Normal diastolic flow through the mitral valve is very low velocity
and rarely exceeds 1.5 m/s. Aliasing is, therefore, seldom seen
during diastole when using a 2.5 MHz transducer. Figure
4.22 demonstrates normal diastolic flow emerging from a superior
pulmonary vein and then entering the left ventricle through the
open mitral valve leaflets.
During systole, the left atrium is usually free from color. In
Figure 4.23 mild mitral regurgitation is seen to be directed
along the posterior mitral leaflet toward the posterior left atrial
wall. Aliasing is present due to the increased velocity and turbulence
through the closed valve orifice, and appears as a bright mosaic
Mitral regurgitation can usually be detected using any view,
even the parasternal long axis when the jet is perpendicular to
the ultrasound beam. This is possible because most abnormal flows
within the heart are turbulent. Many eddy currents exist in literally
hundreds of directions simultaneously. Thus, while the main vector
of the regurgitant jet may be generally perpendicular to the interrogating
beam, some of the eddies within the main jet are oriented parallel
to the beam. In most cases, these signals are sufficiently strong
to be detected by the color flow imaging device. Thus, some spatial
representation of flow will be seen by color flow methods.
Quantifying the severity of valvular regurgitation is based approximately
on the size and configuration of the regurgitant jet. Very small
jets, localized just to the proximal side of the regurgitant valve,
usually signify trivial valvular insufficiency. Large jets that
fill the receiving chamber usually indicate significant valvular
Moderate mitral regurgitation is shown in Figure
4.24. Again, the hallmark is the systolic appearance of a
posteriorly directed jet comprising aliased colors and turbulence.
Regurgitant jets may go in any direction and have virtually any
4.25 demonstrates mitral regurgitation seen from the subcostal
view in a 5-year-old boy where the jet is more diffuse and occupies
almost all of an enlarged left atrium. In this case, severe mitral
regurgitation is present.
It is imperative to remember that many factors influence the
size, configuration, and appearance of regurgitant lesions. Among
them are the volume of the jet, pressure difference between the
regurgitant and receiving chamber, size of the regurgitant orifice,
configuration of the regurgitant orifice and the size of the receiving
chamber. Other factors such as the timing of regurgitation, loading
conditions, heart rate, and rhythm may also be of importance.
As mentioned above, the orientation of the jet to the beam is
also a factor. Considerable work remains in verifying the significance
of these and other influences.
Mitral regurgitation may be found by color flow imaging in any
clinical state associated with this lesion, and may result from
prolapse, rheumatic, infectious or other etiologies. Continued
use of color flow imaging has revealed the frequent association
of mitral regurgitation (Fig.
4.26) in patients with diffuse cardiomyopathies of virtually
any origin. In our laboratory, we have encountered mitral regurgitation
in 100% of patients with this disorder when the left ventricle
measures 6 cm or greater in diastole. In each case, the mitral
regurgitation was quantified at 2+ or greater (out of a scale
of 4). Of further interest is the fact that there is a surprisingly
high prevalence of regurgitation of the other heart valves. In
patients with dilated cardiomyopathy, there is 2+ or greater regurgitation
of the tricuspid valve in 91%, the aortic valve in 23%, and the
pulmonic valve in 58%. In these patients, forward flow is usually
of very low velocity and results in dull hues of color.
Due to the considerable savings of time, we now use only the
color flow approach in routine cases for detection of all valvular
insufficiencies. This is not done, however, without attending
to all the factors that may affect the reliability of our estimation
Operator skill is important. The use of too little gain will
make regurgitant lesions appear unduly small, and can be a prime
source of underestimation. Proper transducer angulation into the
regurgitant lesion is also important. For small and eccentrically
direct jets, extra time is required to be sure of proper identification.
Hastily conducted studies limited only to traditional views may
not reveal these types of abnormalities.