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76
ab
Fig. 7.3 Pulse wave Doppler velocities with and without spectral broadening. (a) Shows the ideal without spectral
broadening. Image in (b) has spectral broadening, which can affect velocity accuracy
E. Ablordeppey and A. Murphy-Crews
Fig. 7.4 Aliasing occurs when Doppler shift exceeds the
Nyquist limit. In this example, high-velocity aortic regurgitation (which should only be seen above the baseline)
appears coming from the bottom of the plot. When using
Aliasing (PRF andNyquist Limit)
PWD and Doppler shift exceeds the Nyquist limit, aliasing will occur. Aortic insufciency velocity seen above
the baseline is “wrapping around” and coming from the
opposite direction toward the baseline
that can be measured. This limit is known as the
Nyquist limit and is a function of the pulse repeti-
Range specicity is a signicant advantage of PW
Doppler modalities, allowing for the measurement
of blood ow at a precise intracardiac location. The
disadvantage of this is a limitation in the frequencies
that can be measured. In PW mode, transducers
alternate between transmitting and receiving pulses,
which puts a limit on the maximum Doppler shift
tion frequency (PRF) and is depicted in the following equation, Nyquist limit = PRF/2. When the
Doppler shift exceeds the Nyquist limit, aliasing will
occur (see Fig.
7.4). In PWD, aliasing presents as a
spectral signal “wrapping around” and coming from
the opposite direction toward the baseline. There are
a few strategies to remove aliasing when present.
ab
7 Transthoracic Doppler Echocardiography
Fig. 7.5 Parasternal long-axis view with color Doppler to look for mitral and aortic valvopathies. Note that the color
box in (a) is unnecessarily large, which will require more machine processing and lower resolution than (b)
77
The sonographer can lower the baseline (though this
is for appearances only and does not change the
characteristics of the signal), increase the scale (if
not already maximal), or nd a view with a shallower sample volume. Lastly, changing the Doppler
mode to CWD will eliminate aliasing and allow for
the measurement of unlimited Doppler shift; however, the range specicity of PWD will be lost.
of moving blood. With color Doppler, aliasing
will appear as a shift in color from red to blue (or
vice versa) when the velocities exceed the
Nyquist limit. The quality and utility of visual
images created with color Doppler is dependent
on the frame rate, which is a function of how
many frames or images can be produced by the
ultrasound machine, measured in frames per second (FPS). The frame rate for color Doppler is
dependent on the pulse repetition frequency, the
Pulse Repetition Frequency
number of scan lines, and the number of pulses
per scan line. The PRF is a function of the depth
The PRF is the number of pulses that are sent and
received in 1 s. The temporal resolution is
improved as a function of the pulse repetition frequency. Given that the speed of the sound in the
medium cannot be controlled, the PRF is dependent on how far the pulses have to travel, i.e., the
depth of the gate. Using the appropriate window
and setting the gate as shallow as possible will
maximize the PRF.
Optimization ofColor Doppler
(Frame Rate andZoom)
of the color sector, once again highlighting the
importance of selecting an appropriate depth for
the area of interest. The scan lines and pulses per
scan line are a function of the size of the color
sector. The larger the sector (color box), the lower
the frame rate and detail. In general, it is best to
limit the size of the color sector as small as possible while covering the necessary area of interest
(see Fig.7.5).
Pro-tip
In general, color sectors should be as small
as possible to optimize temporal resolu-
Color Doppler is based on the principles of PWD
tion.
and is therefore subject to similar constraints
relating to aliasing and dependence of angle of
incidence. Recall from Chap. 1 that color wave
Doppler is created by a series of scan lines, each
with multiple pulse gates, the data being overlayed with color to show the direction and speed
Now that we have discussed tactics to opti-
mize image acquisition, let us turn our discussion
to specic applications of Doppler echocardiography.
78
Stroke V
2
()
I
E. Ablordeppey and A. Murphy-Crews
Clinical Applications forDoppler
Echocardiography
LV Outow/Inow
LV Outow Tract Velocity Time Integral
(LVOT VTI)
TTE can be used to quantitatively assess stroke
volume and cardiac output by measuring the integral of the velocity through the LVOT over time
(Fig.7.6).
To measure the velocity of blood in the left
ventricular outflow tract (LVOT), we start in
the apical five- or three-chamber view with
PWD.Optimize the depth and sector width to
provide the best resolution for the LVOT.Align
the PWD gate in the LVOT on the ventricle
side of the aortic valve. It is important to keep
the Doppler beam as parallel to the LVOT as
possible for accurate measurements. Of note,
some machines have an option for angle correction on Doppler; however, this should be
avoided, and better imaging alignment should
be attempted instead. With settings optimized,
activate the PWD to record the velocity over
time. Note that we are interested in the speed
of blood flow through the LVOT (away from
the probe), so the area of interest will be
below the baseline. Move the baseline up to
provide maximum room to see the data of
interest. The flow velocity is measured over
time and called the velocity-time integral
(VTI; Fig.
7.4 demonstrates a VTI with trac-
ing). In a laminar flow state, the column of
blood moving through the LVOT should be
moving at the same speed, thus the tracing
should have a well- defined and tightly
grouped line with no spectral broadening.
Deviations from this may suggest interference
from poor image quality or gate positions, or
nonlaminar flow, such as in the case of
dynamic outflow obstruction.
Pro-tip
The VTI is affected by the angle of the
probe. When doing serial measurements, it
is important to keep the probe angle
consistent.
Compared to estimates of ejection fraction,
CO is often a more directly relevant clinical variable to the intensivist and is less susceptible to
interpretation bias from tachycardia or mitral
regurgitation. The VTI can also be used to assess
volume responsiveness. Recall that volume
responsiveness means that additional preload
will lead to an increase in SV. By taking serial
VTI measurements before and after a passive leg
raise or uid bolus, changes in SV can be directly
measured. In addition, respirophasic variability
in LVOT VTI morphology can also be used as a
surrogate for uid responsiveness. A temporary
increase in stroke volume with increased venous
return from spontaneous inspiration (or during
exhalation in the mechanically ventilated patient)
may signal that a patient will be responsive to
volume. It is important to note that VTI measurement of CO does require sinus rhythm, as beatbeat variability will make the generalization of
any given measurement unreliable.
Pro-tip
Sometimes respirophasic variability in VTI
may be a reection of cardiac translation or
change in angle with breathing. If the heart
is moving substantially with respiration,
interpret VTI variation with caution.
olume = * *
Fig. 7.6 Stroke volume calculated by measuring an
LVOT VTI and the LVOT diameter. For a shortcut, the
average LVOT is 2cm, so SV≈π∗LVOTVTI.Cardiac
output is the product of SV*HR
LVOT diameter
2
LVOT VT
LV Inow forDiastolic Function
Diastolic function is the ability of the heart to recoil
and relax to receive blood in preparation for ventricular systole. One modality for assessing diastolic
dysfunction is based on patterns in the velocity of
blood owing from the left atrium to the left ventri-
7 Transthoracic Doppler Echocardiography
79
cle during early and late diastole. To obtain LV
inow velocities, start with the apical four-chamber
view and place PWD with the gates in the ventricle
at the tips of the mitral valve (MV) coaptation point.
Color Doppler can be overlaid to visualize the path
of blood ow and help optimize the angle for a more
accurate measurement. Blood owing into the ventricle will appear as peaks above the baseline as
blood is owing toward the direction of the probe.
The rst peak, known as the E-wave, is formed by
early diastolic blood ow and is reective of LV
relaxation. This is followed by the A-wave, which is
caused by additional blood ow into the ventricle
from atrial contraction (if present). The relative
speed of blood during early diastole versus during
atrial contraction can be used to characterize a spectrum of impaired LV relaxation (see Chap. 15 on
diastolic function). LV inow is used in conjunction
with LV tissue relaxation in many standard
approaches to diastolic assessment.
MV E′, A′ andS′
The term prime (denoted “ ′ ”) is added to
describe tissue movement velocity. In an A4C
view, place PWD with activated tissue Doppler
index (TDI) on the septal and lateral insertion
of the mitral valve and record tissue velocities
during early diastole and atrial contraction.
The early and late diastolic waves are called e’
and a’ and are seen below the baseline (as the
tissue is moving away from the probe during
diastole) and correspond to LV relaxation and
atrial contraction (see Fig.7.7). Tissue movement of the LV during systole is represented in
the S′ wave, which is seen above the baseline
from the A4C view. MV S′ is a less commonly
used tool to estimate LV systolic function.
Due to the relatively good performance of TDI
even with limited views, TDI can contribute to
the assessment of both diastolic and systolic
functioning in patients with relatively poor
echo windows.
Pro-tip
Doppler imaging, including tissue Doppler,
can often provide information when 2D
image quality is limited.
RV Inow/Outow
TR Max forPASP
The modied Bernoulli equation (Fig.7.8) allows
us to calculate the pressure gradient across a
valve by measuring the maximum velocity of
regurgitant ow.
Fig. 7.7 Measuring
velocities at the mitral
annulus with tissue
Doppler
80
a
b
E. Ablordeppey and A. Murphy-Crews
Fig. 7.8 The modied Bernoulli equation (a) yields the
pressure gradient (∆P) across a valve as a function of
maximal regurgitant velocity (V
). This can be modied
max
(b) to determine RVSP (which is assumed to equal PASP
in the absence of PS) by measuring the maximal TR
velocity and adding right atrial pressure (RAP)
Fig. 7.9 CWD across the TV in RV inow view with measurement of TRmax. The calculated pressure gradient, when
added to the CVP (measured or estimated from IVC characteristics), will give an estimated PASP
The most useful application of this is estimating the pulmonary artery systolic pressure (PASP)
using tricuspid regurgitation (TR). To determine if
mate the right ventricular systolic pressure, which
is a good surrogate for PASP in the absence of sig-
nicant pulmonic stenosis (Fig.7.9).
TR is present, place the color Doppler over the tricuspid valve in any view. A4C view often allows
for the best Doppler alignment of the TR jet,
though parasternal RV inow or PSX basal views
may also be used. Use continuous wave Doppler
(CWD) over the most visible areas of high velocity through the tricuspid valve to capture ow
away from the probe during ventricular systole.
The maximum velocity (TR max) will give us the
pressure gradient between the RV and RA. By
adding the right atrial pressure (either from CVP
tracing or an estimate based on IVC), we can esti-
Pulmonary Artery Acceleration Time
(PAAT)
Pulmonary artery acceleration time (PAAT) is the
time it takes from the beginning of ow through
the pulmonic valve to peak velocity. This time
reects the gradient pressure between the right
ventricular outow and the pulmonary artery.
Short PAAT is seen when there is elevated pul-
monary artery pressure. From the RVOT view or
PSAX basal view, place the PWD gate proximal
to the pulmonary valve in the RVOT (see
Normal doppler tracing Blunted systolic flow Flow reversal
7 Transthoracic Doppler Echocardiography
81
S
D
A
LV
RV
LA
RA
Fig. 7.10 PWD of pulmonary vein ow from normal evidence of high left atrial pressures
Fig. 7.10). The time from PV opening to peak
velocity is correlated with PA pressure (see Chap.
55 on pulmonary embolism and acute cor pulmo-
nale for more on this).
during early and late ventricular systole, when
the left atrium is being lled. PWD placed in any
of the pulmonary veins (at least 1cm) with the
best Doppler alignment will generate a wave-
D
S
A
form with three peaks. During ventricular sys-
RV S′ forRV Systolic Function
Tissue Doppler can be used to measure the speed
of the right ventricle during systole, which has
been shown to correlate with RVEF and has very
similar test characteristics to TAPSE (see Chap.
13 on RV assessment). To measure RV S′, obtain
an A4C view and place the TD on the RV lateral
wall at the junction of the lateral tricuspid annulus. The peak systolic velocity (above the baseline, as the ventricle moves toward the probe in
an A4C during systole) is measured, with velocities >10cm/s correlating with RVEF >50%.
tole, there are two systolic inections referred to
as S1 and S2. Frequently, these two peaks are
fused and indistinguishable, then they are
referred to as the S-wave. The rst (S1) compo-
nent denotes atrial relaxation (diastole) with suc-
tion of blood into the left atrium and is affected
by LA pressure, contraction, and relaxation. The
second (S2) component occurs when the mitral
annulus is apically displaced with ventricular
systole, decreasing left atrial pressure and creat-
ing a gradient for forward ow. The second
group of deections that occur during ventricu-
lar diastole is known as the D-wave. The down-
Pulmonary Venous Flow (Diastolic Function)
stroke of the D-wave will dip beyond the
baseline, indicating ow away from the trans-
ducer, and is referred to as the AR wave (atrial
reversal). This wave corresponds to atrial conDoppler measurements through the pulmonary
veins allow an understanding of the speed of
blood ow during diastole from the pulmonary
veins into the left atrium. Normal ow has characteristic features, and abnormalities in ow patterns are present when there is impedance from
the left atrium. PWD is used to characterize ow
traction and “reversal” of ow.
A progressive increase in left atrial pressure
(from severe mitral regurgitation or diastolic
dysfunction for example) will blunt the systolic
ow velocities in the pulmonary veins, with the
majority of forward ow increasingly occurring
during diastole. The elevation in left ventricular
D
A
S
82
E. Ablordeppey and A. Murphy-Crews
end- diastolic pressure will exaggerate the ow
reversal that occurs with atrial contraction, prolonging the AR wave. Normal lling patterns
are predominantly systolic, with an S/D
ratio > 1. A pathologic increase in mean left
atrial pressure will reverse this pattern, resulting
in an S/D ratio< 1 and a diastolic lling predominance. Atrial reversal velocity and duration
abnormalities can also suggest elevated lling
pressures, for example, AR peak velocity> 35cm/s implies elevated left atrial pressures. Similarly, pulmonary venous AR should
be similar in duration to the trans-mitral A-wave.
Large discrepancies between the two suggest
elevated lling pressures. It is, however, important to recall that in young or very healthy
patients, pulmonary vein ow may have an
appearance similar to elevated lling pressures
because of the vigorous LV function that generated elevated peak D-wave velocities. There are
some abnormal pulmonary vein ow patterns
from benign etiology such as elevated S/D ratio
and peak AR velocity with age and tachycardia.
Whereas atrial brillation causes decreased
peak S1 and AR velocity because of the lack of
organized atrial contraction. See Fig.7.11 for
possible cardiac pathology seen in various
abnormal pulmonary vein ows.
7 Transthoracic Doppler Echocardiography
Atrial septal defect
Differential Diagnosis
83
Mitral stenosis
Impaired LV relaxation
Pulmonary vein stenosis
PV Doppler
Single
forward
Pattern
Differential Diagnosis
Normal at young age (< 40 years)
waveform
Atrial fibrillation
Moderate or severe MR
Restrictive cardiomyopathy
High LA pressure at older age
High LVEDP
Prolonged
Short PR interval
Intra-atrial conduction delay
A
D
S
D-wave
deceleration
Severe MR
D
S
High velocity
Junctional or
S- and D-wave
idioventricular rhythm
with retrograde conduction
D
PV Doppler
Pattern
S
S < D
D
S
Prominent
A-wave
D
Mid-late or
D
S
SR
reversal
holysystolic
SR
Early
systolic
reversal
Fig. 7.11 Cardiac pathology differential for abnormal pulmonary vein ow
84
Fig. 7.12 Hepatic vein ow waveforms during the normal cardiac cycle
E. Ablordeppey and A. Murphy-Crews
Hepatic Vein Flow
Right heart-sided disease severity, including tricuspid valve, pericardial disease, and cardiomyopathy can be evaluated by hepatic vein ow.
When discussing the ow pattern for the hepatic
veins, we must consider the blood ow pathway
in regard to the circulatory system and transducer. Antegrade is ow toward the heart.
Retrograde is ow away from the heart, toward
the liver. The hepatic veins are considered phasic
waveforms and are predominately antegrade.
They are composed of four parts (Fig.
A-wave occurs during Atrial Systole and is gen-
erated by the increase in RAP from an open
tricuspid valve.
S-wave occurs during Ventricular Systole where
the largest amount of blood ows from hepatic
veins into RA.The RV walls contract, pushing
blood out into the right ventricular outow
tract (RVOT).
V-wave is a Transitional Phase that occurs from
atrial overlling when the tricuspid annulus
returns to resting position.
7.12).
D-wave occurs in Ventricular Diastole when the
tricuspid valve is open and there is the passive
lling of the RA from hepatic veins. This veloc-
ity is less than the S-wave because of decreased
RAP from the rapid diastolic lling of RV.
Hepatic vein ow abnormalities, most commonly from tricuspid regurgitation (TR) and/or
RV failure, begin with triphasic waveforms and
progress to a biphasic waveform and an increased
V-wave. When severe pathology is present, one
fused retrograde ow is seen during diastole. The
more severe the regurgitation, the more pulsatile
the waveform becomes.
Color Doppler forValvular
Regurgitation andStenosis
As described in Chap. 1, there are several modes of
Doppler yet each has the same goal. Doppler shift
is an angle-dependent measurement of blood or tissue velocity. When color is used, velocities within
the frame are averaged but the direction is noted.
By convention, on TTE, the color box is typically
7 Transthoracic Doppler Echocardiography
85
red or blue. Red demonstrates blood ow toward
your ultrasound probe and blue is blood ow away
from the ultrasound probe. When determining if
there is valvular regurgitation or stenosis, color
ow Doppler can be useful in visually identifying
the high-velocity signals or jets that are going
toward or away from the probe. Whether the valve
is regurgitant or stenotic is based on the characteristics of the valve and the native direction of blood
ow. Slightly atypical views may help to align the
jets in a more parallel fashion which is always the
goal. The color box can be moved back and forth
between valves, depending on assessment priority.
Moving a sector box back and forth is much better
than using a large color box that covers both valves
and where the color resolution is poor.
Pulse-Wave/CW Doppler (Aorta Flows)
Because of the properties of PWD and CWD,
interrogation can be made through the aortic
valve to understand and diagnose multiple valvular conditions. PWD in front of the aortic valve
will measure velocities in the left ventricular outow tract (LVOT). These velocities can be used
to estimate left ventricular stroke volume. CWD
through the aortic valve will measure velocities
through the aortic valve. The ratio between in
front of the aortic valve and through the aortic
valve can used to evaluate aortic valve stenosis.
In addition, the shape and speed of the velocities
through the aortic valve can help determine if
there is left ventricular outow obstruction.
Summary Points
• The velocity of blood and tissue in the heart
can be determined by changes in the emitted
ultrasound waves according to the Doppler
shift principle.
• Doppler echo is essential for measuring cardiac output, noninvasive measurement of
intracardiac pressures, diastolic function, and
more.
• Doppler measurements can be optimized with
proper technique. Align the probe with the
direction of blood ow (less than 20° angles)
and minimize depth, sector width, and color
boxes to focus on the areas of clinical interest.
• Abnormalities in velocities of ow through
the pulmonary veins and hepatic veins can
demonstrate pathologic conditions that affect
ventricular lling pressure.
Questions
1. Which of the following is true regarding spec-
tral Doppler imaging?
A. TDI lters out low-velocity signals to
measure tissue rather than blood
B. All modes of spectral Doppler are subject
to aliasing artifacts
C. PWD is ideal for measuring high-velocity
ows
D. PWD offers range specicity
Answer: D.PWD offers range specicity.
TDI lters high-velocity, low-intensity signals to measure blood. Continuous wave
Doppler is not subject to aliasing. PWD is
typically unsuitable for high-velocity ows,
although there are additional settings that can
improve assessments of high-velocity ows.
2. Which of the following can be determined
about intracardiac blood ow with spectral
Doppler?
A. Velocity only
B. Direction only
C. Direction and velocity
D. Neither direction nor velocity
Answer: C.Direction and velocity.
The spectral Doppler waveform assesses
the vector of blood velocity parallel to the
probe. It can only assess the direction in one
dimension (either moving toward or away
from the probe). It will underestimate velocity
as the direction becomes less parallel.
3. Which of the following variables are required
to estimate RVSP via the modied Bernoulli
method?
A. Pulmonary artery acceleration time
B. Maximal velocity of the tricuspid regurgi-
tation jet
C. Right atrial pressure
D. B & C
E. A & C
Answer: D.B&C.