Background: Myocardial perfusion imaging (MPI) with positron emission tomography allows accurate measurements of myocardial blood flow (MBF). Stress MBF thresholds have been proposed to provide diagnostic and prognostic information in different pathology. Most studies relying on dipyridamole use a 5-minute infusion protocol, while current guidelines recommend a 4-minute infusion. The purpose of this study is to compare the effects of different dipyridamole infusion times on stress MBF.
Methods: The charts of 2,207 patients who underwent rubidium-82 MPI were retrospectively reviewed and 147 subjects with low likelihood of significant coronary artery disease (CAD) defined as calcium score = 0, body mass index < 45 kg·m-2, and summed stress score ≤ 3 were included. Of those, 65 were imaged with a 4-minute dipyridamole infusion (0.56 mg·kg-1) protocol and 82 with a 5-minute protocol (0.70 mg·kg-1).
Results: Stress MBF (3.23±0.76 vs 3.02±0.71 mL·min-1·g-1, P = 0.09), myocardial flow reserve (2.70±0.67 vs 2.85±0.74, P = 0.20), and coronary vascular resistance index (30±10 vs 31±9 mmHg × g × min·mL-1, P = 0.38) were not significantly different between the two protocols. The 5-minute protocol was associated with higher prevalence of symptoms (92.7% vs 81.5%, P = 0.04) and greater decrease in systolic blood pressure (- 9 vs - 6 mmHg, P = 0.03).
Conclusions: The 4-minute and 5-minute dipyridamole infusion protocols produce comparable myocardial flow response, hemodynamic changes, and symptoms, in subjects with low likelihood of significant obstructive CAD.
Keywords: Myocardial perfusion imaging; dipyridamole; myocardial blood flow; myocardial flow reserve; positron emission tomography, PET/CT; rubidium.