Without the
use of Doppler, there are no specific signs of mitral regurgitation
by either M-mode or two-dimensional echocardiography. Nevertheless,
echocardiography can contribute significantly to the assessment
of a patient with mitral regurgitation by indicating the hemodynamic
severity and by determining the pathogenesis, both of which have
important prognostic implications.
 |
| Fig. 18 |
The primary echocardiographic features of mitral regurgitation are
volume overloading of both the left atrium and the left ventricle.
This results from the transfer of a proportion of the stroke volume
back and forth between the two chambers. Wall thickness is normal
(though by virtue of enlargement, wall mass increases). Left ventricular
volume overload is recognized by an end- diastolic dimension greater
than 5.5 cm, and hyperdynamic wall motion, most noticeable on the
interventricular septum (Fig. 18). Such profound changes noted by
echocardiography require that the hemodynamic load from mitral regurgitation
be severe.
It is axiomatic that severe mitral regurgitation must cause some
enlargement of the left atrium and pulmonary veins, since they have
to accommodate the regurgitant blood in addition to normal left
side inflow. Unfortunately, however, the proportion of the additional
volume stored in the atrium and the veins varies, as does the relative
duration of systole and diastole, so quantification of regurgitation
from measurement of atrial size has not been useful. In cases of
acute, severe mitral regurgitation, the left atrium is rarely noted
to be enlarged even in the face of marked elevation of atrial pressures.
Changes in left atrial volume are reflected as motion of the aortic
root. This is because the posterior atrial wall is firmly anchored
to the lungs by the pulmonary veins. This forms one of the major
supports of the whole heart, and the posterior atrial wall consequently
moves very little. Expansion of the atrium therefore causes its
anterior wall, which is echocardiographically indistinguishable
from the posterior wall of the aortic root, to be pushed forward.
Thus, vigorous motion of the aortic root indicates high left atrial
stroke volume and is a feature of mitral regurgitation (though it
is also seen in severe mitral regurgitation in the presence of abnormal
ventricular function). Quantification of aortic root motion suffers
from the same limitations as measurement of left atrial dimension.
Thus, without Doppler echocardiography, the severity of mitral regurgitation
can only be deduced from the M-mode or two-dimensional echocardiographic
recordings. Direct imaging of the valves, however, frequently reveals
the etiology of the regurgitation and provides very useful information
for planning surgical approaches. Now that primary valvular reconstruction,
rather than replacement is possible, a surgeon experienced in interpretation
of echocardiographic data may precisely identify disordered valvular
anatomy and predict patient suitability for surgical valvuloplasty.
2004
