Short-axis views, similar to those seen from the parasternal position
but with the right ventricle or right atrium in the foreground,
can be obtained from the subcostal position. However, it is often
difficult to produce clear recordings because the transducer must
be pressed down in order to scan under the rib cage. In addition,
the angle formed by the right and left sixth ribs at the xiphisternum
limits transducer mobility. The main application of the subcostal
short-axis views is therefore to obtain short-axis images in subjects
with hyperinflated lungs where the parasternal approach is impossible.
In such patients the diaphragm is usually low, and this facilitates
a subcostal approach. In contrast, it is very difficult to get adequate
recordings by this method in young normal subjects, even during
deep inspiration.
 |
| Fig. 55 |
Visualizing cardiac structures from the subcostal approach can
also be utilized for M-mode recordings in difficult subjects (Fig.
55). The smaller transducer is easier to position beneath the
rib cage and with practice most cardiac structures can be visualized.
The closest valve to the transducer is the tricuspid, which is seen
by aiming the ultrasound beam almost straight up the center line
of the sternum. Beyond it is the aortic valve. Slight angulation
toward the midclavicular line should reveal the mitral valve. The
same direction with the transducer pressed down to align the beam
almost parallel with the underside of the rib cage brings the pulmonary
valve, farthest from this position, into view.
2004