Remember that Cardiac Output is not the Same Thing as Ejection Fraction
Frank Rosemeier MD
Cardiac output equals the volume of blood pumped by the heart per minute, whereas stroke volume (SV) is the amount pumped on a single beat. Cardiac output can be determined using indicator dilution methods (Fick, thermodilution), Doppler velocity data, ventricular impedance, and radionucleotide methods. Ejection fraction (EF) is measured in percent: EF (%) = (SV/EDV) × 100%; whereas SV is calculated as SV = EDV – ESV, with EDV the end-diastolic volume and ESV the end-systolic volume. Ejection fraction is typically estimated using qualitative two-dimensional echocardiography. However, the accuracy depends on the observer experience. Inadequate definition of the endocardial border and regional wall motion abnormalities with asymmetric ventricular contraction may lead to inaccuracies, which may be overcome by various yet time-consuming ventricular volume formulas.