Cardiac Magnetic Resonance Imaging in Heart Transplant Patients

For patients with end-stage heart failure, heart transplantation (HTX) is the ultimate therapy. Knowledge of pre- and post-operative medical treatment and management resulted in improved graft survival and patient outcome. For tissue and coronary staging after HTX, the reference standards are invasive procedures like coronary angiography, whereas tissue staging is carried out by potentially hazardous myocardial biopsies. Additionally, these procedures expose patients to a substantial radiation dose, and the hazard of nephro-toxic contrast agents. To circumvent these shortcomings, a non-invasive imaging approach would be a helpful tool saving health costs and improve patient′s quality of life. Cardiovascular magnetic resonance (CMR) is the reference standard imaging modality for evaluation of ventricular morphology, volumes and mass due to excellent image quality as compared to other modalities. The ability of CMR to characterize ventricular morphology, systolic and diastolic function, inflammation, fibrosis and infarction makes it an excellent candidate for post HTX staging. CMR techniques like T2 assessment have shown good correlation to biopsy proven heart transplant rejection although the reproducibility of T2 measures as well as limited access have likely hampered the adoption of CMR into routine post HTX clinical care. Improvements in CMR hardware combined with appropriate pulse sequences for T2 quantification make routine ascertainment of T2 relaxation more feasible and improve inter-center reproducibility. Early and late gadolinium enhancement may also prove useful in diagnosing transplant rejection just as it has in the diagnosis of myocarditis. Studies are needed evaluating promising CMR correlates of rejection such as diastolic function, gadolinium enhancement and other contrast agents. Future studies should focus on combining multiple CMR measures into a transplant rejection scoring system to improve the sensitivity in detecting heart transplant rejection and possibly reduce, if not eliminate, the need for endo-myocardial biopsy.