Non-invasive detection of acute cell-mediated graft rejection in paediatric heart transplant recipients: The role of cardiovascular magnetic resonance.

Background: Acute cardiac rejection is currently diagnosed by endomyocardial biopsy (EMB), but multiparametric cardiac magnetic resonance (CMR) may be a non-invasive alternative by its capacity for myocardial structure and function characterization. The primary aim was to determine the utility of multiparametric CMR in identifying acute graft rejection in paediatric heart transplant recipients. The second aim was to compare textural features of parametric maps in cases of rejection versus those without rejection. Methods: Fifteen patients were prospectively enrolled for contrast-enhanced CMR followed by EMB and right heart catheterization.Images were acquired on a 1,5 T scanner including T1 mapping and T2 mapping. The extracellular volume (ECV) was calculated using pre- and post-gadolinium T1 times of blood and myocardium and the patient's hematocrit. Patients were divided into two groups based on degree of rejection at EMB: no rejection with no change in treatment (Group A) and acute rejection requiring new therapy (Group B). Results: Acute rejection was diagnosed in five patients. Mean T1 values were significantly associated with acute rejection. A monotonic, increasing trend was noted in both mean and peak T1 values, with increasing degree of rejection. ECV was significantly higher in Group B. There was no difference in T2 signal between two groups. Conclusions: Multiparametric CMR is emerging as a useful tool for rejection screening and holds promise to substantially improve cardiac allograft rejection surveillance in the paediatric setting.