MRI-Based Septal Curvature Ratio for Differentiating Right Ventricular Pressure and Volume Overload in Repaired Tetralogy of Fallot and Shunt-Associated Pulmonary Hypertension

Background: Cardiac MRI-derived septal-to-free wall curvature ratio is a non-invasive marker to evaluate right ventricular pressure and pulmonary hypertension. Objective: To investigate whether the septal-to-free wall curvature ratio measured by cardiac MRI can differentiate between right ventricle pressure and volume overload in different right ventricle overload conditions. Materials and Methods: Between 2020 and 2025, 149 participants were classified into four groups: controls ( n =21), patients repaired with ( n =55) and without ( n =52) right ventricular outflow tract stenosis, and patients with left-to-right shunt and pulmonary hypertension ( n =21), retrospectively. The association of the septal-to-free wall curvature ratio, calculated using MATLAB, with functional parameters and group differences was analyzed. Results: Significant differences in septal-to-free wall curvature and right-to-left ventricular volume ratios were found across groups (P<0.05). The curvature ratio was lowest in the left-to-right shunt lesions with pulmonary hypertension (0.610 ± 0.238), followed by the tetralogy of Fallot with stenosis group (0.670 ± 0.238). The curvature ratio showed moderate-to-strong correlations with right-to-left ventricular end-diastolic (r = –0.59) and stroke volume ratios (r = –0.54). ROC analysis showed excellent diagnostic performance in detecting pulmonary hypertension (AUC=0.921) and strong discriminatory ability in tetralogy of Fallot without stenosis (AUC=0.877), while moderate performance was observed in tetralogy of Fallot with stenosis (AUC=0.777). Significant negative correlations were identified between curvature ratio and right ventricle volumes and right-to-left ventricle ratios, while a positive correlation was found with right ventricle ejection fraction in the tetralogy of Fallot subgroup. Conclusion: Cardiac MRI-derived septal-to-free wall curvature and volume ratios offer valuable non-invasive markers for distinguishing right ventricular pressure and volume overload.