JACC: CARDIOVASCULAR INTERVENTIONS
VOL. 4, NO. 11, 2011
© 2011 BY THE AMERICAN COLLEGE OF CARDIOLOGY FOUNDATION
PUBLISHED BY ELSEVIER INC.
ISSN 1936-8798/$36.00
DOI: 10.1016/j.jcin.2011.07.014
Aortic Annulus Diameter Determination
by Multidetector Computed Tomography
Reproducibility, Applicability, and Implications for
Transcatheter Aortic Valve Implantation
Ronen Gurvitch, MBBS,* John G. Webb, MD,* Ren Yuan, MD,* Mark Johnson, MBBS,*
Cameron Hague, MD,* Alexander B. Willson, MBBS,* Stefan Toggweiler, MD,*
David A. Wood, MD,* Jian Ye, MD,* Robert Moss, MD,* Christopher R. Thompson, MD,*
Stephan Achenbach, MD,† James K. Min, MD,‡ Troy M. LaBounty, MD,‡
Ricardo Cury, MD,§ Jonathon Leipsic, MD*
British Columbia, Vancouver, Canada; Erlangen, Germany; Los Angeles, California;
and Miami, Florida
Objectives This study sought to determine the most reproducible multidetector computed tomography (MDCT) measurements of the aortic annulus and to determine methods to improve the applicability of these measurements for transcatheter aortic valve implantation.
Background The reproducibility and applicability of MDCT annular measurements to guide transcatheter aortic valve implantation remain unclear.
Methods Annular measurements were performed in 50 patients planed for transcatheter aortic
valve implantation in multiple planes: basal ring (short- and long-axis, mean diameter, area-derived
diameter), coronal, sagittal, and 3-chamber projections. A theoretical model was developed taking
into account the differences between the most reproducible MDCT measurements and transesophageal echocardiography to guide valve size choice.
Results The most reproducible measurements were the area-derived diameter and basal ring average
diameter (inter-reader intraclass correlation coefficient: 0.87 [95% confidence interval: 0.81 to 0.92] and
0.80 [95% confidence interval: 0.70 to 0.87]; respectively; intrareader ⬎0.90 for all readers). These were
generally larger than transesophageal echocardiography diameters (mean difference of 1.5 ⫾ 1.6 mm
and 1.1 ⫾ 1.7 mm, respectively). When a strategy of valve-sizing is undertaken using these CT measurements using an echocardiographic sizing scale, a different THV size would be selected in 44% and 40%
of cases, respectively. When adjusting the sizing cutoffs to account for the differences in observed diameters, this was reduced to 10% to 12% (p ⬍ 0.01 for both, respectively).
Conclusions The most reproducible MDCT measurements of the annulus are the area-derived diameter and
basal ring average diameter, with derived values generally larger than those obtained with echocardiography.
If MDCT is used for valve sizing, a strategy incorporating these differences may be important. MDCT using
these easily derived measurements may be ideally suited to sizing transcatheter aortic valves as they account
for the eccentricity of the aortic annulus, are reproducible, and are noninvasive. (J Am Coll Cardiol Intv 2011;
4:1235–45) © 2011 by the American College of Cardiology Foundation
From the *St. Paul’s Hospital, University of British Columbia, Vancouver, Canada; †University of Erlangen, Erlangen, Germany;
‡Departments of Medicine, Imaging, and Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, California; and the
§Baptist Hospital of Miami, Miami, Florida. Dr. Webb is a consultant for Siemens and Edwards Lifesciences. Dr. Wood is a
consultant for Edwards Lifesciences. Dr. Ye is a consultant to Edwards Lifesciences. Dr. Achenbach receives research support from
Siemens Healthcare and Bayer Schering. Dr. Min is on the Speaker’s Bureau of GE Healthcare; is a consultant for Edwards
Lifesciences; and has equity interest in TC3. Dr. Leipsic is on the Speaker’s Bureau and advisory board of Edwards Lifesciences;
and he is on the Speaker’s Bureau for GE Healthcare and Equity Stakeholder TC3 Corelab. All other authors have reported that
they have no relationships relevant to the contents of this paper to disclose.
Manuscript received April 1, 2011; revised manuscript received June 30, 2011, accepted July 21, 2011.
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Aortic Annulus Diameter Determination by MDCT
Transcatheter aortic valve implantation (TAVI) is becoming an accepted procedure for selected patients with severe
aortic stenosis (1). Accurate evaluation of the native aortic
valve annular dimensions is critical to optimize selection of
the correct bioprosthetic valve size. In contrast to surgical
aortic valve replacement where surgeons perform valve
sizing under direct visualization and with the aid of annular
sizing probes, noninvasive imaging methods are generally
required in the setting of TAVI. Incorrect valve sizing may
lead to paravalvular aortic regurgitation, which is a predictor
of worse long-term outcome (2), valve embolization, patient
prosthesis mismatch, or catastrophic annular rupture (3,4).
Given the complex shape of the aortic annulus, which
includes a generally noncircular profile coupled with a
conical form that is bounded at its nadir by the attachment
of the 3 aortic leaflets (5), accurate evaluation by 2-dimensional
imaging modalities, such as echocardiography, is intrinsically difficult. Recently, 3-dimensional multidetector computed tomography (MDCT), which is not limited by planar
imaging, has been shown to proAbbreviations and
vide fine anatomical detail and
Acronym
accurate assessment of the complex anatomical shape of the
CI ⴝ confidence interval
aortic valve and annulus (6 – 8).
ICC ⴝ intraclass correlation
Whereas some have suggested that
coefficient
MDCT-derived measurements
IQR ⴝ interquartile range
may better serve as a gold stanMDCT ⴝ multidetector
dard for aortic valve sizing, the
computed tomography
reproducibility, reliability, and
TAVI ⴝ transcatheter aortic
applicability of these measurevalve implantation
ments have not been well deTEE ⴝ transesophageal
fined. Furthermore, the clinical
echocardiography
utility of MDCT measures reTTE ⴝ transthoracic
echocardiography
mains limited. Previous studies
have also suggested that despite
propitious clinical outcomes of patients undergoing TAVI
with echo-based aortic valve sizing, an MDCT-based valve
sizing strategy might result in up to 39% of cases requiring
a different valve size or exclusion from candidacy for TAVI
using currently available devices (9 –11). However, these
prior MDCT studies employed aortic annular measurements in limited planes and without systematic adjustment
for discordance between MDCT and echocardiographic
modalities.
In the present study, we thus aimed to: 1) evaluate the
aortic annular dimensions in patients undergoing TAVI
using MDCT in multiple planes; 2) assess which measurements have the greatest interobserver and intraobserver
reproducibility; and 3) determine the difference in valve
sizing recommendations if MDCT measurements are used
according to current (transesophageal echocardiography
[TEE]– based) sizing cutoffs (“unadjusted criteria”) versus a
strategy of incorporating the observed differences between
JACC: CARDIOVASCULAR INTERVENTIONS, VOL. 4, NO. 11, 2011
NOVEMBER 2011:1235– 45
MDCT and echocardiography into the sizing criteria (“adjusted criteria”).
Methods
Patient population. Fifty patients with severe symptomatic
aortic stenosis being considered for TAVI underwent preprocedural evaluation using MDCT imaging. Forty-one of
these patients underwent TAVI, and all these patients had
matched transthoracic echocardiography (TTE) and TEE
images. Patients with bicuspid aortic stenosis were excluded.
MDCT was clinically indicated for evaluation before the
procedure to assess the peripheral vasculature and determine
the optimal angiographic projection angles for valve implantation (12,13). Following implantation, implantation
height was angiographically defined as optimal or suboptimal, with optimal position defined as occurring when
the native leaflet insertion point was within the middle
third of the stent frame. All other valve positions were
defined as suboptimal.
Patients were evaluated by a team of senior cardiologists
and cardiothoracic surgeons to determine if they posed a
prohibitively high surgical risk before being accepted for
TAVI. Patients underwent transfemoral or transapical implants of Edward Sapien/Sapien XT balloon expandable
bioprostheses (Edwards Lifesciences, Irvine, California) of
23-mm, 26-mm, or 29-mm diameter with valve size chosen
based on annulus diameters as derived by TEE as previously
described (14 –18).
CT images acquisition. MDCT examinations were performed on a 64-slice Discovery HD 750 High Definition
scanner (GE Healthcare, Milwaukee, Wisconsin), and 80 to
120 ml of iodixanol 320 (GE Healthcare, Princeton, New
Jersey) were injected at 5 ml/s followed by 30 ml of normal
saline. The timing delay of the scan was determined using a
smart prep of the ascending aorta with a preset threshold of
150 Hounsfield units. The MDCT examinations were
performed in the craniocaudal direction with retrospective
gating from the aortic arch through to the diaphragm. Heart
rate reduction with beta-blockade was avoided as interpretation of the coronary arteries was not required and because
of clinical concern regarding severe aortic stenosis. MDCT
scanner detector collimation width was 0.625 mm, detector
coverage was 40 mm, reconstructed slice thickness was 1.25
mm, and the slice interval was 1.25 mm. Gantry rotation
time was 0.35 s, and the scan pitch ranged between 0.16 and
0.20 (adjusted per heart rate). Depending on the patient
size, the maximum tube current ranged between 450 and
700 mA with a fixed tube voltage of 100 kVp for patients
with a body mass index ⬍30 kg/m2 and 120 kVp used in
larger patients. Electrocardiography-gated dose modulation
was used with tube current reduced to 60% of maximum
tube current in systole. This provided adequate image
JACC: CARDIOVASCULAR INTERVENTIONS, VOL. 4, NO. 11, 2011
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Gurvitch et al.
Aortic Annulus Diameter Determination by MDCT
1237
Figure 1. Aortic Root Reconstructions
Coronal (A) and sagittal oblique (B) views. The arterioventricular plane is elliptical in shape, measuring 25.4 mm in the coronal plane and 21.1 mm in the sagittal plane.
quality for annular assessment in the systolic phases while
reducing the estimated effective radiation dose.
Achieving the different imaging planes and measuring the
aortic annulus. Following MDCT image acquisition, refor-
mats were performed to allow evaluation of the aortic
annulus in multiple planes. A number of reported and
proposed methods for measuring the aortic annulus with
MDCT have been suggested (11,13). We evaluated 6
methods: coronal and sagittal oblique (Fig. 1); 3-chamber;
double oblique transverse short axis of the basal ring (6,9);
Figure 2. Reconstructing a Double Oblique Transverse Image of the Basal Ring
From the coronal projection (A), a vertically oriented oblique tool (dashed line) is placed to produce a sagittal oblique reconstruction of the ascending aorta.
A transverse or axial cutplane is then placed on the sagittal reconstruction (B) at the level of the commisures. This transverse cutplane yields a double oblique
transverse image of the aortic root (C). The dataset is then scrolled up or down until the most caudal attachments of the aortic valve are identified (D).
The nadirs of all 3 cusps must be identified on the 1 transverse image, ensuring the appropriate plane for assessment of the aortic annulus.
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Aortic Annulus Diameter Determination by MDCT
JACC: CARDIOVASCULAR INTERVENTIONS, VOL. 4, NO. 11, 2011
NOVEMBER 2011:1235– 45
long axis of the basal ring; and an area measurement of the
basal ring of the aorta. In addition, we calculated the
area-derived diameter, as well as the basal ring average
diameter (see the next paragraph). For all these measurements, the reader would determine the optimal projection
for measurement. Importantly, all 3 readers had agreed on
the defined principles behind each measurement and had
read 25 previous cases in collaboration to ensure a standardized approach.
As all MDCT studies were performed with retrospective
gating, reading physicians first selected the appropriate
phase of the cardiac cycle. By convention, the annulus was
measured in systole during maximum valve opening. Following this, physicians performed post-processing and analysis beginning in the coronal projection with an axial-cut
plane rotated in a counterclockwise direction such that the
annular plane ran from right-caudal to left-cranial position.
After ensuring that the various imaging planes are locked,
attention is turned to the sagittal projection, which is
vertically oriented to be orthogonal to the long axis of the
aortic annulus (Fig. 2). At this point, the horizontal line
representing the axial cutplane is moved up or down on
either the sagittal or coronal projection to create a double
oblique transverse or axial image of the aortic root. This
horizontal line is then pulled down through the root of the
aorta until the most caudal attachments of the 3 aortic cusps
are identified. Importantly, to accurately define the basal
ring, the plane must be balanced so that all 3 leaflets come
into view when scrolling cephalad at the same time (Fig. 2).
At this point, the short- and long-axis dimensions of the
basal ring are measured (Fig. 3A), and the area is traced out
accurately (Fig. 3B). From the former, a basal ring average
diameter is determined by (basal ring short axis ⫹ basal ring
long axis)/2, and from the latter, the area-derived diameter
is calculated using:
diameter ⫽ 2
冑
area
To generate a 3-chamber projection of the aortic annulus,
a standardized approach is also used. A transverse image of
the mitral valve with maximal visualization of the left
ventricular cavity that allows for identification of the ventricular apex is bisected with an oblique plane creating a
long-axis reconstruction. The left ventricle is then cut in a
plane from the left atrium through the center of the mitral
valve through the left ventricular apex resulting in a
4-chamber projection. An oblique plane is then used to
rotate the left ventricle in a perpendicular fashion to the
interventricular septum to create a short-axis projection.
Finally, a cutplane is placed in an oblique fashion at the base
of the short-axis projection out of the left ventricular
outflow tract and aorta to create a 3-chamber projection
(Fig. 4).
All measurements were conducted in blinded fashion by
the 3 independent readers. Each reader evaluated the
annulus in all planes. Following this, to assess intraobserver
reliability, readers reread 20 randomly selected cases at least
1 month following the original assessment, with the readers
blinded to the original results.
Figure 3. Double Oblique Transverse Reconstruction Just Below the Commissural Insertions of the Aortic Leaflets Demonstrating Various
Basal Ring Measurements
(A) The long- and short-axis dimensions measure 24 mm and 21.6 mm, respectively, with an average diameter of 22.8 mm. (B) The circumference is carefully
traced, generating a direct measurement of the basal ring area (shaded): 425.8 mm2. From this, the area-derived diameter is calculated using:
diameter ⫽ 2
冑
area
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Aortic Annulus Diameter Determination by MDCT
JACC: CARDIOVASCULAR INTERVENTIONS, VOL. 4, NO. 11, 2011
NOVEMBER 2011:1235– 45
Figure 4. The 3-Chamber View
(A) Three-chamber transesophageal view in a zoomed-up image at approximately 120° is used to measure the aortic annulus diameter. The multidetector
computed tomography reconstructed 3-chamber projection (B) is created to measure a similar plane.
Echocardiography. Scans were performed either before or
during the TAVI procedure and interpreted by an echocardiographer experienced in TAVI and pre-procedural evaluation. All patients undergoing TAVI had both TTE and
TEE imaging, with all scans clinically indicated as part
of the routine clinical evaluation of patients undergoing
TAVI. Phillips iE33 or Sonos 5500 ultrasound systems
(Philips HealthCare, Minneapolis, Minnesota) were used
for image evaluation. The aortic annulus was measured at
the base of the leaflet insertion point in a zoomed-up
3-chamber view at approximately 120° (TEE), corresponding to the nadirs of the noncoronary and right coronary
leaflets, or in a parasternal long-axis view in a zoomed-up
view (TTE). All measurements were performed in early
systole as recommended by the American Society of Echocardiography for quantification of stroke volume and aortic
stenosis severity (19). All images were stored on disk for
offline analysis. All patients undergoing TAVI had prehospital discharge TTE evaluation of valvular function and
hemodynamics. The degree and origin of post-procedural
aortic regurgitation was assessed using pre-hospital discharge TTE.
Impact of using MDCT images on valve size selection. To
evaluate the clinical applicability of MDCT images on valve
size selection, a sizing model was created based on annular
diameters and current implantation guideline cutoffs. Given
that we found MDCT images to be generally larger than
TEE measurements, the mean difference between the particular MDCT measurements and TEE measurements were
incorporated into an “adjusted” sizing model. A comparison
was then made between a strategy in which MDCT
measurements were used with existing TEE-based sizing
guidelines for the Sapien valve (23-mm valve for annular
diameters of 18 to 21 mm, a 26-mm valve for 22 to 25 mm,
and a 29-mm valve for 26 to 28 mm) and another strategy
in which these sizing cutoffs were adjusted to incorporate
the observed mean difference between the specific MDCT
views tested and TEE.
Statistical methods. Continuous variables are described as
mean ⫾ SD when normally distributed or as medians with
interquartile ranges (IQR) when not. Normality was tested
using the Shapiro-Wilks goodness-of-fit test. Categorical
variables are described by frequencies and percentages.
Comparison of categorical variables was performed using a
chi-square analysis or the Fisher exact test as appropriate. A
mixed-effect model was used to estimate the betweensubject variance and within-subject variance. Intraclass correlation coefficient (ICC) was defined as the ratio of
between-subject variance to the total variance. The 95%
confidence interval (CI) was calculated using the delta
method (20). The Spearman correlation coefficient was used
to assess the relationship between echocardiographic and
MDCT measurements. All analyses were performed using
SAS (version 9.1.3, SAS Institute, Cary, North Carolina).
Results
Baseline characteristics. A total of 50 patients underwent
evaluation with MDCT (Table 1). The mean age was 81 ⫾
8 years, 48% were women, and the median Society of
Thoracic Surgeons risk score for mortality was 7.5% (IQR:
5.4% to 9.4%). Mean aortic valve area was 0.67 ⫾ 0.21 cm2
Table 1. Baseline Patient Characteristics (N ⴝ 50)
Age, yrs
Female, %
81 ⫾ 8
48
STS risk score
7.5 (5.4–9.4)
Mean AVA, cm2
0.67 ⫾ 0.21
Mean transaortic gradient, mm Hg
41.2 ⫾ 15.1
Baseline atrial fibrillation
7 (17)
Values are mean ⫾ SD, n, median (interquartile range), or n (%).
AVA ⫽ aortic valve area; IQR ⫽ interquartile range; STS ⫽ Society of Thoracic Surgeons.
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Table 2. Procedural Characteristics (N ⴝ 41)
Transfemoral procedure
30 (73)
Transapical procedure
11 (27)
Procedural success
41 (100)
Procedural mortality
0 (0)
Valve embolization
0 (0)
23-mm valve
15 (37)
26-mm valve
23 (56)
29-mm valve
3 (7)
Post-procedural paravalvular aortic regurgitation*
None
4 (10)
Trivial/mild
34 (83)
Moderate
3 (7)
Moderate/severe
0 (0)
Severe
0 (0)
Values are n (%) or n. *No patients had more than trivial valvular regurgitation.
and the mean transaortic baseline gradient was 41.2 ⫾ 15.1
mm Hg. Atrial fibrillation was present in 17% of patients at
baseline. The mean heart rate at the time of CT acquisition
was 74 ⫾ 8.5 beats/min.
Procedural outcomes. Forty-one patients underwent TAVI
(Table 2). All procedures were successful with no procedural
mortality, annular rupture, valve embolization, or coronary
occlusion. All implants were at optimal height but 1 (too
high), with the latter patient having mild paravalvular
regurgitation and no other complications. Thirty patients
had transfemoral procedures, and 11 had access via a
transapical route. A 23-mm valve was used in 15 cases,
26-mm valve in 23 cases, and 29-mm valve in 3 cases. After
the procedure, no paravalvular regurgitation was observed in
4 patients, trivial/mild paravalvular regurgitation in 34
patients, and 3 patients had moderate paravalvular regurgitation. No patients had more than trivial transvalvular
regurgitation.
Interobserver reliability. The interobserver reliability assessed by ICC was only acceptable by statistical standards
(ⱖ0.80) for the area-derived diameter [ICC: 0.87, 95% CI:
0.81 to 0.91) and the basal ring average diameter (ICC:
0.80, 95% CI: 0.70 to 87) (Table 3). The 3-chamber view
had lower reliability (ICC: 0.70, 95% CI: 0.58 to 0.80), and
the sagittal oblique measurement showed the lowest interobserver reliability (ICC: 0.54, 95% CI: 0.39 to 0.69).
Intraobserver reliability. The greatest reliability and the only
2 measurement points that consistently showed ICC ⬎0.90
for each reader, were the area-derived diameter and the
basal ring average diameter (Table 4). The 3-chamber
values were not as reliable (ICC: 0.75 to 0.98).
Correlations between MDCT and echocardiography. The
overall correlation between MDCT and echocardiography
was higher for TEE than for TTE (Table 5). When
compared to the TEE-derived annular diameter, the highest correlation with MDCT was for the 3-chamber view
(r ⫽ 0.80, 95% CI: 0.64 to 0.89, p ⬍ 0.001), followed by the
area-derived diameter (r ⫽ 0.79, 95% CI: 0.63 to 0.88, p ⬍
0.001) and the basal ring average diameter (r ⫽ 0.79, 95%
CI: 0.62 to 0.89, p ⬍ 0.0001) (Fig. 5). The correlation
between TEE and TTE was r ⫽ 0.73, 95% CI: 0.54 to 0.85.
Overall annular dimensions and Bland-Altman plots. Annular dimensions tended to be larger when assessed by TEE
than by TTE. The mean diameter by TEE was 23.0 mm
versus 22.1 mm by TTE (p ⫽ 0.27).
The difference between the TEE measurements and
area-derived diameter, basal ring average diameter, and
3-chamber dimensions were assessed using Bland-Altman
methods. The mean difference was greatest for the areaderived diameter (1.5 ⫾1.6 mm), followed by the basal ring
average diameter (1.1 ⫾ 1.7 mm) and the 3-chamber
dimension (0.2 ⫾ 1.2 mm). This is demonstrated by the
scatters shown in the Bland-Altman plots (Fig. 6).
Applicability of MDCT measurements. To evaluate the potential clinical applicability of MDCT measurements, we
studied the theoretical choice of valve size to be implanted if the annulus diameter was determined by
MDCT. The analysis was performed using the areaderived diameter, basal ring average diameter, and
3-chamber view. Given that we have shown these measurements to be larger than TEE diameters, a comparison
was made between using these diameters with current
TEE-based sizing guidelines versus a strategy where
these observed differences were incorporated into new
“adjusted” sizing criteria.
To adjust the sizing criteria, the observed mean difference
between each of these 3 imaging planes and TEE were
incorporated to current sizing guidelines. For example, the
area-derived diameter is larger than TEE by a mean of 1.5
mm. This resulted in the following theoretical “adjusted”
sizing criteria if using the MDCT area-derived diameter:
23-mm valve for annulus ⱖ19.5 to ⱕ22.5 mm, 26-mm
valve for ⬎22.5 to ⱕ26.5 mm, and 29-mm valve for ⬎26.5
to ⱕ29.5 mm (Table 6).
When MDCT measurements were used with current
sizing criteria, the valve size indicated was frequently dif-
Table 3. Inter-Reader Reliability as Measured by ICC, Estimates and 95% CI for 3 Readers (N ⴝ 50)
Coronal
Sagittal Oblique
Short-Axis Basal Ring
Long-Axis Basal Ring
3-Chamber
Basal Ring Average Diameter
Area-Derived Diameter
0.78 (0.67–0.85)
0.54 (0.39–0.69)
0.71 (0.59–0.81)
0.72 (0.61–0.82)
0.70 (0.58–0.81)
0.80 (0.70–0.87)
0.87 (0.81–0.92)
CI ⫽ confidence interval(s); ICC ⫽ intraclass correlation coefficient.
Gurvitch et al.
Aortic Annulus Diameter Determination by MDCT
JACC: CARDIOVASCULAR INTERVENTIONS, VOL. 4, NO. 11, 2011
NOVEMBER 2011:1235– 45
1241
Table 4. Intra-Reader Reliability as Measured by ICC,* Estimates and 95% CI (n ⴝ 20)
Reader
Coronal
Sagittal Oblique
1
0.93 (0.84–0.97)
0.70 (0.45–0.87)
2
0.89 (0.75–0.95)
0.84 (0.67–0.93)
3
0.88 (0.75–0.95)
0.84 (0.71–0.94)
Short-Axis Basal Ring
Long-Axis Basal Ring
3-Chamber
Basal Ring Average Diameter
Area-Derived Diameter
0.72 (0.47–0.89)
0.87 (0.74–0.95)
0.75 (0.61–0.85)
0.94 (0.87–0.97)
0.93 (0.84–0.97)
0.94 (0.8579–0.9736)
0.87 (0.72–0.94)
0.89 (0.78–0.96)
0.94 (0.86–0.98)
0.93 (0.83–0.97)
0.97 (0.95–0.99)
0.97 (0.93–0.98)
0.98 (0.96–0.99)
0.99 (0.97–0.99)
0.98 (0.94–0.98)
*See Webb and Cribier (1).
Abbreviations as in Table 3.
ferent (area-derived diameter: 44%, basal ring average diameter: 42%, and 3-chamber: 10%). When MDCT measurements were used with the individually adjusted criteria,
the strategy was different in significantly lower numbers
(area-derived diameter: 10% [p ⬍ 0.01], basal ring average
diameter: 12% [p ⬍ 0.01], and 3-chamber: 5% [p ⫽ 0.24])
(Fig. 7).
For the area-derived diameter and basal ring average
diameter, a different valve would have been recommended
according to the adjusted sizing criteria in 4 and 5 cases,
respectively. For both of these, in 3 of the cases (2 ⫻ 23-mm
valves implanted, 1 ⫻ 26-mm valve implanted), greaterthan-or-equal-to moderate paravalvular regurgitation was
noted following implantation. Importantly, these 3 cases
were the only 3 cases of greater-than-or-equal-to moderate
paravalvular regurgitation that we observed following the
procedure.
large amounts of anatomical information regarding the
complex structure of the aortic annulus in various planes, the
most reproducible measurements are those of the areaderived diameter and basal ring average diameter. We found
these measurements to be consistently larger than TEEderived diameters, by a mean of 1.5 mm and 1.1 mm,
respectively. If MDCT-obtained dimensions are used for
Discussion
Overall findings. This study examined patients undergoing
multimodality imaging to assess annular dimensions before
TAVI. We found that even though MDCT can provide
Table 5. Spearman Correlation Statistics
MDCT Variables
Echo
Variable
Correlation
95% Confidence
Interval
p Value
Coronal
TTE
0.43
0.12–0.66
⬍0.01
Sagittal oblique
TTE
0.46
0.15–0.68
⬍0.01
⬍0.01
Short-axis basal ring
TTE
0.54
0.26–0.73
Long-axis basal ring
TTE
0.39
0.07–0.63
0.01
Average axis basal ring
TTE
0.59
0.32–0.76
⬍0.01
Basal ring dimension
TTE
0.51
0.21–0.71
⬍0.01
3-chamber
TTE
0.57
0.29–0.75
⬍0.01
Coronal
TEE
0.70
0.49–0.83
⬍0.01
Sagittal oblique
TEE
0.56
0.29–0.75
⬍0.01
Short-axis basal ring
TEE
0.74
0.54–0.86
⬍0.01
Long-axis basal ring
TEE
0.54
0.25–0.73
⬍0.01
Average axis basal ring
TEE
0.79
0.62–0.89
⬍0.01
Basal ring dimension
TEE
0.79
0.63–0.90
⬍0.01
3-chamber
TEE
0.80
0.64–0.89
⬍0.01
TTE
TEE
0.74
0.54–0.85
⬍0.01
Bold values are statistically significant.
MDCT ⫽ multidetector computed tomography; TEE ⫽ transesophageal echocardiography;
TTE⫽ transthoracic echocardiography.
Figure 5. Bland-Altman Plots
(A) Difference between the area-derived dimension and transesophageal
echocardiography (TEE). (B) Difference between basal ring average diameter
and TEE. (C) Difference between the multidetector computed tomography
(MDCT) derived 3-chamber and TEE.
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Aortic Annulus Diameter Determination by MDCT
JACC: CARDIOVASCULAR INTERVENTIONS, VOL. 4, NO. 11, 2011
NOVEMBER 2011:1235– 45
Figure 6. Spearman Correlation Between Various MDCT Dimensions and TEE
The 3-chamber dimensions have the highest correlation (r ⫽ 0.8), whereas the sagittal oblique has the lowest (r ⫽ 0.56). Abbreviations as in Figure 5.
valve sizing, incorporating these observed differences results
in less, but persistent and potentially important discrepancies when compared with TEE-based cutoffs.
Importance of accurate assessment of annular dimensions.
The evolution of TAVI has brought the importance of
accurate noninvasive assessment of the aortic annulus to a
Table 6. Valve Size Chosen According to Mode of Annulus Assessment
by TEE Versus MDCT Using Area-Derived Diameter
Valve Size Chosen
Imaging Modality and
Sizing Criteria
TEE-guided
MDCT unadjusted
MDCT using adjusted criteria
23 mm
26 mm
29 mm
15
23
3
5
26
10
13
23
5
In the top row, valve sizes were chosen according to TEE measurements and the following
guidelines for implantation: 23-mm valve for annulus ⱖ18.0 to ⱕ21.0 mm; 26-mm valve for ⬎21.0
to ⱕ25.0 mm; and 29-mm valve for ⬎25.0 to ⱕ28.0 mm. In the middle row, valve sizes were
chosen from the MDCT area-derived diameter according to the same cutoff guidelines for implantation. In the bottom row, valve sizes were chosen from the MDCT area-derived diameter but
adjusted by 1.5 mm to account for the mean difference in this measurement from TEE, hence:
23-mm valve for annulus ⱖ19.5 to ⱕ22.5 mm; 26-mm valve for ⬎22.5 to ⱕ26.5 mm; and 29-mm
valve for ⬎26.5 to ⱕ29.5 mm.
Abbreviations as in Table 5.
new spotlight. Previous work has shown that TEE diameters can underestimate the true diameter as measured at
surgery by a mean of 1.2 mm and frequently underestimate
it by ⬎2 mm (21). Despite this, operators have become
accustomed to echocardiography-guided TAVI with good
results. Current implantation guidelines use TEE diameters
to determine the size of the prosthesis to be implanted.
However, aortic regurgitation, valve embolization, annular
rupture, and patient prosthetic mismatch continue to occur,
underscoring the importance of accurate annular evaluation.
Even though MDCT appears to provide data on the true
anatomical shape and dimensions of the aortic annulus, its
applicability has remained limited due partly to uncertainty
in incorporating the additional information into the clinical
context.
Most useful MDCT measurements. In this study, we evaluated previously described MDCT-derived annular dimensions, including the area-derived diameter (11). The latter
considers the entire directly measured circumferential area
of the complex shape of the annulus, and the mathematically derived diameter attempts to provide a “diameter of
best fit” when provided a circular geometry as seen with a
balloon expandable transcatheter valve. We found that in
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Gurvitch et al.
Aortic Annulus Diameter Determination by MDCT
1243
Figure 7. Impact on Valve Size Choice of Unadjusted Versus Adjusted Cutoffs
The graph demonstrates the effect of using MDCT-derived diameters on valve size choice according to current TEE-based cutoffs (unadjusted criteria [blue])
versus cutoffs in which the mean difference between MDCT and TEE has been incorporated (adjusted criteria [brown]). Abbreviations as in Figure 5.
fact this area-derived diameter and the basal ring average
diameter were the most reproducible and reliable measurements obtained by MDCT. The 3-chamber measurement
was less reproducible, and the sagittal oblique diameter had
the lowest interobserver reliability with an ICC of 0.54
(95% CI: 0.39 to 0.69).
While the 3-chamber measurement was not as reproducible, it had the best correlation with TEE diameters. This is
to be expected given that the 3-chamber MDCT projection
in essence is an attempt to replicate the echocardiographic
plane of measurement. However, in understanding MDCT
dimensions, we need to move beyond attempting to replicate the more familiar TEE measurements. The lower
correlation for the area-derived diameter and the basal ring
average diameter is simply explained: they are measuring
different things and provide more anatomical information
than does echocardiography.
The unifying feature of the less reproducible measures
(sagittal, coronal, or 3-chamber) is that unlike the basal ring
measurements, they represent single-plane dimensions of
what is usually a more complex oval structure. Subtle
obliquity or tilting of the root can easily result in significant
variability. Given the elliptical nature of the aortic annulus,
even minor changes in orientation can result in potentially
significant differences. The 3-chamber reconstruction requires additional dataset manipulation to generate and is
subject to the same limitations as the coronal and sagittal
oblique measures regarding orientation.
Application of MDCT measurements. We found that if
MDCT area-derived diameter or basal ring average diameter were used to guide valve size choice, a different valve
size might have been selected in 10% to 12% of patients. In
a previous study, Messika-Zeitoun et al. (9) evaluated the
theoretical impact of the method of measurement of the
annulus diameter on the procedure, finding that when using
the basal ring average diameter, MDCT measurements
would have modified the TAVI strategy in 38% of patients.
Similarly, Tzikas et al. (10) found a change of strategy in
36% of cases if the coronal dimension was used, and Schultz
et al. (11) found that 39% would not be candidates for a
CoreValve prosthesis (Medtronic Inc., Minneapolis, Minnesota) if the long-axis diameter of the basal ring was used.
An important difference in our study is that having demonstrated MDCT measurements to be consistently larger
than TEE measurements, these differences were integrated
before applying diameter criteria that are accepted for TEE
measurements. Using this strategy, we found that when
MDCT was used “unadjusted,” the TAVI strategy might
have been altered in similar frequencies to the previous
studies (42% to 44%), but when the criteria were “adjusted”
to incorporate these differences, these were significantly
reduced to 10% to 12% (p ⬍ 0.01). These particular cases
appear to be especially important. We found in the cases
with residual discrepancies between MDCT and TEE that
exceeded these criteria, the frequency of moderate paravalvular aortic regurgitation following TAVI was very high.
For example, moderate regurgitation was noted in 3 of 4
cases in which a larger valve size was indicated by MDCT
as evaluated by “adjusted” area-derived diameter cutoffs.
Although the cause of aortic regurgitation following
TAVI is multifactorial, this nevertheless raises the possibility that, in specific cases, TEE may underestimate
the true annular dimensions, thus contributing to selec-
1244
Gurvitch et al.
Aortic Annulus Diameter Determination by MDCT
tion of undersized prostheses and important paravalvular
regurgitation.
Based on these findings, we propose that given the
consistent differences in certain measurements, current
manufacturer-recommended sizing cutoffs that are based on
TEE diameters might not be appropriate to directly translate to MDCT cutoffs. For example, 22 mm measured by
TEE is not the same as 22 mm measured by the areaderived diameter from MDCT. The aim of our study is to
help clinicians understand how to best apply MDCT
measurements and help put them into practical clinical
context to aid decision making. We propose that if MDCT
measurements are used to help guide valve size choice, new
strategies taking into account the differences in specific
annular dimensions compared with TEE measurements are
required. Such strategies should use adjusted criteria utilizing the most reproducible MDCT measurements of the
area-derived diameter or basal ring average diameter.
Study limitations. Although we conducted an analysis of the
theoretical choice of valve size according to different annular
measurements, the choice of valve size is multifactorial.
Factors, including annular diameter, degree and extent of
calcification, symmetry of the leaflets, distance to the
coronaries, diameter of the sinotubular ridge, and curvature
of the sinuses of Valsalva might all affect final valve choice.
We could not incorporate these factors into our analysis as
this would be beyond the scope of this study, and we
considered valve size choice by annular dimensions alone.
Also, our study used only the balloon expandable valve and
the results with regards to AR may not be applicable in the
same way to the self-expanding model. However, annulus
determination is crucial regardless of the valve type chosen.
The MDCT scans and echocardiographic assessments
were not always performed at exactly the same time of the
cardiac cycle for each patient. The MDCT measurements
were, however, taken during systolic phases of the cardiac
cycle at the point of maximum valve opening. As well,
annulus size variation during the cardiac cycle is minimal
(7,22), especially in patients with severely stenotic and
restricted valves.
Not all patients underwent valve implantation: 9 patients
are still awaiting a procedure. This relates to practical
considerations of our current waiting list as opposed to any
specific factors that may affect the results or conclusions of
this study.
Conclusions
MDCT imaging provides significant anatomical information regarding the complex elliptical shape of the aortic
annulus. The most reproducible MDCT measurements are
the area-derived diameter and basal ring average diameter,
with derived values generally larger than those obtained
with echocardiography. For MDCT to be used for valve
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NOVEMBER 2011:1235– 45
selection, a strategy incorporating these differences might be
important. MDCT using these easily derived measurements
might be ideally suited to sizing transcatheter aortic valves
as they account for the eccentricity of the aortic annulus, are
reproducible, and are noninvasive. Further larger studies are
required to define the specific cutoffs of annular dimensions
as obtained by different imaging modalities for selection of
valve size.
Reprint requests and correspondence: Dr. Jonathon Leipsic, St
Paul’s Hospital, 1081 Burrard Street, Vancouver, British Columbia V6Z 1Y6, Canada. E-mail: jleipsic@providencehealth.bc.ca.
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Key Words: aortic annulus 䡲 aortic stenosis 䡲 computed
tomography 䡲 transcatheter aortic valve implantation.