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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3795_Библиотеки_им_академика_М_И_Перельмана
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In: Perspectives in Aortic Valve Disease ISBN: 978-1-53618-769-4
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Editor: Giovanni Concistrè © 2020 Nova Science Publishers, Inc.
Chapter 3
NON-INVASIVE IMAGING OF AORTIC
VALVE – ULTRASOUNDS: TRANS-THORACIC,
TRANS-ESOPHAGEAL
AND STRESS ECHOCARDIOGRAPHY
Alberto Giannoni
1,2,
, MD, PhD, Chiara Borrelli
1,3
, MD,
Giulia Elena Mandoli4, MD and Francesco Gentile5, MD
1
Institute of Life Sciences, Scuola Superiore Sant’Anna, Pisa, Italy
2
Division of Cardiology and Cardiovascular Medicine,
Fondazione Toscana G. Monasterio, Pisa, Italy
3
Division of Emergency Medicine, University of Pisa, Pisa, Italy
4
Department of Medical Biotechnologies, Division of Cardiology,
University of Siena, Siena, Italy.
5
Division of Cardiology and Cardiovascular Medicine University of Pisa, Pisa, Italy
ABSTRACT
Echocardiography is the main imaging modality for the characterization of the aortic
valve (AV) anatomy and function and the test of choice for following-up patients with
AV disease. The combination of two dimensional trans-thoracic echocardiography,
transesophageal echocardiography and stress echocardiography togheter with other
imaging modalities and biomarkers help to refine the perfect timing and choice of
treatment (surgical/percutaneus).
Keywords: trans-thoracic, trans-esophageal and stress echocardiography, aortic valve disease
Corresponding Author’s Email: alberto.giannoni@ftgm.it.
Alberto Giannoni, Chiara Borrelli, Giulia Elena Mandoli et al.
38
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INTRODUCTION
Echocardiography still remains the most important imaging modality for the
characterization of the aortic valve (AV) anatomy and function. Due to its widespread
availability, superior assessment of flow haemodynamics, and the possibility to acquire in a
single examination several prognostic parameters, echocardiography is routinely the test of
choice for the assessment and follow-up of patients with AV disease and for the
determination of the timing for surgical referral.
Two dimensional (2D) trans-thoracic echocardiography (TTE) is a key technique to
confirm the diagnosis of AV disease and to assess its severity and prognosis. An integrated
approach taking into accpunt several haemodynamic parameters rather than relying on a
single measurement is usually recommended, together with a thorough clinical evaluation of
patient’s symptoms and potential confounders.
Transesophageal echocardiography (TEE) should be considered when TTE is of
suboptimal quality, when further details on AV anatomy or pathophysiology are needed, or
when thrombosis, prosthetic valve dysfunction or endocarditis is suspected. Threedimensional (3D) echocardiography may warrant unlimited perspective and better outline
complex anatomy of the AV and aortic root, in spite of potentially inaccurate geometric
assumptions.
Finally, stress echocardiography (SE) may implement the assessment of the physical,
haemodynamic, and echocardiographic consequences of exercise, unmasking symptoms in
patients with poorly active lifestyles. Likewise, SE may help stratifying patients showing
discrepancies between the AV area and the transvalvular gradients at rest, in the suspicion of
the so called low-flow/low-gradient aortic stenosis.
TRANS-THORACIC ECHOCARDIOGRAPHY
Anatomic Assessment of the Aortic Valve in Physiology and Pathology
TTE, for its non-invasiveness, feasibility and availability, is the first and most used
approach for the assessment of AV anatomy and disease (aortic stenosis - AS and aortic
regurgitation - AR). The AV apparatus consists of three semilunar leaflets, three interleaflet
triangles, three commissures, the annulus and the aortic wall. The aortic cusps are classified
according to the emergency of the coronary arteries as left, right and non-coronary cusp
(LCC, RCC and NCC, respectively); the latter is adjacent to the interatrial septum and in
direct fibrous continuity with the anterior mitral leaflet [1]. The highest point of attachment of
the cusps to the aortic wall is the sinotubular junction, while the nadir defines the annular
plane [1].
There are different projections for TTE assessment of AV anatomy.
In the parasternal long axis (PLAX) view, the NCC and RCC are visualized, alongside
the aortic root (Figure 1, panel a). This view allows the evaluation of left ventricular outflow
tract (LVOT) and ascending aorta, thus enabling the assessment of left ventricular (LV)
hypertrophy/dilation, aortic coartation or dilation (of the sinotubular junction or the annular
Non-Invasive Imaging of Aortic Valve – Ultrasounds
39
b
c
a
RCC
LCCNCC
RCC
LCC
LVOT
a
b
c
d
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plane), proximal aortic dissection and the presence of membranes, which is essential to
determine the etiology of AS and AR [1].
By rotating the probe clockwise of 90° from the PLAX view, the parasternal short axis
(PSAX) view is obtained. This is the best view for the evaluation of the whole aortic
apparatus, as well as structural and functional anatomy of the three cusps (Figure 1, panel b).
Figure 1. Transthoracic projections for the evaluation of the aortic valve (AV). The parasternal long
axis view allows the evaluation of the right and non-coronary cusps (RCC and NCC, respectively), the
aortic root, the left ventricular outflow tract (LVOT) and left ventricular dimensions (panel a). The
parasternal short axis view allows the evaluation of the whole AV apparatus (from the lower left going
clockwise: NCC, RCC and LCC, left cornary cusp) (panel b). The apical 5 chambers view allows the
evaluation of the LVOT and aorta and it is used for continous wave Doppler evaluation of the aortic
flow.
Figure 2. Echocardiographic evaluation of aortic stenosis (AS). Anatomic parasternal short axis view of
a bicuspid aortic valve with Color Doppler evaluation of valve opening (panels a and b). Velocity time
integral (VTI) of the aortic valve with continuous wave Doppler in apical 5 chambers view (A5Ch)
showing severe AS: Vmax 4.6 m/s, mean pressure gradient 52 mmHg (panel c). VTI of the left
ventricular outflow tract (LVOT) in A5Ch (panel d). Both aortic and LVOT VTI are necessary for the
estimation of the aortic valve area.
Alberto Giannoni, Chiara Borrelli, Giulia Elena Mandoli et al.
40
Quantification of AS severity
Parameters
Sclerosis
Mild
Moderate
Severe
Peak velocity (m/s)
2.5
2.5-2.9
3.0-3.9
4.0
Mean Gradient (mmHg)
-
<20
20-39
40
AVA (cm2)
-
1.5
1.0-1.5
1.0
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When evaluating AS, the number and mobility of the cusps must be assessed to detect
anatomical or functional (leaflet fusion, presence of raphe) bicuspid valve (see further on);
cusps thickness and presence and severity of calcifications (bright, hyperechoic spots seen on
leaflet edges with commissural fusion in rheumatic valve disease; central and annular
calcifications in degenerative valve disease) must also be described (Figure 2, panel a and b)
[2].
When assessing AR, leaflet motion, prolapse, perforation or the presence of calcifications
or vegetations should be evaluated in both PLAX and PSAX views. In PLAX, measurements
of the sinotubular junction and aortic annulus should also be acquired for AR classification
[2].
Another important projection is the apical 5-chambers (A5Ch) view, which is obtained
from the standard apical 4-chamber view, tilting the probe downwards (Figure 1, panel c).
This view is fundamental for accurate Doppler measurements is AS and AR (see below).
Additional views for the AV and aorta are the apical 3-chamber, the subcostal and the
sovraclavear views.
Doppler-Based Assessment of Aortic Stenosis
When assessing AS, integration of 2D and Doppler data with patient’s symptoms is
crucial. The anatomical 2D alterations in AS have been discussed in the previous paragraph.
Simultaneous assessment of flow dependent (peak jet velocity and mean pressure
gradient) and flow independent (AV area – AVA) measures, together with LV systolic
function are required, as summarized in Table 1.
Transaortic jet velocities are measured by recording the maximal transaortic flow signal
using continuous wave (CW) Doppler in different projections, the best one being A5Ch [3].
Peak velocity is measured at the outer edge of the dense spectrum, while velocity time
integral (VTI) is calculated by tracing the entire spectral Doppler (Figure 2, panel c). Precise
alignment with blood flow is required to prevent underestimation of the velocities [3].
The pressure difference between the LV and the aorta during systole (transvalvular aortic
gradient, P) are measured from CW velocity (v) with the simplified Bernoulli equation, as
follows:
P = 4v2
Table 1. Quantification of aortic stenosis (AS) severity with 2D echocardiography
AVA: aortic valve area.
Non-Invasive Imaging of Aortic Valve – Ultrasounds
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While maximum P is estimated from peak velocity, mean P is calculated averaging the
instantaneous gradients over the whole ejection period [4].
Finally, AVA is calculated with the continuity equation, which is based on the principle
that stroke volume (SV) ejected through the LVOT must be equal to SV at valve orifice level:
SV
LVOT
=SVAV
Because SV equals cross sectional area (CSA) times velocity over a set period (hence,
VTI), the above equation can be rewritten as follows:
AVA = CSA
LVOT
* VTI
LVOT
/VTIAV
The VTI
mentioned; while the VTI
can be traced with CW over the entire Doppler spectrum, as previously
AV
is estimated with pulsed wave (PW) at LVOT level in the
LVOT
A5Ch (Figure 2, panel d) or A3Ch [2].
The standard approach for CSA
LVOT (D
), which is assumed to be circular. This measure is obtained in the PLAX view,
LVOT
calculation is the estimation of the diameter of the
LVOT
measuring from septal endocardial border to the anterior mitral leaflet in mid-systole [2].
When interpreting the results, attention should be paid to discrepancies from
velocity/gradient measures and AVA. In case of high flow states (i.e., AR, shunts,
hyperdynamic states), markers of severe hemodynamic impairment can be registered in
presence of an AVA ≥1 cm2.
On the other hand, AVA ≤1cm2 with non-severe gradients can be seen in case of LVEF
<50% and/or SVi <35 mL/m2, a condition known as low-flow low-gradient AS [3].
In this setting, dobutamine SE might help differentiating true from pseudosevere AS, as
described below. Finally, the entity of low-flow low-gradient
AS with preserved EF has been introduced in the recent Guidelines in patients with small,
hypertrophied LV despite normal LVEF [3]. However, this is a rare condition and should be
diagnosed with extreme care.
Doppler-Based Assessment of Aortic Regurgitation
Anatomical 2D evaluation is mandatory to identify the mechanisms of AR (as explained
above), while Color-Doppler (CD), CW and PW measurements are required for severity
assessment (Table 2) [4, 5].
PSAX and A5Ch are the best views to assess AR severity (Figure 3, panel a and b),
although multiple evaluations from different projections should be warranted, especially for
eccentric jets. A comprehensive evaluation of LV function and dimension should also be
performed, especially for chronic severe AR [4].
CD is the most immediate and intuitive way to assess AR severity from the degree of its
extension in the LVOT. However, CD also allows the quantitative evaluation of the three
components of the regurgitant jet: jet width, vena contracta (VC) and flow convergence.
Alberto Giannoni, Chiara Borrelli, Giulia Elena Mandoli et al.
42
Quantification of AR severity
Mild
Moderate
Severe
Qualitative
CD jet in LVOT
small
intermediate
large
CW jet density
faint
inermediate
dense
PHT (msec)
>500
200-500
<200
Semiquantitative
Jet width/D
LVOT
(%)
<25
25-64
65
VC (cm)
<0.3
0.3-0.6
>0.6
Quantitative
EROA (cm2)
<0.10
0.10-0.29
0.30
RF (%)
<30
30-49
50
R
VOL
(mL/beat)
<30
30-59
60
a
b
d
c
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Table 2. Quantification of aortic regurgitation (AR) severity with 2D echocardiography.
CD: Color Doppler; CW: continuous flow Doppler; D
orifice area; LVOT: left ventricular outflow tract; PHT: pressure half-time; RF: regurgitant fraction; R
regurgitant volume; VC: vena contracta.
: diameter of the LVOT; EROA: effective regurgitant
LVOT
VOL
:
Figure 3. Echocardiographic evaluation of aortic regurgitation (AR). Anatomic parasternal short axis
view of aortic valve regurgitation (panel a). Parasternal long axis view of left ventricular outflow tract
(LVOT), with and without color Doppler. In this projection the diameter of the LVOT (dLVOT) and
the jet width are calculated, allowing for the estimation of jet width/dLVOT ratio (panel b). The vena
contracta can also be calculated in this projection. Pressure half time of AR in apical 5 chambers view
with continuous wave Doppler (panel c). Diastolic flow reversal in the aortic arch with pulsed wave
Doppler (panel d).
Jet width to D
ratio can be assessed for central jets only; it is measured in PLAX, just
LVOT
below the AV. VC is defined as the smallest neck of the regurgitant jet at the level of the AV,
immediately below the flow convergence region, and is preferably measured in PLAX. Flow
Non-Invasive Imaging of Aortic Valve – Ultrasounds
43
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convergence (with proximal isovelocity surface area - PISA method) allows the quantification
of the effective regurgitant orifice area (EROA), regurgitant volume (R
) and regurgitant
vol
fraction (RF). This method is based on the principle that blood flow converges to the
regurgitant orifice in hemispheric shells of increasing velocity and decreasing area. At this
level, lowering the Nyquist limit in the direction of the flow to 30-40 cm/s, the velocity is
known as the aliasing velocity (Va) at the brusk red-blue interface. The PISA radius (rPISA)
can also be measured from the aliasing interface to the regurgitant orifice. Finally, knowing
the VTI of the regurgitant jet (VTIAR) with CW, RF, EROA and R
can be calculated:
VOL
RF = 2rPISA2 * Va
EROA = RF/VTIAR
R
= EROA * VTIAR
VOL
The isovelocity surface area is not always optimally visualized. In such cases, an
alternative option is the comparison of SV at both mitral annulus (MA) and LVOT with PW
as follows:
R
VOL
= SV
LVOT
-SVMA
RF = R
VOL
/SV
LVOT
* 100
EROA = R
VOL
* VTI
AR
CW is used for the calculation of VTI
(as explained above) and of pressure half-time
AR
(PHT) (Figure 3, panel c). PHT is derived from the regurgitant velocity spectrum and it is
defined as the time required for the difference in pressure across the aorta to be halved; the
fastest the equilibration, the steepest the PHT. Nevertheless, PHT is highly dependent on LV
compliance and therefore loses its accuracy in cases of abnormal relaxation or acute AR [5].
Lastly, the density of the regurgitant spectrum is also considered as a marker of AR severity
[4].
Finally, the combined use of PW and CD allows the detection of backflow in thoracic or
abdominal aorta, which is present if AR is at least moderate (Figure 3, panel d).
TRANS-ESOPHAGEAL ECHOCARDIOGRAPHY
TEE allows a complete assessment of the AV apparatus. Anatomy is easily examined
using standard views, mostly from mid-esophagus. The use of CD is essential to assess
valvular function and can be applied to each view while the correct alignment for spectral
Doppler is only obtained in deep transgastric (TG) view.
Alberto Giannoni, Chiara Borrelli, Giulia Elena Mandoli et al.
44
a b
RCC
LCC
NCC
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Figure 4. Transesophageal mid-esophageal (ME) AV short axis view (SAX). ME AV SAX is displayed
starting from a standard ME 4 chamber view, with a slight probe withdrawal and rotation, up to 30-45°.
In case of a tricuspid valve, the typical Mercedes Benz sign in diastole is displayed (the non coronary
cusp - NCC on the left, close to interatrial septum, the left coronary cusp - LCC on the right and
posterior, the right coronary cusp - RCC on the right and anterior). SAX is the key view for the
diagnosis of bicuspid AV (BAV). In panel b the most common phenotype or type I BAV is shown with
LCC-RCC fusion.
The mid-esophageal (ME) AV short axis view (SAX) is displayed starting from a
standard ME 4 chamber view, with a slight probe withdrawal and rotation, up to 30-45°. Its
position is then varied, with clockwise or counterclockwise small movements, to put the valve
in the middle of the screen, ensuring the identification of all AV cusps and commissures. In a
tricuspid AV a triangular orifice during systole and the typical Mercedes Benz sign in diastole
are observed; the NCC is on the left, close to interatrial septum, the LCC is on the right and
posterior, the RCC is the anterior leaflet (at the bottom of the screen) (Figure 4, panel a).
A minimal further withdrawal of the probe shows the origin of the coronary arteries from
the left and right cusps (helping in the detection of abnormal origin and proximal course).
SAX is the key view for the diagnosis of bicuspid AV (BAV), showing the 2 unequal-sized
leaflets with the typical systolic fish mouth sign (Figure 4, panel b). Congenital type I BAV is
characterized by an LCC-RCC fusion and represents the most common phenotype followed
by RCC-NCC fusion (type II). Usually, a raphe replaces the corresponding commissure.
Starting from the paramount assumption that BAV is not only an AV disease but also an
aortic vessel disease, aortic root and ascending aorta must be carefully evaluated in all
patients. Interestingly, the rheologic differences, consequent to the fusion pattern, lead to
variable changes in aortic shear stress. The blood flow passing through a type I BAV usually
promotes aortic root and ascending aorta dilatation while RCC-NCC fusion is most
commonly associated with dilatation of the tubular portion of the ascending aorta and the
aortic arch (the root is preserved) [6]. BAV can also be associated with other congenital
defects, the most common of which being aortic coartation [7]. Thus, TEE examination must
evaluate all accessible aortic portions. TEE report should describe the degree of
atrioventricular sclero-calcific remodeling up to acquired form of BAV (consequent to
extensive calcifications, previous endocarditis – rare – or rheumatic disease). Quadricuspid or
unicuspid AV are other extremely rare congenital abnormalities.
From standard ME long-axis view, with a slight withdrawal or rotation of the probe up to
120-140° from an AV short axis-view, the ME AV long-axis view (LAX) is obtained. The
anterior (inferior) aortic leaflet is the RCC while the closest cusp to the probe is either NCC
Non-Invasive Imaging of Aortic Valve – Ultrasounds
45
Absolute values (cm)
Indexed values (cm/m2)
Men
Women
Men
Women
Mid-systolic*
Annulus
2.6 ± 0.3
2.3 ± 0.2
1.3 ± 0.1
1.3 ± 0.1
End-diastolic**
Sinuses of Valsalva
3.4 ± 0.3
3.0 ± 0.3
1.7 ± 0.2
1.8 ± 0.2
STJ
2.9 ± 0.3
2.6 ± 0.3
1.5 ± 0.2
1.5 ± 0.2
Proximal ascending aorta
3.0 ± 0.4
20.7 ± 0.4
1.5 ± 0.2
1.6 ± 0.3
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or LCC (accordingly to rotation) (Figure 5, panel a). A magnified visualization of the aorta
(by applying zoom mode or by reducing depth) is recommended to reduce errors in the
measurement of aortic sections (annulus, sinuses of Valsalva, sino-tubular-junction). Normal
cut-off values are listed in Table 3. Systolic valve doming, asymmetrical diastolic coaptation
(both typical of BAV) and diastolic prolapse can be easily seen in this view. LVOT can also
be measured.
The assessment of the LVOT and the AV can be completed at mid-esophagus with a five-
chambers view, opened by slightly withdrawing or ante-flexing the probe from a standard ME
four-chambers view. The anterior cusp is the RCC while the closest to the left atrium is the
NCC.
Advancing the probe into the stomach and increasing the angle up to 120-140°, both the
LVOT and the AV are included in the image (TG long axis view). Cusps motion and structure
can be further evaluated here. Finally, going back to 0°, with an additional advance and
anteflexion of the probe (in contact with gastric wall), we display a deep TG view, in which
the LVOT anatomy and dimension can be studied and the perfect alignment with the AV
allows spectral Doppler interrogation.
Table 3. Aortic root dimensions: reference values
*inner edge to inner edge ** leading edge to leading edge.
Adapted from Lang et al. [8] STJ = Sinotubular junction.
Aortic Stenosis
TEE examination helps to discriminate between the valvular stenosis and the much rarer
sub- and supra-valvular defects. In ME AV short axis view, planimetry of the valve
(anatomical area) can be obtained in systole even if it is more complicated in case of very
severe calcifications. CD imaging can reveal a typical mosaic pattern in the LVOT due to the
turbulent blood flow. CW and LVOT PW interrogation in deep TG view allow the
calculations of jet velocity and gradients across AV and the estimation of AVA by continuity
equation. However, TTE remains the best method for this purpose.
Aortic Regurgitation
The assessment of AR starts from the investigation of its etiology. In each view, the AV
anatomy should be accurately evaluated to verify if AR is related to acquired or congenital
diseases. The surgical classification of AR recognizes 3 different patterns: enlargement of
Alberto Giannoni, Chiara Borrelli, Giulia Elena Mandoli et al.
46
a b
a b
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aortic root with normal cusps (type 1); cusps prolapse or fenestration with excessive motion
(type 2); poor cusp tissue quality or quantity with restricted motion (type 3) [9]. If the clinical
suspect is endocarditis, vegetations must be carefully investigated (Figure 5, panel a and b).
The use of CD must complete every TEE exam. In ME AV SAX, AR is seen as a
continuous flow during diastole and the origin of the jet can be described as central or
commissural. In all other views, the direction of the flow can be central or eccentric (typical
of BAV, fenestrated or prolapsed cusps, with an opposite-directed jet). In ME AV LAX,
quantitative parameters for the estimation of AR can be calculated, including jet width/LVOT
width, jet area/LVOT area, VC width, PISA radius (Figure 6, panel b).
A good alignment of the ultrasound beam in the deep TG view is useful to obtain the CW
Doppler spectral trace for the evaluation of other AR indexes such as PHT, EROA, R
VOL
and
RF. Methods and cut-off values are described in TTE section. The demonstration of reversal
flow in descending aorta by PW is associated with a higher AR severity.
Figure 5. Transesophageal evaluation of aortic valve (AV) endocarditis. Mid-esophageal long axis
(panel a) and short axis (panel b) views of AV showing an endocarditis mass on the non coronary cusp.
Figure 6. Transesophageal mid-esophageal (ME) aortic valve (AV) long-axis view (LAX). From a ME
AV short axis-view (SAX) with a slight withdrawal or rotation of the probe up to 120-140°, we obtain a
ME AV LAX (panel a). The anterior (inferior) aortic leaflet is the RCC while the closest cusp to the
probe is either NCC or LCC (accordingly to rotation). From this view it is possible to obtain
measurements of different aortic sections (annulus, sinuses of Valsalva, sino-tubular-junction) and left
ventricular outflow tract (LVOT). By applying color-Doppler (panel b) the regurgitant jet may be
visualized (central/eccentric) and quantitative parameters for the estimation of aortic regurgitation AR
can be calculated, including jet width/LVOT width, jet area/LVOT area, vena contracta width
and PISA radius.
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