Diffuse fibrosis is common in the left, but not in the right ventricle in patients with transposition of the great arteries late after atrial switch operation.

In adult patients with transposition of the great arteries (TGA) late after atrial switch operation (AtSO), each of the ventricles is faced with a profoundly different pressure regimen from the one they are meant to support in normal conditions. The extent of diffuse fibrosis of the right ventricle (RV) and left ventricle (LV) in these patients remains incompletely investigated. Aim of this study was to quantify the degree of fibrosis of the unloaded LV and of the overloaded RV by determining the myocardial extracellular volume (ECV) with non-invasive techniques as T1 mapping. We determined ECV by cardiac magnetic resonance (CMR) in 10 patients (36.8 ± 5.3 years old) with TGA late after AtSO, without relevant pulmonary stenosis, by acquiring T1-maps of the myocardium before and 10 min after injection of Gadolinium-based contrast agent. ECV of the inferior wall (36% (33-41%)) and of the lateral wall (37% (35-39%)) of the LV was significantly increased compared to the ECV of the RV (27% (25-29%)), in both comparisons P < 0.0001. Long-time LV unloading following atrial switch procedures leads to severe myocardial fibrosis of the subpulmonary LV. T1 mapping CMR might be useful for selection of patients with atrial switch operation, in whom reestablishment of the LV as a systemic ventricle by staged arterial switch operation is planned. However larger studies and newer higher resolution methods for T1-mapping are needed to determine the role of ECV in the decision of a surgical intervention in this kind of population.