Quantitation of Cardiac Output Change by Impedance Cardiography in Subjects Undergoing Exercise Gated Stress/Rest Tc-99m CZT-SPECT MPI (NICAS)

Single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is a well-established noninvasive procedure for the evaluation and risk stratification of patients with coronary artery disease (CAD) (1). However, it has been recognized that in certain patients SPECT MPI is unable to detect the presence of or underestimates the extent of CAD. The fact that moderate to severe perfusion defects are noted in less than half of the patients with significant left main disease (2) has stimulated studies to improve the diagnostic accuracy of SPECT MPI. Such studies have analyzed post-stress parameters such as left ventricular (LV) ejection fraction (EF) (3, 4), wall motion abnormalities (5) and transient LV dilation (6) with images acquired on conventional Anger cameras as long as 60 minutes after the stress tracer injection. Such delayed assessment may miss early ischemic stunning as a result of its transient nature. However, detection of an early post-stress decrease in cardiac output (CO) may serve as a potential marker for the presence of significant or extensive ischemia. The aim of this study is to test for an early post-stress CO change by impedance cardiography and its relation to the severity and extent of myocardial ischemia and angiographic coronary disease in subjects undergoing exercise stress testing using a novel cadmium-zinc-telluride (CZT) SPECT camera.