Abstract
BACKGROUND: Myocardial flow reserve (MFR), measured by PET MPI, provides valuable information on epicardial coronary disease, diffuse atherosclerosis, and microvascular function. Despite its routine use, the prognostic efficacy of (13)N-ammonia PET MFR remains unconfirmed in larger multicenter cohorts of patients with suspected or known coronary artery disease (CAD). METHODS: We considered patients from five sites in the REFINE PET registry who underwent (13)N-ammonia PET MPI for CAD. Clinical and imaging data were collected at the time of MPI. MFR was quantified as the ratio of stress to rest myocardial blood flow, using QPET software (Cedars-Sinai Medical Center, Los Angeles, CA). The primary outcome was all-cause mortality (ACM). Survival analyses were performed using Kaplan-Meier and Cox regression models adjusted for clinical and imaging covariates. RESULTS: In total, 6277 patients were included (mean age of 64 years, 56% male). Median follow-up time was 3.8 years. There were 1895 patients with MFR ≤2 and 4382 with MFR >2. Patients with MFR ≤2 had significantly higher mortality than those with MFR >2 (n=701 [37.0%] vs. n=537 [12.3%], respectively; p<0.001). Annualized ACM rates by MFR and SSS ranged from 1.7 to 11.6. In multivariable analysis, MFR ≤2 was independently associated with increased ACM in the overall population (HR 2.70, 95% CI 2.41-3.03, p<0.001), even among patients with no perfusion defects (HR 2.36, 95% CI 1.93-2.89; p<0.001). Mortality risk decreased across increasing MFR deciles ranging from HR 2.73 (95% CI 2.39-3.11) to HR 0.35 (95% CI 0.25-0.49). CONCLUSION: In this large multicenter cohort, MFR derived from (13)N-ammonia PET MPI is a strong, independent predictor of ACM, even in patients with normal perfusion. An MFR of ≤2.0 identifies elevated risk, while higher values are associated with improved survival. These findings support the routine integration of MFR to enhance risk stratification in patients with suspected or known CAD.