Objective: To review the experience of the laboratory on exercise-redistribution thalium-201 scintigraphy after myocardial infarction, and to compare scintigraphy results with those of exercise test and coronary angiography.
Design/setting/patients: Retrospective analysis of data from scintigraphy, exercise test and coronary angiography from all patients evaluated after myocardial infarction at Nuclear Medicine Department of Instituto do Coração with treadmill exercise-redistribution thallium-201 SPECT, if they were also submitted to cardiac catheterization. These criteria were met by 185 patients, studied between March 1988 and July 1993.
Material and methods: Micro-Delta system with a Siemens Orbiter gamma camera. Visual analysis of intensity and reversibility of perfusion defects in 5 segments per patient, using oblique reconstruction of images.
Results: Perfusion defects were found in 97% of patients and in 418/925 analysed segments. Variable degrees of reversibility were found in 78% of patients. On patients with single-vessel disease, vessel occlusion was associated with a slightly higher prevalence of reversibility (81% vs 71%; ns), and, for anterior infarcts, also with a higher prevalence of defects in areas supposed to be remote territories (44% vs 15%, p < 0.05). For 159 patients with a conclusive exercise test, ability of exercise test in diagnosing defects with reversibility was studied. Negative predictive accuracy of exercise test was poor (33%). Angina was 86% specific. Use of isolated ST depression, depression plus elevation or isolated ST elevation as criteria for a positive test result in a progressive improvement of sensitivity, but at cost of a decrease in specificity, more marked when using isolated ST elevation.
Conclusions: Thallium scintigraphy revealed perfusion defects with some degree of reversibility in a large number of patients studied after myocardial infarction, even when considering single-vessel disease or occluded infarct-related artery. Electrocardiographic treadmill exercise test had a poor negative predictive accuracy, being reasonably sensible in multivessel disease, but poorer in single vessel disease. After infarction, typical angina should probably be also considered as criterion for ischemia, regardless of electrocardiographic changes. In a perspective of eventual use of revascularization after infarction, thallium-201 scintigraphy is a valuable tool, and should probably be considered in most patients.