Normal MPI was defined as SSS = 0 and near-normal MPI as SSS = 1-3. ![]() All patients had normal left ventricular ejection fraction (LVEF) ≥ 50%. Normal scans were present in 4398 patients and near-normal scans in 2404 patients. The study population consisted of 6802 patients who underwent regadenoson SPECT MPI over a 6-year period. 7 examine the prognostic significance of completely normal MPI compared to mildly abnormal images or borderline myocardial ischemia. The concept of a low-risk scan is well-established, and there has been little investigation of prognosis with normal versus mildly abnormal MPI. 4, 5 These findings were extensively validated by many other nuclear cardiology laboratories with similar results. Subsequent prognostic studies from the Cedars-Sinai laboratory demonstrated that patients with normal or mildly normal MPI (SSS 0-3) constituted a low-risk group, with annual risk of cardiac death or non-fatal myocardial infarction (MI) < 1%. An ischemic defect was defined as moderately reduced uptake on the stress images (grading ≥ 2) with a rest score ≤ 1, or a stress defect with absent uptake (grading 4) with a rest score of 2. Thus, a normal SSS was not limited to only SSS = 0 but to a score range of 0-3. 2, 3 Realizing that imaging artifact accounts for many mildly abnormal scans, they required in their initial studies that an abnormal stress image had to have two or more segments with perfusion scores ≥ 2 (at least moderately reduced isotope uptake). 1 The Cedars-Sinai laboratory introduced and popularized this summed scoring scheme. The difference between SSS and SRS is the summed difference score (SDS), a measure of the extent and severity of ischemia. SSS represents the extent and severity of combined ischemia and infarction, and SRS represents the extent and severity of infarction. 1 The summation of the perfusion grades on the stress images is the summed stress score (SSS) and on the rest images the summed rest score (SRS). The standard for interpreting and reporting MPI applies a 17-segment model of the left ventricle with perfusion graded in each segment using a 5-point scale.
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