1356325 - T1 mapping: A Roadmap to Dysfunction in Systemic Right Ventricles

Background: Parametric mapping has been widely accepted as a non-invasive method of quantitative myocardial tissue characterization, though its applicability in complex congenital heart disease remains uncertain. Patients with L-transposition of the great arteries (L-TGA) or D-transposition of the great arteries (D-TGA) status post atrial switch operation (Senning or Mustard procedure) have a morphologic RV that chronically faces systemic afterload. This burden on an ill-equipped RV as well as atrophy in the morphologic LV leads to biventricular histologic changes with eventual systolic dysfunction. Prior studies have supported patterns of diffuse fibrosis in this patient population, however the utility of T1 mapping in systemic RV is unclear. The aim of our study was to understand the correlation of native T1 mapping parameters to ventricular function in adult patients with systemic RVs.

Methods: This was a retrospective single-center study of 13 patients with biventricular circulation with the morphologic RV serving as the systemic ventricle who underwent clinically-indicated CMR on a 1.5T Siemens Sola (Siemens Healthcare, Erlangen, Germany). Standard MOLLI T1 maps were acquired in a mid-ventricular short axis slice and regions of interest (ROI) were manually drawn in the RV free wall, LV free wall, interventricular septum (IVS), the superior insertion point (SIP), and the inferior ventricular insertion points (IIP) (Figure 1). Spearman correlation compared standard ventricular volumetric parameters with T1 variables using SPSS v27.0 (SPSS, Inc., Chicago, IL).

Results: Thirteen patients with median age 36 years (IQR, 27-48 years) included 5 patients with L-TGA and 8 patients with D-TGA status post atrial switch (5 Mustards, 3 Sennings). The RV free wall (T1=1052 ± 82 ms), IVS (T1=1064 ± 80 ms), and SIP (T1=1045 ± 101 ms), had normal T1 values that trended toward elevation. The LV (T1=1122 ± 183 ms), and IIP (T1=1117 ±103 ms) had more pronounced T1 elevation. There was a strong negative correlation between LVEF and RV free wall T1 values (r= -0.68, p= 0.01) and the RV:IVS T1 ratio (r= -0.80, p= 0.001). There was also a moderate negative correlation between RVEF and the IIP T1 values (r= -0.64, p= 0.02) as well as the IIP:IVS T1 ratio (r= -0.58, p= 0.04).

Conclusion: T1 mapping can be leveraged to understand the biventricular myocardial changes in the setting of a systemic RV. Our data demonstrate the impact of fibrosis as estimated by T1 elevation on the function of the contralateral ventricle.  This study highlights the importance of ventricular interdependence in the setting of the systemic RV and offers T1 mapping as a useful metric to better understand risk stratification and the efficacy of medical therapies in this complex population.