Two of the
most common causes of left ventricular volume overload, mitral and
aortic regurgitation, have been discussed in an earlier unit of
this series. The basic feature of left ventricular volume overload
is that the end-diastolic volume of the ventricle is increased showing
a greater than normal cavity dimension at end-diastole.
Good myocardial function stimulates a powerful contraction. Through
the Frank-Starling law the additional volume is ejected rapidly
(though not necessarily into the aorta), and the end-diastolic dimension
and volume remain normal. The relative reduction in cavity size,
expressed as ejection fraction or shortening fraction, is therefore
increased. Since ejection time is not prolonged (it may even be
reduced if a lot of the blood is ejected into a low-pressure cavity),
both the peak and mean values of Vcf, defined as reduction in chamber
circumference divided by ejection time, are increased.
 |
| Fig. 10 |
Much of this information can be deduced from simple inspection of
an M-mode recording and confirmed by calculations derived from the
cavity dimensions
(Fig. 10). Wall thickness usually remains normal;
this would be expected in the case of mitral regurgitation or ventricular
septal defect, but is perhaps surprising in the case of aortic regurgitation
where the increased volume must be ejected into a high-pressure
cavity.
 |
| Fig. 11 |
Most patients tolerate even quite severe left ventricular volume
overload very well for many years, but eventually myocardial function
becomes impaired. The only way in which a sufficiently large stroke
volume can then be ejected is if the ventricle dilates still further.
If this trend is unchecked, myocardial performance deteriorates
rapidly, to the point where the risk associated with surgical correction
of the original lesion becomes high. (Fig. 11) demonstrates a parasternal
long axis from a patient with severe aortic and mitral regurgitations.
The selected frame is in systole, showing marked left ventricular
dilatation and very poor contraction.
 |
| Fig. 12 |
Echocardiography contributes valuable, regular monitoring of ventricular
function in such patients. Evidence of increasing systolic dimension
should alert the physician to review carefully the other clinical
signs and symptoms, particularly the patient's exercise tolerance.
If the physician's review confirms the deterioration, surgery should
be considered. Now that Doppler echocardiography is routinely available,
the severity of chronic, or acute, left sided valvular regurgitation
may also be followed. In this way surgical intervention can be considered
before deleterious changes occur.
 |
| Fig. 13 |
In most cases, however, a great deal of useful information may be
deduced from the appearance of the left ventricle without Doppler.
(Fig. 12) shows a systolic frame from a patient who had previously
undergone an aortic valve replacement. The patient had done well
for several years and presented acutely short of breath. The prosthetic
valve had torn away from the annulus and was held by only a few
sutures (Fig. 13). Note that the ventricular systolic diameter was
increased (nearly 5 cm), indicating deterioration of ventricular
performance.
2004