Background Cardiovascular magnetic resonance (CMR) is emerging as an important tool for cardiac allograft assessment. Native T1 mapping may add value in identifying rejection and in assessing graft dysfunction and myocardial fibrosis burden. We hypothesized that CMR native T1 values and features of textural analysis of T1 maps would identify acute rejection, and in a secondary analysis, correlate with markers of graft dysfunction, and with fibrosis percentage from endomyocardial biopsy (EMB). Methods Fifty cases with simultaneous EMB, right heart catheterization, and 1.5 T CMR with breath-held T1 mapping via modified Look-Locker inversion recovery (MOLLI) in 8 short-axis slices and subsequent quantification of mean and peak native T1 values, were performed on 24 pediatric subjects. A single mid-ventricular slice was used for image texture analysis using nine gray-level co-occurrence matrix features. Digital quantification of Masson trichrome stained EMB samples established degree of fibrosis. Markers of graft dysfunction, including serum brain natriuretic peptide levels and hemodynamic measurements from echocardiography, catheterization, and CMR were collated. Subjects were divided into three groups based on degree of rejection: acute rejection requiring new therapy, mild rejection requiring increased ongoing therapy, and no rejection with no change in treatment. Statistical analysis included student’s t-test and linear regression. Results Peak and mean T1 values were significantly associated with acute rejection, with a monotonic trend observed with increased grade of rejection. Texture analysis demonstrated greater spatial heterogeneity in T1 values, as demonstrated by energy, entropy, and variance, in cases requiring treatment. Interestingly, 2 subjects who required increased therapy despite low grade EMB results had abnormal peak T1 values. Peak T1 values also correlated with increased BNP, right-sided filling pressures, and capillary wedge pressures. There was no difference in histopathological fibrosis percentage among the 3 groups; histopathological fibrosis did not correlate with T1 values or markers of graft dysfunction. Conclusion In pediatric heart transplant patients, native T1 values identify acute rejection requiring treatment and may identify graft dysfunction. CMR shows promise as an important tool for evaluation of cardiac grafts in children, with T1 imaging outperforming biopsy findings in the assessment of rejection.

Introduction: The use of z scores to describe growth of normal structures is necessary in the management of pediatric cardiac disorders, particularly in babies and toddlers. Z score calculators for cardiac magnetic resonance (CMR) have traditionally relied on a convenience sample given complexity of the test. A recently published, novel z score calculator from prospectively-imaged, awake, healthy children ages 0-12 years may add value to assessments of ventricular size compared to traditional calculators. Hypothesis: A novel z score calculator (“Olivieri et al”) with robust prediction in younger, smaller children may reclassify right and left ventricular end diastolic volumes and mass (RVEDV, LVEDV, LVM) compared to the traditional calculator (“Buechel et al”). Methods: A retrospective cohort of subjects less than 12 years of age who underwent clinical CMR imaging on a 1.5T scanner (n=96; median age 5.5 years (IQR 3.7-7.6 years); 42% female) was studied. Z scores were calculated using both novel and traditional models for RVEDV, LVEDV and LVM. Subjects were categorized into the agreement group (both calculators agree) or disagreement groups, where novel calculator reclassified to normal (z< ± 2) or abnormal (z> ±2). Reclassified subject characteristics were compared with ANOVA and t-test. Results: Novel and traditional z scores agreed for 77%, 58% and 62% of cases for RVEDV, LVEDV and LVM, respectively. Amongst disagreements, subjects reclassified from abnormal to normal by the novel calculator had significantly lower age, BSA and RV size (Table 1). Reclassified subjects showed no association with specific diagnoses. Conclusion: The novel z score calculator reclassifies younger, smaller children away from severe z scores into more normal z scores. Ventricular volume assessment is highly relevant to critical decision-making in the first years of life in borderline lesions.

Introduction: Cardiac Magnetic Resonance (CMR) is an emerging tool for cardiac graft assessment in heart transplant recipients, with native T1 mapping directed at identifying both rejection and graft fibrosis to predict and guide management of graft dysfunction. Hypothesis: CMR native T1 values may identify acute rejection, predict graft dysfunction, and in secondary analysis, correlate with fibrosis percentage from right ventricle (RV) endomyocardial biopsy (EMB). Methods: Pediatric subjects (n=34, age 12.4±4.9 y, graft age 5.4±4.3 y, LVEF 62.9±5.6%) underwent simultaneous EMB and 1.5T CMR with breath-held T1 mapping via Modified Look-Locker Inversion recovery in 8 short-axis slices, from which global mean and peak native T1 values were quantified. EMB analyzed for histopathological fibrosis% using digital analysis of Maisson’s trichrome stained slides. Patients were stratified into three groups by decision to treat: acute rejection with new treatment initiated, ongoing treatment modified, or no change in treatment. In patients without acute rejection, linear regression was used to compare T1 values with clinical markers of right atrial (RA) mean pressure and brain natriuretic peptide (BNP). Results: Mean T1 values were higher in patients with acute rejection compared to those without, with stratified groups demonstrating a monotonic trend; peak T1 values trended towards significance. In patients without acute rejection, peak T1 values correlated with BNP (r=0.53, p=0.004) and RA mean pressure (r=0.39, p=0.046). Fibrosis% from random RV EMB did not correlate with native T1 values or clinical markers of graft dysfunction. Conclusion: In pediatric heart transplant patients, T1 values from comprehensive CMR identified acute rejection requiring initiation of treatment and graft dysfunction, with regional analysis key to capturing correlation with clinical markers. CMR shows promise as an important tool for evaluation of graft health in children.