Download Echocardiographic Assessment of Right Ventricular Volumes after

Echocardiographic Assessment of Right
Ventricular Volumes after Surgical Repair
of Tetralogy of Fallot: Clinical Validation of a New
Echocardiographic Method
Andreea Dragulescu, MD, PhD, Lars Grosse-Wortmann, MD, Cheryl Fackoury, RDCS, Sonja Riffle, RDCS,
Mary Waiss, RDCS, Edgar Jaeggi, MD, Shi-Joon Yoo, MD, Mark K. Friedberg, MD,
and Luc Mertens, MD, PhD, Toronto, Ontario, Canada; Seattle, Washington
Background: Assessment of right ventricular (RV) volumes and function is important in patients after tetralogy
of Fallot (TOF) repair. Currently, cardiac magnetic resonance imaging (MRI) is considered the clinical reference
method for RV volume and function measurements. Three-dimensional (3D) knowledge-based reconstruction
derived from two-dimensional echocardiographic imaging with magnetic tracking is a novel approach to RV
volumetrics. The aim of this study was to assess the feasibility and reliability of this novel echocardiographic
technique in patients after TOF repair. The accuracy of the method was assessed by comparison with
measurements obtained by cardiac MRI.
Methods: Thirty patients (mean age, 13.7 6 2.8 years) after TOF repair, referred for cardiac MRI, were
included. Immediately after MRI, echocardiographic image acquisition was performed using a standard ultrasound scanner linked to a Ventripoint Medical Systems unit. Echocardiographic and MRI measurements were
performed offline. Parameters analyzed were end-diastolic volume (EDV), end-systolic volume (ESV), and
ejection fraction. Intraobserver, interobserver, and intertechnique variability was assessed using Pearson’s
correlation analysis, coefficients of variation, and Bland-Altman analysis.
Results: Echocardiographic two-dimensionally based 3D reconstruction was highly feasible, with low intraobserver and interobserver variability for EDV and slightly higher variability for ESV and ejection fraction. The 3D
reconstruction values for EDV, ESV, and ejection fraction were correlated highly with MRI values, with low
coefficients of variation. The agreement between both methods was high. Three-dimensional reconstruction
slightly underestimated RV volumes, by 2.5% for EDV and 4.6% for ESV compared with MRI volumes.
Conclusions: In patients after TOF repair, echocardiographic 3D reconstruction is highly feasible, with good
reproducibility for measurements of RV EDV. There is good agreement with MRI measurements, with a small
underestimation of RV volumes. The use of this method in clinical practice warrants further investigation. (J Am
Soc Echocardiogr 2011;-:---.)
Keywords: Echocardiography, Cardiac volume, Tetralogy of Fallot, Magnetic resonance imaging
From the Division of Cardiology, The Labatt Family Heart Centre, Department of
Paediatrics (A.D., L.G.-W., C.F., E.J., S.-J.Y., M.K.F., L.M.), and the Department
of Diagnostic Imaging (L.G.-W., S.-J.Y.), Hospital for Sick Children and
University of Toronto, Toronto, Ontario, Canada; and Ventripoint, Inc., Seattle,
Washington (S.R., M.W.).
This study was funded through The Labatt Family Heart Centre Innovation Fund.
Ms Waiss is vice president of clinical affairs at Ventripoint. Ms Riffle is a clinical
application specialist and former employee at Ventripoint. There was no financial
support from Ventripoint for this study.
Michael H. Picard, MD, FASE served as Guest Editor for this article.
Reprint requests: Luc Mertens, MD, PhD, The Labatt Family Heart Centre, The
Hospital for Sick Children, 555 University Avenue, Toronto, ON M5G 1X8, Canada
(E-mail: [email protected]).
0894-7317/$36.00
Copyright 2011 by the American Society of Echocardiography.
doi:10.1016/j.echo.2011.08.006
Assessment of right ventricular (RV) volumes and function is important in the follow-up of cardiac lesions when the right ventricle is affected.1-3 This is particularly relevant in patients after surgical repair
of tetralogy of Fallot (TOF), who often develop progressive RV
dilatation and dysfunction, related to postoperative pulmonary
regurgitation.4,5 Currently, cardiac magnetic resonance imaging
(MRI) is considered the method of choice for the assessment of RV
volumes and ejection fraction (EF).6 Quantitative three-dimensional
(3D) echocardiography using real-time volumetric acquisition and
dedicated RV volume analysis software has emerged as a promising
clinical alternative to MRI.7,8 However, the feasibility of this
method is problematic, especially in postoperative patients with
significantly dilated RV volumes. Poor echocardiographic windows
can limit RV endocardial border detection in about 20% to 50% of
all patients, limiting the feasibility of the method.8,9 Additionally,
3D echocardiography was shown to underestimate RV volumes by
up to 15% to 25%, with the underestimation being more important
1
2 Dragulescu et al
in more dilated ventricles.8,9
Therefore, alternative echoEDV = End-diastolic volume
cardiographic methods are
worthwhile investigating. In this
EF = Ejection fraction
study, we used a twoESV = End-systolic volume
dimensional (2D) method that
localizes different anatomic landMRI = Magnetic resonance
marks in a magnetic 3D space
imaging
and reconstructs the RV volumes
RV = Right ventricular
using a database of various RV
shapes and sizes obtained in pa3D = Three-dimensional
tients after TOF repair.
3DR = Three-dimensional
The aim of the present study
reconstruction
was to assess the feasibility,
TOF = Tetralogy of Fallot
reliability, and accuracy of the
echocardiographic knowledge2D = Two-dimensional
based 3D reconstruction (3DR)
method to measure RV volumes and EFs in patients after TOF repair
and compare the results with RV measurements obtained by cardiac
MRI.
Abbreviations
METHODS
This was a single-center, prospective, observational study. The study
was approved by the institutional research ethics board. Informed
consent was obtained from all participants and/or their legal guardians before enrollment.
Patients after TOF repair, aged 8 to 17 years, who were scheduled
to undergo cardiac MRI for clinical indications were included.
Exclusion criteria were an inability to cooperate, known or detected
arrhythmia interfering with image acquisition, and pacemakers or
any contraindication to MRI. We also excluded patients after surgical
repair with right ventricle–to–pulmonary artery conduits. The current
TOF database used for RV volume reconstruction does not include
patients with conduits. A different catalog for patients with conduits
has been developed but was not used in the present study. Just before
or immediately after cardiac MRI, a limited echocardiographic study
was performed, including image acquisition for 3DR. All echocardiographic studies were performed using a GE Vivid 7 machine (GE
Healthcare, Milwaukee, WI). Data were digitally stored and analyzed
offline. RV end-diastolic volume (EDV), end-systolic volume (ESV),
and EF were calculated. Intraobserver variability was performed using
repeated analysis for the 3DR method, with $2 weeks between the
analyses. For interobserver variability, two independent observers
analyzed the 20 first echocardiographic data sets. Both observers
were experienced with the technique.
3DR Method
The 3DR method enables 2D-based full volumetric reconstructions
of cardiac chambers from 2D echocardiographic images localized in
3D space, using proprietary software and a catalog of heart shapes.
This knowledge-based 3DR of ventricular volumes has been previously described and validated in vitro from 3D echocardiographic
data sets using the piecewise smooth subdivision surface reconstruction method.10 It was also clinically validated for the left ventricle,11
and more recently, a catalog of fully traced MRI acquisitions of
a wide range of RV shapes and sizes was shown to allow accurate
knowledge-based reconstructions of RV volumes using MRI data
sets.12 On the basis of the same principles, an echocardiographic
Journal of the American Society of Echocardiography
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method was developed. The method involves the acquisition of 2D
echocardiographic images with a magnetic localizer attached to the
ultrasound probe, allowing localization of the different 2D images
in 3D space. The image acquisition protocol should provide good coverage of the different parts of the right ventricle. After acquisition, offline analysis is performed, including the identification of different
anatomic landmarks on the 2D images. The data points (anatomic
landmarks with their spatial localization) are matched to a catalog
of 3D shapes obtained from cardiac MRI studies in patients after
TOF repair, and the RV volumes and EFs are calculated. The different
steps are explained in more detail.
Image Acquisition. The acquisition involves freehand 2D transthoracic scanning using a standard 2D probe with a magnetic field localizing system (Ascension Technology Corporation, Andover, MA)
to track the position and orientation of the ultrasound probe in 3D
space. The system consists of a magnetic field transmitter located under the exam bed. This generates different orthogonal magnetic fields
that are sensed by the receiver, which is attached to the ultrasound
probe. The position and orientation of the receiver and thus the plane
of the 2D picture can be computed and placed within the volume created by the magnetic transmitter. Different 2D images of the right
ventricle are obtained. To obtain maximal coverage of the right ventricle, 10 to 15 different echocardiographic views should be acquired
in each patient. These are summarized in Table 1 and illustrated in
Figure 1. For each view, short clips of 2 to 4 sec are recorded to
include at least three full cardiac cycles. Subjects are not allowed to
change position on the exam bed during the acquisition process,
and when possible, we obtained each clip using breath holding at
end-expiration. The ultrasound scanner is linked to a computer
(Ventripoint Medical Systems; Ventripoint, Inc., Seattle, WA) through
the video output, and every clip is digitized at 30 frames/sec. The
magnetic field data are entered at the same time, and 3D localizing
data are linked in the computer online. The entire acquisition protocol generally takes about 5 min.
Image Analysis. The images and spatial information are stored on
the Ventripoint Medical Systems computer, which has an Internet connection to the centralized database. First, timing of the cardiac cycle
needs to be performed, with identification of end-diastole and endsystole. End-diastole is automatically set to correspond to the electrocardiographic R wave but can be adjusted manually. End-systole is
identified manually on one clip, and the time interval is
automatically applied to all clips on the basis of the electrocardiogram.
This requires the heart rate to be relatively stable during the acquisition
process. After the user approves the timing, identification of the different anatomic landmarks is performed on the different images. A small
number of key anatomic points need to be identified for both enddiastole and end-systole. This includes the tricuspid and pulmonary
valve annuli, the RV apex, the RV side of the interventricular septum,
the RV free wall, the subpulmonary area (just below the pulmonary
valve), and the subtricuspid area (on the RV inferior wall). For full
3DR, 17 to 23 points need to be identified on the 2D images. No additional anatomic tracing or border detection is required.
Surface Generation Using Catalog-Based Method. Once the
anatomic points have been identified and localized in the magnetic
3D space, the RV volumetric reconstruction is performed by sending
the data to the online database. The ‘‘knowledge’’ MRI database consists of fully traced RV volumes of postoperative patients after TOF
repair with a wide spectrum of different RV volumes and shapes.
The identified landmarks on the 2D images with their location in
Dragulescu et al 3
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Table 1 Image acquisition protocol
View
Region of interest
1. Apical four-chamber view
2. Apical two-chamber view of the right ventricle
3. Foreshortened apical three-chamber view
4. Modified oblique view of the true RV apex
5. Parasternal long-axis view, mitral valve
6. Parasternal long-axis view, tricuspid valve
7. Parasternal long-axis view, pulmonary valve
8. Parasternal short-axis view, pulmonary valve
9. Short-axis view, base
10. Short-axis view, mid/apex
11. Rotated apical views
12. Foreshortened apical view, RV outflow
13. Subcostal four-chamber view
14. Subcostal sagittal view
Tricuspid annulus, basal bulge, RV endocardium, RV apex, RV septum
Tricuspid annulus, subtricuspid inferior wall, RV endocardium, pulmonary annulus
Tricuspid annulus, RV endocardium, RV septum, RV outflow
RV apex
Interventricular septum, RV endocardium
Tricuspid annulus, RV endocardium
Pulmonary annulus, RV endocardium, RV outflow
Pulmonary annulus, subpulmonary area, RV endocardium
Interventricular septum, RV endocardium
Interventricular septum, RV endocardium
Tricuspid annulus, basal bulge, RV endocardium, RV apex, RV septum
RV endocardium, pulmonary annulus, RV outflow
RV endocardium, RV apex, RV septum
RV endocardium, RV outflow
3D space are matched with the database, and the best fit is computed
using a proprietary algorithm. Once a minimum number of points
have been placed on the anatomic structures, ideally 15 to 20, the first
reconstruction can be run. The reconstructed RV volume is projected
on the 2D data set (Figure 1), and on the basis of this quality check,
the placement of points can be adjusted and more points can be
added to refine the RV volumetric modeling and end up with the
best fit for EDV (Figure 2). For calculating ESV, the same process is
repeated. RV volumes and EF are calculated by the system.
Cardiac MRI
MRI scans were performed on a 1.5-T scanner (Avanto; Siemens
Medical Systems, Erlangen, Germany). For ventricular volumetry,
a short-axis cine stack was acquired during breath hold, using a balanced steady-state free precession gradient-echo sequence with minimum echo and repetition times, a flip angle of 45 , bandwidth of
31.25 kHz, one excitation, views (lines) per segment to allow for
20 true reconstructed phases per cardiac cycle, 5 to 6 mm of slice
thickness, 10 to 12 slices, gap adjusted to cover both ventricles, and
in-plane spatial resolution of 1.5 to 2.5 mm. The MRI data were analyzed with commercially available software packages (Mass Analysis
and CV Flow, Medis Medical Imaging Systems, Leiden, The
Netherlands). Left ventricular and RV end-diastolic (maximal) and
end-systolic (minimal) volumes, stroke volumes, and EFs were measured. The interobserver variability of the RV volumes was assessed
by independent analysis of the first 20 studies by two experienced
observers.
Statistical Analysis
Different statistical methods were used to analyze intraobserver, interobserver, and intertechnique variability. The agreement between the
measurements is described using Bland-Altman statistics, including
the calculation of mean bias (average difference between measurements), with standard deviation. The statistical significance of the
mean bias was tested using a paired, two-tailed t test (the null hypothesis was zero bias). The lower and upper limits of agreement (95%
limits of agreement of mean bias) were calculated. The percentage differences (the difference between paired measurements divided by
the average of the two measurements times 100) and percentage
bias were calculated for the different Bland-Altman analysis. The correlation between observers and techniques was calculated using
Pearson’s correlations. Variability of the measurements was also
assessed by calculating the coefficient of variation as the standard
deviation of the difference of paired samples divided by the average
of the paired samples.
RESULTS
Feasibility
Thirty children (mean age, 13.7 6 2.8 years) were included in the
study. The 3DR analysis was successfully completed in all studies.
Small respiratory artifacts were noted in a few patients, but they did
not preclude the reconstructions. Generally, three to four reconstructions with point adjustments were required to obtain optimal reconstructions, with easier adjustments when fewer initial points were
entered. Overall image acquisition took about 5 min, and the analysis
took about 15 min.
Reproducibility
The results of the intraobserver and interobserver variability analysis
are shown in Table 2, and the Bland-Altman plots are depicted in
Figure 3. The intraobserver and interobserver variability of 3DR for
calculating EDV was low, with excellent correlation coefficients,
low coefficients of variation, no significant bias, and narrow limits of
agreement. Intraobserver and interobserver variability was slightly
higher for ESV and less good for EF. The differences between intraobserver and interobserver measurements were not significant for any of
the parameters analyzed. The reproducibility of MRI measurements
between observers is presented in Table 2, with overall good agreement between the two observers, especially for EDV and less so for
ESV and EF. A small but significant bias was detected between the
two observers: a 2.4% (5.3 mL) difference for EDV (P = .01) and
a 4.4% (5.7 mL) difference for ESV (P = .002).
Accuracy
The accuracy of the 3DR method was evaluated for the entire group
of patients by comparing the echocardiographic and MRI measurements. The results are presented in Table 3 and Figure 4. The correlation coefficients between both methods were high for all three
measurements. The coefficient of variation was low for EDV and
slightly higher for ESV and EF. The 3DR method resulted in a small
but statistically significant underestimation of RV volumes (negative
4 Dragulescu et al
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Figure 1 Two-dimensional views used for 3DR. Anatomic landmarks are identified on 2D images (colored points). Once the volume is
calculated, projections of the reconstructed RV on the acquired 2D images can be visualized (yellow tracings).
bias): EDV by 2.5% (7 mL; P = .002) and ESV by 4.6% (6.9 mL; P =
.0004). The 95% limits of agreement were relatively narrow for EDV
and EF but wider for ESV.
The most biased RV volume reconstructions were obtained in
patients with RV hypertrophy, estimated by the thickness of the RV
anterior wall in the parasternal long-axis view. Overall, there was
a significant correlation between RV thickness and the observed
bias (R = 0.54 for EDV and R = 0.51 for ESV, P < .001).
DISCUSSION
RV dilatation and failure is the main cause of morbidity and mortality
in patients after TOF repair with significant pulmonary regurgitation.
RV EDV and EF were shown to predict outcomes, defined as death,
the occurrence of sustained ventricular tachycardia, and functional
status (New York Heart Association class III or IV).13 RV EDV has
also been shown to be an important predictor of RV remodeling after
pulmonary valve replacement.14,15 Thus, the availability of a reliable
and accurate echocardiographic method to assess RV volumes and
function is clinically important for this patient population. In the
present study, we evaluated a new echocardiographic method for
assessing RV volumes using a 3DR technique based on 2D images
localized in 3D space. We demonstrate that this method has low
intraobserver and interobserver variability and that the
intertechnique agreement between the echocardiographic and MRI
methods was high. In a previous study, the principle of the method
was validated on MRI data used to build the TOF catalog.12 It was
Dragulescu et al 5
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Table 2 Reproducibility of 3DR and MRI measurements of
RV volumes and EF
Correlation Coefficient of
Intramethod variability coefficient*
variation
Mean bias (mL)
3DR intraobserver (n = 20)
EDV
.997
ESV
.984
EF
.733
3DR interobserver (n = 20)
EDV
.995
ESV
.989
EF
.611
MRI interobserver (n = 20)
EDV
.993
ESV
.986
EF
.911
P
3.4
7.4
7.9
1.1 6 7.6
1.6 6 9.5
0.7 6 3.7
.68
.75
.51
3.8
5.7
8.4
2.2 6 8.8
0.5 6 7.2
0.5 6 3.8
.28
.78
.56
3.5
5.3
6.6
5.3 6 8.5
5.7 6 7.2
1 6 2.9
.01
.002
.11
*All correlations were significant at the .001 level.
shown that there was very high agreement between the reconstructed and traced RV volumes.12 Our study is the first independent
validation study using echocardiographic data from patients who
were not included in the reference database used for 3DR.
We show in our pediatric study group that the method is highly
feasible, as we could calculate RV volumes in every patient. This is because the method is based on 2D recognition of anatomic landmarks,
which are generally easy to identify on 2D images, even when the image quality is suboptimal. It is important that during the image acquisition, these key anatomic landmarks are visualized as well as possible
(the tricuspid annulus in at least two planes, the pulmonary valve, the
RV apex, and the different RV walls [lateral, anterior, inferior, and septum]). Because the model ‘‘fills in’’ the volumes on the basis of the
knowledge database, identification of the entire endocardial borders
is not as necessary, contrary to the endocardial border detection
methods. This is possibly an advantage when comparing 3DR to
real-time 3D echocardiographic methods, which are dependent on
border detection. Especially the RV anterior wall and the apical part
of the RV lateral wall can be difficult to visualize in postoperative
Figure 2 Visualization of the right ventricular EDV estimation using different representation features of the 3DR system. The two circles represent the levels of the tricuspid and pulmonary valves, the open line represents the contour of the septal wall, and the colored
points represent the anatomic landmarks used for reconstruction. (A) Key points on a mesh surface, used to visualize the coverage
and the position of the points in relation to the calculated shape and volume. (B) Intersection planes, used to visualize the projections
of the 2D planes in the reconstructed volume and assess the coverage obtained. (C) Combined EDV and ESV rendering, used to
visualize the inward movement of different segments of the right ventricle. (D) Scan plane showing how the 2D plane containing a specific point intersects with the 3D model.
6 Dragulescu et al
Journal of the American Society of Echocardiography
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Figure 3 Intraobserver variability for 3DR (top row), interobserver variability for 3DR (middle row), and interobserver variability for
cardiac MRI (bottom row) represented by Bland-Altman plots.
Table 3 Intermethod variability comparing measurements of
RV volumes and EF using 3DR and MRI
Intermethod
variability
Correlation
coefficient*
3DR versus MRI (n = 30)
EDV
.995
ESV
.994
EF
.871
Coefficient of
variation
4.3
6.7
7.6
Mean bias (mL)
7 6 11.4
6.9 6 9.4
1.2 6 2.9
P
.002
.0004
.03
*All correlations were significant at the .001 level.
patients with dilated ventricles. This possibly explains why the feasibility of 3D echocardiography has been reported to vary between 50%
and 80% of all patients after TOF repair.9,16 Compared with previous
studies, our patients were younger, with potentially better imaging
windows. The feasibility of the 3DR method needs to be further
explored in an adult group of postoperative patients with TOF.
The reproducibility of the RV volumetric calculations as represented by the intraobserver and interobserver variability was relatively
good. Compared with the interobserver variability of cardiac MRI
measurements, the 3DR method had slightly wider limits of agreement, although the MRI measurements also varied between the
two experienced observers. This suggests that the measurement of
RV volumes in postoperative patients with TOF is complicated by different intrinsic factors, independent of the volumetric imaging
method used. The right ventricle is heavily trabeculated, and RV
volumes will be influenced dependent on whether trabeculations
are included or excluded in the measurements.17 Our MRI analysis
of RV volumes included RV trabeculations, because this has been
shown to improve the reproducibility of measurements in the
systemic right ventricle.17 We used the same approach for the echocardiographic 3DR method, also based on the fact that the ‘‘knowledge’’ used for 3DR consisted of MRI volumetric data sets
including RV trabeculations. It can be difficult, in any method, to identify the base of the trabeculations, because the RV ‘‘compacted zone’’
is relatively thin. The higher spatial resolution of cardiac MRI is an advantage compared to echocardiographic imaging. This problem is
even more important during systole, because the trabeculations are
compressed and it can be extremely difficult to delineate the RV compacted layer. This probably contributes to the higher intrinsic variability of any imaging method used to measure RV ESV. We observed
higher variability in ESV compared with EDV in both 3DR and
MRI. Despite the generally acceptable 2D resolution, the identification of anatomic landmarks can sometimes be difficult, and this
may also affect RV volume analysis. For severely dilated right ventricles, it can be challenging or impossible to define the RV apex from
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Figure 4 Correlations (top row) represented by regression analysis and intertechnique agreement (bottom row) represented by
Bland-Altman plots between 3DR and MRI measurements for right ventricular EDV (A,B), ESV (C,D), and EF (E,F).
apical four-chamber views, because of ventricular foreshortening. As
a possible solution to this, we used modified RV views to better identify the RV apex (Figure 1, scan 4). Identification of the pulmonary
valve can be difficult in patients with large transannular patches and
only remnants of the pulmonary valve. This influences the correct depiction of the RV outflow tract distal limits on both echocardiography
and cardiac MRI, which can cause variability in the measurements independent of the technique used. We found that in the 3DR method,
the pulmonary valve can be extremely difficult to identify, especially
in systole when the valve is open. This can further contribute to
the higher variability of ESV measurements compared with EDV
measurements.
The results of intraobserver and interobserver variability of 3DR
were comparable with previously published data on 3D echocardiography7,16,18 and MRI.19 In our study, 3DR variability was slightly
higher compared with MRI, but no significant differences could be
observed. Despite intrinsic limitations influencing reliability, cardiac
MRI is considered to be the reference technique for RV volume calculation, and current clinical recommendations rely on MRI volumetric measurements.14,15 Previous studies have looked at using 2D
echocardiographic estimations of RV volumes using different
mathematical assumptions of RV shape, but these methods resulted
in RV volumetric measurements that were not in good agreement
with the MRI calculations.20 A recent study used a simplified linear
regression formula (RV EDV index = 11.5 + [7 indexed enddiastolic area]), on the basis of the good agreement between RV diastolic area measured from the apical four-chamber view and RV EDV
on MRI.21 The interobserver variability of this method, however, was
high, and in a prospective validation, the limits of agreement between
this method and MRI-based RV EDV were relatively wide. The use of
3D echocardiography and offline volumetric analysis resulted in better agreement of RV volumes with the MRI measurements, but some
studies have reported underestimations of RV EDV of up 25%, especially in patients with dilated right ventricles.9,16 No good explanation
has been given for this underestimation, but the lower 2D resolution
of 3D echocardiography can make it difficult to identify the RV walls
and structures. In our study, we found very good agreement between
the 3DR method and MRI. We noted a small underestimation of RV
volumes by 3DR compared with MRI. The underestimation we
found with the 3DR method is much smaller compared with the
previously published data on 3D echocardiography, and we did not
find an effect of RV dilatation on the observed bias. Interestingly,
we found an effect of RV hypertrophy with significant bur relatively
weak correlations between the RV wall thickness and the detected
bias between the two methods. This indicated that in the thicker
RV walls, it is more difficult to delineate the base of the
trabeculations, especially by echocardiography, resulting in a minor
underestimation of the echocardiographic measurements.
Limitations and Future Perspectives
We acknowledge that our study group was relatively small, because
we could only include children and adolescents undergoing MRI
without sedation. Still, a wide spectrum of different RV sizes, ranging
between 114.6 and 281 mL/m2, was included in the study. The
patients underwent MRI studies that were clinically indicated and ordered by treating physicians. This likely introduced bias toward higher
ventricular volumes, which may have influenced the results.
Apart from our study limitations, the 3DR method currently has
important limitations: it requires an additional computer linked to
the ultrasound machine and a magnetic tracker attached to the probe.
A very weak magnetic field is generated to localize the probe in 3D
space, and this requires the study to be performed on a special nonferromagnetic bed. This influences the integration of the method
within a busy clinical echocardiography laboratory. During image acquisition, which takes about 5 min, the patient is not allowed to move.
This can be a challenge, especially in smaller children. Motion between the different acquired 2D images changes the relative position
of the cardiac structures and creates artifacts precluding an accurate
3D surface reconstruction. Special equipment is required that
8 Dragulescu et al
currently is not readily available, which is a major limitation. The
method also requires additional time. After the learning curve, we
could acquire the images within 5 to 6 min. Apart from the extra
time required for acquisition, the offline analysis can sometimes be
prolonged, especially when the image quality is not optimal. After
the initial learning curve, we currently need about 10 to 15 min of offline analysis for each patient. The interesting aspect of this method is
that it uses information on RV shape and volume to fill in the gaps in
the echocardiographic images. It is encouraging to see that applying
this concept results in reproducible and reliable assessment of RV
volumes. Ideally, this method should be applicable to quantify RV
volumes using 3D volumetric data sets. What cannot be seen very
well on the images is intelligently filled into the data sets on the basis
of a knowledge database of a certain disease. This intelligent form of
scanning is an exciting concept that potentially could be applied to
other diseases in which image quality limitation is a major problem.
Finally, the method is critically dependent on the completeness and
accuracy of the database used in the reconstructions. Because postoperative patients with TOF with conduits are not included in the database, they had to be excluded from our study. A separate database has
been created specifically for these patients, but this has not been
validated yet.
CONCLUSIONS
Three-dimensional reconstruction seems to be a highly feasible
method to measure RV volumes. Compared with cardiac MRI, it
has similar reproducibility of the measurements, and when clinical
MRI is used as reference, its accuracy seems high. Further improvements and wider applicability of this method are needed before establishing its place in clinical practice.
REFERENCES
1. Haddad F, Doyle R, Murphy DJ, Hunt SA. Right ventricular function in
cardiovascular disease, part II: pathophysiology, clinical importance, and
management of right ventricular failure. Circulation 2008;117:1717-31.
2. Haddad F, Hunt SA, Rosenthal DN, Murphy DJ. Right ventricular function
in cardiovascular disease, part I: anatomy, physiology, aging, and functional assessment of the right ventricle. Circulation 2008;117:1436-48.
3. Mertens LL, Friedberg MK. Imaging the right ventricle—current state of the
art. Nat Rev Cardiol 2010;7:551-63.
4. Hickey EJ, Veldtman G, Bradley TJ, Gengsakul A, Manlhiot C,
Williams WG, et al. Late risk of outcomes for adults with repaired tetralogy
of Fallot from an inception cohort spanning four decades. Eur J Cardiothorac Surg 2009;35:156-64.
5. Discigil B, Dearani JA, Puga FJ, Schaff HV, Hagler DJ, Warnes CA, et al.
Late pulmonary valve replacement after repair of tetralogy of Fallot.
J Thorac Cardiovasc Surg 2001;121:344-51.
6. Baumgartner H, Bonhoeffer P, De Groot NM, de Haan F, Deanfield JE,
Galie N, et al. ESC guidelines for the management of grown-up congenital
heart disease (new version 2010). Eur Heart J 2010;31:2915-57.
7. Niemann PS, Pinho L, Balbach T, Galuschky C, Blankenhagen M,
Silberbach M, et al. Anatomically oriented right ventricular volume mea-
Journal of the American Society of Echocardiography
- 2011
surements with dynamic three-dimensional echocardiography validated
by 3-Tesla magnetic resonance imaging. J Am Coll Cardiol 2007;23(50):
1668-76.
8. van der Zwaan HB, Helbing WA, McGhie JS, Geleijnse ML,
Luijnenburg SE, Roos-Hesselink JW, et al. Clinical value of real-time
three-dimensional echocardiography for right ventricular quantification
in congenital heart disease: validation with cardiac magnetic resonance imaging. J Am Soc Echocardiogr 2010;23:134-40.
9. Khoo NS, Young A, Occleshaw C, Cowan B, Zeng IS, Gentles TL. Assessments of right ventricular volume and function using three-dimensional
echocardiography in older children and adults with congenital heart disease: comparison with cardiac magnetic resonance imaging. J Am Soc
Echocardiogr 2009;22:1279-88.
10. Hubka M, Bolson EL, McDonald JA, Martin RW, Munt B, Sheehan FH.
Three-dimensional echocardiographic measurement of left and right
ventricular mass and volume: in vitro validation. Int J Cardiovasc Imaging
2002;18:111-8.
11. Wong SP, Johnson RK, Sheehan FH. Rapid and accurate left ventricular
surface generation from three-dimensional echocardiography by a catalog
based method. Rapid LV surface generation by three-dimensional echo. Int
J Cardiovasc Imaging 2003;19:9-17.
12. Sheehan FH, Kilner PJ, Sahn DJ, Vick GW III, Stout KK, Ge S, et al.
Accuracy of knowledge-based reconstruction for measurement of right
ventricular volume and function in patients with tetralogy of Fallot. Am
J Cardiol 2010;105:993-9.
13. Knauth AL, Gauvreau K, Powell AJ, Landzberg MJ, Walsh EP, Lock JE,
et al. Ventricular size and function assessed by cardiac MRI predict major
adverse clinical outcomes late after tetralogy of Fallot repair. Heart 2008;
94:211-6.
14. Oosterhof T, van Straten A, Vliegen HW, Meijboom FJ, van Dijk AP,
Spijkerboer AM, et al. Preoperative thresholds for pulmonary valve
replacement in patients with corrected tetralogy of Fallot using cardiovascular magnetic resonance. Circulation 2007;116:545-51.
15. Therrien J, Provost Y, Merchant N, Williams W, Colman J, Webb G.
Optimal timing for pulmonary valve replacement in adults after tetralogy
of Fallot repair. Am J Cardiol 2005;95:779-82.
16. Grewal J, Majdalany D, Syed I, Pellikka P, Warnes CA. Three-dimensional
echocardiographic assessment of right ventricular volume and function in
adult patients with congenital heart disease: comparison with magnetic
resonance imaging. J Am Soc Echocardiogr 2010;23:127-33.
17. Winter MM, Bernink FJ, Groenink M, Bouma BJ, van Dijk AP, Helbing WA,
et al. Evaluating the systemic right ventricle by CMR: the importance of
consistent and reproducible delineation of the cavity. J Cardiovasc Magn
Reson 2008;10:40.
18. Iriart X, Montaudon M, Lafitte S, Chabaneix J, Reant P, Balbach T, et al.
Right ventricle three-dimensional echography in corrected tetralogy of
Fallot: accuracy and variability. Eur J Echocardiogr 2009;10:784-92.
19. Mooij CF, de Wit CJ, Graham DA, Powell AJ, Geva T. Reproducibility
of MRI measurements of right ventricular size and function in patients
with normal and dilated ventricles. J Magn Reson Imaging 2008;28:
67-73.
20. Helbing WA, Bosch HG, Maliepaard C, Rebergen SA, van der Geest RJ,
Hansen B, et al. Comparison of echocardiographic methods with
magnetic resonance imaging for assessment of right ventricular function
in children. Am J Cardiol 1995;76:589-94.
21. Greutmann M, Tobler D, Biaggi P, Mah ML, Crean A, Oechslin EN, et al.
Echocardiography for assessment of right ventricular volumes revisited:
a cardiac magnetic resonance comparison study in adults with repaired
tetralogy of Fallot. J Am Soc Echocardiogr 2010;23:905-11.