A common mistake made by many clinicians is that they confuse cardiac output for Left Ventricular Ejection Fraction. Lets see how Cardiac Output is not Left Ventricular Ejection Fraction .
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) Ã— 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.
Although a satisfactory ejection fraction would suggest a similar adequate cardiac output, this relationship does not always hold true.
In mitral regurgitation, ejection fraction can be excellent, yet part of the left ventricular end-diastolic volume is ejected back into the left atrium via the incompetent mitral valve during ventricular systole.
In this scenario, ejection fraction can be normal, yet cardiac output is diminished. In contrast, cardiac output is supranormal in aortic incompetence, but part of the forward stroke volume regurgitates back into the left ventricle during ventricular diastole.
As the disease progresses, heart failure will develop with a reduction of ejection fraction pseudonormalizing cardiac output, eventually reaching a point at which both hemodynamic parameters are severely depressed.
Regurgitant volume and regurgitant fraction are used in grading the severity of these valvular lesions, adding more valuable information to the assessment of cardiac function.
Temperature thermodilution methods for cardiac output determination remain accurate because these are typically measured in the pulmonary artery using a Swan-Ganz catheter and right-sided cardiac output must equal left-sided cardiac output.
Thus we under stand why Cardiac Output is not Left Ventricular Ejection Fraction.
Fink MP, Abrahams E, Vincent J, et al., eds. Textbook of Critical Care, 5th ed. Philadelphia: Elsevier Saunders, 2005:735
Savage RM, Aronson S, eds. Comprehensive Textbook of Intraoperative Transesophageal Echocardiography. Philadelphia: Lippincott Williams & Wilkins, 2005:129