Comparison of regadenoson and dypiridamole myocardial blood flow and coronary flow reserve hyperemic response by non-invasive quantitative N-13 ammonia PET.

Introduction: Regadenoson is currently the most commonly used drug for pharmacologic stress myocardial perfusion imaging. Given its more selective A2A agonist-driven vasodilatory properties when compared to adenosine or dipyridamole, the accuracy of measuring true hyperemia after the standard bolus of N-13 ammonia injection remains to be fully established. Our aim was to use quantitative N-13 ammonia PET myocardial perfusion for assessing myocardial blood flow (MBF) and coronary flow reserve (CFR) response to regadenoson (REG) and dipyridamole (DIP) in patients with an intermediate pre-test likelihood of coronary artery disease (CAD). We hypothesized that the global flow response to regadenoson is comparable to that with dipyridamole. Additionally, we sought to determine whether the magnitude of the flow response to regadenoson is influenced by the lack of weight adjustment of the injected dose, and from the physical characteristics of N-13 ammonia myocardial pharmacodynamics. To avoid interfering effects from flow-limiting coronary artery stenosis, 45 patients (23 REG, 22 DIP) with normal left ventricular ejection fraction (LVEF >45%) on PET scan and no prior history of overt disease CAD were included in the study. Patients with cardiomyopathy, prior myocardial infarction, or elevated coronary calcium score (CAC > 400) were also excluded from the study. Standard dynamic PET images were acquired after 20 mCi of N-13 ammonia at rest and following the clinical standard administration of regadenoson or dipyridamole. Myocardial vascular resistance was similar between groups at rest (137 ± 36 vs. 140±51 mmHg/ml/min/g for REG and DIP respectively) or in response to the vasodilator (49±22 for REG vs. 48±26 mmHg/ml/min/g for DIP). Overall hemodynamic changes were similar with comparable rest and hyperemic global myocardial blood flow (rest REG and DIP 1.01±0.25, 0.92±0.18 mL/g,/min respectively; hyperemic REG and DIP 2.4±0.81, 2.42±1.14 mL/g/min respectively). CFR remains similar between both agents (REG 2.45±0.68, DIP 2.47±0.85). These results indicate that regadenoson provides similar hyperemic myocardial blood flow changes than pure vasodilator agents when using N-13 ammonia PET imaging.