For patients with significant LV or RV dysfunction, pulmonary valve replacement may not be tolerated or sufficient; therefore, evalua- tion by ACHD cardiologists and HF cardiologists is appropriate to decide appropriate course of action, particularly in deciding if a patient may be appropriate for mechanical circulatory support or heart transplant. Table 27. TOF: 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 Holter monitor As needed As needed 12 24 12 24 *See Tables 3 and 4 for details on the ACHD AP classification system. 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 right ventricular size and function, pulmonary valve function, pulmonary artery anatomy and left heart abnormalities. Baseline study is recommended with periodic follow-up CMR, with frequency of repeat imaging determined by anatomic and physiological findings. CCT may be used if CMR is not feasible and to evaluate origin and course of the coronary arteries, and cross-sectional imaging status post-stent therapy. If cardiac CCT is used instead of CMR imaging, the frequency should be weighed against radiation exposure. 6-minute walk 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; ECG, electrocardiogram; TOF, tetralogy of Fallot; and TTE, transthoracic echocardiogram. CLINICAL STATEMENTS AND GUIDELINES 6. There are data that indicate that pulmonary valve replacement performed prior to specific ventric- ular size is associated with normalization of RV volumes. However, it is not yet evident that this correlates with an improvement in mortality. 