It can now
be generally accepted that Doppler echocardiography is a reliable
method for the detection of the presence of valvular regurgitation.
Doppler assessment of the severity of valvular regurgitation has
also been moderately successful in comparison with angiographic
techniques. The invasive "gold standard" for quantifying valvular
insufficiency is the volume of regurgitant blood flow calculated
by subtracting the total cardiac output, calculated angiographically,
from the forward output (calculated by some other method-usually
by the Fick principle). The regurgitant volume divided by the total
angiographic stroke volume (i.e., the sum total of blood ejected
forwards and backwards out of the left ventricle with each systole)
is referred to as the regurgitant fraction and the formula is:
Regurgitant fraction =
total output — forward output.
This approach requires considerable time and effort and is not in
widespread use in most catheterization laboratories.
The other commonly used measure of severity is a subjective grading
(usually 0-4+) based on a visual evaluation of the amount of regurgitation
judged by progressive opacification of the receiving chamber as
seen by contrast angiography. Both methods have limitations, and
there is only an approximate correlation between them. Thus, it
has been difficult to find a suitable "gold standard" for comparison
with Doppler methods. Remember that the subjective angiographic
criteria are based upon progressive opacification of a receiving
chamber, usually over several heart beats. When Doppler methods
are used, regurgitation is detected on a beat-to-beat basis and
differences between any comparisons should be expected.
Many approaches have been proposed to estimate the severity of valvular
regurgitation using Doppler. One method relies on the use of PW
Doppler to map the size and distribution of the regurgitant jet
within a cardiac chamber and is the most common method used. Another
is based upon the relationship of forward to reverse flow, while
another has attempted to quantify the absolute flow through each
valve orifice and then use these flow volumes to calculate the regurgitant
fraction. The latter two methods are more complex and not easily
performed by beginners to Doppler echocardiography. Another method
based upon rate of descent of the velocity spectrum in diastole
has been proposed for estimation of the severity of aortic insufficiency.
2004