Morbidity and mortality are high when closure of a shunt is attempted in patients with Eisenmenger physiology with elevated pulmonary pressure and net right-to-left shunting.S4.1.5-5 Table 16. PDA: Routine Follow-Up and Testing Intervals Frequency of Routine Follow-Up and Testing Physiological Stage A* (mo) Physiological Stage B* (mo) Physiological Stage C* (mo) Physiological Stage D* (mo) Pulse oximetry As needed As needed Each visit Each visit Exercise test As needed As needed 12 24 6 12 *See Tables 3 and 4 for details on the ACHD AP classification system. Upper and lower extremity. 6-minute walk test or CPET, depending on the clinical indication. ACHD indicates adult congenital heart disease; ECG, electrocardiogram; CPET, cardiopulmonary exercise test; PDA, patent ductus arteriosus; and TTE, transthoracic echocardiogram. CLINICAL STATEMENTS AND GUIDELINES 4.2. Left-Sided Obstructive Lesions 4.2.1. Cor Triatriatum Recommendations for Cor Triatriatum Referenced studies that support recommendations are summarized in Online Data Supplement 31. COR LOE Recommendations Diagnostic I B-NR Adults presenting with cor triatriatum sinister should be evaluated for other congenital abnormalities, particularly ASD, VSD, and anomalous pulmonary venous connection.S4.2.1-1 IIa B-NR In adults with prior repair of cor triatriatum sinister and recurrent symptoms, it is reasonable to evaluate for pulmonary vein Therapeutic I B-NR Surgical repair is indicated for adults with cor triatriatum sinister for symptoms attributable to the obstruction or a substantial gradient across the membraneS4.2.1-3 Synopsis Cor triatriatum occurs when a membrane divides either the left atrium (sinister), or right atrium (dexter). Cor tria- triatum sinister is usually associated with other congen- ital malformations, specifically ASD, VSD, or anomalous pulmonary venous connection (partial or total).S4.2.1-1 The left atrial appendage is invariably in the same chamber as the mitral valve, separated from the pulmo- nary veins by the membrane. 