Baffle leaks should be sought because they are common and may alter treatment considerations such as thromboembolic concerns or options for closure. Echocardiography using agitated saline con- trast is a sensitive method for this assessment. It is unnecessary on every study, but interval assess- ment of baffle leak is appropriate, especially in circumstances where therapy may be altered by the result. In some patients, injection in upper and lower extremities may be necessary to eval- uate superior and/or inferior systemic venous baffle leak, respectively, because a negative study from an injection in upper extremity may not exclude an inferior systemic venous baffle leak. Assessment for baffle leak may involve use of TTE with agitated saline contrast, TEE, intracardiac echocardiography, or angiography.S4.4.1.1-1 4. Sustained intra-atrial reentrant tachycardia is a po- tential cause of SCD in adults who have undergone atrial switch and puts patients at risk for throm- boembolism. Treatment to maintain sinus rhythm may involve antiarrhythmic medication or catheter ablation. Although there are not data demonstrat- ing that maintenance of sinus rhythm prevents SCD, there is evidence that atrial arrhythmias preceded or coexisted with VT in 50% of cases, suggesting that atrial arrhythmias are a common trigger for ventricular arrhythmias.S4.4.1.1-2,S4.4.1.1-11 Table 29. d-TGA With Atrial 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) Pulse oximetry 12 12 Each visit Each visit *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 ventricular size and function, systemic and venous baffle obstruction and leaks, and valvular function. 