Although left-to-right shunting was the initial research model of triggered PAH, pulmonary hypertension in patients with ACHD can be caused by, or associated with, any of the factors described above. Effective therapies may be spe- cific to the primary mechanism of pulmonary hyperten- sion in a given patient, so patients with CHD should have thorough investigation for all potential contributing eti- ologies to pulmonary hypertension that may require spe- cific therapy if best clinical outcomes are to be achieved. Adverse effects of pulmonary hypertension therapies in patients with ACHD with pulmonary hypertension may differ from those noted in other patients, because of concomitant multiorgan and vascular effects from long- standing congenital heart and vascular disease. Shunt-related PAH in patients with ACHD can de- velop in the pre- or perioperative period but also may develop years to decades after closure of defects. Mechanisms for development of PAH may include ge- netic factors and environmental exposures. Severity of PAH may range from incidentally noted mild pressure and resistance elevation to profound systemic or supra- systemic levels of PA pressure and pulmonary vascular resistance. If an anatomic defect that allows shunting is present, shunt reversal and cyanosis may develop as pulmonary resistance rises above systemic resistance (ie, Eisenmenger syndrome). See Section 3.3 for recommendations on who should perform surgeries, cardiac catheterization, and other procedures in these patients; Section 3.4 for rec- ommendations on diagnostic evaluation; and Table 33 for routine testing and follow-up intervals. Recommendation-Specific Supportive Text 1. Patients with ACHD with pulmonary hyperten- sion, particularly PAH, have a poorer prognosis than do patients with ACHD with similar histo- ries and anatomic abnormalities who do not have pulmonary hypertension. 