Timing of Regadenoson-induced Peak Hyperemia and the Effects on Coronary Flow Reserve.

Background: Regadenoson is used to induce hyperemia in cardiac imaging, facilitating diagnosis of ischemia and assessment of coronary flow reserve (CFR). While the regadenoson package insert recommends administration of radionuclide tracer 10-20 seconds after injection, peak hyperemia has been observed at approximately 100 seconds after injection in healthy volunteers undergoing cardiovascular magnetic resonance imaging (CMR). It is unclear when peak hyperemia occurs in a patient population. Objectives: The goal of this study was to determine time to peak hyperemia after regadenoson injection in healthy volunteers and patients, and whether the recommended image timing in the package insert underestimates CFR. Methods: Healthy volunteers (n=15) and patients (n=25) underwent stress CMR, including phase-contrast imaging of the coronary sinus at rest and multiple timepoints after 0.4 mg regadenoson injection. Coronary sinus flow (ml/min) was divided by resting values to yield CFR. Smoothed, time-resolved curves for CFR were generated with pointwise 95% confidence intervals. Results: CFR between 60 and 120 seconds was significantly higher than CFR at 30 seconds after regadenoson injection (p < 0.05) as shown by non-overlapping 95% confidence intervals for both healthy volunteers (30 s, [2.8, 3.4]; 60 s, [3.8, 4.4]; 90 s, [4.1, 4.7]; 120 s, [3.6, 4.3]) and patients (30 s, [2.1, 2.5]; 60 s, [2.6, 3.1]; 90 s, [2.7, 3.2]; 120 s, [2.5, 3.1]). Conclusion: Imaging at 90 seconds following regadenoson injection is the optimal approach to capture peak hyperemia. Imaging at 30 seconds, which is more aligned with the package insert recommendation, would yield an underestimate of CFR and confound assessment of microvascular dysfunction.