A 5% change in the percent of ischemic myocardium (based on extent and severity) has been suggested by some investigators as a threshold that indicates clinically significant change for stress nuclear MPI.306,1251 The findings from different exercise or stress imaging modalities (echocardiography versus nuclear MPI) can be even more difficult to compare, such that clinicians should use the same imaging modality over time whenever possible. Despite these concerns, significant changes in risk category (such as shifting to a lower- or higher-risk patient subset) may be used to guide interpretabil- ity of interval change in repeat testing,306,333 and the presence of significant interval change can alter risk assessment. For example, in the ACME (Angioplasty Compared to Medicine) trial, patients whose exercise nuclear MPI normalized after 6 months of randomized treatment had an improved survival Figure 15. Incidence of cardiac death or nonfatal MI during follow-up after a nor- mal stress MPI. Adapted with permission from Hachamovitch et al.327 MI indicates myocardial infarction; MPI, myocardial perfusion imaging. Fihn et al Stable Ischemic Heart Disease: Full Text e433 rate (92%) compared with those with persistent ischemia (82%, P50.02).333 The ongoing technical evolution within imaging modalities is, in part, aimed at minimizing intraob- server, interobserver, and intertest variability. 6.3.7. Future Developments Numerous opportunities to improve the diagnosis and man- agement of SIHD remain. Large registries have the potential to improve the diagnosis of IHD and to assess risk according to clinical information and results from noninvasive testing. Risk-assessment strategies from older databases should be updated with modern information and statistical techniques. Technical development across all cardiac imaging modalities continues to evolve rapidly, often outpacing the ability to perform rigorous clinical validation and application. 