123I-mIBG SPECT Imaging

123I-mIBG (MIBG) cardiac scintigraphy can be used to assess cardiac sympathetic activity and predicts prognosis in patients with heart failure. The results of prognostic studies were validated in the AdreView Myocardial Imaging for Risk Evaluation in Heart Failure (ADMIRE-HF) trial, which was a large multi-centre prospective international study of 961 patients with NYHA Class II - III Heart Failure and LV ejection fraction \> 35%2. This landmark study used planar imaging for calculation of the heart-to-mediastinal ratio (H/M) as a quantitative analysis of global uptake. The H/M on 4 hour delayed planar imaging was predictive of heart failure progression, arrhythmic events and cardiac death and provided incremental value to B-type natriuretic peptide and left ventricular (LV) ejection fraction. In a study using quantitative MIBG SPECT, a new method for the calculation of the H/M ratio was developed, compared several reconstruction methods and demonstrated that the H/M ratio from SPECT was equivalent to the planar H/M ratio for differentiating normal participants from heart failure patients. The ability of SPECT imaging to provide more accurate quantitative measurement of myocardial activity may also provide more accurate measurements of MIBG washout, which has been shown to be predictive of sudden cardiac death using planar imaging. SPECT imaging also can provide information about the regional distribution of MIBG, which has been demonstrated to be predictive of sudden cardiac death. Similarly, mismatch of regional MIBG uptake and perfusion reflecting deinnervation of viable tissue may identify myocardium with potential for development of ventricular arrhythmias. Thus, SPECT MIBG imaging may provide much useful prognostic information in addition to the H/M ratio. Participants will have a single dose of the isotope and the H/M ratio will be measured using 3 types of imaging techniques with cameras and software currently used at the University of Ottawa Heart Institute: 1. Planar (2D) imaging, as used in the ADMIRE-HF trial 2. Hawkeye Infinia 3D SPECT imaging, which is conventional SPECT 3. Discovery NM-530 CZT 3D SPECT imaging, a newer SPECT technology Images will be taken at predetermined time points over a 5 hour period on the study /injection day. Participants will be monitored for any clinical changes with routine lab work and physical observations during the study.