Pediatric Track Session
SCMR 22nd Annual Scientific Sessions
Noninvasive characterization of transplant graft status is of interest to risk-stratify patients for endomyocardial biopsy (EMB). In healthy pediatric heart transplant (PHT) recipients without acute rejection (AR), cardiac MRI (CMR) extracellular volume fraction (ECV) represents diffuse myocardial fibrosis. In the setting of AR, native T1 and ECV also rise due to myocardial edema. Myocardial strain may identify AR as well. We sought to compare the association of native T1, ECV, and myocardial strain (longitudinal and circumferential) in PHT recipients undergoing EMB and research CMR with the hypothesis of higher T1 times, higher ECV, and abnormal strain in acute rejection.
After informed consent, PHT recipients ≥ 13 years of age and ≥ 9 months post-transplant underwent CMR with gadolinium contrast on a 1.5T CMR (Siemens) within 24 hours prior to EMB. In addition to routine CMR of the left ventricle, T1 mapping and hematocrit were used to obtain native T1 time and ECV. Circle42 (Circle CV Imaging, Canada) derived strain from standard SSFP cine imaging. T-test and ANOVA compared groups<./p>
PHT recipients (n=29, mean age 18.4 ± 5.3 years) were compared to 12 healthy young adult controls. Among PHT recipients, 9 (31%) had EMB rejection grades 1R-2R (old grades 1A-3A), none with heart failure symptoms or hemodynamic compromise. There was no difference in LVEF or mass between recipients and controls. However, mean native T1 times and ECV were higher among PHT recipients with versus without AR (1054.9 ms and 28.2% vs. 1014.9 ms and 24.3%, respectively; p ≤ 0.002). Neither strain measure differed by AR status. Application of a native T1 time of 1025ms and ECV 26% provides 100% sensitivity and 90.9% specificity for AR which when applied to our cohort would spare 20 patients from EMB with only 3 false positives.
Elevated native T1 time and ECV in PHT recipients are associated with grade 1R-2R AR by EMB, whereas myocardial strain did not discriminate. These data suggest combined T1 and ECV values identified by CMR prior to invasive EMB can predict likelihood of AR. CMR-guided decision-making in PHT rejection surveillance may be feasible should larger studies confirm these findings.