Step 1: Measure the left ventricular diameter in end-diastole and end-systole. Do not measure the based upon the image end-systole or end-diastole. Position the frame where the mechanical end-systole and mechanical end-diastole 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 end-diastolic 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. |