The potential for myocardial imaging with hypoxia markers

Direct "hot spot" imaging of myocardial tissue hypoxia is potentially of gr eat clinical importance because available noninvasive approaches for the de tection of myocardial ischemia have generally been based on the detection o f flow heterogeneity or identification of regional alterations of myocardia l metabolism. These existing approaches provide only an indirect assessment of regional myocardial ischemia, and may be affected by either sympathetic activation or substrate availability. The assessment of tissue oxygenation with hypoxic compounds may be the best indicator of the balance of flow an d oxygen consumption. These compounds may provide a means of identifying dy sfunctional chronically ischemic but viable "hibernating" myocardium and fi nd a critical place in the assessment of angiogenesis, Nitroimidazole compo unds hold promise for positive imaging of hypoxia in the heart, However, re finement of these compounds is needed to improve target specificity. The po tential of technetium-99m (Tc99m) complexes derived from removal of the nit roimidazole moiety from a nitroimid-azole-containing ligand is interesting and warrants further investigation. Experimental studies support the possib ility of identifying myocardial hypoxia with the positron-emitting compound F18-fluoromisonidazole noninvasively. The potential of a Tc99m labeled nit roimidazole for positive imaging of myocardial ischemia is tremendous becau se single-photon imaging is more widely available. The true clinical potent ial of these nitroimidazole compounds can only be defined with future exper imental and clinical studies. Ideally, these studies should include compari sons of tracer uptake with independent measures of regional ischemia or mea sures of oxygen tension, potentially using magnetic resonance imaging. Copy right (C) 1999 by W.B. Saunders Company.