 |
| Fig.2.9 |
Doppler echocardiography
also has its limitations. A beginner should always remember that
Doppler detects the velocity and direction of moving blood. In situations
where there is a small leak across a given valve there will be a
large pressure gradient rendering high velocity of flow. This is
illustrated in (Fig. 2.9 left panel) for trivial aortic insufficiency.
Aortic insufficiency gradients occur in diastole. With large gradients
(Fig. 2.9, right panel) the resultant high velocities might readily
be detected. For very severe leaks, such as total absence of the
aortic valve, little pressure differential would occur and result
in very low velocities of flow. In this situation, the abnormal
lesion might be missed. Indeed, we have encountered some cases where
we have missed severe valvular regurgitation by Doppler that has
been readily detected at catheterization by angiographic means.
In addition, the quality of Doppler signals is quite variable from
patient to patient. Users of traditional ultrasound imaging methods
are quite familiar with differences in the quality of images between
patients. These differences may be accounted for by patient age,
the presence of lung disease, chest wall configuration or other
factors.
2004