Imaging in Heart Transplant Patients

Heart transplantation is an accepted treatment for select patients with end-stage heart failure. Improvements to immunosuppressive therapies and patient management have increased the half-life of heart transplant patients to over 10 years. Despite this success, rejection remains the "Achilles heel" of heart transplantation. The early detection of acute rejection and cardiac allograft vasculopathy are paramount to avoiding graft loss. Unlike in kidney and liver transplantation, there are no clinically validated biomarkers for detecting heart transplant rejection. Existing methods for monitoring the cardiac allograft are invasive. The endomyocardial biopsy is the standard-of-care for monitoring for acute rejection but carries risks of complications, and histologic assessment is often subjective. Equally, intracoronary angiography remains the standard-of-care for detecting cardiac allograft vasculopathy, but it is invasive and less than ideally sensitive. Newer echocardiographic techniques, computed tomography, magnetic resonance, and positron emission tomography are less invasive than conventional biopsy and show promise in excluding rejection thereby potentially decreasing the frequency of biopsies in low-risk patients. Intravascular ultrasonography and optical coherence tomography, although still invasive, improve on the assessment of the coronary tree through increased resolution, evaluation of the microvasculature, and visualization of the vessel wall. This review outlines the invasive and noninvasive imaging modalities that are employed in the routine care of heart transplant patients and examines newer techniques that are under evaluation.