups, CL and LSA did not correlate with LV systolic or diastolic dimensions. Although CL did not correlate with LSA in the FMR group, a moderate correlation ( R = 0.62) was observed in the PMR group.
Conclusions
In patients with FMR with greater than mild mitral regurgitation, the chords retain normal length, despite LSA and LV enlargement. In patients with PMR with flail P2 scallops, CL elongation of primary chords is associated with larger LSA but not with LV dimensions. This information may have implications for clinical strategies for mitral valve repair surgery, including the submitral approach and percutaneous procedures.
In patients with primary (degenerative) mitral regurgitation (PMR), the superiority of mitral valve (MV) repair over replacement in terms of improved outcomes is well established. The strategy for MV repair has recently focused on the restoration of the submitral apparatus, using neochord implantation, frequently performed without leaflet resection. In patients with functional (secondary) mitral regurgitation (FMR) with severely tethered leaflets, it has been reported that the insertion of an undersized annuloplasty ring frequently fails to control mitral regurgitation (MR), and accordingly, additional submitral surgery strategies have been proposed, including chordal cutting, papillary muscle approximation, and/or suspension. In both these clinical scenarios, preoperative quantification of the submitral apparatus would be of clinical benefit. However, data on echocardiographic imaging aimed at quantifying the submitral apparatus are scarce.
Degenerative MV disease includes chordal abnormalities that are associated with a spectrum of leaflet lesions. In FMR, leaflet adaptation accompanied by secondary chordal elongation has been described as a compensatory mechanism. In both these scenarios, three-dimensional (3D) echocardiographic imaging has provided valuable volumetric measurements of the mitral leaflets, but little has been described with respect to chordal morphology. To date, it remains unclear whether leaflet elongation in FMR and PMR is associated with chordal elongation. Accordingly, the aim of this study was to measure chordal length (CL) in PMR and secondary MR and determine the relationship between CL and leaflet surface area (LSA) in patients with FMR and PMR and in normal subjects.
Methods
Patients
A total of 72 patients, including 27 with severe PMR (mean age, 60 ± 14 years; 22 men) and 25 with FMR with more than mild MR due to dilated left ventricles with reduced left ventricular (LV) function (mean age, 62 ± 13 years; 20 men), as well as 20 patients with normal MV morphology (the normal control group; mean age, 56 ± 13 years old; 16 men) were studied with 3D transesophageal echocardiography (TEE). Normal controls were selected from patients who underwent 3D TEE for the assessment of a cardioembolic source of stroke. In this group, patients were excluded if they had more than mild MR, reduced LV ejection fraction (LVEF) (<52% in men, <54% in women) or increased LVEF (>72% in men, >74% in women), or dilated left ventricles, according to current guidelines. The normal range of LV size was defined as a linear LV end-diastolic dimension (LVDd) between 42.0 and 58.4 mm in men and between 37.8 and 52.2 mm in women. The FMR group included 11 patients with ischemic and 14 with nonischemic etiologies. This group consisted of patients with LVDd > 60 mm and LVEF < 30%, who were studied at the time of coronary artery bypass graft surgery with ( n = 3) or without ( n = 1) MV surgery, MV surgery alone ( n = 4), and LV assist device implantation ( n = 17). Patients with structurally abnormal MVs were excluded. The PMR group consisted of patients who underwent MV repair surgery for severe MR with isolated P2 ruptured chord(s) without evidence for significant leaflet thickening or excess tissue in other leaflet scallops. In both the FMR and PMR groups, 3D TEE was performed in the operating room after the induction of anesthesia and endotracheal intubation and before cardiopulmonary bypass.
Three-Dimensional Imaging and Analysis
Images were acquired using an iE33 imaging system equipped with a fully sampled 3D matrix-array TEE transducer (model X72t; Philips Medical Systems, Andover, MA). Electrocardiographically gated full-volume data sets of the MV were acquired from the midesophageal and transgastric approach over four consecutive cardiac cycles. When imaging from the midesophageal approach, attention was paid to ensure that the central ultrasound beam was kept parallel to the LV long axis. This allowed the ultrasound beam to traverse the mitral annular plane and optimize MV leaflet visualization. When imaging from the transgastric approach, care was taken to have the ultrasound beam perpendicular to the LV long axis to optimize chordal visualization. From both approaches, sector width and imaging depth were minimized to maximize spatial and temporal resolution.
Analysis of Transgastric Images
Full-volume data sets obtained from the transgastric approach were exported to dedicated analysis software (QLAB version 9.0 with the 3DQ plug-in; Philips Medical Systems) for multiplanar reconstruction. The detailed primary chordal measurement method using 3D TEE has been recently described by our group. Briefly, after the short-axis plane ( Figure 1 , left ) was extracted to identify the root of the chords and their distribution, the long-axis plane ( Figure 2 , middle row ) was visualized to separate primary chords from secondary or tertiary chords. Fine adjustment of the reference line in this long-axis plane allows visualization of the entire CL of the primary chord in the corresponding mitral bicommissural plane ( Figure 2 , right row ). In each patient, the entire length of the primary chords was visualized in all eight segments: A2 lateral, A1, P1, P2 lateral, A2 medial, A3, P3, and P2 medial ( Figure 1 , right ). The dominant chord in each segment was selected for measurement. Accordingly, eight CLs were measured in each patient, and the lengths of the eight chords were averaged to calculate CL. LVDd and LV end-systolic dimension were measured in the extracted LV short-axis multiplanar reconstructed view at the papillary muscle level.
Analysis of Midesophageal Images
The full-volume data sets acquired from the midesophageal approach were exported to different analysis software (Image Arena, 4D-MV Assessment 2.3; TomTec Imaging Systems, Unterschleissheim, Germany). A midsystolic volume data set was selected, and the leaflet surface was automatically identified. Rotational cross-sections of the mitral annular plane centered at the midanterior annulus as well as the center point of the mitral annulus were used to verify the correct positioning of the data set. Manual edits were performed in cases of inadequate automated tracing. Cine loops were used for precise identification of leaflet configuration at midsystole. In addition to LSA, annular height and annular perimeter were measured.
Two-Dimensional Imaging and Analysis
Standard two-dimensional (2D) transthoracic echocardiography was also performed before surgery on the iE33 (Philips Medical Systems). LV end-diastolic volume (LVEDV) and end-systolic volume (LVESV) were measured using the biplane disk summation method, and LVEF was calculated as [(LVEDV − LVESV)/LVEDV] × 100. The MR grade in the FMR group was quantified during intraoperative 2D TEE, using vena contracta width, which was measured as the narrowest portion of the regurgitant jet as it enters the receiving chamber in the long-axis view perpendicular to the coaptation line at midsystole. More than mild MR in the FMR group was defined as vena contracta width ≥ 0.3 cm.
Reproducibility
Inter- and intraobserver variability for the CL measurements was assessed in 10 randomly selected patients by repeated measurements. To determine interobserver variability, two observers independently measured 60 chords in these patients, while being blinded to all prior measurements. To determine intraobserver variability, one observer repeated the measurements in 80 chords ≥1 month later to minimize recall bias.
Statistical Analysis
All measurements are expressed as mean ± SD. Comparisons between groups were performed using two-tailed t tests. P values < .05 were considered significant. The relationships among the measurements of CL, LSA, LV dimensions, annular height, and perimeter were calculated using linear regression analysis with Pearson correlation coefficients. Inter- and intraobserver variability was evaluated by calculating interclass correlation coefficients and absolute differences between the corresponding repeated measurements as percentages of their mean values.
Results
There were no intergroup differences in age and body surface area. LVDd was largest in the FMR group, followed by the PMR group. LV end-systolic dimension was largest and LVEF was lowest in the FMR group, while no difference in LV end-systolic dimension and LVEF were noted between the normal and PMR groups. Three-dimensional measurements of annular perimeter and LSA were largest in the PMR group, followed by FMR, and smallest in the normal group. Annular height was lowest in the FMR group, whereas no differences were noted between the normal and PMR groups ( Table 1 ). Examples of representative reconstruction images of the 3D measurements of annulus and leaflets in a normal subject and in patients with FMR and PMR are shown in Figure 3 .
| Variable | NL group ( n = 20) | FMR group ( n = 25) | PMR group ( n = 27) |
|---|---|---|---|
| Age (y) | 56 ± 13 | 62 ± 13 | 60 ± 14 |
| Body surface area (m 2 ) | 2.04 ± 0.28 | 1.94 ± 0.26 | 1.92 ± 0.23 |
| LVDd (cm) | 4.8 ± 0.5 | 7.2 ± 1.0 ∗ | 5.3 ± 0.6 †‡ |
| LV end-systolic dimension (cm) | 3.2 ± 0.4 | 6.5 ± 1.0 ∗ | 3.4 ± 0.5 ‡ |
| LVEF (%) | 62.9 ± 6.3 | 20.6 ± 5.8 ∗ | 61.4 ± 6.3 ‡ |
| Annular height (cm) | 0.56 ± 0.14 | 0.45 ± 0.15 ∗ | 0.66 ± 0.21 ‡ |
| Annular perimeter (cm) | 10.7 ± 1.0 | 11.9 ± 1.3 ∗ | 13.3 ± 1.8 †‡ |
| LSA (cm 2 ) | 9.3 ± 1.7 | 13.1 ± 3.0 ∗ | 15.2 ± 4.3 †‡ |
| Averaged CL (cm) | 1.65 ± 0.29 | 1.62 ± 0.27 | 2.13 ± 0.34 †‡ |
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