## 3 Results
### RV Longitudinal Function and TMAD of the Tricuspid Valve  
Anatomical studies have shown that the longitudinal fibers are predominant in the RV, localized in the subendocardial layer, whereas less circumferential fibers are found in the superficial layer in healthy children. This explains why the longitudinal shortening is a greater contributor to RV stroke volume [17; 18; 19].  
Echocardiographic assessment of RV longitudinal function, according to the present guidelines [3; 13; 14], includes the following parameters: FAC, TAPSE and RV strain measurements.  
The TMAD is a novel parameter derived from speckle-tracking echocardiography and is based on tracking bright echoes within the myocardium [15]. Although it was determined offline in our study with specialized software, the new echo machines allow an easy way to obtain this parameter.  
The TMAD of tricuspid valve is a method to evaluate the longitudinal motion of the tricuspid annulus in different points (lateral, medial and midpoint). It was validated against magnetic resonance imaging (MRI) derived RV ejection fraction (EF) in assessing RV function [10; 20]. Although tricuspid annular plane systolic excursion (TAPSE) using M-mode is a widely used parameter for assessing RV function, it evaluates only the motion of the tricuspid annulus. We speculate that TMAD, especially TMADm%, are more reliable parameters as they consider the complete longitudinal contraction (from base to apex), so is factoring the RV length from end-diastole to end-systole.  
Our study demonstrated that TMADlat was higher than TMADmid and TMADsept, so the values differed based on the site of measurements. [PERSON], Y. et al. found the same distribution of the different TMAD values [20]. According to these values, the displacement was higher at the level of the RV free wall than the septal wall, likely explained by the interventricular mechanical coupling between the two ventricles through the interventricular septum. This finding is consistent with prior studies demonstrating the ventricular interdependence [20; 21].  
Moreover, tricuspid annulus midpoint fractional displacement (TMADm%) also known as right ventricular longitudinal shortening fraction (RV-LSF), calculated as the maximum displacement of the tricuspid midpoint throughout the cardiac cycle, is a more complex parameter that factors the RV length throughout the cardiac cycle. The TMADm% has been studied as a marker of the RV dysfunction. [PERSON] et al. found that a poor RV systolic function, expressed by 3-dimensional echocardiography--measured RVEF < 45%--was detected by a TMADm% < 14.7% with a high sensitivity and specificity of 93% and 95%, respectively, followed by RV free wall longitudinal strain [22]. [PERSON] et al. found that TMADm% is the best predictor for RV dysfunction expressed by MRI-derived RVEF in PAH patients, with an optimal cut-off value of 16.05% [20]. In a study conducted in infants (age ranged from 3 to 11 months) with dominant right ventricular physiology who underwent bidirectional Glenn anastomosis, [PERSON] et al. demonstrated that TMAD of the tricuspid valve is an independent predictor of midterm mortality or heart transplantation in these children, with a mean value of 10% for non-survivors or heart transplanted [23]. [PERSON] et al. found that TMADm% (named RV longitudinal shortening fraction in their study) was markedly decreased in COVID-19 patients with acute cor pulmonale, and a cut-off value of 17% is able to identify RV dysfunction in these patients, with high specificity and sensibility [24].