Myocardial T1 and T2 values are associated with patient age in healthy pediatric heart transplant recipients

BACKGROUND: In pediatric heart transplant recipients (PHTR), myocardial T1 and T2 values are elevated in the setting of acute rejection and with cardiac allograft vasculopathy. In normal, healthy children, T1 and T2 values vary with patient age. Our goal was to identify associations between T1, extracellular volume fraction (ECV), and T2 values and patient- and donor-characteristics in PHTR without history of significant graft pathology. METHODS: We performed a single-center, retrospective chart review of consecutive cardiac magnetic resonance (CMR) studies in PHTR from 2017 to 2023. Exclusion criteria were a prior CMR during the study period, history of any prior antibody-mediated rejection (AMR), acute cellular rejection (ACR) >1R, or treated, biopsy-negative rejection. PHTR were also excluded for any history of elevated donor-derived cell-free DNA > 0.15%, CAV, right ventricular, or left ventricular systolic dysfunction by CMR, or presence of late gadolinium enhancement. T1 and T2 mapping were performed. A single reviewer performed parametric mapping analysis. We evaluated differences in global mapping values based on patient- and donor-characteristics in PHTR. T1 and extracellular volume fraction (ECV) values in PHTR were compared to those of pediatric control patients. RESULTS: Out of the 137 PHTR meeting inclusion criteria, 28 remained in the final cohort after exclusion criteria were applied. Median age was 10.6 years (5.9-14.9) with time since transplant of 4.6 years (3.9-8.0). Univariate regression analysis identified significant negative associations between both patient age and donor age with native T1. By multivariate regression analysis, patient age remained negatively correlated with native T1 (β = -5.2, SE = 2.3, p = 0.033), ECV (β = -0.41, SE = 0.19, p = 0.044), and T2 (β = -0.47, SE = 0.18, p = 0.018), independent of donor age. Compared to pediatric control patients >10 years of age, PHTR > 10 years of age demonstrated significantly higher native T1 (1020 ms (1002-1033) vs 980 ms (942-995), p