## 4 Discussion
### Role of CMR-FT in the Perioperative Assessment of Right Ventricular Function
In normal hearts, RV systolic function is primarily governed by the contraction of longitudinal fibers, leading to a peristaltic movement from the inflow to the outflow tract [19]. In the context of EA, the RV function appears to depend more on the shortening of circumferential fibers [20]. Our hypothesis suggested that in EA, compared to other heart diseases with TR, longitudinal fibers have a propensity to favor backflow. This could elucidate the initially normal GLS values in EA before surgical intervention and the subsequent decline in longitudinal function following the restoration of valve competency. Despite sustained pulmonary artery flow indicating that the postoperative deterioration of GLS is primarily due to increased postoperative afterload, other factors might also contribute to this observation. First, it is important to note that GLS calculations encompassed the previously atrialized RV wall after Cone repair, typically characterized by thinness and fibrotic changes [7]. As a result, the impaired movement in this region may also contribute to the altered postoperative RV longitudinal performance. Even though the atrialized portion of the RV also contributes to radial and circumferential strain measurements, we observed improvements in these parameters. This could be explained by the fact that GRS and GCS are given by strain analysis at basal, mid, and apical levels. Therefore, a postoperative deterioration in basal strain could, in the case of improved mid and apical strain, still result in overall improved strain measurements. The precise role of the former atrialized segment of the RV in postoperative systolic RV function remains uncertain. Therefore, conducting an FT analysis of the basal (septal) area before and after surgery would be valuable in gaining a deeper understanding. It is also worth noting that the longitudinal fibers constitute the innermost layer of the RV wall [19] and that this layer is particularly susceptible to ischemia [21]. Thus, potential hypoxic damage through aortic cross clamping during Cone repair might also contribute to postoperatively impaired GLS. Furthermore, it is conceivable that the delamination of the leaflets from the underlying myocardium during Cone repair could damage the inner myocardial layer, contributing to the reduced postoperative GLS [3]. While GLS was demonstrated to be effective in detecting early myocardial dysfunction in other diseases [12,13], our previous study evidenced that this does not seem to be the case in EA [10]. The results of this study might explain the limited diagnostic value of this parameter in EA. Conversely, GRS and GCS do not seem to be much affected by the hemodynamic changes caused by Cone repair. We hypothesized that, unlike GLS, GRS and GCS might favor forward flow more than backflow and, therefore, could be more independent of after-load changes caused by the restored TV function. Hence, GCS and GRS might reflect true myocardial changes. The observed postoperative improvement could therefore indicate an actual improvement in myocardial function after Cone repair. Whether this is due to direct effects on myocardial function from the postoperatively reduced volume overload or due to myocardial remodeling over the time remains unclear, as our postoperative follow-up times vary too widely to provide a clear explanation for the time course of the suspected improvement. However, it is important to note that minimal improvements in strain most likely do not always directly translate into increased forward stroke volume, especially given the reduced ventricular volume after surgery. This can be explained by the fact that strain is defined as the percentage of shortening (or, in the case of radial strain, the percentage of thickening) of the myocardium between end-diastole and end-systole measured in a certain slice. The effectively ejected stroke volume given a certain percentage of shortening, therefore, depends on the RVEDV. In cases of higher RVEDV, the same strain values mean higher ejected volumes than in cases where EDV is low.