Vasodilator myocardial imaging.

T he use of vasodilator thallium-201 myocardial imaging, although still investigational, is finding wide application. The principle of vasodilator thallium-201 myocar-dial imaging was first put forward by Strauss and Pitt,' who used dimethyladenosine in dogs with experimental coronary artery narrowing. They demonstrated that dimethyladenosine increased coronary blood flow and thallium-201 uptake to normal areas of myocardium, whereas areas of myocardium served by a coronary artery with hemodynamically significant coronary artery narrowing had a reduced flow reserve and hence less thallium-201 uptake. Subsequent studies with dipyridamole, which blocks cellular uptake of adenosine,2 have demonstrated that the resultant ateriolar vasodilitation can induce myocar-dial ischemia by causing a coronary "steal."34 Gould et al5 were the first to apply this principle to clinical investigation using dipyridamole. Over the past decade , dipyridamole thallium-201 myocardial imaging See p 80 has been found useful in evaluating patients with peripheral vascular disease who cannot perform an adequate submaximal exercise test to detect myocar-dial ischemia.6 Use of this test before elective vascu-lar surgery has allowed the detection of patients with significant coronary artery narrowing and protection of areas of jeopardized myocardium by appropriate medical therapy, PTCA, or bypass graft surgery, thereby diminishing the morbidity and mortality associated with vascular repair in these high-risk individuals.7 Dipyridamole thallium-201 myocardial imaging is also increasingly used to evaluate patients with acute myocardial infarction before hospital discharge in an attempt to select patients for coronary angiography, possible PTCA, or coronary bypass graft surgery.8 The excellent sensitivity and specificity of dipyridamole thallium-201 myocardial imaging and relative ease of administration of intravenous dipyridamole has suggested that vasodilator thallium-201 myocardial imaging might be a useful substitute for exercise thallium-201 myocardial imaging. How-The opinions expressed in this editorial comment are not necessarily those of the editors or of the American Heart Association. ever, the risks of inducing a coronary steal and death with an arteriolar vasodilator such as dipyridamole9 makes the routine substitution of vasodilator myocar-dial imaging with dipyridamole for exercise stress testing unlikely. The report by Verani et al,10 which demonstrates an 83% sensitivity and 94% specificity for vasodilator thallium-201 myocardial imaging with adenosine, is a further modification of the concept of vasodilator thallium-201 myocardial imaging and is potentially an important advance. Although the side-effect profile of adenosine is, as expected, similar to that of dipyridamole, its shorter half life in the plasma could prove to be an advantage. The fact that Verani et al10 did …