Extracellular Volume by T1 Mapping Is Elevated after Pediatric Heart Transplantation

Objectives: T1 Mapping with and without contrast agent is a method to quantify extracellular volume (ECV) as a marker for interstitial fibrosis using magnetic resonance imaging (MRI). There are only few studies in children; results are difficult to interpret due to maturation of the heart during childhood as well as technical differences of MRI hardware. This study was started in a cross sectional design investigating pediatric patients after HTx with the intention for later longitudinal follow up.

Methods: 9 consecutive outpatients post HTx (N = 9, age 16–28 years) were compared with healthy controls (HC). T1 mapping using the T1 MOLLI sequence and estimation of the ejection fraction (EF) of the left ventricle using Balanced TFE Cine Sequences was done using a 3Tesla system (3T TX Achieva with dStream technology, R5.3, Philips). T1 mapping was performed before and 10 minutes after application of intravenous contrast agent (0.1 mL/kg body weight, 1.0 mmol/mL Gadovist). To estimate the ECV and the EF of the left ventricle we used the HDZ MR-Tools (HDZ-NRW, Bad Oeynhausen). ECV of patients was compared with HC and published standard values (between 24% and 27%). Intraindividual comparisons of global ECV with regional ECV in 4 specific segmental parts of the heart: (1) septal (AHA Segments 2, 3, 8, 9, 14], (2) anterior (AHA Segments 1, 7, 13), (3) lateral (AHA Segments 5, 6, 11, 12, 16), (4) inferior (AHA Segments 4, 10, 15), with left ventricular EF (mean: 55%, range: 46–62%) and with the time after HTx (mean = 110, range: 22–237 months; median = 163 months) were analyzed in patients.

Results: There is a significant (p = 0.03) increase of ECV in post HTx patients (mean ECV: 28.6%) compared with controls (mean ECV: 23.4%) as well as literature. A correlation between ECV, LV-EF or time post HTx could not be verified. There were no regional differences of ECV according to the 4 described heart segments in comparison to the global ECV.

Conclusion: Significant increase of global ECV independent from time post HTx mirrors the potential of T1-Mapping in the follow up of young patients. Even if cardiac function is excellent, early detection of fibrosis may influence medical therapy as well as further diagnostic workup for chronic rejection but higher sample size is needed to define the role of ECV quantification in these patients.

No conflict of interest has been declared by the author(s).