 |
| Figs. 56-57 |
Further views, useful for studying the right side of the heart,
can be obtained from the subcostal position. With the transducer
placed a little to the right of the xiphoid process and directed
posteriorly, with the scan in a caudocranial plane, the inferior
vena cava (IVC) can be seen passing behind the liver, crossing the
diaphragm, and entering the right atrium (Figs.
56 and 57). At this level, the IVC is lateral and anterior to
the descending aorta. If in doubt, the two can be distinguished
by the pulsation of the aorta or by asking the subject to inhale
deeply, which sucks blood into the chest and causes the IVC to collapse.
Angling the scan plane toward the head shows more of the right atrium.
With careful manipulation it is sometimes possible to align the
scan to show the IVC, right atium, tricuspid valve, pulmonary valve,
and proximal pulmonary artery simultaneously (Figs.
58 and 59).
 |
| Figs. 58-59 |
Rotating the transducer through 90 degrees and directing it posteriorly
shows the IVC in cross- section. Caudal tilt moves the section down
into the liver, where hepatic vessels can be seen joining the IVC.
In cases of right heart failure, the hepatic veins will be engorged
and echo contrast agent injected into a peripheral vein can be seen
carried down into the liver.
It is also possible to visualize the IVC by M-mode in almost all
subjects. Although this is sometimes more difficult than by two-dimensional
echocardiography, it can be helped by obtaining a two-dimensional
image first, and then performing the respiratory maneuver described
above. M-mode shows precise timing relationships, thereby increasing
the specificity of the echo-contrast technique in the diagnosis
of tricuspid regurgitation. An M-mode recording of the IVC is made
with the ECG during a contrast injection. If initial arrival of
contrast in the IVC is during systole, tricuspid regurgitation is
most likely present, if in diastole, it merely indicates high right-sided
pressures.
2004