Detection of myocardial viability with 99mTc-labelled myocardial perfusion agents.

Detection of myocardial viability is an important clinical issue in the time course of acute myocardial infarction and in chronic coronary artery disease. The wide availability of myocardial revascularization procedures requires a refinement of specific indications for revascularization whenever left ventricular failure is the most prominent feature of coronary artery disease. In this instance the risk/benefit ratio has to be attentively evaluated with diagnostic tests able to predict favourable changes in regional and global left ventricular function, symptoms, life quality, risk of adverse events and ultimately prognosis. 201Tl has been shown to provide clinically televant information regarding the presence of myocardial viability in patients with extensive regional or global ventricular dysfunction. However, the increasing use of 99mTc labeled myocardial perfusion agents requires a careful evaluation of diagnostic and predictive accuracy of these agents also for the issue of myocardial viability. The widely accepted opinion of a lower predictive accuracy of these agents compared to 201Tl could be no longer true. The available clinical and experimental data indicate, at least for 99mTc-sestamibi, a comparable accuracy when independent and clinically relevant gold standard of viability like post-revascularization functional recovery is considered. Preliminary data indicate that protocols, like nitrate administration, slow infusion or delayed imaging, and accurate quantitation of 99mTc-sestamibi SPECT studies could enhance the predictive accuracy to a level comparable or even better than that of 201Tl and similar to the more demanding PET technology.