Comparison of myocardial thallium-201 clearance after maximal and submaximal exercise: implications for diagnosis of coronary disease: concise communication.

Recently the quantitation of regional thallium-201 clearance has been shown to increase the sensitivity of the scintigraphic detection of coronary disease. Although TI-201 clearance rates might be expected to vary with the degree of exercise, this relationship has not been explored. We therefore evaluated the rate of decrease in myocardial TI-201 activity following maximal and submaximal stress in seven normal subjects and 21 patients with chest pain, using the seven-pinhole tomographic reconstruction technique. In normals, the mean TI-201 clearance rate declined from 41% +/- 7 over a 3-hr period with maximal exercise to 25% +/- 5 after 3 hr at a submaximal level (p less than 0.001). Similar differences in clearance rates were found in the normally perfused regions of the left ventricle in patients with chest pain, depending on whether or not a maximal end point (defined as either the appearance of ischemia or reaching 85% of age-predicted heart rate) was achieved. In five patients who did not reach these end points, 3-hr clearance rates in uninvolved regions averaged 25% +/- 2, in contrast to a mean of 38% +/- 5 for such regions in 15 patients who exercised to ischemia or an adequate heart rate. These findings indicate that clearance criteria derived from normals can be applied to patients who are stressed maximally, even if the duration of exercise is limited, but that caution must be used in interpreting clearance rates in those who do not exercise to an accepted end point.