The classic definition of “congenitally corrected transposition of the great arteries” (CC-TGA) derived from the observation that the effects of such transposition are “corrected” by the congenital inversion of the two ventricles, with the two circulatory pathways “physiologically” in series despite morphologic derangements. Basically the same as “two negative gives a positive,” this condition comprises less than 1 percent of all congenital heart defects.

CC-TGA is created by a “double discordance” between the atria and ventricles on the one hand [atrioventricular (AV) discordance], and the ventricles and the great vessels on the other (ventriculoarterial discordance). Thus, the right atrium is connected through a mitral valve to a morphologic left ventricle (LV), from which the pulmonary artery (PA) arises; conversely, the left atrium is connected via a tricuspid valve (TV) to the anatomic right ventricle (RV), from which the aorta arises. To avoid confusion throughout this chapter, we will try to avoid the use of the terms “left ventricle” and “right ventricle,” calling them either morphologically left or subpulmonary ventricle, and morphologically right or subaortic ventricle.

The AV and ventriculoarterial sequence is most frequently associated with a visceroatrial “situs solitus,” in which the ventricular loop (see Chapter 59) is located on the left side (L-loop). The concept of “loop” and “handedness” is simplified in Fig. 75-1 by imagining a hand positioned on the convexity of the septum, with the thumb through the AV valve and the index finger through the ventriculoarterial connection. The hand that can be placed with the palm following the convexity of the septum defines the loop. In normally connected hearts, the right hand will be positioned on the septum, the index finger through the pulmonary valve, and the thumb through the TV (D-loop) (Fig. 75-1). L-loop is seen in CC-TGA, where the left hand is positioned on the septum and the thumb goes through the TV (morphology of the AV valve follows and defines that of the underlying ventricle) and the index through the aortic valve.

Rarely, CC-TGA can present with visceroatrial situs inversus, with a normal ventricular “loop” (D-loop). The segmental anatomy is then (I,d,d), that is atrial situs inversus, D-looped ventricles (normal), and D-transposed great arteries. This type of physiologically corrected transposition (sometimes called “mirror-image” form of (S,L,L) CC-TGA) is often accompanied by additional cardiac malformations such as pulmonary valve stenosis, hypoplastic ventricles and AV valves. Dextrocardia is often seen. Frequently, a single-ventricle approach is necessary in (I,d,d) hearts. This chapter will be dealing with the most common form of corrected transposition, namely (S,L,L) CC-TGA.

The cardiac apex in the most common form of CC-TGA is related to the peculiar position of the anatomic LV, and it is located in a more central position than normal (Fig. 75-2). This location exists even in situs inversus, where the cardiac apex is rotated on the right side and more centrally. Heterotaxy is not observed in CC-TGA.

In isolated CC-TGA, blood from inferior and superior venae cavae and from the coronary sinus drains into the right atrium and then through a bicuspid (mitral) AV orifice into the morphologic LV (physiologic RV, or subpulmonary ventricle). The pulmonary veins drain into the left atrium and blood is transported via the tricuspid AV orifice into the morphologic RV (physiologic LV, or subaortic ventricle). This ventricle pumps the blood into the aorta and therefore into the systemic and coronary circulation. Thus, in CC-TGA, the physiology of the circulation is normal. As a consequence, oxygen saturation within the heart chambers and in the great arteries is normal, even if the blood flows through “wrong” AV valves and ventricles. The PA is in the pathway of the unsaturated blood, while the aorta in the pathway of oxygenated blood. In these hearts one of the most important physiologic aspects that dominates the natural history of CC-TGA is the fact that the morphologic RV has to propel blood into the aorta against systemic resistance and high afterload.

Patients with CC-TGA are usually seen because of the additional lesions that are commonly associated. The most relevant associations are TV regurgitation (the systemic AV valve), often associated with varying degrees of Ebstein malformation of the tricuspid valve, ventricular septal defect (VSD), right ventricular outflow tract obstruction [RVOTO, typically pulmonary stenosis (PS) or atresia], malposition of the cardiac apex, and conduction defects (more frequently complete heart block). The clinical presentation of CC-TGA is dependent on the cumulative effect of associated lesions on pulmonary blood flow. Indication for surgery is also determined by the nature and severity of the associated cardiac defects.^2–4

As mentioned above, the most frequent form of “double discordance” occurs with situs solitus and L-loop of the ventricles. The course of the AV conduction tissue therefore differs from that in the normal heart with ventricular D-loop. Although the sinus node is normally located at the superior atriocaval junction, the AV conduction tissue is grossly abnormal. Because of its malalignment with the ventricular septum, the node fails to give rise to a penetrating bundle.^5–8

In the normal heart, the bundle of His runs in an inferoposterior position with respect to the membranous septum; in SLL CC-TGA, however, the bundle of His is located in an anterosuperior position and has a much longer course than normal. Such a condition poses the risk that the subject with CC-TGA will go on to develop complete AV block, either spontaneously or postoperatively. On the other hand, when CC-TGA presents with situs inversus (I,d,d segmental anatomy), the normal anatomic position of the RV (D-loop) allows the bundle of His to follow a normal course. Anderson and coworkers in 1973 first clarified the distribution of the conduction tissue is this anomaly (Fig. 75-3).^8–10

When CC-TGA is isolated (without associated cardiac defects) it can remain totally asymptomatic for life, and the diagnosis is often incidental. The electrocardiogram (ECG) is typical for the absence of a QRS transition complex in the precordial leads. The chest x-ray shows a midline cardiac position in the frontal view, with a linear left upper cardiac border due to the levoposition of the aorta.

The subxiphoid and apical four-chamber echocardiographic views allow identification of the sequential anatomy and visualization of associated ventricular perimembranous defects, valvar and subvalvar pulmonary obstruction, and TV morphology and function.

Cardiac catheterization and angiography and/or cardiac magnetic resonance complete the functional and structural assessment. The clinical presentation depends on the associated defects and pathophysiologic patterns.

In forms associated with a nonrestrictive VSD, pulmonary overcirculation with left-to-right shunting is observed, with elevated pulmonary blood flow (PBF) and various degrees of pulmonary hypertension. In such cases, the infant may present with active precordium, tachypnea, failure to thrive, and recurrent pulmonary infections.

When the VSD is associated with valvular and/or subvalvular PS, progressive cyanosis secondary to right-to-left shunting is seen.

In the isolated form, symptoms may be absent until the sixth or seventh decade of life, and the individual may have a near normal life expectancy. Onset of complete AV block or systemic AV valve incompetence with congestive heart failure is fairly frequent. However, in atrial situs inversus, because of the considerably higher prevalence of a normally positioned AV node, there is less likelihood of the spontaneous development complete heart block. When heart block develops, pacemaker implantation is of course necessary.

The surgical history of patient with double discordance can start either with palliative procedures and continue with intracardiac repair or begin with primary complete surgical correction.

Palliative Procedures

Depending on the initial anatomy (RVOTO, VSD, etc), and on the clinical presentation, many patients first undergo an initial palliative operation such as a systemic to pulmonary shunt, PA band, or even stage I Norwood. If they are not slated for single-ventricle pathway, they receive an anatomic or physiologic intracardiac repair after one or more surgical palliative operations (see below). Correct timing of surgery in such patients is another determining factor of early and late outcome, with the goal of preserving biventricular systolic and diastolic function. If any surgical palliation should be needed before repair, it should aim at obtaining a Q_p/Q_s of approximately 1:1.¹¹

In general terms, two major categories can be identified according to the pattern of PBF: (1) those with restrictive PBF and (2) those with unrestricted PBF. Patients with restrictive PBF, depending on the severity of PS, might require surgical palliation at different ages. A systemic-to-PA shunt should be preferred in patients younger than 4 to 6 months. In older patients, a bidirectional superior cavopulmonary anastomosis (Glenn shunt, see Chapter 62) should be the palliation of choice, allowing growth and protection of the pulmonary vascular bed. A bidirectional cavopulmonary anastomosis brings the advantage of dramatically reducing the volume load of the RV to normal values and diverting desaturated blood directly to the lungs, thus increasing effective pulmonary blood flow. Patients with unrestricted PBF have a rather usual clinical presentation, with congestive heart failure during the first months of life and failure to thrive: These are babies with a Q_p/Q_s often greater than 2:1. This represents a significant volume overload, which, in the long run, may impair ventricular function. All these findings indicate the need for surgical intervention early in life. If the great arteries do not show severe discrepancy in size (aorta not too small compared with PA) PA banding (PAB) may represent a good surgical option.