Treadmill Exercise Produces Larger Perfusion Defects Than Dipyridamole Stress N-13 Ammonia Positron Emission Tomography

Abstract

The aim of this study was to compare treadmill exercise (TEX) and dipyridamole stress on the uptake and retention of N-13 ammonia. Size and severity of stress-induced myocardial perfusion defects are clinically important. Because ammonia uptake and retention seems to be related to perfusion, viability, and metabolism, exercise stress might induce larger perfusion defects than dipyridamole stress. Twenty-six patients underwent TEX and dipyridamole stress N-13 ammonia positron emission tomography (PET). Images were assessed with a 17-segment model and a five-point score. Summed stress score (SSS), summed rest score (SRS), and summed difference score (SDS) were calculated. Left ventricular (LV) defect sizes were measured quantitatively with a 70% threshold for abnormal perfusion. Compared with dipyridamole stress, TEX yielded larger SSS (9.1 +/- 5.7 vs. 6.9 +/- 5.9; p < 0.01), SDS (5.8 +/- 4.7 vs. 3.7 +/- 4.6; p < 0.02), and percentage of LV stress defect (19.3 +/- 11.5% vs. 13.8 +/- 13.6%; p < 0.02). In patients achieving adequate exercise, TEX N-13 ammonia PET myocardial perfusion imaging (MPI) yields larger stress perfusion defects than dipyridamole stress and might reflect the true myocardial ischemic burden. Treadmill exercise might be the preferred method of stress for routine N-13 ammonia PET MPI.