There are not data to support a specific aortic diam- eter beyond which the risk of dissection or rup- ture increases sufficiently to warrant prophylactic aortic replacement. 7. PS affects 5% to 15% of patients after arterial and may occur anywhere in the pulmonary tree including the pulmonary valve, main PA, and branch pulmo- nary arteries. Interventional decisions should be guided by a combination of symptoms and se- verity of stenosis. Table 30. d-TGA With Arterial Switch: 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) *See ACHD AP classification Table 4. Routine TTE may be unnecessary in a year when CMR imaging is performed unless clinical indications warrant otherwise. CMR may be indicated for assessment of neoaortic size, the origin and proximal course of the coronary arteries, branch pulmonary arteries, ventricular function and valvular function. Baseline study is recommended with periodic follow-up CMR, with frequency of repeat imaging determined by anatomic and physiological findings. CCT or catheterization once to establish knowledge of coronary artery anatomy and then as warranted by clinical condition. CCT may be used if CMR is not feasible and to evaluate coronary artery anatomy and cross-sectional imaging status-post stent therapy. If CCT is used instead of CMR imaging, the frequency should be weighed against radiation exposure. 6-minute exercise test or CPET, depending on clinical indication. ACHD indicates adult congenital heart disease; CCT, cardiac computed tomography; CMR, cardiovascular magnetic resonance imaging; CPET, cardiopulmonary exercise test; d-TGA, dextro-transposition of the great arteries; ECG, electrocardiogram; and TTE, transthoracic echocardiogram. CLINICAL STATEMENTS AND GUIDELINES 4.4.1.3. 