Effect of end-diastolic volume on the canine left ventricular ejection fraction.

Left ventricular ejection fraction is commonly used in the clinical assessment of ventricular function. However, the effect of changes in end-diastolic volume on ejection fraction is controversial. The present study examines the effect of changes in end-diastolic volume on ejection fraction in 26 anesthetized dogs on right heart bypass with controlled hemodynamics. At the end of each experiment, pressure-volume relationships were obtained in the potassium arrested heart following suturing of the mitral valve leaflets and clamping of the aortic root. This technique allowed determination of the end-diastolic volume from the end-diastolic pressure. Ejection fraction is highly dependent on end-diastolic volume and end-diastolic pressure at lower levels of end-diastolic volume and end-diastolic pressure. Ejection fraction increased from 30 +/- 1% (SEM) to 64 +/- 2% (p less than 0.001) when end-diastolic pressure was increased from 4 +/- 0.5 to 11 +/- 0.5 cm H2O. The corresponding end-diastolic volumes were 22 +/- 0.5 and 38 +/- 1 ml, respectively (p less than 0.01). Ejection fraction only increased from 64 +/- 2% to 71 +/- 1% (p less than 0.01) when end-diastolic pressure was increased from 11 +/- 0.5 to 18 +/- 1 cm H2O. The corresponding end-diastolic volumes were 38 +/- 1 and 50 +/- 1 ml (p less than 0.01), respectively. This dependence of ejection fraction on preload is present over a wide range of levels of aortic pressure. Similar directional changes in ejection fraction with preload were present after an adequate autonomic blockade, in the presence of either increased or decreased inotropic state and in the presence of an open or closed pericardium. Thus, the present study demonstrates that ejection fraction can be substantially altered by acute changes in end-diastolic volume. This factor should be taken into account when using ejection fraction for the clinical assessment of ventricular function.