Step 1: Measure the left ventricular
diameter in enddiastole and endsystole. Do
not measure the based upon the image endsystole
or enddiastole. Position the frame where
the mechanical endsystole and mechanical enddiastole
occur on the ECG (below).
The optimal view for measuring the left ventricular
diastolic area is the left ventricular short axis
view from the mid transgastric acoustic window.
This view has been shown to be predictive of the
ejection fraction. Each area is converted
into left ventricular volume during systole and
diastole. The difference between the left
ventricular volumes in systole and diastole is the
ejection volume. The ejection volume divided
by the enddiastolic volume is the ejection fraction.
The formula used is the Tiecholz formula which
is based upon the spherical volume of the heart
multiplied by a correction factor. Since the
volume of a sphere is the cube of the radius, and
the left ventricle is almost a sphere, a correction
factor to account for the non spherical qualities
of the left ventricle yields a surprisingly accurate
result.
LV Volume
= [7/(2.4 + LVID)] * LVID3
RWMA, either close or distant, may cause the volume
analysis to be incorrect. If the endocardial
boarder is poorly seen, then the area of the left
ventricular cavity may be inaccurate. Failing
hearts (i.e. cardiomyopathy) tend to be more spherical
than normal hearts so the spherical formula may
be more accurate.
