Potassium-43 myocardial perfusion scanning for the noninvasive evaluation of patients with false-positive exercise tests.

Twelve patients with false-positive ECG exercise tests presented with ischemic ECG responses (greater than one mm ST segment depression) during graded maximal treadmill exercise testing in the absence of exercise-induced chest pain or clinical coronary heart disease. Coronary arteriography, left ventriculography and hemodynamic evaluation revealed no significant abnormality in these patients. Transmyocardial lactate analysis during atrial pacing revealed a normal extraction (mean 21%) during pacing stress in five patients. Nine of 12 patients were evaluated with exercise potassium-43 myocardial perfusion imaging whereby the radioactive tracer was administered intravenously during exercise at a time when abnormal ECG changes were present. Myocardial images in these nine patients all showed a normal homogeneous pattern of radioisotope distribution. These results are in direct contrast to findings in patients with coronary heart disease in whom reproducibly demonstrable abnormal regions of decreased potassium-43 accumulation have been noted in myocardial images obtained following injection of the radioactive tracer during exercise. Potassium-43 exercise myocardial perfusion scanning thus appears to be an accurate noninvasive method of assessing patients with suspected false-positive exercise tests and provides a means of increasing the specificity of exercise testing.