Reduced ¹³N-Ammonia PET Myocardial Flow Reserve and Heart-Failure-Related Risk Independent of Relative Ischemia in Chronic Coronary Syndrome.

PURPOSE: This study evaluated whether uncorrected global myocardial flow reserve (MFR) below 2.0 on ¹³N-ammonia PET stratified risk in chronic coronary syndrome (CCS), and how rate-pressure-product (RPP) correction reclassified patients. METHODS: Consecutive adults with suspected or established CCS undergoing ¹³N-ammonia PET/CT at a single Japanese center were retrospectively studied. Uncorrected global MFR below 2.0 was the primary exposure, with RPP-corrected MFR reported alongside. The primary endpoint was a hard non-revascularization composite of death, non-fatal myocardial infarction, heart-failure hospitalization, or malignant ventricular arrhythmia. The pre-specified Cox model, stratified by scanner generation, adjusted for age, sex, and summed difference score. RESULTS: Of 168 patients, 102 (60.7%) had MFR below 2.0, with higher rest and lower stress flow (P = 0.001 and P < 0.001). Over a median 3.5 years, the endpoint occurred in 28 of 102 (27.5%) versus 5 of 66 (7.6%; log-rank P < 0.001). In the primary model, MFR below 2.0 remained independently associated with the endpoint (hazard ratio 4.5182, 95% CI 1.7121-11.9236, P = 0.002), and after excluding baseline heart failure (4.1693, P = 0.011). RPP correction reclassified 52 patients (31.0%), mostly downward. Event rates were 7.0% after downward reclassification and 29.0% in patients impaired on both values (four-group log-rank P = 0.003). CONCLUSION: Uncorrected global MFR below 2.0 identified higher-risk patients with CCS independently of relative ischemia, including those without baseline heart failure. RPP correction reclassified 43 patients below the threshold, supporting reporting of the uncorrected reserve with explicit labeling of any corrected value.