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432
JACC Vol. 32, No. 2
August 1998:432–7
Three-Dimensional Echocardiographic Planimetry of Maximal
Regurgitant Orifice Area in Myxomatous Mitral Regurgitation:
Intraoperative Comparison With Proximal Flow Convergence
CHRISTIAN S. BREBURDA, MD,* BRIAN P. GRIFFIN, MD, FACC, MIN PU, MD,
LEONARDO RODRIGUEZ, MD, DELOS M. COSGROVE, III, MD, JAMES D. THOMAS, MD, FACC
Cleveland, Ohio
Objectives. We sought to validate direct planimetry of mitral
regurgitant orifice area from three-dimensional echocardiographic reconstructions.
Background. Regurgitant orifice area (ROA) is an important
measure of the severity of mitral regurgitation (MR) that up to
now has been calculated from hemodynamic data rather than
measured directly. We hypothesized that improved spatial resolution of the mitral valve (MV) with three-dimensional (3D) echo
might allow accurate planimetry of ROA.
Methods. We reconstructed the MV using 3D echo with 3°
rotational acquisitions (TomTec) using a transesophageal (TEE)
multiplane probe in 15 patients undergoing MV repair (age 59 6
11 years). One observer reconstructed the prolapsing mitral
leaflet in a left atrial plane parallel to the ROA and planimetered
the two-dimensional (2D) projection of the maximal ROA. A
second observer, blinded to the results of the first, calculated
maximal ROA using the proximal convergence method defined as
maximal flow rate (2pr2va, where r is the radius of a color alias
contour with velocity va) divided by regurgitant peak velocity
(obtained by continuous wave [CW] Doppler) and corrected as
necessary for proximal flow constraint.
Results. Maximal ROA was 0.79 6 0.39 (mean 6 SD) cm2 by 3D
and 0.86 6 0.42 cm2 by proximal convergence (p 5 NS). Maximal
ROA by 3D echo (y) was highly correlated with the corresponding
flow measurement (x) (y 5 0.87x 1 0.03, r 5 0.95, p < 0.001) with
close agreement seen (DROA (y 2 x) 5 0.07 6 0.12 cm2).
Conclusions. 3D echo imaging of the MV allows direct visualization and planimetry of the ROA in patients with severe MR
with good agreement to flow-based proximal convergence measurements.
(J Am Coll Cardiol 1998;32:432–7)
©1998 by the American College of Cardiology
The mitral valve (MV) apparatus has a complex threedimensional (3D) structure, especially in the presence of
myxomatous degeneration with leaflet prolapse or flail. Although excellent images of the MV are obtainable by twodimensional (2D) echocardiography (1), a full appreciation of
the 3D morphology is often lacking.
The regurgitant orifice area (ROA) is a fundamental measure of valvular incompetence, which may be used to follow the
regurgitant severity over time. ROA may be measured using
Doppler echocardiographic examination of the proximal convergence zone (2), the difference in flow across regurgitant and
nonregurgitant valves (3), and direct measurement of the jet
vena contracta (4), but these techniques are time consuming,
technically demanding, and affected by the geometry of the
regurgitant flow field and by machine factors, limiting utilization in the clinical setting. Ideally, ROA would be measured
directly similar to the orifice area of stenotic valves, but 2D
echocardiographic definition of ROA is difficult because of the
complex geometry involved. This is unfortunate because an
integrated assessment of mitral morphology and regurgitant
severity is used in deciding the repairability of the MV and the
appropriate timing of surgery (5–7).
Three-dimensional echocardiography is an evolving technology (8) that can improve on 2D echo in the depiction of MV
pathology (9,10). We have recently used intraoperative 3D
reconstruction of the MV to better characterize the location
and extent of leaflet prolapse (11), suggesting that the improved spatial orientation and resolution of 3D echo would
allow direct planimetry of ROA. The purposes of this study
therefore were: (1) to quantify the ‘anatomical’ size of the
maximal ROA by 3D echo, comparing the size with that
measured by Doppler techniques; and (2) to determine
whether the area and volume of prolapsing tissue measured by
3D echo correlates with the severity of mitral regurgitation.
From the Cardiovascular Imaging Center, Department of Cardiology, The
Cleveland Clinic Foundation, Cleveland, Ohio. This report was presented in part
at the 69th Annual Meeting of the American Heart Association, November 1996,
New Orleans, Louisiana. Dr. Thomas was supported in part by Grant NCC 9-60,
from the National Aeronautics and Space Administration, Houston, Texas and
Grant 1R01HL56688, National Heart Lung and Blood Institute, Bethesda,
Maryland.
Manuscript received December 11, 1997; revised manuscript received March
19, 1998, accepted April 17, 1998.
*Present address: The Thoraxcentre, Rotterdam, The Netherlands.
Address for correspondence: Dr. James D. Thomas, Department of
Cardiology/F-15, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, Ohio 44195. E-mail: [email protected].
©1998 by the American College of Cardiology
Published by Elsevier Science Inc.
0735-1097/98/$19.00
PII S0735-1097(98)00239-3
JACC Vol. 32, No. 2
August 1998:432–7
BREBURDA ET AL.
QUANTIFICATION OF MITRAL REGURGITATION BY THREE-DIMENSIONAL ECHO
Abbreviations and Acronyms
2D 5 Two-dimensional
3D 5 Three-dimensional
CW 5 Continuous wave
MR 5 Mitral regurgitation
MV 5 Mitral valve
ROA 5 Regurgitant orifice area
RSV 5 Regurgitant stroke volume
TEE 5 Transesophageal echocardiography
Methods
Patient selection. We studied 15 patients (32–75 years,
mean 59 6 11 years, nine men and six women) with myxomatous MV prolapse or leaflet flail with severe mitral regurgitation (MR) undergoing MV repair. The patients were selected
at random based on the logistics of the intraoperative echocardiography schedule, with typically one patient per day being
studied. Patients were not excluded on the basis of image
quality, although patients in atrial fibrillation were excluded
because of difficulties in 3D reconstruction. All patients underwent a preoperative transthoracic echo and an intraoperative transesophageal echocardiography (TEE) pre- and postcardiac bypass. The prebypass intraoperative exam preceded
the 3D acquisition and was recorded on 0.5 in. VHS video tape
by an experienced independent clinician with complete interrogation of the MV apparatus.
Three-dimensional echocardiography and reconstruction.
Three-dimensional TEE was performed in conjunction with
the preoperative exam, utilizing a 5-MHz phased-array multiplane probe (12), interfaced with a Hewlett-Packard Sonos
1500 (77035A) or 2500 (M2406A) (Andover, MA), equipped
with investigational 3D acquisition software. Electrocardiographic gating was obtained from the Hewlett-Packard system
leads using a preset RR interval to reject data from all heart
cycles .100 ms above or below this limit. Images were
acquired only at expiration using input from a nasal thermistor
placed in the endotracheal tube. After completing the clinical
study, the probe was positioned in the midesophagus, with the
central axis placed at the leaflet coaptation point around which
the image plane was rotated to encompass the whole MV
apparatus. A TomTec Echo Scan (3.0, TomTec Imaging
Systems, Inc., Boulder, CO) was interfaced with the HewlettPackard system via the composite video output port. Data were
stored on videotape and digitally on the TomTec hard disk
with later transfer to 650 MB magneto-optical discs. Conical
data sets consisted of 60 sequential cross sections acquired at
3° increments for a complete heart cycle (20 to 25 frames) (13).
Data were processed off-line by the TomTec analysis program,
synchronizing the cross sections with the phase of the cardiac
cycle, converting from polar to Cartesian coordinates, and
interpolating to fill gaps between the sequential cross sections.
The images were displayed in a dynamic 2D format, allowing
arbitrarily oriented planes to be viewed independently of the
original ultrasonic window. From a selected cut plane, up to
433
eight parallel planes were computed at predetermined intervals and displayed in motion for quantitative volumetric analysis. Three-dimensional surface rendering was also performed
using border-detection algorithms based on ultrasonic intensity
(threshold) and rate of change along the line of sight (gradient), optimized to differentiate cardiac structures from the
blood pool, background and noise artifacts; a distance and
gradient shading algorithm was applied to enhance the perception of depth.
Measurements. Two-dimensional slices from the 3D data
set were displayed similar to conventional transesophageal
orientations (14). The surgical view from the left atrium facing
the mitral annulus was reconstructed using surface rendering,
and the location of prolapse was evaluated under direct 3D
visualization.
Three-dimensional echocardiography. The volume of prolapse was calculated using the short axis view of the mitral
annulus as a reference image for multiple parallel 2 chamber
long axis views to be reconstructed orthogonal to the mitral
annulus from the medial to the lateral commissural point.
Multiple, 1-mm-thick equidistant cut planes were displayed,
covering the total extent of the prolapse from its maximal area
to the edges. The anterior and posterior leaflet hinge points
were connected with a line to define the annular plane as
described previously (1), and the area of the first parallel plane
was highlighted and copied as a label to the next 1-mm slice,
allowing a consistent determination of the annular plane in all
analyzed cut planes. The 2D area of prolapse between the
leaflet and the annular plane was then traced manually in each
long axis view and the volume of prolapse calculated as the
sum of each traced area multiplied by the slice thickness:
O
L
V5
ADx,
M
where V 5 volume of prolapse, L 5 lateral, M 5 medial, A 5
area, and Dx 5 multiple 1-mm-thick (planes). The area of
prolapse was planimetered in the volume-rendered 3D reconstruction of the MV from a view plane parallel to the mitral
annulus in the left atrium facing the mitral annulus just above
the maximal extent of prolapse.
The maximal area of the regurgitant orifice was visualized
from a cut plane parallel to the gap between the prolapsing
leaflet and orthogonal to the annular plane in the standard 2D
echo long axis view. Thus, the 3D reconstruction imaged the
orifice in its maximal extent as viewed from the left atrium
above the mitral annulus. The image was then transferred to
the Hewlett-Packard system and recalibrated using the 5-cm
reference scale on the 3D image. The maximal orifice opening
was then traced manually.
Proximal convergence method. The proximal convergence
field was optimized by baseline shifting the color Doppler
aliasing velocity to between 34 and 69 cm/s or ;10% to 15% of
peak mitral velocity. The radial distance (r) between the first
aliasing contour (red/blue interface) and the center of the
regurgitant orifice was measured at the time of the largest
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BREBURDA ET AL.
QUANTIFICATION OF MITRAL REGURGITATION BY THREE-DIMENSIONAL ECHO
convergence image. For patients with nonflail mitral leaflets,
the orifice was assumed to be at the plane passing through the
tips of the mitral leaflets; for flail mitral leaflets, the orifice was
assumed to lie in the plane of the nonflail leaflet. Maximal
instantaneous regurgitant flow (Qmax) was calculated as Qmax
5 2pr2va, where r is the maximal distance to the contour of
velocity va, with a hemispheric contour assumed. The regurgitant orifice area was obtained by dividing maximal flow by the
peak regurgitant velocity (vp) obtained by continuous-wave
(CW) Doppler: ROA 5 Qmax/vp. Regurgitant stroke volume
(RSV) was obtained by multiplying ROA by the velocity–time
integral of CW regurgitant velocity (VTICW): ROA 3 VTICW
or 2pr2va 3 VTICW/vp. If the proximal flow field was distorted
by wall contact in any transesophageal plane, the geometric
convergence angle (a) was determined and corrected. ROA
(cROA) and RSV (cRSV) were calculated as cROA 5
ROA 3 a/180 and cRSV 5 RSV 3 a/180 as validated
previously (15).
Statistical analysis. All values are expressed as mean 6
SE. For the validation of 3D echo, planimetered ROA was
compared with proximal convergence ROA by linear regression and analysis of agreement to give the bias and scatter in
the measurements. Doppler RSV and ROA as well as the 3D
estimate of the severity of prolapse by prolapse area and
volume were compared with 3D ROA using linear regression.
Interobserver and intraobserver variability. In 10 patients
selected randomly, the proximal flow convergence and 3D
echo planimetry were obtained independently by two observers. Intraobserver variability was also calculated by repeating
measurements 1 month after the initial measurement.
Results
Table 1 lists the demographic and clinical characteristics of
the patients. Salient features include male dominance (60%)
and relative lack of symptomatology.
Imaging of the regurgitant orifice. Under optimal conditions, the 3D ROA quantification took ;15 min to complete,
with 3 to 4 min for image acquisition, 8 to 10 min for processing
and reconstruction of the image, and 2 to 3 min for recalibration and planimetry of the ROA. In three patients, electrocautery from adjacent surgical suites interfered with image quality
and slowed acquisition, but the regurgitant orifice could be
successfully reconstructed in all patients.
Figure 1 shows a 3D echo reconstruction of the MV at the
level of the mitral annulus. The regurgitant orifice is viewed
with a posterior projection from a position in the anterior left
atrium, showing deep prolapse and partial flail of the middle
scallop of the posterior mitral leaflet. Figure 2 shows an
example of an eccentric proximal flow convergence zone with
wall constraint.
Echocardiographic findings. Table 2 summarizes the findings from the clinical intraoperative echo studies. Cases were
divided approximately equally between leaflet flail and pure
prolapse, with the expected posterior leaflet predominance.
JACC Vol. 32, No. 2
August 1998:432–7
Table 1. Demographic and Clinical Data of the Patient Population
Continuous Variables
Mean 6 SD
(Minimum and Maximum)
Age (years)
Height (cm)
Weight (kg)
Systolic BP (mm Hg)
Diastolic BP (mm Hg)
Heart rate (beats/min)
Onset of murmur (years)
Ejection fraction (%)
59.1 6 11.2
172.8 6 10.2
75.9 6 14.2
125 6 13
71 6 11
84 6 7
9.4 6 17.2
59 6 8
(32–75)
(157–189)
(53.7–109)
(104 –148)
(50 – 86)
(76 –100)
(0 – 60)
(40 –70)
Categorical Variables
n
%
Gender
Hypertension
Coronary artery disease
Congestive heart failure
CHF class I
CHF class II
CHF class III
Dyspnea
Palpitations
Chest pain
9 men
5
3
3
8
4
3
5
4
3
60
33
20
20
53
27
20
33
27
20
(BP) blood pressure; (CHF) congestive heart failure (grading based on New
York Heart Association).
The left ventricular ejection fraction was normal in most cases,
although it ranged as low as 40%.
Measurements of the regurgitant orifice area. The proximal
convergence zone was well visualized in all cases. Because of
the preponderance of posterior prolapse and flail pathology,
all but one of these zones were constrained by the adjacent
posterior wall, requiring correction of the ROA by the constraining angle a. Maximal ROA by 3D echo (y) was 0.79 6
0.39 cm2 (mean and SD, range 0.37 to 1.97 cm2) and 0.86 6
0.42 cm2 (range 0.31 to 1.63 cm2) by proximal convergence (x).
Regression analysis demonstrated excellent correlation and
Figure 1. Three-dimensional visualization of a flail posterior leaflet.
The vantage is of an observer on the anterior mitral annulus looking
posterior toward the posterior mitral leaflets, which is flail in its middle
scallop. LA 5 left atrium; LV 5 left ventricle; PL 5 posterior leaflet.
Medial and Lateral 5 respective mitral commissures.
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QUANTIFICATION OF MITRAL REGURGITATION BY THREE-DIMENSIONAL ECHO
435
Figure 2. Flail posterior leaflet (transesophageal
view) demonstrating proximal flow convergence
with wall constraint because of the proximetry of
the posterior wall. To adjust for the predictable
overestimation due to this geometric distortion,
regurgitant flow rate and orifica area are adjusted
by a/180. LA 5 left atrium; LV 5 left ventricle.
agreement: y 5 0.87x 1 0.03, r 5 0.95, p , 0.001, DROA (y 2
x) 5 20.07 6 0.13 cm2 (mean 6 SD), with a range of 20.31 to
0.14 cm2 (Fig. 3). Figure 4 shows the difference between ROA
planimetered by 3D echo and calculated by proximal convergence plotted against the mean of these measurements.
Correlation of ROA with area and volume of prolapse. The
area (x) and volume (y) of prolapse, each quantified by 3D
echo, were closely correlated with r 5 0.79, p , 0.001, y 5
0.91x 1 0.39. Three-dimensional area of prolapse correlated
slightly better with the 3D ROA (r 5 0.58, p , 0.04) than with
calculated ROA by proximal convergence (r 5 0.43, p 5 NS),
although wide scatter was seen in the relationship. Threedimensional prolapse volume correlated neither with 3D nor
flow ROA (see Table 3).
Reproducibility. The intraobserver and intraobserver variability averaged 1.1 6 11% (mean difference 6 SD) for radius
measurement, 6.7 6 11% (mean difference 6 SD) for convergence angle measurement and 1 6 10% (mean difference 6
SD) for 3D ROA planimetry, 1.3 6 12% for area and 1.2 6 8%
volume of 3D mitral valve prolapse.
Discussion
This study demonstrates that MV ROA planimetry is feasible
with 3D echocardiography even in patients with severely
Table 2. Two-Dimensional Echocardiographic Findings
Findings
n
%
Flail posterior leaflet
Pure prolapse
Posterior involvement
Bileaflet involvement
Moderately severe MR
Severe MR
Ejection fraction (%)
8
7
12
3
1
14
59 6 8
53
47
80
20
7
93
(40 –70)
distorted valvular geometries resulting from leaflet flail. ROA
measured by 3D echo correlated well with that calculated by
the proximal convergence method.
Quantification of mitral regurgitation. Despite the importance of accurate quantitation of mitral regurgitation (MR) for
surgical timing and assessing medical therapy, semiquantitative
methods such as contrast ventriculography (15) and visual
assessment of color Doppler regurgitant jet size (17) and
morphology (18) within the left atrium are mostly used to
characterize MR in the routine clinical setting. Although
quantitative angiography (19) and 2D Doppler methods (20)
are well validated and considered reference standards, they are
technically demanding and not used routinely. Semiquantitative methods are easy to use but grade regurgitant severity on
a simple linear scale from 1 to 4. Extremes of regurgitant
severity are easily differentiated, but the classification of
moderate lesions is difficult, especially because these tech-
Figure 3. Regression analysis relating effective ROA calculated by
flow convergence and planimetered regurgitant orifice area by 3D
echocardiography. (r 5 0.95; p , 0.001; y 5 0.87x 1 0.03; standard
error of estimate (SEE) 5 0.125.)
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BREBURDA ET AL.
QUANTIFICATION OF MITRAL REGURGITATION BY THREE-DIMENSIONAL ECHO
Figure 4. Difference in ROA estimation by 3D echo and proximal
convergence plotted against mean ROA by the two techniques.
niques are influenced by technical factors and loading conditions.
Convergence method. The proximal convergence method
has been proposed as a simple quantitative method, requiring
only a single acoustic window. Regurgitant flow is measured
directly and can be combined with CW Doppler estimate of
peak regurgitant velocity to predict ROA. It is generally based
on an assumed hemispherical contour shape (2), although
prior experimental studies have shown this to be incorrect near
the regurgitant orifice (21) or when the proximal flow is
constrained by surrounding structures (15,22). Although formulae have been proposed to overcome the overestimation
because of proximal constraint (15); in practice only onedimensional corrections have been applied (as in this study),
rather than the more valid 3D adjustment (23). This and other
technical difficulties in performing the proximal convergence
method have limited its use in practice.
Three-dimensional echo planimetry. Planimetry is an established method for stenotic orifices, especially in mitral stenosis
(24). More recently, multiplane TEE has allowed direct
planimetry of the stenotic aortic valve (25). Planimetry is thus
potentially a method to measure ROA as a flow-independent
measure of regurgitant severity, but 2D echo can only occasionally define the area of malcoaptation and ROA, typically in
cases of incomplete MV closure due to severe left ventricular
dilatation (26). In myxomatous MV disease, however, the
Table 3. Correlations among Three-Dimensional Area of Prolapse,
3D Volume of Prolapse Compared to ROA by Convergence
Method, and 3D Echo Planimetry
Parameter
Parameter
r
p Value
3D area
3D area
3D volume
3D volume
3D volume
3D ROA
ROAPC
3D ROA
ROAPC
3D area
0.58
0.43
0.25
0.14
0.79
, 0.04
NS
NS
NS
, 0.001
ROAPC 5 calculated regurgitant orifice area using the proximal flow
convergence method; area 5 prolapse area; volume 5 prolapse volume.
JACC Vol. 32, No. 2
August 1998:432–7
ROA occurs in planes not readily imaged by conventional 2D
imaging, necessitating 3D imaging.
Several approaches have been described for 3D echo, not
all of them applicable to planimetry of the ROA. Levine and
coworkers have used acoustic and electromagnetic localizing
devices to position randomly acquired 2D echo planes in 3D
space (8). Manual segmentation is required to identify endocardial borders and other structures from which volumes and
areas may be calculated. Although good accuracy has been
reported for LV volume (27–30) and ventricular septal defect
size (31), the inhomogeneous sampling of this technique would
make characterization of the mitral regurgitant orifice difficult.
In contrast, the TomTec device adopts a structured data
acquisition strategy from a single echocardiographic window to
yield a nearly isotropic data set. Such a structured approach
can be a linear or fan-like sweep or a rotational acquisition
from either the transthoracic or (as done here) TEE approach,
which is especially effective for reconstructing the MV, as it is
in the near field of the TEE probe, allowing it to be densely
sampled by the rotating 3D plane. At a 5-cm depth, the edges
of successive 3° sector scans are ,2 mm apart, becoming
progressively closer as one moves toward the center of the
imaging field (where the ROA usually fell). A potential
problem is the misregistration of planes when patient or probe
movement occurs during the acquisition, a problem exacerbated when arrhythmia or artifact from electrocautery prolongs the acquisition.
Finally, an instrument that performs 3D echo in real time
has recently been developed (31). Using 16:1 parallel processing and a 2D-phased array crystal, it is capable of generating
3D data sets consisting of 64 scan lines and 64 scan planes at 20
to 40 Hz. Although very promising—and likely the long-term
approach to 3D echo—this device cannot yet be used with
TEE, and the resolution from the chest wall is likely to be
inferior (pending technical improvements) to the approach
used in this study.
Limitations. We demonstrated that the MV ROA may be
imaged and measured by 3D echocardiography, even in patients with distorted MV geometry. One limitation is the lack
of a true reference standard for regurgitant severity, especially
as the 3D and Doppler methods used in this study measured
slightly different entities. Three-dimensional planimetry defines the anatomical ROA, whereas the proximal convergence
method should yield the narrowest flow stream (vena contracta), which is smaller than the anatomic orifice by the
coefficient of contraction (generally 0.8 to 0.9). Thus, it may be
surprising that planimetered areas were slightly smaller than
the flow areas. Although this likely relates in large part to
measurement noise in both data sets, there may be some
systematic overestimation of the flow areas because of incomplete adjustment for flow constraint. The previously validated
one-dimensional angle adjustment corrects ;80% of the overestimation; in the future, 3D echo may be used to more fully
correct for this complex geometric constraint. Another potential source of error is that 3D ROA was based on a planar
projection of the largest apparent orifice but might have
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QUANTIFICATION OF MITRAL REGURGITATION BY THREE-DIMENSIONAL ECHO
missed additional areas in other planes. Additionally it is
possible that ROA may be underestimated (if beam width
artifact thickens the mitral leaflets) or overestimated (if the
thin mitral leaflets are not captured in the surfacing algorithm,
resulting in drop-out). Artifact from electrocautery is a major
problem, sometimes seen even from an adjacent operating
room. Atrial fibrillation can significantly prolong 3D reconstruction (although no patients in the current study were in this
rhythm) but may be less important with real-time 3D imaging.
These results should thus only be considered applicable to
patients in sinus rhythm. To minimize the effects of dynamic
changes in ROA between the two techniques (33,34), we
compared maximal rather than mean values.
Conclusions. In this study we have demonstrated that it is
feasible to perform quantitative 3D echocardiography for
measurement of the mitral ROA in the intraoperative setting.
We further showed that 3D ROA agrees closely with that
derived by the flow-based proximal convergence method. As
3D acquisition and analysis become faster, quantitative applications such as this should become more common.
We thank Sheila Wallace for assistance with the manuscript and Paula Shalling
for assistance with the illustrations.
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