 |
| Fig.2.10 |
PW Doppler has been reported to have a sensitivity ranging between
86% and 100% for the detection of aortic regurgitation. PW Doppler
examinations for this lesion are best begun using the apical two-or
four-chamber two-dimensional views for operator guidance. Figure
2.10 demonstrates a PW Doppler recording from just at the
coaptation point of the aortic valve in a normal patient when
the transducer was placed at the ventricular apex. Note that some
low frequency diastolic sounds are normally encountered, which
likely result from blood swirling through the mitral orifice and
around the left ventricular outflow tract. The novice should not
mistake these low velocity events for evidence of aortic insufficiency.
 |
| Fig.2.11 |
When regurgitation is present, careful searching just on the
ventricular side of the aortic valve with PW Doppler reveals the
high frequency sounds and diastolic spectral broadening typical
of aortic insufficiency. This is shown in Figure
2.11, where almost all regurgitation jets are severely aliased
and the top of the spectral trace appears cut off and placed at
the bottom of the display. Note that the zero baseline of the
spectral display has been moved to the bottom of the display,
as described in Unit 1, in an attempt to eliminate the aliased
diastolic signal and to provide as much display of the spectral
profile as possible. Even with this maneuver, the top of the aliased
signal is still missing.
 |
| Fig.2.12 |
Similarly, the best window for the evaluation of aortic insufficiency
with CW Doppler is the apical window. Using this approach, aortic
insufficiency appears as a holodiastolic, high frequency turbulent
jet with spectral broadening and flow toward the transducer as
noted in Figure
2.12. The resultant spectral shift is positive (i.e., above
the baseline). Doppler spectral recordings of aortic insufficiency
are invariably holodiastolic.
It is usually of interest to beginners to Doppler echocardiography
who are familiar with auscultation, that the Doppler spectrum
in aortic insufficiency has a holodiastolic duration and its duration
does not vary with severity. This example serves to highlight
the differences between the audible sounds generated by the Doppler
shift device and those heard by auscultation. Using the latter
approach, the typical murmur of aortic insufficiency is early
diastolic and decrescendo. These differences emphasize the fact
that the Doppler instrument is not an elaborate electronic stethoscope.
 |
| Fig.2.13 |
The operator should keep in mind some possible causes for false
positive or false negative examinations when evaluating patients
with suspected aortic insufficiency. One common reason for a false
positive test is confusion with mitral valve diastolic inflow,
particularly when mitral stenosis is present.
Figure 2.13 shows a CW recording taken from the apical window
in a patient with aortic valve disease. Note the different timing
of the aortic diastolic jet and the mitral inflow signal. The
duration of diastole is longer in aortic insufficiency than mitral
inflow.
 |
| Fig.2.14 |
A maneuver performed from the apical window using a CW Doppler
transducer is demonstrated in Figure
2.14. The first two beats were obtained with the beam angled
toward the left ventricular outflow tract, and demonstrate aortic
insufficiency. The beam is then angled toward the mitral orifice
where the diastolic jet of mitral stenosis is encountered in the
second two beats.
These jets are both diastolic events and are quite similar in
contour. Note also that the spectral distribution of both abnormal
jets is wide, but much less intense in aortic insufficiency when
compared with mitral stenosis. Recognition of the different features
of the spectral display in these two lesions, plus a thorough
examination of the location of the suspected abnormal diastolic
jet using the PW approach, should allow the operator to reliable
separate aortic insufficiency from mitral stenosis in most cases.
It is also possible that a false positive recording of aortic
insufficiency may result from inadvertent detection of coronary
blood flow. Although coronary flow is mostly diastolic and the
size of the Doppler beam is usually large at remote distances
from the transducer, it seems unlikely that this is a very frequent
cause of false positives in clinical practice.
It is worthwhile to keep in mind that detection of aortic regurgitation
by Doppler with a negative cardiac catheterization may not necessarily
constitute a false positive study. However, the amount of regurgitation
in this situation is probably minimal. Rapid dilution of a small
aortic regurgitant jet into the large left ventricular cavity
probably accounts for the failure to appreciate this event by
angiographic means.
 |
| Fig.2.15 |
The probable reason for a false negative diagnosis of aortic
insufficiency is that the jet is small and not easily detected
with either pulsed or continuous wave Doppler. Not only may the
jet be small, it may move through the interrogating beam with
the phases of the cardiac cycle. This makes it difficult to record
a full profile because the jet is never positioned in the Doppler
beam long enough to record the entire event, as seen in Figure
2.15.
 |
| Fig.2.16 |
Such an occurrence is the likely explanation for the PW Doppler
spectral recording shown in
Figure 2.16. Here, the full diastolic duration of the aortic
insufficiency jet is poorly appreciated on some beats. The recording
was obtained with the transducer held at the ventricular apex.
 |
| Fig.2.17 |
This phenomenon also may occur due to the phases of the respiratory
cycle. This is not because the volume of the jet is varying with
respiration. Rather, the direction of the jet is probably changing
slightly with respect to the direction of the interrogating Doppler
beam as the heart moves up and down with the moving diaphragm.
This phenomenon is demonstrated in Figure
2.17 where the full profile of aortic insufficiency is seen
from the ventricular apex using CW Doppler. Here the full profile
of aortic insufficiency is recorded on some beats and not on others.
When this occurs, and differences due to respiration are suspected,
the operator should try many different transducer positions and
angulations to record as much of the suspected abnormal profile
as possible.
 |
| Fig.2.18 |
Some jets may be so small as to require interrogation from slightly
different transducer positions to record the full profile. The
spectral profiles in Figure
2.18 are not the result of a continuous strip recording but
are a five-panel composite demonstration of the diastolic appearance
of aortic insufficiency from five slightly different apical positions
in a patient with aortic insufficiency. The only way to overcome
this problem is to be assured that every possible area has been
adequately interrogated for aortic insufficiency during the Doppler
examination.
Although the apical approach is the most profitable window for
the detection of aortic insufficiency, it is worth keeping in
mind that some jets are directed eccentrically and may be detectable
only from some other window such as the left parasternal. Caution
should be exercised, however, when using CW Doppler from parasternal
windows. It might be possible to mistake pulmonic insufficiency,
which can be recorded in many subjects, for aortic valve insufficiency.
Fortunately, most aortic insufficiency encountered from the left
parasternal approach is directed posteriorly toward the mitral
valve and away from the transducer (a negative jet). This contrasts
with pulmonic insufficiency, which is uniformly directed anteriorly
into the right ventricle toward the transducer (a positive jet).
Some information as to left ventricular end-diastolic pressure
may be gained in the setting of aortic insufficiency. Since the
velocity of any jet relates to the pressure drop across the valve,
there exists a pressure gradient between the aorta and left ventricle
at end-diastole. This pressure gradient may be estimated by measuring
the velocity of the aortic regurgitant jet at end-diastole using
the simplified Bernoulli equation. Subtracting this pressure from
diastolic blood pressure (as measured by cuff at the time of the
Doppler examination) provides an estimate of left ventricle end-diastolic
pressure.
 |
| Fig.2.19 |
A typical aortic regurgitant jet obtained by CW Doppler from
the left ventricular apex is shown in Figure
2.19. In the example shown, the end-diastolic velocity is
approximately 1.9 m/sec which corresponds to a pressure gradient
estimate of 14mmHg. This patient had severe aortic insufficiency,
and the measure diastolic blood pressure was 55mmHg by brachial
arterial cuff measurement. This resulted in an end-diastolic pressure
estimate of 41 mmHg. At catheterization, the actual measured pressure
was 38 mmHg.
It should be noted, however, that this approach only shows satisfactory
correlation in patients with severe (3+ to 4+) angiographic aortic
insufficiency. Application of this method to individuals with
lesser degrees of insufficiency does not yield good correlations
with catheterization measurements of left ventricular end-diastolic
pressure.
2004