2025 SELECT ABSTRACTS FROM THE 18^th ANNUAL INTERNATIONAL CONFERENCE ON NEONATAL AND CHILDHOOD PULMONARY VASCULAR DISEASE

Chronic Thromboembolic Pulmonary Hypertension (CTEPH) is a rare cause of Pulmonary Hypertension (PH) in children.There is limited data on long-term outcomes following pulmonary endarterectomy (PEA) in this demographic.We conducted a retrospective analysis of the United Kingdom National Registry for Paediatric Pulmonary Hypertension (2001-2024) identifying 5 children with CTEPH diagnosed through standardised criteria including cardiac catheterisation and cross-sectional imaging.Among our cohort (60% female, mean age 12 years, range 4-14 years), 80% had identifiable thromboembolic risk factors, predominantly indwelling lines (60%) and thrombophillic conditions (20%).Follow-up duration ranged from 1-5years, with 2 patients followed up for over 4 years.At diagnosis, patients demonstrated reduced exercise capacity (mean six-minute walking distance 361m, range 299-349m) and had echocardiographic evidence of PH (mean TR Vmax 3.67m/s).All patients underwent Cardiac MRI, demonstrating right ventricular (RV) enlargement (mean RV end diastolic volume 109.6ml/m 2 ) and mild-moderate RV systolic impairment (mean RVEF 39.2%).Invasive haemodynamic assessment confirmed significant pressure elevation with mean mPAP 55.6mmHg (range 29-68mmHg) and mean pulmonary vascular resistance index 12.2 WU.m 2 (range 5-21WU.m2).Following PEA (100%), improvements were observed in six-minute walking distance (+45m, p=0.0276),RV volumes (-30ml/m 2 , p=0.0113), RV systolic function (+14.8%,p=0.0031), and haemodynamics (mPAP -28.6mmHg p=0.010;PVRI -11.4WU.m 2 , p=0.0172).However normalisation of pulmonary haemodynamics to mPAP < 20mmHg was achieved in only 1 patient (20%).In this paediatric CTEPH cohort, thromboembolic risk factors were highly prevalent.While PEA resulted in significant haemodynamic and functional improvement, complete normalization of pulmonary haemodynamics was uncommon.This suggests residual PH following PEA may be more frequent in paediatric CTEPH compared to adult cohorts.Longitudinal follow-up into adulthood is important to determine long term outcomes in this population.