Abstract 11979: Cardiac MRI Adds Value in Discerning Pediatric Heart Transplant Rejection and Its Management

Abstract

Introduction: Endomyocardial biopsy (EMB) drives rejection diagnosis in pediatric heart transplant patients but is subject to false negatives and carries risk. Cardiac MRI can detect and quantify myocardial fibrosis and edema with T1 and T2 mapping. Hypothesis: Cardiac MRI may improve discernment of acute rejection in pediatric transplant patients. Methods: Pediatric heart transplant patients referred for clinically indicated EMB underwent noncontrast MRI with T1 +T2 mapping prior to EMB. Segmental T1 and T2 values were measured for base/mid/apex segments. Mean and peak T1+ T2 were quantified per encounter. Rejection treatment was per institutional protocol, and categorized as (A) no changes, (B) oral therapy initiated, or (C) IV therapy initiated. Treatment decisions were blinded to MRI results. Treatment category and T1+T2 were compared with Fisher’s exact test and logistic regression. Results: 89 encounters in 34 patients (median age 13.2y (IQR 8.3-16.8), BSA 1.39 m2 (1.09-1.65), 44.1% female) were successfully completed, with treatment groups A 11%, B 8%, C 81%. Median T1 mean and T1 peak values were (1022 ms (994-1040) and 1077 ms (1056, 1113)), respectively. Median T2 mean and T2 peak values were (50.4 ms (48.4-53.2) and 57.4 ms (53.1-60.8)), respectively. Higher T2 mean and T2 peak predict need for IV therapy; the strongest discriminator was T2 mean > 54.5 (AUC = 0.801, 95% CI: 0.630, 0.972) Table 1. T1 mean and T1 peak were not significant in predicting rejection requiring IV therapy. Adding T1 mean to T2 mean did not improve the AUC (0.804 (95% CI: 0.637, 0.971), DeLong p=0.74). Finally, the odds ratio of new IV rejection therapy for T2 mean values > 54.5 ms is 16.1 (95% confidence interval: 3.6 - 72.6, p<0.001). Conclusions: Average T2 values (cutoff > 54.5 ms) were efficacious at identifying need for IV treatment for rejection in pediatric heart transplant patients, regardless of T1 values. MRI is a promising noninvasive test to identify children at risk of rejection.