Patients with D-TGA and atrial switch typically have normal growth and development, but have limited exercise capacity compared with their peers. Over time, chronic pressure overload of the systemic RV leads to RV systolic and diastolic dysfunction, which typically presents in the fourth to fifth decades of life as congestive heart failure. Furthermore, functional tricuspid regurgitation from RV dilation may exacerbate these symptoms.

Patients who have undergone the atrial switch are prone to arrhythmias, which affect 60% of patients by 20 years after atrial switch. Sinus node dysfunction is the most common cause of bradyarrhythmia presumably because of scarring related to the superior portion of the atrial redirection. Atrioventricular (AV) nodal dysfunction may also occur. Supraventricular tachyarrhythmias are very common, because of extensive intra-atrial scar.²

The intracardiac baffles may become obstructed or may develop baffle leaks. Obstruction of the SVC limb of the baffle mimics SVC syndrome with edema of the head and upper extremities. Obstruction of the IVC limb may result in hepatic congestion, abdominal bloating, early satiety, and lower extremity edema. Baffle leaks result in atrial-level shunting, typically “left-to-right” from the pulmonary venous atrium into the systemic venous atrium. As with all atrial-level shunts, this may increase the risk of paradoxical embolism. Large baffle leaks may cause volume loading of the subpulmonic LV and heart failure symptoms.

Suspected arrhythmias should be evaluated with ambulatory electrocardiographic (ECG) monitoring. Transthoracic echocardiography (TTE) is useful to monitor valve and ventricular function and for surveillance of outflow tract obstruction, baffle leaks, or baffle stenosis. Transesophageal echocardiography (TEE) is superior to TTE for visualization of the baffles. Cardiac magnetic resonance imaging (CMRI) is an excellent tool for evaluation of RV size and function, baffle stenoses, and baffle leaks, particularly when combined with four-dimensional (4D) flow imaging. Computed tomography (CT) scans are a reasonable
alternative to CMRI, particularly if patients have implantable devices that are not compatible with CMRI. CT scans have high spatial resolution and are useful in identifying baffle stenoses.

Bradyarrhythmias necessitate permanent pacemaker in a median of 10% of patients.² Atrial arrhythmias after atrial switch can be malignant and predispose to sudden cardiac death.² An upfront rhythm control strategy, with antiarrhythmic therapy and/or catheter ablation, is hence preferred.³

Pharmacotherapy for systemic RV dysfunction currently lacks robust evidence and is not recommended by current guidelines,³ though β-blockers may offer protection against appropriate implantable cardioverter-defibrillator (ICD) shocks,⁴ and angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) should be considered for patients with diabetes or hypertension.

Percutaneous baffle interventions such as angioplasty, stenting, and plugging of leaks have periprocedural success rates of 90% to 95%⁵ and are preferred over surgical reoperation, where mortality can be as high as 26%.⁶

The most common complications after arterial switch operation are supravalvar PA stenosis from anastomotic scarring or stretching of the branch PAs, and progressive dilation of the neoaorta with consequent neoaortic valvular regurgitation. Neoaortic stenosis and AV block are less common.⁷,⁸ Ostial stenosis from the reimplanted coronary buttons may occur, and symptoms of angina, heart failure, or ventricular arrhythmias should prompt evaluation of the coronary arteries.⁷

TTE, CMRI, and cardiac CT can define great vessel dilation/stenosis as well as ventricular and valvular function. Exercise testing, cardiac CT, and invasive angiography are useful if coronary stenosis is suspected. Baseline imaging of the coronary arteries as adult is recommended.¹

Transcatheter balloon angioplasty and stenting is preferred over surgery for treating PA stenosis.⁷,⁸ Severe neoaortic valvular regurgitation is usually accompanied by significant neoaortic dilation and is managed with surgical valve replacement with concomitant aortic grafting.⁸ Coronary stenting and aortocoronary bypass grafting are management options for coronary artery stenosis.³,⁷

The mean life span of a RV-PA conduit in an adult is 10 to 15 years, with significant stenosis or regurgitation necessitating reoperation in 80% of patients by 20 years.³,⁹ Obstruction and leak of the LV-aorta baffle can cause heart failure, whereas arrhythmias occur because of ventricular scarring from surgery. Conduit endocarditis can occur, especially in bovine xenografts.¹⁰

Although TTE is valuable to evaluate biventricular function and pressures, the RV-PA conduit is often not well seen with this imaging modality. CMRI or cardiac CT is useful for conduit visualization and accurate quantification of RV size and function, which helps inform the decision to intervene on the conduit.

Conduit degeneration is preferably managed via transcatheter pulmonary valve replacement with concomitant conduit angioplasty and stenting if indicated, though the conduit may need surgical replacement if this approach fails.³,⁹ Percutaneous approaches are also preferred for baffle complications. Arrhythmias may necessitate pharmacotherapy, pacemakers, ICDs, and/or catheter ablation.

Patients are usually not cyanotic and are sometimes diagnosed in adulthood, either incidentally or for evaluation of a murmur or heart failure symptoms. Systemic RV failure develops
in up to 67% of patients by age 40, whereas over 50% develop significant tricuspid regurgitation because of Ebstein-like malformation of the tricuspid valve or functional tricuspid regurgitation.¹¹ Also, abnormal anterior displacement of the AV node confers a 2% annual risk of premature AV block,¹² which may be the presenting symptom leading to the diagnosis of cc-TGA in adulthood.

TTE establishes the diagnosis of cc-TGA in adults and delineates ventricular and valvular function. CMRI is useful for quantification of RV (systemic ventricle) function, whereas ambulatory ECG monitors may reveal transient AV block in symptomatic patients.

Common interventions in cc-TGA patients include pacemaker implantation (45% of patients with cc-TGA) and surgical tricuspid valve replacement for tricuspid regurgitation.³,¹¹ Valve replacement for tricuspid regurgitation has better outcomes than surgical repair, but must be done before RV (systemic ventricle) failure develops.¹³ Transcatheter technologies for AV valve regurgitation may be useful in TGA patients, particularly if surgical risk is prohibitive because of systemic RV dysfunction.¹⁴ Transplantation may be considered for severe RV systolic and/or diastolic failure refractory to medical management.

Patients with severe systemic RV dysfunction may benefit from ICD therapy for primary sudden cardiac death prevention, though current selection criteria lack robust evidence.¹⁵ Advances in multimodality imaging for procedural planning and guidance can improve success rates of these interventions.

In CHD, the goal of surgical repair is to establish a biventricular circulation whenever possible, with two circuits in series: one atrium and ventricle receives systemic venous return and pumps it forward to the pulmonary circulation, whereas a second atrium and ventricle receives pulmonary venous return and pumps it forward to the systemic circulation. In some congenital heart defects, the cardiac anatomy prohibits separation of the systemic and venous circulations. For example, in mitral atresia with a hypoplastic LV, or tricuspid or pulmonary atresia with a hypoplastic RV, the hypoplastic ventricle is too small to accommodate normal cardiac output, and attempting to partition the ventricles would result in severely elevated filling pressures within the hypoplastic ventricle and poor cardiac output. In other cases, such as unbalanced AV canal, the AV subvalvar apparatus may straddle the ventricular septum and prevent partitioning of the AV valve into left and right orifices. In such patients, the Fontan procedure allows for separation of the systemic venous and arterial circulations by redirecting flow from the systemic veins directly to the PA. In the absence of a subpulmonary ventricle, blood is propelled forward through the pulmonary circulation by negative intrathoracic pressure with inspiration. The pulmonary venous flow then returns to the dominant ventricle, which serves as the systemic ventricle pumping oxygenated blood to the aorta.