Effect of the degree of effort on the sensitivity of the exercise thallium-201 stress test in symptomatic coronary artery disease

The sensitivity of ST-segment depression on the electrocardiogram during exercise is influenced by the level of effort. Whether such is the case with thallium-201 imaging (initial defect or redistribution) has not been established. Accordingly, the prevalence of these parameters was evaluated in 288 patients (age 59 ± 10 years, 88% men) with coronary artery disease who underwent both exercise thallium-201 imaging and coronary anglography within 3 months of each other: 159 had a prior myocardial infarction, 72 had 1-vessel, and 216 had multivessel disease. The degree of effort was evaluated by 3 criteria: (1) percentage of maximal predicted heart rate (≤ 65, > 65 to 85, > 85%); (2) workload during exercise (≤ 4, > 4 to 8, > 8 METs); and (3) duration of exercise (≤ 3, > 3 to 6, > 6 minutes). The prevalence of defects on initial images was higher than both redistribution on delayed images and ST-segment depression on the electrocardiogram (p < 0.01). The overall prevalence of initial defects remained the same for all levels of effort and was not influenced by the presence or absence of a prior infarction. However, it decreased in patients with 1-vessel disease who exercised to higher workloads. The prevalence of redistribution on delayed thallium-201 images was higher than that of ST-segment depression on the electrocardiogram (p < 0.01), except at higher levels of effort where they were similar. This decrease in the prevalence of redistribution at high levels of effort occurred predominantly in patients with a prior infarction or those with 1-vessel disease. It was concluded that the overall prevalence of abnormal findings on thallium-201 imaging (initial defect and redistribution) is not significantly affected by the degree of effort in patients undergoing symptom-limited exercise testing. Because of the higher yield of these findings compared with ST-segment depression in most patients, thallium-201 imaging should be added to routine exercise stress testing for the detection of coronary artery disease,.