Cardiac Magnetic Resonance Strain Imaging for Detection of Acute Heart Transplant Rejection

Background Cardiac magnetic resonance imaging (CMR) T1 and T2 mapping accurately detect acute heart transplant rejection, but the diagnostic value of CMR-derived strain imaging remains uncertain, particularly for right ventricular strain. Data incorporating donor-derived cell-free DNA (dd-cfDNA) into a composite reference standard are limited. We evaluated the diagnostic accuracy of CMR-derived left and right ventricular strain and ejection fraction for detecting acute rejection in pediatric and adult heart transplant recipients. Methods Blinded analysis of 1.5T CMR studies was performed in pediatric and adult heart transplant recipients 1-24 months post-transplant, as well as during five additional episodes of acute rejection occurring 3-14 years post-transplant. Left and right ventricular strain and ejection fraction were quantified using semi-automated post-processing. Acute rejection was defined using a composite reference standard comprising endomyocardial biopsy (EMB), clinical assessment, and dd-cfDNA. Diagnostic performance was assessed using cut-off values derived from receiver operator characteristic (ROC) analysis. Results Among 214 CMR studies in 58 patients, 13 cases of acute rejection were identified. Diagnostic performance for detecting acute rejection was moderate for pediatric right ventricular longitudinal strain (AUC 0.782, 95% CI 0.565-0.999), whereas all other cardiac functional parameters demonstrated limited discrimination in both pediatric and adult patients (AUC 0.536-0.739). Models based on individual rejection indicators (EMB, clinical assessment, and dd-cfDNA) also showed poor diagnostic accuracy. Conclusion CMR-derived left and right ventricular strain and ejection fraction demonstrated limited ability to independently detect acute rejection. However, strain abnormalities, particularly RVLS in pediatric patients, may reflect downstream functional effects in more advanced rejection and may complement T1 and T2 mapping in assessing rejection severity.