690 GB Kim •Pulmonary hypertension in infants with bronchopulmonary dysplasia limitations, is recommended as the main screening tool for PH in the BPD patients in many centers. In Seoul National University Children’s Hospital, we conduct monthly echocardiographic examination of the preterm infants with BPD in the NICU to screen for PH and of the follow-up patients with moderate to severe BPD in the cardiologic division after discharge from the hospital even though the patients did not have PH in the NICU. A report from Boston Children’s Hospital recommended that echocardiographic screening for PH should be conducted in preterm infants with BPD who meet any of the following criteria: (1) extreme prematurity (gestational age at birth of ≤25 weeks or birth weight of ≤600 g), (2) small for gestational age, (3) requirement for prolonged mechanical ventilatory support (duration depends on age), (4) oxygen requirement out of proportion to the severity of lung disease, or (5) persistent poor growth despite adequate caloric intake8). Estimated systolic pulmonary artery pressure can be derived from the tricuspid regurgitant (TR) jet flow, which if present, is measured by echocardiography by using the modified Bernoulli equation [systolic pulmonary artery pressure=4×(TR peak jet velocity)2+right atrial pressure]18). However, estimation of systolic pulmonary artery pressure may not be possible in all the patients. A recent study revealed that estimation of systolic pulmonary artery pressure was possible in only 61% of the young children with PH19). In the absence of TR jet flow, other qualitative echocardiographic findings, including right atrial enlargement, RV hypertrophy and/or dilation, septal flattening, increased RV wall thickness, dilated main pulmonary artery, increased velocity of pulmonary valve regurgitation, and a short acceleration time of RV ejection into the pulmonary artery, can be used to detect PH; however, the sensitivity of these findings is questionable10, 12). Among these qualitative echocardiographic findings, interventricular septal configuration is very useful for evaluating the severity of PH in the BPD patients. Systolic RV pressure can be graded according to the position of the interventricular septum: (1) <50% of the systemic systolic pressure if the interventricular septum appears round at end-systole, (2) 50-100% of the systemic systolic pressure if the septum shows flattening at end-systole, and (3) ≥100% of the systemic systolic pressure if the interventricular septum bows into the left ventricle at end-systole (Fig. 1)20). Another useful parameter for the evaluation of PH severity is biochemical marker. B-type natriuretic peptide (BNP) and N- terminal proBNP (NT-proBNP) are representatives of biomarker and showed good positive correlations with mean pulmonary artery pressure, pulmonary vascular resistance and mean right atrial pressure. BNP also showed good negative correlation with RV ejection fraction21) even though normal value of children’s age is not known well until now through extensive studies22). We have to be alert if the BPD patients with PH show high serum level or increasing level of BNP or NT-proBNP, because these parameters reflect disease status including severity. In some centers, cardiac catheterization is generally recom- mended to evaluate the severity of PH, to rule out unsuspected associated anatomic cardiac diseases, to define the presence of systemic-to-pulmonary collateral vessels, pulmonary venous obstruction, or left heart dysfunction, and to assess pulmonary vascular reactivity in patients who fail to respond to oxygen treatment alone12). Fig. 1. Interventricular septal configuration (IVS) for predicting the severity of pulmonary hypertension. (A), round IVS at end-systole, systolic right ventricular (RV) pressure is estimated to be less than 50% of the systemic systolic pressure. (B), flat IVS at end-systole, systolic RV pressure is estimated to be between 50 and 100% of the systemic systolic pressure. (C), IVS bowed into the left ventricle (LV) at end- systole, systolic RV pressure is estimated to be greater than 100% of the systemic systolic pressure.