Multi-modal imaging of the pediatric heart transplant recipient

Abstract

The assessment of pediatric patients after orthotropic heart transplantation (OHT) relies heavily on non-invasive imaging. Because of the potential risks associated with cardiac catheterization, expanding the role of non-invasive imaging is appealing. Echocardiography is fast, widely available, and can provide an accurate assessment of chamber sizes and function. Advanced echocardiographic methods, such as myocardial deformation, have potential to assess for acute rejection or cardiac allograft vasculopathy (CAV). While not currently part of routine care, cardiac magnetic resonance imaging (CMR) and computed tomography may potentially aid in the detection of graft complications following OHT. In particular, CMR tissue characterization holds promise for diagnosing rejection, while quantitative perfusion and myocardial late gadolinium enhancement may have a role in the detection of CAV. This review will evaluate standard and novel methods for non-invasive assessment of pediatric patients after OHT.

Keywords: Cardiac imaging; cardiac computed tomography; cardiac magnetic resonance imaging (CMR); echocardiography; orthotopic heart transplantation (OHT).

Figure 1

Figure demonstrating representative mitral valve inflow Doppler (A), aortic valve outflow Doppler (B), and septal tissue Doppler (C). The left ventricular (LV) myocardial performance index (MPI) can be calculated using spectral Doppler of the mitral inflow and aortic outflow (assuming similar heart rates) or tissue Doppler. It is calculated from tissue Doppler by adding the isovolumic contraction time (IVCT) to the isovolumic relaxation time (IVRT) and dividing by the left ventricular ejection time (LVET). It can also be calculated by subtracting the LVET from the time from mitral valve close to open (which results in the sum of the IVCT and IVRT) and dividing by the LVET.

Figure 2

The myocardial T1 relaxation curve can be calculated by plotting signal intensities at varying inversion times. The T1 time is 63% of full recovery. This figure demonstrates T1 relaxation curves for native (pre-contrast) and post-contrast myocardium. Reproduced from (86), originally published by BMC.

Figure 3

Tissue characterization using native T1 and extracellular volume (ECV). T1 values listed are for MOLLI sequences at 1.5 T. Reproduced from (88), originally published by BMC.

Figure 4

Extracellular volume (ECV) maps in the short axis at the base (A), mid left ventricle (B), and apex (C) in a pediatric patient with acute rejection. Bullseye (D) demonstrates significant ECV elevation. ECV maps at the base (E), mid left ventricle (F), and apex (G) in a pediatric transplant patient who presented for routine endomyocardial biopsy without evidence of rejection. Bullseye (H) demonstrates ECV values in the normal range.