Effects of exercise-induced alterations of cardiac physiology on nuclear perfusion imaging

The effects produced on nuclear perfusion images by exercise-induced changes in the heart and respiration rate and possible transient myocardial stunning are not well understood. In this study we attempted to indirectly evaluate the potential artifacts created by exercise-induced changes in cardiac physiology. Twenty patients with prior myocardial infarction and suspected peri-infarct ischemia were studied by 99mTc-MIBI imaging. Two SPECT perfusion studies were performed after 99mTc-MIBI administration at rest. The first acquisition was carried out 90 minutes after injection of the tracer. Immediately afterwards, the patients underwent a stress test followed by a second acquisition (exercise stress superimposed on rest tracer distribution). A standard stress perfusion scan was also performed 48 hours later. Superimposed exercise stress produced artifactual defects in the resting distribution of the tracer in 15 out of 20 patients (68 of 360 segments). Standard stress images demonstrated concordant defects in 48 of these segments, indicating the concomitant presence of ischemia and stunning. This study indicates that exercise-induced changes in cardiac physiology may result in artifactual perfusion defects in scintigraphic images acquired shortly after the stress.