| | Three-Dimensional Quantitation of Mitral Valve Coaptation by a Novel Software System with Transthoracic Real-Time Three-Dimensional Echocardiography published online 12 July 2007. We investigated the degree of mitral valve coaptation with a custom quantitation software system using transthoracic three-dimensional (3D) echocardiography. With real-time 3D echocardiography, we obtained transthoracic volumetric images in 20 healthy subjects and 20 patients with dilated cardiomyopathy. With our novel software system, the surface area of mitral valve tenting in the onset of mitral leaflet closure [O] and the timing of maximum closure of mitral leaflet [M] were reconstructed for quantitative measurement. The coaptation index was calculated by the following formula: [(3D tenting surface area in O-3D tenting surface area in M)/3D tenting surface area in O]. The coaptation index in patients with dilated cardiomyopathy was significantly smaller than that in healthy subjects (11% ± 4.1% vs. 18% ± 8.0%, P = .004). The custom quantitation software system with 3D echocardiography allowed us to assess the degree of mitral valve coaptation. Functional mitral regurgitation (MR) occurs as a consequence of regional or global left ventricular (LV) dysfunction despite a structurally normal mitral valve. It is widely noted that development of functional MR in ischemic or nonischemic dilated cardiomyopathy (DCM) predicts a poor clinical outcome.1, 2, 3 Mitral valve repair with an undersized annuloplasty ring has traditionally focused on restoring coaptation of mitral leaflets in these patients.4 In functional MR, restriction of leaflet closure occurs as a result of dilatation of the mitral annulus, enhanced tethering force of the mitral valve leaflets, papillary muscles displacement, and reduced closing force of the leaflets.5, 6, 7, 8 The degree of mitral valve leaflet coaptation should be an important parameter in the assessment of functional MR. However, there have been no imaging modalities to evaluate the actual degree of coaptation, so that tenting area,9, 10 tenting depth,11 or tenting length12 has been used as a substitute for the coaptation in the clinical setting. Recently, we successfully demonstrated the three-dimensional (3D) quantitation of mitral apparatus geometry using a custom software system with 3D echocardiography in human beings, and our previous reports clearly showed bulged mitral leaflets toward the LV in functional MR with LV dysfunction.13, 14, 15, 16, 17 In this study, we investigated the degree of mitral valve coaptation with the use of the custom quantitation software system with transthoracic real-time 3D echocardiography. Methods  Patient Population Twenty patients with DCM were recruited for 3D echocariographic examination (14 men, age 67 ± 15 years). Twenty healthy subjects were also examined as controls (16 men, age 62 ± 8.0 years). Exclusion criteria were (1) organic mitral valve or subvalvular lesions (e.g., mitral leaflet prolapse or rheumatic disease); (2) other cardiac disease (e.g., ischemic, pericardial, congenital, or infiltrative heart disease); and (3) arrythmia (e.g., atrial fiblilation). The study protocol was approved by the Human Subjects Committee at Kawasaki Medical School. Echocardiographic Protocol All of the echocardiographic examinations were performed by using ultrasound equipment (SONOS 7500 and iE33, Philips Medical Systems, Bothell, WA) with S3 probe for two-dimensional (2D) images and X4 or X3-1 probe for real-time 3D images. Two-Dimensional Echocardiographic Study All patients underwent a standard 2D echocardiographic examination. LV end-diastolic volume (EDV) and end-systolic volume (ESV) were measured by biplane Simpson’s method. Ejection fraction (percent) was calculated by the equation: 100 × (EDV-ESV)/EDV. MR was evaluated by color Doppler echocardiography. Three-Dimensional Echocardiographic Study Volumetric image acquisition Transthoracic volumetric images (full-volume mode) with the apical view were obtained using a real-time 3D echocardiographic system in all the subjects. The volumetric frame rate was 15 to 19 frames/second, with an imaging depth of 15 to 18 cm. Before acquiring the full volume image, we carefully adjusted the transducer position at the apex in a biplane mode. All of the volumetric images were digitally stored on compact disk and transferred to a personal computer for offline analysis. Quantification of mitral valve coaptation by three-dimensional echocardiography Our custom quantitation software system was used to analyze the volumetric images. First, in a cross-sectional plane of the mitral annulus, we defined the center of the mitral annulus in the volumetric image to set the axis through the transducer position and the center of the annulus. We also determined the anterior-posterior axis and commissure-commissure axis in the volumetric image. The 3D data were automatically cropped into 18 radial planes spaced 10 degrees apart (Figure 1). We manually marked the annulus (Figure 1, left) and traced the leaflets (Figure 1, right) in each cropped plane in the following two frames: (1) the onset of mitral leaflet closure [O] and (2) the timing of maximum closure of mitral leaflet [M]. The onset of mitral leaflet closure [O] and the timing of maximum closure of mitral leaflet [M] were defined by careful visual inspection. From these data, anatomic 3D images of the mitral valve apparatus were reconstructed for quantitative measurement (mitral annular area, circumference, and leaflet tenting volume). 3D tenting surface area was calculated from the 3D dataset as well. The 3D tenting surface area does not include coaptated leaflet area in this study (Figure 2, top). When the mitral valve closes, the tips of leaflets firstly touch and then as the leaflets coapt, the tenting surface area decreases. Thus, changes in the tenting surface area in these two frames reflect the degree of mitral valve coaptation. Coaptation index was defined as the following formula: [(3D tenting surface area in O-3D tenting surface area in M)/3D tenting surface area in O]. These data were compared in the two groups. Statistical Analysis Data are expressed as the mean value ± standard deviation. The comparisons between the groups were performed with the Student t test. A P value less than .05 was considered significant. Results Baseline Characteristics The baseline characteristics were shown in Table. There were no differences in age, sex, and body surface area between the two groups. LV end-diastolic diameter, LV end-systolic diameter, and left atrial diameter in patients with DCM were significantly larger comparing with the healthy subjects. Ejection fraction in patients with DCM significantly decreased compared with those in the healthy subjects. More than moderate MR was seen in 9 of 20 patients with DCM. | ⁎ Measured in the timing of maximum closure of mitral leaflets. |
Mitral Annular and Leaflet Geometry The 3D images in the two particular frames reconstructed by our custom quantitation software system are shown in Figure 2 (bottom). The mitral annular area and mitral annular circumference in patients with DCM were larger than those in the healthy subjects. Coaptation index in patients with DCM was significantly smaller than that in the healthy subjects (11% ± 4.1% vs. 18% ± 8.0%, P = .004). The results of the 3D measurements are summarized in the Table. Discussion In the present study, we investigated whether the degree of mitral valve coaptation in patients with DCM was significantly smaller than that in healthy subjects by using a novel software system with transthoracic real-time 3D echocardiography. Functional MR characterized by structurally normal leaflets and subvalvular apparatus is associated with excess mortality. Mitral annular dilatation, tethering of mitral leaflets secondary to LV dilatation with outward displacement of papillary muscles, and reduced transmitral pressure to coapt the leaflets are implicated as mechanisms for functional MR. However, it has been difficult to appreciate the 3D morphology of the complicated mitral valve leaflets and annulus by conventional 2D echocardiography. Real-time 3D echocardiography is a promising tool that allows us to address the mechanisms of functional MR in patients with global LV dysfunction. Recently, we successfully demonstrated the geometric deformity of the whole mitral leaflet and annulus by using our custom software with transthoracic real-time 3D echocardiography. Our previous report clearly showed globally bulged mitral leaflets toward the LV in patients with functional MR.13, 14, 15, 16, 17 Coaptation of the mitral valve is displaced apically away from the level of the mitral annulus in LV dysfunction, such as DCM or ischemic cardiomyopathy. In such conditions, the coaptated leaflet area should be decreased. The degree of mitral valve leaflet coaptation should be an important parameter in the assessment of functional MR. However, there have been no imaging modalities to evaluate the actual degree of coaptation. Thus, tenting area,9, 10 tenting depth,11 or tenting length12 by conventional 2D echocardiography has been used as a substitute for the coaptation in the clinical setting. Annuloplasty is an effective surgical strategy that has significant advantages over valve replacement in functional MR.18, 19 The degree of leaflet coaptation should be an important parameter in the assessment of pre- and postoperative valve geometry and function. However, evaluation of the actual degree of coaptation has been limited by conventional 2D echocardiography. 3D echocardiography is a promising technique that can provide precise 3D geometry, which has been difficult to understand by conventional 2D echocardiography. The present study demonstrated the feasibility of 3D echocardiography in the quantitative assessment of mitral leaflet coaptation. Further clinical trials are needed to assess whether quantitative parameters obtained from real-time 3D echocardiography would contribute to evaluate further mechanism of functional MR and then be a guide in selecting the proper surgical strategy in each individual in the clinical setting. Study Limitations The study limitations are as follows: (1) The real-time 3D echocardiography that is currently available in the clinical setting provides images with a lower frame rate than conventional 2D echocardiography. (2) This method is based on the hypothesis that the mitral leaflets closure is almost symmetric in patients with DCM. Another approach should be considered in particular conditions such as apparent detachment or gap of the tips of the leaflets during systole. Conclusions The custom quantitation software system with 3D echocardiography allows us to assess the degree of mitral valve coaptation. The coaptation index in patients with DCM was significantly smaller than that in control subjects. References 1. 1Junker A, Thayssen P, Nielsen B, Andersen PE. The hemodynamic and prognostic significance of echo-Doppler-proven mitral regurgitation in patients with dilated cardiomyopathy. Cardiology. 1993;83:14–20. 2. 2Blondheim DS, Jacobs LE, Kotler MN, Costacurta GA, Parry WR. Dilated cardiomyopathy with mitral regurgitation: decreased survival despite a low frequency of left ventricular thrombus. Am Heart J. 1991;122:763–771. MEDLINE |
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a Department of Cardiology, Kawasaki Medical School, Kurashiki, Japan b Department of Medical Engineering and Systems of Cardiology, Kawasaki Medical School, Kurashiki, Japan.  Reprint requests: Miwako Tsukiji, MD, Department of Cardiology, Kawasaki Medical School, 577 Matsushima, Kurashiki, 701-0192, Japan.
PII: S0894-7317(07)00398-7 doi:10.1016/j.echo.2007.05.023 © 2008 American Society of Echocardiography. Published by Elsevier Inc. All rights reserved. | |
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