Effect of the geometry of the left ventricle on the calculation of ejection fraction.

We used a cylindrical model for the left ventricle contracting both radially and longitudinally to show how the ejection fraction is related to different variables that describe the ventricular geometry. The relations during ventricular contraction between wall thickening, midwall radius shortening and longitudinal shortening are used to derive precise formulas for the calculation of ventricular blood flow velocity and ejection fraction. Validation of the model is given by results from the literature and by a study of 40 patients. The formulas derived can be used to validate angiographic measurements or to assess more precisely blood flow velocity and ejection fraction from the M-mode echocardiogram. Ejection fraction is determined not only by the extent of myocardial shortening, but also by the relationship of ventricular wall thickness to ventricular cavity size.