Is regadenoson an appropriate stressor for MPI in patients with left bundle branch block or pacemakers?

Patients with LBBB or ventricular pacemaker undergoing MPI are at risk for false positive MPI results in the setting of an elevated heart rate (HR) with exercise or dobutamine stress. The areas of increased apparent ischemia are typically the LAD and septal territories. In a subanalysis of the ADVANCE MPI 1 and 2 studies, perfusion on an initial adenosine and a second MPI study with regadenoson or adenosine was compared by visual and quantitative analysis. Among 2,015 patients, 64 had LBBB and 93 had pacemakers. The hemodynamic response during the second scan was compared in those with and without LBBB and PM. Following regadenoson, peak HR in the LBBB group increased by a mean of 25.4 compared to 15.3 bpm following adenosine (P = .0083). In the pacemaker group HR was blunted, 11.8 and 8.1 following regadenoson and adenosine, respectively (P = .1262). However, the visually assessed summed difference score and the quantitatively assessed extent of ischemia for the LAD and septal territories and the entire LV did not differ between the initial adenosine and subsequent regadenoson scans. The significant increase in HR observed with regadenoson compared to adenosine did not translate into greater perfusion defects in the LAD or septal territories in patients undergoing regadenoson stress.