Abstract
Pulmonary hypertension is a known complication of scimitar syndrome; however, its risk factors and outcomes are not well understood. This study aimed to assess the prevalence, clinical features, risk factors, and outcomes of pulmonary hypertension in patients with scimitar syndrome. In this retrospective cohort study, patients diagnosed with scimitar syndrome and treated at a tertiary center between June 2015 and June 2024 were reviewed. Pulmonary hypertension was defined as a mean pulmonary arterial pressure > 20 mmHg based on cardiac catheterization. PH developed in 77.5% of pediatric SS patients. PVR and PCWP differed significantly across hemodynamic characteristics (p = 0.038) (p = 0.001), respectively with 67.7% of PH patients exhibiting a pre-capillary phenotype. Patients selected for surgery demonstrated higher baseline severity, including greater Qp:Qs ratio (1.99 vs. 1.49, p = 0.033) and more frequent ASDs (57.1% vs. 8.3%, p = 0.005). Resolution was achieved in 74.2% of patients with longer resolution time found in surgical cases (median 8.1-12.3 years) compared to non-surgical cases (3.2 years). Of the 8 patients with persistent PH, 25% (n = 2) were found to have pathogenic variants associated with non-mechanical factors linked to PH in SS. PH is highly prevalent in patients with scimitar syndrome, particularly in those with infantile type and congenital heart defects. While the majority of patients achieve resolution, the extended timeline in surgical cases reflects the higher baseline severity and complexity, along with advanced vascular remodeling. 25% of persistent PH cases harbored pathogenic variants that may contribute to a biological "second hit" that is linked to therapy resistance. Further multicenter and prospective studies are warranted to expand on these findings.