Based on their 8615-patient study in which 133 patients had C 0.5 mm of ST depression during regadenoson stress, Doukky and colleagues propose the use of a new threshold to define electrocardiographic ischemia during vasodilator stress. 1 Previous investigators evaluated the diagnostic and prognostic significance of ST depression during vasodilator stress using the same thresholds as those used for exercise-induced ischemia-either (1) 1 mm of horizontal or downsloping ST depression, as recommended in the 2002 ACC/AHA guidelines, 2-5 or (2) 1 mm of horizontal or downsloping ST depression or 1.5 mm of upsloping ST depression, 6-10 the latter as defined by Ellestad. 11,12 The concept of using different thresholds for exercise and vasodilator induced ischemia has merit as the causes of ST depression are thought to be different, demand ischemia during exercise testing compared to myocardial steal or differential coronary flow reserve in different coronary territories during vasodilator stress. 9,13 ST depression during vasodilator stress with normal SPECT perfusion images is unusual, typically occurring in 1% to 2% of studies. Table 1 summarizes the findings of many of the key studies that have examined this

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