The nuclear utility in the community (NUC) study: Technetium ^99m based myocardial perfusion imaging predicts outcome in the community outpatient setting

Background. While the prognostic value of myocardial perfusion imaging (MPI) has been well validated in academic centres, the feasibility of extending this data to community-based MPI remains uncertain. Additionally, while ^99mTc-based radioisotopes have become the predominant tracers used for MPI in the United States (US), often performed with pharmacologic stress, most prognostic studies have reported on patients undergoing thallium ²⁰¹ studies performed with exercise stress. This study was carried out to evaluate the prognostic value of community-based MPI and to assess the incremental value of individual elements of ^99mTc SPECT. Methods. We prospectively followed 1,612 consecutive patients undergoing stress ^99mTc-based SPECT in a US outpatient community laboratory who experienced 71 hard events (cardiac death or nonfatal MI) over 24±7 months. Mean age was 65±12 years and 612 women were included. Patients were censored from further follow-up at the time of revascularisation. Results. Patients whose scans were normal incurred an annualised event rate of 0.4%, compared to 2.3% for those with abnormal scans (p<0.0001). Subset analysis demonstrated comparable risk stratification for women and men and those referred for pharmacologic and exercise stress. After adjusting for pre-test variables, multivariable Cox regression analysis found the most potent independent components of MPI to be, in decreasing order of importance, transient ischaemic dilation, extent of reversibility, post-stress ejection fraction, extent and severity of the stress perfusion defect, and the overall test result (normal or abnormal). Each 1% decrement of ejection fraction (EF) predicted a 3% increase in risk (p=0.0009). Post-MPI angiography and revascularisation increased commensurate with the extent and severity of the MPI result including decreasing post-stress EF. Conclusion. A normal myocardial perfusion study predicts extraordinarily low 2-year risk. A study that is abnormal should not be regarded as simply abnormal; its components allow further independent predictive power. Based on the Nuclear Utility in the Community study, perfusion imaging is portable and transferable to the outpatient community setting in the US and, by implication, worldwide.