Download Integration of 3D Imaging Data in the Assessment of Aortic Stenosis

Integration of 3D Imaging Data in the Assessment of
Aortic Stenosis
Impact on Classification of Disease Severity
Bridget O’Brien, MD; Paul Schoenhagen, MD; Samir R. Kapadia, MD; Lars G. Svensson, MD, PhD;
Leonardo Rodriguez, MD; Brian P. Griffin, MD; E. Murat Tuzcu, MD; Milind Y. Desai, MD
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Background—In patients with aortic stenosis (AS), precise assessment of severity is critical for treatment decisions.
Estimation of aortic valve area (AVA) with transthoracic echocardiographic (TTE)-continuity equation (CE) assumes
a circular left ventricular outflow tract (LVOT). We evaluated incremental utility of 3D multidetector computed
tomography (MDCT) over TTE assessment of AS severity.
Methods and Results—We included 51 patients (age, 81⫾8 years; 61% men; mean gradient, 42⫾12 mm Hg) with calcific
AS who underwent evaluation for treatment options. TTE parameters included systolic LVOT diameter (D) and
continuous and pulsed wave (CW and PW) velocity-time integrals (VTI) through the LVOT and mean transaortic
gradient. MDCT parameters included systolic LVOT area, ratio of maximal to minimal LVOT diameter (eccentricity
index), and aortic planimetry (AVAp). TTE-CE AVA [(D2⫻0.786⫻VTIpw)/VTIcw] and dimensionless index (DI)
[VTIpw/VTIcw] were calculated. Corrected AVA was calculated by substituting MDCT LVOT area into CE. The
majority (96%) of patients had eccentric LVOT. LVOT area, measured on MDCT, was higher than on TTE (3.84⫾0.8
cm2 versus 3.03⫾0.5 cm2, P⬍0.01). TTE-AVA was smaller than AVAp and corrected AVA (0.67⫾0.1cm2, 0.82⫾0.3
cm2, and 0.86⫾0.3 cm2, P⬍0.01). Using TTE measurements alone, 73% of patients had congruence for severe AS (DI
ⱕ0.25 and CE AVA ⬍0.8 cm2), which increased to 92% using corrected CE.
Conclusions—In patients with suspected severe AS, incorporation of MDCT-LVOT area into CE improves congruence for
AS severity. (Circ Cardiovasc Imaging. 2011;4:566-573.)
Key Words: aortic stenosis 䡲 transthoracic echocardiography 䡲 multidetector computed tomography
䡲 aortic valve area
A
equation is based on the assumption of a circular shape of the
left ventricular outflow tract (LVOT). However, previous
studies describe a high prevalence of oval LVOT shape,
potentially causing underestimation of AVA calculation with
the continuity equation.4 – 8
The recent use of multidetector computed tomography
(MDCT) for preprocedural assessment of the aortic valve/
root in the context of TAVI allows us to evaluate the impact
of 3D image analysis on the congruence between severity
criteria.4 –7,9 –13 The aim of our study was to evaluate (1)
differences in echocardiographic and MDCT-derived AVA
and (2) whether incorporation of MDCT LVOT area into
continuity equation improves congruence between various
criteria for severity of AS.
ortic stenosis (AS) is the most common acquired valve
disease in the developed world, with an age-related
increase in prevalence.1 In symptomatic patients with severe
AS, conventional aortic valve replacement still remains the
standard of care; however, elderly patients frequently have
several comorbidities that make surgery potentially prohibitive. Because of recent advances in percutaneous techniques
such as transcatheter aortic valve implantation (TAVI), the
therapeutic options have expanded to include patients considered at high risk for surgery.2
Clinical Perspective on p 573
Precise assessment of AS severity is essential for appropriate treatment decision-making. Standard echocardiographic assessment of aortic valve area (AVA) relies on congruence of several criteria including transaortic gradients and
AVA, calculated by continuity equation and/or planimetry.3
The standard 2D estimation of AVA using the continuity
Methods
Fifty-one consecutive symptomatic patients, with suspected severe
AS referred to our institution for evaluation for potential surgical
versus percutaneous treatment options between the years 2006 to
Received March 4, 2011; accepted June 29, 2011.
From the Heart and Vascular Institute (B.O., P.S., S.R.K., L.G.S., L.R., B.P.G., E.M.T., M.Y.D.) and Imaging Institute (P.S., L.R., M.Y.D.), the
Cleveland Clinic, Cleveland, OH.
Correspondence to Milind Y. Desai, MD, Tomsich Department of Cardiovascular Medicine, Heart and Vascular Institute, Cleveland Clinic, 9500
Euclid Ave, Desk J1-5, Cleveland, OH 44195. E-mail [email protected]
© 2011 American Heart Association, Inc.
Circ Cardiovasc Imaging is available at http://circimaging.ahajournals.org
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DOI: 10.1161/CIRCIMAGING.111.964916
O’Brien et al
Aortic Stenosis, MDCT, and Echocardiography
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Figure 1. Patient with suspected severe aortic stenosis. Ejection fraction was 55%. On transthoracic echocardiography, left ventricular
outflow tract (LVOT) diameter was measured as 1.8 cm (A). Notice the heavily calcified valve in short axis (B). AorticVTI was 127 and
LVOTVTI was 35 (C and D). Based on that, aortic valve area (AVA) was measured as 0.70 cm2. However, after multiplanar reformatting,
the LVOT was elliptical on multidetector computed tomography, with an eccentricity index of 1.2, measured as a ratio of the largest
(dark line)/shortest (white line) diameter (E), and measured LVOT area was 3.24 cm2. Putting that in the continuity equation gave a corrected AVA of 0.9 cm2. CT planimetry AVA was 0.98 cm2 (F).
2007, were included in this observational study. Patients were
included if they had undergone clinically indicated comprehensive
standard and Doppler echocardiography and contrast-enhanced
MDCT of the aortic root at our institution within 1 week of each
other. We excluded patients with bicuspid aortic valve morphology
because there is a high proportion of aortic root and annular
eccentricity. Patients with advanced renal insufficiency or other
contraindications to intravenous contrast dye were excluded. Baseline, clinical, demographic, and imaging data were collected. Surgical risk was assessed, based on clinical and imaging data, and a
Euroscore was calculated in each patient.14 This observational study
was approved by the institutional review board, with waiver of
individual informed consent.
Transthoracic Echocardiography
Surface echocardiograms were obtained using commercially available systems (Siemens, Erlangen, Germany; General Electric, Milwaukee, WI, and Philips, Best, The Netherlands). Left ventricular
ejection fraction (EF) was calculated according to guidelines.15 Peak
and mean transaortic valvular gradients were measured in all patients
using continuous wave Doppler in standard echocardiographic
views. Velocity time integrals (VTI) across aortic valve (using
continuous wave Doppler) and LVOT (using pulsed wave Doppler)
were also recorded. Diameter of the LVOT was measured from the
parasternal long-axis in a standard fashion during midsystole. LVOT
area was derived from this measurement in a standard fashion.
Transthoracic AVA (TTE-AVA) was calculated by using the continuity equation in a standard fashion using the following formula
(Figure 1A through 1D): (LVOT diameter2⫻0.786⫻LVOTVTI)/
Aortic valveVTI. In addition, dimensionless index (DI) was recorded
as follows: LVOTVTI/Aortic valveVTI. All measurements were performed according to previously published guidelines.3
MDCT Acquisition and Analysis
All subjects were scanned on standard MDCT scanner (Siemens
Medical Solutions, Definition Dual Source, Erlangen, Germany)
after administration of an iodinated contrast agent (80 to 100 mL of
Ultravist 370) at 4 to 5 mL/s followed by 30 to 50 mL of normal
saline at the same rate. A contrast bolus tracking technique using a
region of interest in the ascending aorta was used. Once the desired
attenuation was reached, scanning was initiated in the craniocaudal
direction during a single inspiratory breath-hold. All patients were
scanned from the level of the carina to the mid left ventricle. Spiral
data were acquired with retrospective ECG gating using the follow-
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Figure 1 (Continued).
ing parameters: gantry rotation time⫽330 ms; beam collimation⫽32⫻0.6 mm; tube voltage⫽120 kVp; tube current-time product per rotation⫽250 to 410 mAs/rotation; and beam pitch of 0.2 to
0.5. ECG-based tube current modulation was used for all patients,
with maximum current turned on between 30% to 70% phases of the
cardiac cycle. For the remaining phases, the current was reduced.
Images were reconstructed during 10 to 14 phases of the cardiac
cycle, depending on the patient heart rate with a temporal resolution
of 83 ms and section thickness of 0.75 mm. Typical radiation in the
study sample was ⬍12 mSEV.
MDCT images were analyzed on a dedicated CT workstation
(Terra Recon, CA). The investigator (M.D.), experienced in interpreting cardiac CT, was blinded to the subject’s clinical status and
TTE images. The largest cross-sectional area of the LVOT was
measured in systole (30% to 40% of the R-R phase), using double
oblique images to identify the true short axis, approximately 0.5 to
0.7 cm below the aortic valve “hinge point.” The maximum and
minimum diameters of the LVOT were also measured to calculate
the eccentricity index (maximum/minimum LVOT diameter after
multiplanar reformatting, Figure 1E). Quantitatively, the AVA was
determined by planimetry of the aortic valve using a plane parallel to
the short axis of the aortic root. The time point of maximal aortic
valve opening was identified during systole (usually at 30% to 40%
of the R-R interval). The area of the aortic valve opening was found
by scrolling through the short axis images toward the tip of the cusps
until the smallest opening was found. The planimetered AVA on
MDCT (AVAp) was determined by tracing the inside borders of the
coronary cusps with electronic calipers and reported in square
centimeters (Figure 1F).
Corrected Multimodality AVA
We then used the LVOT area, measured on MDCT, as part of the
continuity equation, to generate a corrected multimodality AVA as
follows: (Maximum LVOT areaMDCT⫻LVOTVTI)/Aortic valve VTI.
Statistical Analysis
All values presented are mean⫾SD values for continuous variables
and as percentage of total patients for categorical variables. The 2
independent samples and paired t tests were used to compare
continuous variables for comparison between and within groups,
respectively. ␹2 was used for comparison of categoric variables.
Pearson correlation coefficient was used to test associations between
continuous variables. In addition, interobserver (B.O. and M.D.) and
intraobserver (M.D.) reproducibility of various MDCT parameters
was measured by using intraclass correlation coefficients. BlandAltman analysis was performed to systematically assess the differences between LVOT area measured using 2 different imaging
techniques (echocardiography and MDCT).16 All probability values
were 2-sided. A probability value of ⬍0.05 was considered significant. Data assembly statistical comparisons were performed with
JMP Software version 6.0.2 and SPSS version 11.5 (SPSS Inc,
Chicago, IL).
Results
Baseline Characteristics
The baseline characteristics of the total group and 2 subgroups divided on basis of preserved or low LV EF are shown
in Table 1. Mean age was 81⫾8 years, of which 61% were
men (with a significantly higher proportion of men in the
depressed LV EF subgroup). The mean Euroscore was high,
suggesting a fairly high-risk sample at baseline. Approximately two-thirds of the study group had a history of prior
open heart surgery. In the study sample, 10 (20%) patients
qualified and subsequently underwent TAVI, as part of a
clinical trial, whereas 15 (29%) underwent aortic valve
replacement and 4 (8%) underwent percutaneous balloon
valvuloplasty.
The baseline echocardiographic measurements of the total
group and 2 subgroups, divided on the basis of preserved or
low LV EF, are shown in Table 2. As shown in Table 2, only
31 (59%) patients had an EF ⬎50%, whereas 9 (18%) had EF
between 40% and 50% and 11 (24%) had EF ⬍40%. In terms
of mean transaortic gradients, 27 (53%) had values
ⱖ40 mm Hg, 15 (29%) between 30 to 40 mm Hg and 9 (18%)
⬍30 mm Hg. Only 8% of patients had greater than 2⫹ aortic
regurgitation. The MDCT characteristics are also shown in
Table 2. The maximum LVOT diameter measured on MDCT
O’Brien et al
Table 1.
Baseline Characteristics of the Study Sample
Aortic Stenosis, MDCT, and Echocardiography
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(96%) had an oval-shaped LVOT (based on an eccentricity
index ⬎1.0) as measured on CT.
Intraclass correlation coefficients, used to measure reproducibility of various MDCT measurements, were as follows:
LVOT area (intraobserver: 0.98 [0.92 to 0.99], interobserver:
0.92 [0.68 to 0.98], both P⬍0.001) and MDCT AVA (intraobserver: 0.93 [0.70 to 0.98], interobserver: 0.82 [0.26 to
0.95], both P⬍0.001).
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Variable
Total
Group
(n⫽51)
LV EF
⬍50%
(n⫽21)
LV EF
ⱖ50%
(n⫽30)
P
Value
Age
81⫾8
82⫾7
80⫾8
0.2
Male sex
31 (61%)
18 (86%)
13 (43%)
Hypertension
37 (73%)
13 (62%)
24 (65%)
0.2
Diabetes mellitus
23 (45%)
7 (33%)
16 (53%)
0.2
Smoking history
28 (55%)
11 (52%)
17 (57%)
0.8
Assessment of AVA
Documented coronary artery
disease
42 (82%)
19 (90%)
23 (77%)
0.2
Documented stroke
7 (14%)
4 (19%)
3 (10%)
0.4
Chronic obstructive
pulmonary disease
21 (41%)
8 (38%)
13 (43%)
0.7
Previous cardiac surgery
35 (69%)
17 (81%)
18 (60%)
0.1
Serum creatinine
1.3⫾0.8
1.5⫾1.1
1.2⫾0.4
0.1
AVAp was significantly higher than what was measured by
continuity equation on echocardiography (0.82⫾0.25 cm2
versus 0.67⫾0.13 cm2, P⬍0.001). The mean corrected AVA
was 0.86⫾0.28 cm2 (which was similar to AVAp, P⫽NS).
The mean corrected AVA was similar in patients with
preserved versus depressed LV EF, 0.8⫾0.3 cm2 versus
0.9⫾0.3 cm2 (P⫽NS).
Body mass index
27⫾5
28⫾5
27⫾5
0.6
Euroscore
25⫾18
37⫾19
16⫾12
⬍0.001
0.002
LV EF indicates left ventricular ejection fraction.
was significantly greater than that on echocardiography
(2.73⫾0.4 cm versus 1.96⫾0.15 cm, P⬍0.001). Similarly,
LVOT area measured on MDCT was significantly higher
than that measured on transthoracic echocardiography
(3.84⫾0.8 versus 3.03⫾0.5, P⬍0.01). Bland-Altman analysis
(Figure 2) demonstrates that transthoracic echocardiography
systematically underestimates LVOT area. Also, 49 patients
Table 2.
Imaging Characteristics of the Study Sample
Congruence Between MDCT and
Echocardiography Parameters
We subsequently tested the correlation between various
Doppler-derived measurements and AVA measured by different techniques, as shown in Table 3 and Figure 3A through
3C. Correlation of mean transaortic gradient with TTE-AVA
(measured on continuity) was only modest. However, the
correlation of mean transaortic gradient with AVAp measured
on MDCT and corrected” AVA was significantly improved
as compared with TTE-AVA (probability value for “improvement” in correlation was ⬍0.01). When contrasting patients
with normal and abnormal EF, the correlation between mean
gradient and TTE-AVA, AVAp, and corrected AVA were
much lower in patients with EF ⬍50% than in patients with
EF ⱖ50% (probability value for “improvement” in various
corresponding correlations were ⬍0.01).
Total
Group
(n⫽51)
LV EF
⬍50%
(n⫽21)
LV EF
ⱖ50%
(n⫽30)
P
Value
LVOT diameter, cm
1.96⫾0.2
2.02⫾0.2
1.92⫾0.2
0.03
Congruence Between DI and AVA
LVOT area
3.03⫾0.5
3.21⫾0.5
2.92⫾0.5
0.03
In terms of TTE-AVA (by continuity equation), 40 (78%)
patients had an AVA of ⬍0.8 cm2. The DI was ⱕ0.25 in only
30 (59%) cases. In the study sample, only 37 (73%) of the
patients had congruence of criteria for severe AS (DI ⱕ0.25
and TTE-AVA ⬍0.8 cm2). However using an AVAp
(MDCT-based) cutoff of ⬍0.8 cm2 for severe AS, the
congruence increased to 80% patients. Similarly, if corrected
AVA with a cutoff of ⬍0.8 cm2 was used, the number of
patients with congruence increased to 92% (probability value
for comparison ⬍0.05).
Variable
Echocardiography
25⫾12
20⫾5
28⫾15
0.02
Aortic valve VTI
LVOT VTI
113⫾51
100⫾25
123⫾62
0.1
AVA, continuity equation,
cm2
0.67⫾0.1
0.65⫾0.1
0.68⫾0.2
0.5
Peak aortic valve
gradient, mm Hg
73⫾18
71⫾23
74⫾14
0.6
Mean aortic valve
gradient, mm Hg
42⫾12
41⫾14
42⫾10
0.9
Dimensionless index
Aortic insufficiency (⬎2⫹)
0.23⫾0.06 0.21⫾0.05 0.24⫾0.06
4 (8%)
1 (5%)
3 (10%)
0.09
0.5
MDCT
Maximum LVOT diameter,
cm
2.73⫾0.4
2.84⫾0.3
2.66⫾0.4
0.08
Minimum LVOT diameter,
cm
2.2⫾0.3
2.3⫾0.3
2.1⫾0.3
0.02
Eccentricity index
1.27⫾0.2
1.24⫾0.1
1.29⫾0.2
0.3
LVOT area, cm2
3.84⫾0.8
3.83⫾0.8
3.84⫾0.8
0.9
AVA, cm2
0.82⫾0.3
0.74⫾0.2
0.87⫾0.3
0.07
LV EF indicates left ventricular ejection fraction; LVOT, left ventricular
outflow tract; VTI, velocity-time integral; AVA, aortic valve area; and MDCT,
multidetector computed tomography.
Discussion
In the present study, we found that in patients with suspected
severe AS, integration of 3D imaging data are associated with
increased congruence between DI and AVA, leading to
improved classification of stenosis severity. Specifically,
TTE-AVA calculated using standard continuity equation with
assumed circular LVOT geometry was significantly smaller
than corrected AVA, based on MDCT-derived LVOT area.
Corrected AVA showed good correlation with AVAp measured on MDCT.
The differences in standard and corrected AVA appear
secondary to consistently smaller LVOT dimensions mea-
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Difference
Differenc
ce in LVOT
T area
CT-TTE, cm
m)
(MDC
1
Mean Difference
0.5
Mean Diff. ± 2SD
0
-0.5
25
2.5
3
35
3.5
4
45
4.5
5
Figure 2. Bland-Altman analysis demonstrating the
association between multidetector computed
tomography (MDCT) left ventricular outflow tract
(LVOT) area and transthoracic (TTE) LVOT area.
-1
-1.5
-2
-2.5
3
-3
-3.5
Mean LVOT area (MDCT and TTE, cm)
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sured with TTE as compared with MDCT. TTE calculates
LVOT based on a single measured diameter, whereas the
LVOT was measured with CT by planimetry. The calculation
from a single diameter is limited because of the known
frequent eccentricity of the annulus and squaring of the
Table 3. Correlation Between Aortic Valve Area
Measurements Using Various Techniques and Transaortic
Gradients and Dimensionless Index
Linear Regression
r Value
P Value
Mean transaortic gradient
Total group
TTE-AVA (continuity)
⫺0.28
0.05
AVAp
⫺0.39
0.004
Corrected AVA
⫺0.39
0.005
LV EF ⱖ50%
TTE-AVA (continuity)
⫺0.37
0.05
AVAp
⫺0.43
0.02
Corrected AVA
⫺0.45
0.04
LV EF ⬍50%
TTE-AVA (continuity)
⫺0.21
0.4
AVAp
⫺0.43
0.05
Corrected AVA
⫺0.37
0.05
Dimensionless index
Total group
TTE-AVA (continuity)
0.69
⬍0.001
AVAp
0.77
⬍0.001
Corrected AVA
0.73
⬍0.001
LV EF ⱖ50%
TTE-AVA (continuity)
0.77
⬍0.001
AVAp
0.79
⬍0.001
Corrected AVA
0.75
⬍0.001
LV EF ⬍50%
TTE-AVA (continuity)
0.54
0.01
AVAp
0.73
⬍0.001
Corrected AVA
0.70
⬍0.001
TTE indicates transthoracic echocardiography; AVA, aortic valve area; AVAp,
AVA by computed tomography planimetry; and LV EF, left ventricular ejection
fraction.
diameter to derive the area augments even small errors. Our
study sample was consistent with this observation as a vast
majority of patient had an elliptical LVOT. Prior groups have
also found that a high proportion of patients have an elliptical
LVOT.4 – 8
Previous studies have also demonstrated that TTE underestimates AVA compared with MDCT, cardiac magnetic
resonance, transesophageal echocardiography, Gorlin formula, and even surgical sizers.8,12,17–20 One study compared
AVA from planimetry on MDCT to AVA calculated using
traditional TTE and found good concordance between the 2
measurements with small underestimation of area by TTE.18
A previous report has also demonstrated good concordance
between TTE-AVA and AVAp on MDCT, with a tendency
for underestimation of AVA by TTE (similar to the current
study).21 Another study also measured the coronal and sagittal
diameter of the aortic annulus on MDCT and found that
MDCT-derived diameters were significantly larger than diameters measured on echocardiography.12
On further analysis, it was also apparent that patients with
low LV EF had a significantly higher LVOT diameter on
TTE, probably reflecting changes concomitant with LV
remodeling. These patients also had a lower LVOTVTI, as
would be expected. As a result, there was a significant impact
of LV EF on the association between TTE-AVA and
transaortic gradient, with lower EF resulting in much poorer
correlation. The correlation between corrected AVA and
mean gradient improved significantly in particular in the low
EF group. Similarly, EF had a significant impact on the
association between TTE-AVA and DI, with low EF resulting
in much poorer correlation. The most likely reason behind
this is the improved accuracy of measurements using MDCT
LVOT area.
Importantly, we demonstrate that when using AVAp and
corrected AVA, more patients had congruent criteria for
severity of AS, especially low EF patients. This is potentially
important because severity of AS is the ultimate deciding
factor in timing of intervention. Based on the results of this
study, it appears that in patients with discrepant calculated
valve areas, transaortic gradients, and DI, an accurate 3D
assessment of LVOT area would be crucial to classifying
severity of AS. Further, severity of AS may be reclassified in
a number of patients and potentially alter management.
Hence, multimodality imaging could play complementary (as
O’Brien et al
Aortic Stenosis, MDCT, and Echocardiography
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Figure 3. Correlation between dimensionless index and aortic valve area measured by transthoracic echocardiography (TTE) (A), multidetector computed tomography (MDCT) (B), and corrected multimodality imaging technique (C).
opposed to competing) roles in assessment of AS. Of course,
with rapid evolution of 3D echocardiography (especially
TEE), LVOT assessment can also potentially be performed
using that technique.4,17 However, it must be kept in mind that
in the current study, we included only patients with severe
AS, and, as such, the increased elliptical nature of the LVOT
might not be applicable to patients with mild-moderate AS.
Similar to our study, others have attempted to measure a
cross section of the LVOT or planimetered LVOT area on
MDCT and compare it with other imaging modalities as well
as incorporate this measurement into assessments of AVA. In
one study, it was demonstrated that the ellipse-derived LVOT
diameter measurement, when incorporated into the continuity
equation, correlated more closely with planimetered LVOT
area compared with the traditional circle-derived LVOT
area.8 However, only 11 patients in this study had both
MDCT and TTE for comparison, and none of the patients had
significant AS. Another study compared MDCT planimetered
LVOT area to 2D TEE circular-derived LVOT area, 3D TEE
circular-derived LVOT area, and 3D TEE planimetered
LVOT area in patients with severe AS.4 All TEE methods
significantly underestimated LVOT area compared with
MDCT. Recalculating AVA using 3D TEE circular, 3D TEE
planimetered, and MDCT planimetered LVOT areas, a respective 10%, 25%, and 25% of patients were reclassified as
moderate stenosis highlighting the importance of accurate
LVOT measurements. However, the sample was different
from the current study such that the EF was substantially
higher, all patients in that study underwent TAVI (despite
⬇25% being reclassified as moderate AS in retrospect), and
a substantially smaller number had a history of prior open
heart surgery. Finally, another group also substituted CT
planimetered LVOT area into the continuity equation and
their corrected AVA was not only systematically larger
compared with AVA derived from standard continuity equation but also improved correlation between various severity
measurements.22 However, this study sample was much
younger (average age, 58 years) and included only 10 patients
with moderate to severe AS. Our study predominantly included patients with severe AS (that had a need for invasive
therapies). In addition, we included a sizable proportion of
patients with abnormal EF (where multimodality imaging
evaluation is likely to have the most significant impact).
Recently, MDCT has evolved as an important modality for
aortic valve assessment and its therapeutic planning; perhaps
out of necessity. With an increasing number of redo cardiac
surgical procedures, MDCT has become an invaluable tool
for preoperative planning. Indeed, in our study sample, a
substantial proportion of patients had a history of prior
cardiac surgeries and were being considered for redo procedures, in which MDCT has been demonstrated to have
incremental diagnostic utility and is considered an appropriate indication.23–25 Furthermore, TAVI is rapidly emerging as
a viable therapeutic option in patients with severe AS.2
However, due to lack of direct visualization during TAVI, the
operator is more reliant on preprocedural and intraprocedural
imaging both for appropriate patient selection and to guide
the procedure. One of the major advantages of a traditional
open surgical approach is that direct visualization of the
valvular apparatus is feasible, enabling appropriate valve
prosthesis selection. Hence, MDCT has become routine in
assessment of such patients to evaluate for aortic valve/aortic
calcification, assessment of aortic root morphology, and
evaluation of the anatomic relationship between coronary
artery takeoff and aortic annulus.4 –7,9 –13 On the basis of the
results of this study, we can potentially use information about
LVOT area obtained on MDCT for the above indications at
no additional cost of radiation or nephrotoxicity in this
sample. However, it must be recognized that most outcomes
data in AS are based on echocardiographic measures, and
multimodality evaluation of severity of AS needs validation
for its potential incremental value.
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The current study has following limitations. This is an
observational study with a relatively small sample size.
Hence, there is low power to detect differences between
groups of patients. Also, there is a possibility of severely
inflated type I error because of multiple testing without
adjusting the significance level. MDCT is limited by the need
for iodine-based contrast administration, which brings in the
added burden potential nephrotoxicity, especially in an older
sample (typical of severe, nonbicuspid AS). Although MDCT
is also associated with significant radiation exposure, the
risks of long-term deleterious effects of radiation are of lesser
concern in an elderly population of AS patients. Still, for the
MDCT community, it is important to continue to work on
minimizing radiation exposure. With availability of newer
scanners and newer imaging techniques, the concept of
aggressive radiation reduction is rapidly evolving. Another
limitation is that of establishing the gold standard for assessment of AVA: planimetry by standard TTE, TEE, and 3D
TEE MDCT, or the Gorlin formula. Unfortunately, not all
patients in the study sample had a transesophageal echocardiogram performed in the current study sample; with no one
having 3D TEE images. As a result, that data are not
presented for the study sample. It is possible that the LVOT
assessment can potentially be performed using that technique.
Indeed, previous studies have attempted to incorporate that in
assessment of AS. However, transesophageal echocardiography is invasive, necessitating sedation in this already frail
sample. As demonstrated in the current study, information on
LVOT area on MDCT is available without any additional
ramifications to the patient. Also, AVA estimated by the
Gorlin formula was not uniformly available in the study
sample, probably reflecting the current practice of increased
reliance on noninvasive measures.
Conclusions
We demonstrate that in the vast majority of older patients
with severe AS, AVA is typically underestimated using
standard surface echocardiography measurements alone. Incorporating the LVOT area, which is frequently elliptical
when measured using a 3D technique such as MDCT, into the
continuity equation reduces the discrepant classification of
severity of AS, especially in patients with lower EF. Improved congruence in AVA measurements could help selection of appropriate patients for both conventional surgical
treatment and TAVI. In addition, it could also help in further
refinements in shape and size of future percutaneous aortic
valves.
Disclosures
None.
References
1. Carabello BA, Paulus WJ. Aortic stenosis. Lancet. 2009;373:956 –966.
2. Leon MB, Smith CR, Mack M, Miller DC, Moses JW, Svensson LG,
Tuzcu EM, Webb JG, Fontana GP, Makkar RR, Brown DL, Block PC,
Guyton RA, Pichard AD, Bavaria JE, Herrmann HC, Douglas PS,
Petersen JL, Akin JJ, Anderson WN, Wang D, Pocock S. Transcatheter
aortic-valve implantation for aortic stenosis in patients who cannot
undergo surgery. N Engl J Med. 2010;363:1597–1607.
3. Baumgartner H, Hung J, Bermejo J, Chambers JB, Evangelista A, Griffin
BP, Iung B, Otto CM, Pellikka PA, Quinones M. Echocardiographic
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
assessment of valve stenosis: EAE/ASE recommendations for clinical
practice. J Am Soc Echocardiogr. 2009;22:1–23.
Ng AC, Delgado V, van der Kley F, Shanks M, van de Veire NR, Bertini
M, Nucifora G, van Bommel RJ, Tops LF, de Weger A, Tavilla G, de
Roos A, Kroft LJ, Leung DY, Schuijf J, Schalij MJ, Bax JJ. Comparison
of aortic root dimensions and geometries before and after transcatheter
aortic valve implantation by 2- and 3D transesophageal echocardiography
and multislice computed tomography. Circ Cardiovasc Imaging. 2009;3:
94 –102.
Tops LF, Wood DA, Delgado V, Schuijf JD, Mayo JR, Pasupati S,
Lamers FP, van der Wall EE, Schalij MJ, Webb JG, Bax JJ. Noninvasive
evaluation of the aortic root with multislice computed tomography implications for transcatheter aortic valve replacement. J Am Coll Cardiol
Cardiovasc Imaging. 2008;1:321–330.
Akhtar M, Tuzcu EM, Kapadia SR, Svensson LG, Greenberg RK, Roselli
EE, Halliburton S, Kurra V, Schoenhagen P, Sola S. Aortic root morphology in patients undergoing percutaneous aortic valve replacement:
evidence of aortic root remodeling. J Thorac Cardiovasc Surg. 2009;137:
950 –956.
Doddamani S, Grushko MJ, Makaryus AN, Jain VR, Bello R, Friedman
MA, Ostfeld RJ, Malhotra D, Boxt LM, Haramati L, Spevack DM.
Demonstration of left ventricular outflow tract eccentricity by 64-slice
multi-detector CT. Int J Cardiovasc Imaging. 2009;25:175–181.
Doddamani S, Bello R, Friedman MA, Banerjee A, Bowers JH Jr, Kim B,
Vennalaganti PR, Ostfeld RJ, Gordon GM, Malhotra D, Spevack DM.
Demonstration of left ventricular outflow tract eccentricity by real time
3D echocardiography: implications for the determination of aortic valve
area. Echocardiography. 2007;24:860 – 866.
Kurra V, Kapadia SR, Tuzcu EM, Halliburton SS, Svensson L, Roselli
EE, Schoenhagen P. Pre-procedural imaging of aortic root orientation and
dimensions: comparison between X-ray angiographic planar imaging and
3D multidetector row computed tomography. J Am Coll Cardiol Cardiovasc Interv. 2010;3:105–113.
Schoenhagen P, Numburi U, Halliburton SS, Aulbach P, von Roden M,
Desai MY, Rodriguez LL, Kapadia SR, Tuzcu EM, Lytle BW. Threedimensional imaging in the context of minimally invasive and transcatheter cardiovascular interventions using multi-detector computed tomography: from pre-operative planning to intra-operative guidance. Eur
Heart J. 2010;31:2727–2740.
Schoenhagen P, Tuzcu EM, Kapadia SR, Desai MY, Svensson LG.
Three-dimensional imaging of the aortic valve and aortic root with
computed tomography: new standards in an era of transcatheter valve
repair/implantation. Eur Heart J. 2009;30:2079 –2086.
Delgado V, Ng AC, van de Veire NR, van der Kley F, Schuijf JD, Tops
LF, de Weger A, Tavilla G, de Roos A, Kroft LJ, Schalij MJ, Bax JJ.
Transcatheter aortic valve implantation: role of multi-detector row
computed tomography to evaluate prosthesis positioning and deployment
in relation to valve function. Eur Heart J. 2010;31:1114 –1123.
Tops LF, Delgado V, van der Kley F, Bax JJ. Percutaneous aortic valve
therapy: clinical experience and the role of multi-modality imaging.
Heart. 2009;95:1538 –1546.
Nashef SA, Roques F, Michel P, Gauducheau E, Lemeshow S, Salamon
R. European system for cardiac operative risk evaluation (EuroSCORE).
Eur J Cardiothorac Surg. 1999;16:9 –13.
Lang RM, Bierig M, Devereux RB, Flachskampf FA, Foster E, Pellikka
PA, Picard MH, Roman MJ, Seward J, Shanewise JS, Solomon SD,
Spencer KT, Sutton MS, Stewart WJ. Recommendations for chamber
quantification: a report from the American Society of Echocardiography’s
Guidelines and Standards Committee and the Chamber Quantification
Writing Group, developed in conjunction with the European Association
of Echocardiography, a branch of the European Society of Cardiology.
J Am Soc Echocardiogr. 2005;18:1440 –1463.
Bland JM, Altman DG. Statistical methods for assessing agreement
between two methods of clinical measurement. Lancet. 1986;1:307–310.
Poh KK, Levine RA, Solis J, Shen L, Flaherty M, Kang YJ, Guerrero JL,
Hung J. Assessing aortic valve area in aortic stenosis by continuity
equation: a novel approach using real-time three-dimensional echocardiography. Eur Heart J. 2008;29:2526 –2535.
Feuchtner GM, Dichtl W, Friedrich GJ, Frick M, Alber H, Schachner T,
Bonatti J, Mallouhi A, Frede T, Pachinger O, zur Nedden D, Muller S.
Multislice computed tomography for detection of patients with aortic
valve stenosis and quantification of severity. J Am Coll Cardiol. 2006;
47:1410 –1417.
Babaliaros VC, Liff D, Chen EP, Rogers JH, Brown RA, Thourani VH,
Guyton RA, Lerakis S, Stillman AE, Raggi P, Cheesborough JE, Veledar
O’Brien et al
20.
21.
22.
23.
E, Green JT, Block PC. Can balloon aortic valvuloplasty help determine
appropriate transcatheter aortic valve size? J Am Coll Cardiol Cardiovasc
Interv. 2008;1:580 –586.
Okura H, Yoshida K, Hozumi T, Akasaka T, Yoshikawa J. Planimetry
and transthoracic two-dimensional echocardiography in noninvasive
assessment of aortic valve area in patients with valvular aortic stenosis.
J Am Coll Cardiol. 1997;30:753–759.
Ropers D, Ropers U, Marwan M, Schepis T, Pflederer T, Wechsel M,
Klinghammer L, Flachskampf FA, Daniel WG, Achenbach S. Comparison of dual-source computed tomography for the quantification of the
aortic valve area in patients with aortic stenosis versus transthoracic
echocardiography and invasive hemodynamic assessment. Am J Cardiol.
2009;104:1561–1567.
Halpern EJ, Mallya R, Sewell M, Shulman M, Zwas DR. Differences in
aortic valve area measured with CT planimetry and echocardiography
(continuity equation) are related to divergent estimates of left ventricular
outflow tract area. AJR Am J Roentgenol. 2009;192:1668 –1673.
Kamdar AR, Meadows TA, Roselli EE, Gorodeski EZ, Curtin RJ, Sabik
JF, Schoenhagen P, White RD, Lytle BW, Flamm SD, Desai MY. Multidetector computed tomographic angiography in planning of reoperative
cardiothoracic surgery. Ann Thorac Surg. 2008;85:1239 –1245.
Aortic Stenosis, MDCT, and Echocardiography
573
24. Maluenda G, Goldstein MA, Lemesle G, Weissman G, Weigold G,
Landsman MJ, Hill PC, Pita F, Corso PJ, Boyce SW, Pichard AD,
Waksman R, Taylor AJ. Perioperative outcomes in reoperative cardiac
surgery guided by cardiac multidetector computed tomographic
angiography. Am Heart J. 2010;159:301–306.
25. Taylor AJ, Cerqueira M, Hodgson JM, Mark D, Min J, O’Gara P,
Rubin GD, Kramer CM, Berman D, Brown A, Chaudhry FA, Cury RC,
Desai MY, Einstein AJ, Gomes AS, Harrington R, Hoffmann U, Khare
R, Lesser J, McGann C, Rosenberg A, Schwartz R, Shelton M,
Smetana GW, Smith SC Jr. ACCF/SCCT/ACR/AHA/ASE/ASNC/
NASCI/SCAI/SCMR 2010 Appropriate Use Criteria for Cardiac
Computed Tomography: a Report of the American College of Cardiology Foundation Appropriate Use Criteria Task Force, the Society
of Cardiovascular Computed Tomography, the American College of
Radiology, the American Heart Association, the American Society of
Echocardiography, the American Society of Nuclear Cardiology, the
North American Society for Cardiovascular Imaging, the Society for
Cardiovascular Angiography and Interventions, and the Society for
Cardiovascular Magnetic Resonance. J Am Coll Cardiol.
2010;56:1864 –1894.
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CLINICAL PERSPECTIVE
In aortic stenosis (AS), the precise assessment of its severity is essential for appropriate therapeutic decision-making. It
relies on standard echocardiographic criteria, including transaortic gradients, dimensionless index, and aortic valve area,
which is typically calculated by the continuity equation. Continuity equation utilizes left ventricular outflow tract (LVOT)
diameter to calculate aortic valve area with the assumption that LVOT is circular. However, LVOT is very often elliptical
in shape, potentially creating a discrepancy between the actual and calculated aortic valve area. The discrepancy is more
noted in patients with reduced ejection fraction. The use of multidetector computed tomography enables us to
3-dimensionally measure LVOT area, which could be incorporated into the continuity equation. The current study of
patients with severe AS demonstrates that integration of 3D LVOT area significantly increases the congruence between
various AS severity criteria (including corrected aortic valve area, transaortic gradients, and dimensionless index), leading
to improved classification of AS severity, especially in the setting of reduced ejection fraction. Improved congruence in
aortic valve area measurements could help in selection of appropriate timing for surgical and percutaneous treatments. In
addition, it could also help in further refinements in shape and size of future percutaneous aortic valves.
Integration of 3D Imaging Data in the Assessment of Aortic Stenosis: Impact on
Classification of Disease Severity
Bridget O'Brien, Paul Schoenhagen, Samir R. Kapadia, Lars G. Svensson, Leonardo Rodriguez,
Brian P. Griffin, E. Murat Tuzcu and Milind Y. Desai
Downloaded from http://circimaging.ahajournals.org/ by guest on May 11, 2017
Circ Cardiovasc Imaging. 2011;4:566-573; originally published online July 7, 2011;
doi: 10.1161/CIRCIMAGING.111.964916
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