Various pharmacologic stress agents are currently available, including adenosine, dipyridamole, and most recently regadenoson. These agents have a common mechanism, mediated through activation (nonselective or selective) of adenosine A2A receptors with resultant coronary vasodilation. Adenosine and dipyridamole have been the mainstays of vasodilator myocardial perfusion imaging (MPI) for almost two decades . Radionuclide scintigraphy , positron emission tomography , and magnetic resonance imaging  have been the modalities traditionally utilized for myocardial perfusion imaging. Adenosine stress testing is a procedure in which patients are exposed to an intravenous infusion of adenosine while simultaneous monitoring of symptoms, hemodynamic parameters, electrocardiogram, and imaging occurs . Adenosine is a secondgeneration vasodilator adenosinergic stress agent, evolving from the first-generation prototype, dipyridamole, which acts by triggering accumulation of endogenous adenosine  (Table 14.1). Perfusion imaging with scintigraphy is the dominant application of adenosine stress testing with up to 63 % of overall perfusion studies performed with adenosine and 30 % with dipyridamole in the USA . The 2009 update of the American Society of Nuclear Cardiology guidelines for nuclear cardiology procedures illustrates the different protocols in place for these vasodilator agents .
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