[Evaluation of exercise thallium-201 myocardial single photon emission computed tomography in silent myocardial ischemia].

: To evaluate the diagnostic significance of exercise Tl-201 myocardial SPECT in silent myocardial ischemia, 41 patients with angiographically-proven coronary artery disease (27 effort angina, 14 post-infarction angina) were tested using this method. Double product (blood pressure x heart rate) during exercise was used as a hemodynamic parameter. Thirty-two projections were obtained throughout 180 degrees by a rotating gamma camera, immediately, and four hours after exercise. Myocardial Tl-201 washout rate of the entire left ventricle was presented in two-dimensional polar function maps. Normal lower limit of myocardial Tl-201 washout rate was defined as mean-2SD of normals, and the region with a washout rate lower than normal was defined as an ischemic region. The location of myocardial ischemia was visually determined using a Bull's eye polar map. The ischemic size was quantified by the defect volume ratio (ratio of the ischemic myocardium to total myocardium). Coronary lesions were quantitatively assessed by the Pujadas score using coronary angiography. Results were as follows: There was no significant difference between painful myocardial ischemia and silent myocardial ischemia according to double product and the Pujadas scores. In most silent ischemia, the region of the reduced washout rate was in the inferior or lateral area of the Bull's eye polar map, whereas it was in the anterior area in painful ischemia. The defect volume ratio indicating the extent of ischemia was smaller in silent ischemia than in painful ischemia. In conclusion, the ischemic location and size may be contributing factors in silent myocardial ischemia.