Right ventricular
volume overload is commonly caused by pulmonary or tricuspid regurgitation,
or an atrial septal defect (not ventricular septal defect, as this
presents the right ventricle with increased blood volume only after
the onset of systole, therefore end-diastolic volume remains normal).
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| Fig. 14 |
As in left ventricular volume overload, end-diastolic volume is
increased and the force of contractions enhanced. This is reflected
in the echocardiogram as increased end-diastolic dimension of the
right ventricular cavity (an effect increased by rotation of the
heart). The other striking echocardiographic finding is that the
movement of the interventricular septum appears to reverse (Fig.
14). Instead of moving towards the left ventricle during systole,
immediately after the ECG QRS complex, it begins to move anteriorly,
then moves posteriorly again during diastole.
The mechanism of this reversed or `paradoxical' septal motion was
for a long time a subject of controversy. It is now fairly well
established from two-dimensional studies that the major factor causing
the apparent reversal is simply the overall motion of the left ventricle
relative to the chest wall. Thus, in normal subjects the symmetrical
inward contraction of the left ventricular walls is combined with
an overall anterior motion during systole. This causes an apparent
increase in the motion of the posterior wall and a correspondingly
reduction in the motion of the septum. When right ventricular contraction
is hyperdynamic, the anterior motion of the entire left ventricle
becomes so great that there is actually a net anterior displacement
of the septum relative to the ultrasound transducer. The shape and
contraction pattern of the left ventricle itself remain normal.
Although most commonly associated with ventricular volume overload,
paradoxical septal movement is found in several other conditions,
(e.g., in the presence of a large pericardial effusion or following
cardiac surgery). In such cases, this mechanism may be more complex:
altered left ventricular function may play a part, as may the lack
of restraint to cardiac motion if the pericardium is left opened
after surgery.
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| Fig. 15 |
Another case where a more complex situation exists is that of combined
right ventricular pressure and volume overload, for example in severe
pulmonary hypertension with secondary pulmonary and tricuspid regurgitation.
On M-mode recordings the septal motion is strongly reversed, but
has a much more `square' appearance than in simple volume overload.
Two-dimensional short axis views show the septum to be flattened
so that the two chambers seem to exchange profiles: the right ventricle
becomes circular while the left ventricle becomes more elliptical
(Fig. 15).
2004