Regadenoson vs. Dipyridamole Hyperemia for Cardiac PET Imaging | Journal Scan

Study Questions:

Do regadenoson and dipyridamole result in a similar degree of coronary dilation?


A total of 176 subjects, some with clinical indications for cardiac stress testing, underwent two rest-stress cardiac positron emission tomography (PET) scans. The first was performed with dipyridamole and the second was done with regadenoson (n = 126) or repeated with dipyridamole (n = 50). Regadenoson was injected at one of five times relative to the radiotracer injection (15 seconds before, or 10, 40, 55, or 80 seconds after). Quantitative assessments of the PET images were performed to quantify myocardial blood flow (MBF) at rest and stress in ml/min/g myocardium, and to compute coronary flow reserve (CFR) as the ratio of stress/rest MBF.


Rest MBF, stress MBF, and CFR with dipyridamole were 0.85 ± 0.25 ml/min/g, 2.27 ± 0.57 ml/min/g, and 2.80 ± 0.65 ml/min/g, respectively. No significant differences were noted in any of these parameters between initial and repeat stress testing when dipyridamole was used in both scans. However, significant differences in stress MBF and CFR were seen between dipyridamole and regadenoson scans. When at least 40 seconds was allowed to elapse between regadenoson administration and radiotracer infusion, stress MBF was underestimated by 0.21-0.31 ml/min/g, depending on the time elapsed. Correspondingly, CFR was underestimated by 0.36-0.38. Even larger degrees of underestimation were observed with shorter intervals between regadenoson and vasodilator administration, as recommended by the package insert.


Use of regadenoson according to the package insert results in approximately 20% less hyperemia than dipyridamole. Slightly longer injection delays of approximately 1 minute reduce this underestimation to approximately 10%.


This work done by an eminent group in the area raises concerns over the use of regadenoson for clinical stress testing, whether done by PET or SPECT. Invasive and pharmacologic studies had previously demonstrated peak regadenoson effect at approximately 1-2 minutes after injection, consistent with the findings of the present study. Stress labs which are not already following a 1- to 2-minute delay may wish to consider introducing one.

There are several reasons to view these results with caution, however. First, many prior studies had compared regadenoson to other vasodilators using a variety of techniques including PET, SPECT, and invasive methods. In general, no significant differences or only minimal differences, below the level of clinical relevance, were observed. The reasons for the discrepancies are unclear.

One longstanding concern with regards to regadenoson has been the use of a single fixed dose without weight adjustment, as is usually done for other vasodilators. The investigators of this study evaluated whether body mass index resulted in a differential effect of regadenoson or dipyridamole. Although this is highly reassuring, they did not also report whether weight had an effect.

Clinical Topics: Noninvasive Imaging, Vascular Medicine, Statins, Computed Tomography, Nuclear Imaging

Keywords: Dipyridamole, Hyperemia, Myocardium, Positron-Emission Tomography, Product Labeling, Vasodilator Agents, Diagnostic Imaging, Purines, Pyrazoles

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