Patients with AVSD are at risk of LVOT obstruc- tion because of the abnormal anatomy of the LVOT. Surgical resection of LVOT obstruction in association with AVSD is reasonable when there is moderate-to-severe obstruction or less obstruc- tion but associated HF or mitral regurgitation or AR. In isolated subAS studies, worse outcomes were revealed in patients with maximum gradi- ents 50 mm Hg or with gradients <50 mm Hg in association with symptoms of HF.S4.1.4-14 S4.1.4-17 Importantly the LVOT obstruction in AVSD may not be discrete and, therefore, surgical repair may be more complex. When evaluating patients with tunnel-like or complex LVOT obstruction, the peak Doppler gradients and Bernoulli equa- tion may inaccurately reflect the severity of ob- struction, and cardiac catheterization may be needed. 5. Patients with AVSD, particularly those with Down syndrome, are at high risk of developing pulmo- nary vascular disease resulting in Eisenmenger For those who continue to have a net left-to-right shunt despite elevated PA pressures, closure of the defect may prevent exacerbation of PAH. This is an unusual circum- stance and decision-making requires collabora- tion with ACHD and pulmonary hypertension providers. 6. Morbidity and mortality are prohibitively high when surgical repair is attempted in patients with open shunts such as AVSD when Eisenmenger syndrome is present.S4.1.4-5,S4.1.4-6 4.1.5. Patent Ductus Arteriosus Recommendations for Patent Ductus Arteriosus Referenced studies that support recommendations are summarized in Online Data Supplement 30. COR LOE Recommendations Diagnostic I C-EO Measurement of oxygen saturation should be performed in feet and both hands in adults with a PDA to assess for the presence of right-to-left shunting. IIa C-EO In addition to the standard diagnostic tools, cardiac catheterization can be useful in patients with PDA and suspected pulmonary hypertension (Section 3.5). 