In many patients with coronary artery disease (CAD), impaired left ventricular (LV) function arises on the basis of regionally ischemic or hibernating myocardium rather than irreversibly infarcted myocardium. We have previously demonstrated that thallium-201 scintigraphy (using a stress-redistribution-reinjection protocol) is an accurate method to identify dysfunctional but viable myocardial regions, as verified by evidence of preserved metabolic activity by positron emission tomography (PET) and by improved regional function after myocardial revascularization.These findings have been extended during the past year by 4 series of investigations. 1.) Studies employing gated spin echo magnetic resonance imaging (MRI) to assess regional end-diastolic wall thickness and systolic wall thickening have confirmed that regions identified as viable by thallium uptake have preserved wall thickening. 2.) We have also shown that thallium injected at rest (with imaging initially and after a 4 hour redistribution period) is also a valuable technique for identifying viable myocardium in comparison to the results of both PET and MRI. 3.) We have demonstrated that regions with parallel reduction in blood flow and glucose utilization (as measured by uptake of (18)F-fluorodeoxyglucose, or FDG have preserved wall thickening, as long as the reduction in FDG activity is not severe. Thus, regions with reduced blood flow need not manifest enhanced FDG uptake relative to flow (termed the FDG-blood flow """"""""mismatch"""""""") to be identified as viable, and the severity of the metabolic defect must be taken into consideration in the assessment of viable myocardium using PET imaging. 4.) We have shown that regions with reduced FDG uptake with normal regional blood flow (considered a """"""""normal"""""""" finding by other investigators) occurs predominantly in regions of jeopardized myocardium capable of undergoing reversible ischemia. The cause of this metabolic defect, leading to reduced rather than enhanced glucose uptake, remains to be clarified.
