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[Assessment of exercise-induced silent myocardial ischemia by dipyridamole thallium imaging. (2). Its significance in Q wave myocardial infarction].

The clinical significance of silent myocardial ischemia (SMI) in the elderly was assessed in 91 patients with Q wave infarction who showed ischemic ST depression during treadmill stress testing, as well as reversible defect (RD) during dipyridamole thallium imaging. They were divided into two groups (47 patients with silent ST depression and 44 patients with painful ST depression) and compared for scintigraphic and coronary arteriographic features, and prognosis. There was no significant difference in age, gender and site of infarction between the two groups. The prevalence of single and double vessel coronary stenosis was higher in patients with SMI (66%) than in those with painful ischemia (p < 0.05). The results of treadmill stress testing showed a longer exercise duration (4.7 +/- 1.7 vs. 4.1 +/- 1.8 min) and higher maximal heart rate (138 +/- 15/vs. 126 +/- 20/min) in patients with SMI than in those with painful ischemia (p < 0.01). Dipyridamole thallium imaging revealed a larger infact (18.8 +/- 9.1 vs. 14.6 +/- 10.2 segments) in patients with SMI than in those with painful ischemia (p < 0.05). The prevalence of RD in the area of infarction was also higher in patients with SMI (74%) than in those with painful ischemia (45%) (p < 0.05). Although a higher proportion of the patients with painful ischemia (42%) underwent CABG or PTCA as their initial therapy, compared with those with SMI (25%) (ns), there was no difference in the cardiac event rate between the two groups who were initially treated medically. Dipyridamole thallium imaging is useful in the assessment of SMI in elderly patients with Q wave myocardial infarction. Those with SMI may have a larger infarct and a higher prevalence of ischemia localized within the infarction than those with painful ischemia.