 |
|
Fig. 27
|
If the transducer is rotated clockwise through 90 degrees from
the parasternal long-axis view, the short-axis view is obtained.
Provided the mitral valve was in the center of the sector before
rotation, the short-axis section will be at mitral valve level.
As shown in Figs.
28 and 29, the tomographic section of the heart shows the left
ventricle, bounded by thick, muscular walls comprising the anterior
and posterior portions of the interventricular septum on the left
and the lateral free wall to the right. Within the left ventricular
cavity are the two leaflets of the mitral valve, the upper being
the anterior and the lower the posterior. To the upper left of the
left ventricle a portion of the right ventricle is seen as a crescent.
The section cuts it between the tricuspid valve and the apex of
the right ventricle, below the crista.
 |
| Figs. 28-29 |
The major feature of the ultrasound image (Figs.
30 and 31) is the motion of the mitral valve leaflets that form
a shape like the mouth of a goldfish, viewed head-on. The large,
curved upper leaflet, and the flatter lower leaflets separate and
come together as blood flow through the orifice varies. In early
diastole, they separate widely during rapid ventricular filling,
then partially come together in mid-diastole as the filling rate
falls. With the advent of atrial systole, they again separate, before
closing completely at the beginning of systole, where they remain
until the beginning of the subsequent diastole.
 |
| Figs. 30-31 |
It is possible from this view to estimate mitral valve orifice
area, a measurement that has been shown to correlate well with the
actual area assessed at surgery. It therefore forms probably the
best echocardiographic method for determining the severity of mitral
stenosis. However, considerable care needs to be taken to obtain
accurate measurements.
2004