Ann Thorac Surg 1999;67:494-499
© 1999 The Society of Thoracic Surgeons
Original Articles
Assessment of mitral regurgitant jets by three-dimensional color Doppler1
Raffaele De Simone, MDa,
Gerald Glombitza, PhDb,
Christian-Friedrich Vahl, MDa,
Jörg Albers, MDa,
Hans-Peter Meinzer, PhDb,
Siegfried Hagl, MDa
a Department of Cardiac Surgery, University of Heidelberg, Heidelberg, Germany
b Department of Medical and Biological Informatics, Deutsches Krebsforschungszentrum, Heidelberg, Germany
Accepted for publication September 12, 1998.
Address reprint requests to Dr De Simone, University of Heidelberg, Abteilung für Herzchirurgie, Im Neuenheimer Feld, 120 D-69120 Heidelberg, Germany
e-mail: r.de.simone{at}urz.uni-heidelberg.de
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Abstract
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Background. Color Doppler echocardiography is a standard technique for assessing mitral regurgitation before and after mitral valvuloplasty. Mitral valve prolapse produces complex eccentric jet flows that cannot be visualized and measured by two-dimensional color Doppler echocardiography. The aim of this study was to evaluate the clinical impact of three-dimensional color Doppler echocardiography, a new technique developed at our institution, for assessing mitral regurgitation.
Methods. Forty-five patients with mitral regurgitation underwent intraoperative transesophageal echocardiography and three-dimensional Doppler data acquisition. The grade of mitral regurgitation was assessed by angiography. The jet areas were calculated by planimetry from conventional color Doppler; the jet volumes were obtained by three-dimensional Doppler data.
Results. New patterns of mitral regurgitant flows were recognized according to the origin, direction, and spatial spreading into the left atrium. Conventional jet areas failed to separate the groups of patients with different degrees of regurgitation, whereas the jet volumes were able to divide patients with different regurgitation grades. No significant correlation was found between jet area and angiographic grading (r = 0.63, p = NS). Jet volumes were significantly correlated to angiography (r = 0.89, p < 0.001).
Conclusions. Three-dimensional color Doppler echocardiography revealed new patterns of regurgitant flow and allowed a more accurate semiquantitative assessment of complex asymmetrical regurgitant jets.
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Introduction
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Two-dimensional (2D) Doppler (or color Doppler) is the most popular technique for assessing patients with heart valve disease in clinical practice. Up to now the indications for surgical intervention and intraoperative decisions after valve repair have been based on the subjective estimation of regurgitation by color Doppler. However, most patients with mitral valve prolapse who undergo mitral valve repair show regurgitant jet flows that are so geometrically complex that they cannot be visualized and measured by 2D techniques. Color Doppler underestimates the severity of mitral regurgitation in those patients with a higher degree of regurgitation. Three-dimensional (3D) echocardiography [1–3] has been mainly applied for assessing intracardiac anatomy [4, 5] and for quantifying heart volumes [6–11]. We use a technique for 3D reconstruction of Doppler signals using the digital data directly derived from the echocardiographic scanner. Intracardiac Doppler flow images were displayed and studied in 3D and in original color coding, which provided new parameters for quantitative assessment of mitral regurgitation.
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Patients and methods
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Patients
Forty-five patients (mean age, 48.9 ± 13.1 years) with mitral regurgitation underwent echocardiographic examinations during cardiac operations. The grade of mitral regurgitation was assessed by left ventricular angiography on a scale from I to IV according to Sellers and colleagues [12]. Ten patients had grade I mitral regurgitation, 13 patients grade II, 10 patients grade III, and 12 patients grade IV, according to preoperative left ventricular angiography.
Data acquisition and analysis
The echocardiographic examinations were performed using commercially available equipment (Sonos 2500, Hewlett-Packard, Andover, MA) with a multiplanar transesophageal probe (5 MHz). The 3D acquisitions were obtained by rotating the transesophageal transducer, which was steered by a step motor. The acquisition was accomplished by 2-degree increments to obtain 90 slices during 90 heart cycles. The data acquisition was triggered to the R wave on electrocardiography and to the respiratory cycle. The Doppler data stored on magneto-optical disks contain information on velocity and turbulence. Regurgitant jets were defined as the fast, turbulent flow component located above the atrioventricular valves (Fig 1). The areas of the regurgitant jet (in square centimeters) were traced on the systolic frame from the 2D images taken at the rotation angle at which the greatest area could be measured. The volumes of the regurgitant jet (in cubic centimeters) were calculated from the Doppler data by counting the units of volume (voxels) with high velocity and turbulence from 3D Doppler images.
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Fig 1. Example of the segmentation procedure. (Left) Color Doppler image showing a typical turbulent, high-velocity regurgitant jet. (Right) Extraction of turbulence and high-velocity components. (LA = left atrium; LV = left ventricle; m = mitral valve.)
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The 3D reconstructions of Doppler data were obtained by means of the Heidelberg Raytracing Algorithm, initially developed at our institutions [13, 14] for visualizing computed tomographic and magnetic resonance images. Jet morphology was classified according to the spatial distribution within the left atrium [15]: eccentric (or asymmetrical) jets were directed toward lateral or septal left atrial walls or along the mitral valve leaflets; and central jets originated from the middle of the mitral valve and did not strike atrial walls or mitral valve leaflets.
Statistical analysis
All data are reported as mean ± SD. Linear regression analysis was used to describe the correlations of jet volumes and jet areas with the angiographic grade of mitral regurgitation. Differences between groups with a different degree of mitral regurgitation and between groups of patients with central and eccentric jets were assessed by Student’s t test for unpaired data. Differences were considered statistically significant at a value of p less than 0.01.
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Results
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The 3D images of the mitral regurgitant jets provided unique geometric information about the origin, direction, shape, extension, and size of the regurgitant jets and provided a useful parameter for semiquantitative and quantitative assessment of mitral regurgitation. A movie simulating the rotation of the observer from 0° to 360° around the 3D images showed the details, direction, and morphology of the jets. To maintain the examiner’s orientation, the rotational axis of the observer was the same as that used for data acquisition by transesophageal echocardiography.
Adequate reconstructions of the Doppler signals were achieved in all patients. The 3D reconstructions and jet volume measurements were obtained in 3 to 5 minutes according to the different angle resolutions. The 3D images were displayed on a portable personal computer (PowerBook, Apple Computer, Cupertino, CA). The regurgitant jets were visualized in 3D by showing the systolic frame with the largest jet volume. Central, symmetrical regurgitant jets were found in 21 of 45 patients. Twenty-four patients showed eccentric, asymmetrical regurgitant jets. The 3D reconstructions of the asymmetrical regurgitant jets allowed us to describe completely new patterns of mitral regurgitant flows not observed before.
Morphology of regurgitant jets
This technique allowed the 3D and four-dimensional visualization of valvular regurgitant jets and a classification according to their spatial distribution (Table 1). Examples of different regurgitant jet patterns are shown in Figures 2–5.
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Fig 2. Three-dimensional reconstruction of color Doppler echocardiography. (Left) Conventional two-dimensional Doppler image showing a central regurgitant jet. (Right) Three-dimensional images of central jets do not provide additional information about the geometry and the spreading of the regurgitant flow into the left atrium. (LA = left atrium; LV = left ventricle; m = mitral valve.)
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Fig 3. The regurgitant jets in patients with prolapse of the posterior mitral leaflet are mainly directed along the atrial surface of the anterior leaflet and are parallel to the main mitral annulus plane. (Left) Conventional two-dimensional color Doppler image. (Right) Three-dimensional color Doppler image. (Upper panels) Circular regurgitant orifice generates a jet with a "cylinder" pattern. (Lower panels) Elliptical regurgitant orifice produces a jet with a "tongue" pattern.
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Fig 4. Regurgitant jets in patients with prolapse of the anterior mitral leaflet. (Left) Conventional two-dimensional color Doppler image. (Right) Three-dimensional color Doppler image. (Upper panels) Circular regurgitant orifice generates a jet with a "spiral" pattern. (Lower panels) Elliptical regurgitant orifice produces a jet with a "fan" pattern. Three-dimensional Doppler image shows that the lateral expansion of the jet cannot be perceived by conventional two-dimensional Doppler echocardiography.
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Fig 5. Different patterns of mitral regurgitant jets. The irregular morphology of these jets can be visualized by three-dimensional Doppler echocardiography. (Left) Conventional two-dimensional color Doppler image. (Right) Three-dimensional color Doppler image. (Upper panels) Conventional two-dimensional Doppler echocardiography can visualize only a small portion of the regurgitant jets. Three-dimensional Doppler echocardiography reveals that the mitral regurgitation consists of two separate jets (arrowheads). (Lower panels) Severe mitral valve regurgitation with systolic reverse flow in the pulmonary veins (*).
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In patients with central jets the spatial distribution and the degree of mitral regurgitation can also be assessed by 2D imaging because its geometry is well predictable, as can be observed in Figure 2. In contrast, 3D reconstruction of more complex regurgitant jets renders 3D images that cannot be "mentally" conceived even by the most experienced examiner. In patients with eccentric jets because of mitral valve prolapse, two main patterns of regurgitant jets can be distinguished according to 3D Doppler images: (1) those deriving from posterior leaflet prolapse and (2) those from anterior leaflet prolapse. In our series of patients these patterns of regurgitant jets could be systematically recognized. The jets coming out from the posterior leaflet were directed along the atrial surface of the anterior leaflet and could be compared with a "cylinder" or a "tongue" of flow oriented parallel to the main mitral annulus plane (Fig 3), according to the shape of the regurgitant orifice. A circular regurgitant orifice generates jets with a cylinder pattern; elliptical regurgitant orifices produce jets with the tongue pattern. The regurgitant jets coming out from the anterior leaflet also showed two different patterns. The first, caused by a circular regurgitant orifice, appears like a "spiral" with a thin initial portion perpendicular to the annulus plane; these jets impinge on the roof of the left atrium and curve their directions to form an arch according to the curvature of the atrial wall (Fig 4). The second pattern, caused by elliptical regurgitant orifices, includes jets with a wide and relatively short initial portion, parallel to the annulus plane; they strike the posterior atrial wall and spread laterally, like a "fan" or a "spoon," according to the lateral curvature of the atrial walls (Fig 4). Other irregular shapes of the regurgitant orifice produce different patterns of regurgitant jet flows (Fig 5).
Quantitative assessment of regurgitant jets
Table 2 shows the data of the patients with central and eccentric jets. The angiographic degree of mitral regurgitation, maximal jet area, and 3D jet volume were significantly greater in patients with eccentric jets. The jet areas, measured by conventional 2D color Doppler, failed to separate the groups of patients with different degrees of mitral regurgitation, whereas the jet volumes calculated by 3D Doppler, were able to separate these groups of patients. Jet area did not show a significant correlation to the angiographic grading (r = 0.63; 
p = NS). In contrast, jet volumes were significantly correlated (r = 0.77; 
p < 0.001) to the angiographic grade of mitral regurgitation (Fig 6).
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Fig 6. (A) Scatterplot of jet area and angiographic grading of mitral regurgitation. Considerable overlap between the groups is evident. (B) Scatterplot of jet volume and angiographic grading shows significant separation of groups of patients with different degrees of mitral regurgitation. (*p < 0.01 compared with grade I; **p < 0.01 compared with grade II; ***p < 0.01 compared with grade III; otherwise, p = NS.)
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Comment
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The assessment of mitral valve regurgitation in clinical settings has been commonly based on the semiquantitative evaluation of color Doppler (2D Doppler) [16–18]; however, color Doppler underestimates the severity of mitral regurgitation, particularly in those patients with eccentric jets, caused by mitral valve prolapse, and a higher degree of regurgitation [15]. The clinical management, indications for surgical intervention, and intraoperative decisions after valve repair [19–22] have been based on a subjective estimation of valve regurgitation by conventional 2D color Doppler. The present study shows the clinical applications of 3D color Doppler. Although the technique is still under development, this investigation offers insights that may change the clinical management of patients with valvular regurgitation [23]. The quantification of mitral valve regurgitation is still a controversial issue in spite of the large number of investigations that have dealt with this topic. Invasive assessment of mitral regurgitation, which is based on the calculation of mitral regurgitant volumes (obtained by thermodilution or indicator dilution and by angiography) has two obvious, major limitations: the use of two different methods for volume measurements and the dependence of angiography on geometric assumptions about the left ventricular cavity. There is common agreement that no gold standard is available for the clinical measurement of regurgitant volumes [24]. In contrast, the 3D reconstruction of color Doppler signals provides unique information about the direction, extent, and size of regurgitant jets. New patterns of regurgitant flow, not described previously, can be observed and studied by this technique (Figs 2–5). The value of 3D Doppler imaging of regurgitant jets goes beyond the mere visualization of the complex geometry of asymmetrical regurgitation flows; indeed, it provides a system for displaying and measuring the turbulence and high-velocity components of the jets. Two fully automated procedures were used for jet volume measurements: (1) the jet segmentation, based on the selection of turbulence and high-velocity components, and (2) the computation of all volume units (voxels) containing the selected Doppler information (Fig 1). Both procedures are independent of manual planimetry or subjective estimation and allow more precise measurements not only of 3D jet volumes but also of 2D jet areas. These procedures hold promise of becoming essential tools for a reliable quantitative assessment of mitral regurgitation in clinical practice.
Many methods based on the size of regurgitant jets have been proposed for clinical quantification of mitral regurgitation by color Doppler echocardiography [18–20]. However, conventional 2D assessment of asymmetrical regurgitant jets fails to estimate the severity of mitral regurgitation [15]. An important finding of our investigation was the significant correlation found between 3D jet volumes and the angiographic grade of mitral regurgitation in patients with eccentric jets.
The absence of a gold standard for quantitative assessment of valve regurgitation is a major limitation of all clinical studies that have dealt with mitral regurgitation. The angiographic grade of mitral regurgitation [12, 25], used in our study for comparing the quantitative assessments of 3D jet volumes, is an imperfect but clinically accepted parameter. The changes of jet volumes during systole should be taken into account to understand the actual correlation between the volumes obtained from color Doppler data. In our study, maximal systolic jet volumes were used for comparison with conventional jet areas (taken at maximal systolic expansion) to preserve the comparability of our data to previously published studies [15, 16, 18, 20]. Mitral regurgitation depends not only on the pressure gradient (or driving pressure), but also on the orifice size. We analyzed the relationship between the driving pressure (difference between left ventricular systolic pressure and mean pulmonary wedge pressure) and the angiographic degree of mitral regurgitation, jet areas, and jet volumes: no correlation was found. These findings demonstrate that, in addition to the driving pressure, the orifice size plays an important (and perhaps major) role in determining the jet appearance and the magnitude of mitral regurgitation. Previous attempts to quantify the orifice size of mitral regurgitation have been unsuccessful.
The primary aim of the present study was not to assess the precision of Doppler echocardiography for quantifying mitral regurgitation, but rather to assess the clinical practicality of 3D color Doppler echocardiography and to investigate its possible clinical applications. The significant correlations between 3D jet measurements and angiography showed that this technique provides a good estimation of mitral regurgitation; however, these findings need to be confirmed by a systemic use of this parameter in clinical practice.
The 3D reconstruction of color Doppler signals and the visualization in original color coding is still under investigation [26–28]. Formerly, regurgitant jets could only be visualized in gray-scale format [26]. These previous approaches did not allow the separation between cardiac structures and flow and the separation between the different components of intracavitary flow. These methods use video signals, which only carry poor information and prevent a separate visualization of cardiac structures and flow. In addition, the quantitative analysis of single-flow jet components and the differentiation of slow velocities from turbulent flows could not be performed. By using digital signals coming directly from the echo equipment, the Doppler signals can be distinguished from cardiac structures, thus avoiding inaccurate manual segmentation for visualizing the regurgitant jets and for measuring the jet volumes.
In conclusion, these 3D Doppler images reveal how complex the geometry and how misleading the visual assessment or the planimetry of the regurgitant jets based on 2D Doppler echocardiography can be. The perioperative assessment of mitral valve regurgitation during valvuloplasty needs a major revision according to the new insights derived from 3D reconstructions of Doppler flow signals. Whether this new technique can provide the surgeon with an active assistance in the operating room during valve repair still needs to be assessed by a systematic intraoperative use of 3D Doppler echocardiography. Although this study clearly proves the important impact of 3D color Doppler for the assessment of valvular regurgitation, further investigations are needed to atest the clinical usefulness of this technique.
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Acknowledgments
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This work was supported by the German National Foundation for Scientific Research (SFB 414).
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Footnotes
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1 A video clip of this procedure can be viewed on the Internet at http://www.sts.org/section/atsvideo/ 
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Abstract
Introduction
