Prognostic Significance of Myocardial Blood Flow Reserve and Stress Myocardial Blood Flow in the Assessment of Cardiac Allograft Vasculopathy in Heart Transplant Recipients.

INTRODUCTION: Cardiac allograft vasculopathy limits longevity following heart transplantation (HT). Non-invasive physiologic assessment with cardiac PET provides prognostic significance. We sought to assess the relative prognostic relevance of stress myocardial blood flow (sMBF) and myocardial blood flow reserve (MBFR) on post-transplant outcomes. METHODS: All adult single-organ HT recipients who underwent 13N-ammonia PET myocardial perfusion imaging between 2016-2019 were included with a median follow-up of 7.2 years. Patients were categorized by MBFR (normal MBFR >2.0, low MBFR ≤2.0) and sMBF (normal sMBF >1.7 mL/min/g, low sMBF ≤1.7 mL/min/g) values into three groups: concordant normal, discordant, or concordant low. RESULTS: Among 454 patients (25.8% female, median age 59 years, median time since HT 7.2 years), 287 (63.2%) had concordant normal MBFR and sMBF, 72 (15.9%) had discordant values (37 MBFR low, 35 sMBF low), and 95 (20.9%) were concordant low. Reductions in both MBFR and sMBF had an over 3-fold increased risk of death or retransplantation compared to those with both normal values (HR 3.3, 95% CI 2.2-4.8, p<0.0001). The risk remained elevated for those with discordant values, though magnitude of risk was lower (HR 2.5, 95% CI 1.6-3.9, p=0.0001). Only an isolated reduction in MBFR (HR 3.3, 95% CI 1.9-5.6, p<0.0001), not in sMBF (HR 1.7, 95% CI 0.8-3.3, p=0.14), conferred significant risk. Rate pressure product correction did not impact results. CONCLUSION: In this cohort, reduction in both sMBF and MBFR was associated with the highest risk of death or retransplant during a median follow-up of 7 years.