ORIGINAL ARTICLE Prognostic value of regadenoson stress myocardial perfusion imaging in patients with left bundle branch block or ventricular paced rhythm Fady Iskander, MD, MSc, a Mina Iskander, MD, MSc, a Javier Gomez, MD, MSc, a and Rami Doukky, MD, MSc, FASNC a,b a Division of Cardiology, Cook County Health, Chicago, IL b Division of Cardiology, Rush University Medical Center, Chicago, IL Received Apr 6, 2019; accepted May 14, 2019 doi:10.1007/s12350-019-01762-4 Background. Vasodilator stress myocardial perfusion imaging (MPI) is the provocative test of choice in patients with left bundle branch block (LBBB) or ventricular paced (V-paced) rhythm. The prognostic value of regadenoson SPECT myocardial perfusion imaging (MPI) in these patients has not been studied. Methods and Results. We conducted a retrospective cohort study of 562 patients [mean age, 69 ± 11 years; men, 53.3%] with LBBB (50.7%) or V-paced rhythm (49.3%) who underwent regadenoson stress SPECT-MPI. There were 321 (57.1%) subjects with abnormal MPI and 192 (34.2%) with myocardial ischemia. During a mean follow-up of 2.5 ± 1.9 years, 39 (6.9%) patients had a major adverse cardiac event (MACE), defined as cardiac death or myocardial infarction. The annualized MACE rate in patients with normal MPI was 0.9% (LBBB, 0.8%; V-paced, 1.0%). There was a significant stepwise increase in MACE rates with increasing burdens of perfusion abnormality (P < 0.001) and myocardial ischemia (P = 0.001). Increased risk with abnormal MPI [adjusted hazard ratio, 4.26; P = 0.001] and myocardial ischemia [adjusted hazard ratio, 2.70; P = 0.003] was independent of and incremental to important clinical covariates. Abnormal MPI and myocardial ischemia predicted MACE similarly in both LBBB and V-paced subgroups (interaction P values > 0.05). Conclusion. In patients with LBBB and V-paced rhythm, regadenoson stress SPECT-MPI provides independent and incremental prognostic value in predicting adverse cardiac events. (J Nucl Cardiol 2019) Key Words: Left bundle branch block (LBBB) Æ ventricular paced rhythm Æ regadenoson Æ myocardial perfusion imaging (MPI) Æ coronary artery disease Æ prognosis Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12350-019-01762-4) contains sup- plementary material, which is available to authorized users. The authors of this article have provided a PowerPoint file, available for download at SpringerLink, which summarizes the contents of the paper and is free for re-use at meetings and presentations. Search for the article DOI on SpringerLink.com. Reprint requests: Rami Doukky, MD, MSc, FASNC, Division of Cardiology, Cook County Health, 1901 W. Harrison St., Chicago, IL, 60612; rdoukky@cookcounthhs.org 1071-3581/$34.00 Copyright Ó 2019 American Society of Nuclear Cardiology.