 |
| Fig.2.20 |
A number of
studies have shown that Doppler echocardiography is both very sensitive
and very specific for the detection of mitral regurgitation when
compared with cardiac catheterization. Using PW Doppler, most cases
of mitral regurgitation can be detected with the transducer at the
apex and the sample volume located in the left atrium just behind
the mitral valve (Fig. 2.20). Because of the high velocities of
the regurgitant jet and the distance from the transducer to the
jet, aliasing of the mitral regurgitant jet invariably occurs. As
with all regurgitant lesions, location of the abnormal turbulence
is done in pulsed Doppler mode and continuous wave Doppler is then
used to record the full spectral profile.
 |
| Fig.2.21 |
The full spectral profile of mitral regurgitation obtained from
the ventricular apex by CW Doppler commonly reaches peak velocities
of between 3 and 6 m/sec, depending on the systolic pressure gradient
between the two chambers. It is usually quite symmetric, as seen
in Figure
2.21. The opening and closing motions of the mitral valve
will sometimes result in sharp spikes on the spectral velocity
recording because the rapidly moving valves will also render a
Doppler signal.
 |
| Fig.2.22 |
This phenomenon of valve opening and closing is seen in Figure
2.22.
 |
| Fig.2.23 |
Mitral regurgitation associated with endocarditis, ruptured chordae
tendinae and/or partial leaflet flail, is frequently associated
with loud clicking noises and high frequency spikes on the spectral
recording. These are created by rapid movements of the diseased
target through the field of view. Thus, multiple high velocity spikes
may be demonstrated on the spectral recording as seen in Figure
2.23. Occasionally, the systolic profile of mitral regurgitation
peaks slightly early, as is seen in this patient with endocarditis
when the regurgitation is severe and end-systolic pressures are
high. These results occur because the gradient between left ventricle
and left atrium is small.
 |
| Fig.2.24 |
Other factors may alter the usually symmetry of the mitral regurgitant
spectral tracing. The left panel of Figure 2.24 shows combined aortic
insufficiency with aortic outflow tract obstruction. This tracing
was obtained from an individual with hypertrophic cardiomyopathy
and a resting outflow tract gradient. Note that the systolic peak
velocity approaches almost 5 m/sec. Interrogation of the mitral
valve (Fig. 2.24, top panel) shows a clear, late systolic profile
typical of the late systolic mitral regurgitation seen in this disorder.
This presumably occurs because the pressure within the left ventricle
rises rapidly with the dynamic outflow obstruction and creates a
very high gradient between left ventricle and atrium in mid-to-late
systole.
 |
| Fig.2.25 |
False positive examinations for mitral regurgitation do occur. One
common reason for false positive examinations is confusion of the
aortic outflow signal with that of the mitral regurgitation. The
similarity between the systolic flow profile away from the transducer
in mitral regurgitation and aortic stenosis is shown in Figure 2.25.
As previously mentioned, the longer duration of mitral systole may
help to differentiate these two lesions. In addition, it is usual
to see mitral diastolic flow in the same spectral recording with
mitral insufficiency.
 |
| Fig.2.26 |
Even though the use of PW Doppler may help to locate the systolic
turbulent jet in the left atrium rather than the aortic outflow
tract, it is important to remember that the size of the sample volume
becomes larger at remote distances from the transducer. For example,
when the sample volume is positioned in the left atrium from an
apical transducer location, the sample volume is almost always larger
than it appears on the two-dimensional display (because of the diverging
shape of the ultrasound beam). Therefore, it is best to use caution
when a negative jet within the left atrium can be detected only
in the vicinity of the aortic root, as it may represent aortic outflow
(Fig. 2.26) rather than mitral regurgitation.
 |
| Fig.2.27 |
It is also possible to confuse tricuspid with mitral regurgitation.
This is more of a problem with CW than with PW echocardiography
for a beginner, and the use of PW with concurrent imaging helps
in recognizing this error. Another reason for false positives is
the interpretation of a loud systolic closure sound of the mitral
valve leaflets, commonly known as "valve slap", as partial recording
of the early profile of a moving mitral regurgitation jet (Fig.
2.27).
Detection of mitral regurgitation when it has not been found by
angiography is uncommon, especially when an apical transducer position
is used. It is, however, possible that a very small amount of regurgitation
may be detected by Doppler and yet fail to be seen on left ventriculography,
particularly if there is rapid dilution and poor opacification of
the left ventricle with a contrast agent.
False negative evaluations for mitral regurgitation insufficiency
also may occur and are probably most frequently due to a small jet
that was missed on examination. A moving jet may also be encountered
but is frequently difficult to differentiate from "valve slap" demonstrated
in Figure 2.27.
 |
| Fig.2.28 |
Mitral insufficiency jets may also vary in appearance with arrhythmias.
The CW spectral recording shown in Figure
2.28 illustrates the altering profiles of mitral regurgitation
encountered with premature ventricular contractions. As with all
abnormal jets, mitral regurgitation can change its appearance
with phases of the respiratory cycle as the orientation of the
jet to the interrogating beam alters with the movement of the
heart.
 |
| Fig.2.29 |
Figure 2.29 demonstrates the effect of these changing relationships
on the mitral insufficiency recording. Mitral insufficiency may
also be obscured by significant aortic stenotic lesions.
Mitral regurgitant jets, like others, are often eccentrically directed,
and it is important to examine the left atrium from all available
windows. Besides the apical window, the left parasternal region
is very useful for this purpose.
2004