An increasing number of patients are unable to achieve 85% of their maximum predicted heart rate on exercise testing either due to physical limitations or medications such as beta-blockers. In order to evaluate the reliability of this test at achieved heart rates of less than 85%, exercise 201T1 images and interpretable electrocardiograms of 99 patients with coronary artery disease diagnosed by coronary angiography were reviewed and compared. Tests were considered positive on the basis of 201T1 defects and/or ≥0.1 mV S-T segment depression on electrocardiogram. The patients were divided into three groups according to percent maximum predicted heart rate achieved;group I: 85% or greater; group II: 70-84%, and group III: less than 70%. For these categories, 89, 85 and 86% of the patients, respectively, had one or more segmental 201T1 defects. In contrast, the electrocardiogram was positive in 67,69 and 60% of the patients. Although 201T1 imaging was more predictive of coronary artery disease than electrocardiogram alone in groups I and II, neither was statistically significant. However, in group III 201T1 imaging was significantly better than the electrocardiogram in predicting disease (86 vs. 60%; p < 0.05). Although there was no significant decrease in the sensitivity of either 201T1 imaging or the electrocardiogram with beta-blocker therapy, for patients taking beta-blockers 201T1 imaging was significantly better than the electrocardiogram alone. It is concluded that patients unlikely to achieve adequate chronotropic respone with exercise may be more reliably evaluated with exercise 201T1 imaging than with electrocardiography alone.

Keywords:
Thallium-201 imaging, Exercise testing, Coronary artery disease, Myocardial ischemia
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1991
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