Overestimation of the LVEF by quantitative gated SPECT in simulated left ventricles

During routine myocardial perfusion imaging, a common observation is that p atients with normal cardiac function and small hearts, in particular small women, have higher left ventricular ejection fractions (LVEFs), as measured by quantitative gated SPECT (QGS) software, than anticipated, often marked ly so. The goal of this project was to determine if the QGS LVEF varies wit h the change in end-diastolic left ventricular volume (EDV) and in particul ar to verify that the clinically observed phenomenon of falsely elevated QG S LVEF in patients with small hearts is actually occurring, Methods: A seri es of mathematically defined left ventricles (LVs) was produced by varying the EDV and targeted LVEF (tLVEF). These were created using concentric hemi ellipsoids with nine different EDVs, The tLVEF was varied from 15% to 75% b y 5% increments for a total of 13 different ejection fractions. These datas ets were then smoothed, creating a total of 234 sets. The smoothed and unsm oothed images were then processed using QGS software. The LVEFs and EDVs we re recorded. Results: For lower LVEFs the agreement between the QGS LVEF an d the tLVEF is good. A marked overestimation occurs when the EDVs are low a nd the ejection fractions are in the higher range. This effect is greater i n the smoothed images, Conclusion: An artifactual increase in the LVEF can occur when measurements are made with the QGS software. These data argue ag ainst using QGS LVEF for monitoring the LVEF in patients with small hearts, Our data imply that a mildly decreased LVEF may still appear to be in the normal range when measured by QGS software.