Congenitally corrected transposition of the great arteries

Anatomic considerations

Transposition of the great arteries is characterized by chambers that are joined concordantly at the atrioventricular junction, but discordantly at the ventriculo-great arterial junction ventricles (see Chapter 24 ). The pulmonary artery arises from a morphologic left ventricle, and the aorta arises from a morphologic right ventricle (RV). The circulations are in parallel rather than in series. Congenitally corrected transposition is characterized by chambers that are joined discordantly at the atrioventricular junction and ventricles that are joined discordantly at the ventriculo-great arterial junction–atrioventricular alignments and ventriculoarterial alignments are both discordant ( Figs. 6.1 and 6.2 ). ^, The double discordance– atrioventricular and ventriculoarterial– physiologically corrects the discordance intrinsic to each (see Fig. 6.1 ). Blood from a morphologic right atrium reaches the pulmonary artery by traversing a morphologic mitral valve and a morphologic left ventricle, and blood from a morphologic left atrium reaches the aorta by traversing a morphologic tricuspid valve and a morphologic RV (see Figs. 6.1 and 6.3 ). ^, The terms atrioventricular discordance, l-transposition, ventricular inversion, and congenitally corrected transposition are used interchangeably. Atrioventricular discordance requires the presence of two morphologically distinct atria and two morphologically distinct ventricles. Hearts in which two morphologically distinct atria are aligned with one ventricle (univentricular atrioventricular connection) are the subject of Chapter 23 .

The terms used in this chapter were defined in Chapter 3 but are repeated here for the reader’s convenience.

• Transposition: Discordant origin of the arterial trunks from the ventricular mass. The aorta arises discordantly from a morphologic RV and the pulmonary trunk arises discordantly from a morphologic left ventricle. The pulmonary circulation and the systemic circulations are in parallel.

• Congenitally corrected transposition: A morphologic right atrium is discordantly aligned with a morphologic left ventricle from which the pulmonary artery arises, and a morphologic left atrium is discordantly aligned with a morphologic RV from which the aorta arises (see Figs. 6.1 , 6.3 and 6.4 ). Systemic venous blood from the right atrium finds its way into the pulmonary artery, and pulmonary venous blood from the left atrium finds its way into the aorta, so the circulation is physiologically corrected. The pulmonary circulation and the systemic circulations are in series.

  

• Ventricular inversion refers to atrioventricular discordance with ventriculoarterial concordance. A morphologic right atrium is aligned with a morphologic left ventricle that gives rise to the aorta, and a morphologic left atrium is aligned with a morphologic right ventricle that gives rise to the pulmonary trunk. ^,

• l-Transposition: An l-loop in situs solitus . The sinus or inflow portion of the morphologic RV is to the left of the morphologic left ventricle.

• Inversion: Reversal of position but not mirror image . Ventricular inversion refers to a morphologic left ventricle in the right side of the heart, and a morphologic RV in the left side of the heart. Morphologic tricuspid and mitral valves are concordant with morphologic right and left ventricles, so inversion of the ventricles implies inversion of the atrioventricular valves. Isolated infundibuloarterial inversion is a rare anomaly in which the infundibulum and great arteries are inverted, but the atria and ventricles are not inverted. The inverted pulmonary trunk and its subpulmonary infundibulum originate from the morphologic left ventricle, and the inverted aorta originates from a morphologic RV, so the physiology of the circulation is analogous to complete transposition of the great arteries (see Chapter 24 ).

• Chamber designations: Right atrium and left atrium, and RV and left ventricle refer to anatomic (morphologic) characteristics, not to position.

• The great arteries: The ascending aorta and pulmonary trunk are defined by their ventricle of origin and by their lateral and anteroposterior spatial relationships.

• D loop: Refers to the normal rightward (dextro = d) bend or loop in the developing straight heart tube of the embryo, and indicates that the sinus or inflow portion of the morphologic RV lies to the right of the morphologic left ventricle.

• L-Loop: Refers to a leftward (levo = l) bend or loop in the straight heart tube of the embryo, and indicates that the sinus or inflow portion of the morphologic RV lies to the left of the morphologic left ventricle.

• Concordant: Harmonious, appropriate.

• Discordant: Disharmonious, inappropriate.

• Discordant loop: An l-loop in situs solitus and a d-loop in situs inversus .

• Atrioventricular discordance: Alignment of a morphologic right atrium with a morphologic left ventricle, and alignment of a morphologic left atrium with a morphologic RV.

• Ventriculoarterial discordance: Origin of the pulmonary trunk from a morphologic left ventricle, and origin of the aorta from a morphologic RV.

• Criss-cross hearts: Described by Lev and Rowlatt in 1961 and so named by Anderson, Shinebourne, and Gerlis in 1974. In normal hearts, the atrioventricular connections (inflow tracts) are parallel to each other when viewed from the front. In criss-cross hearts, the atrioventricular connections are not parallel, but are angulated as much as 90 degrees. Criss-cross hearts result from abnormal rotation of the ventricular mass around its long axis, resulting in relationships that could not be inferred from the inflow tracts. There are several types of criss-cross hearts. Those with discordant atrioventricular alignments and concordant ventriculoarterial alignments are called isolated ventricular inversion (see earlier). The physiology of the circulation is analogous to complete transposition of the great arteries. Criss-cross hearts with ventricles that are in a superoinferior or upstairs-downstairs relationship reflect rotation of the ventricular mass along its horizontal axis. Criss-cross hearts and superoinferior ventricles may coexist or occur separately. Morphologic patterns in criss-cross hearts include deficiency of the subpulmonary infundibulum, subpulmonary stenosis, a subaortic infundibulum, a nonrestrictive ventricular septal defect, and visceroatrial situs solitus.

• Segmental approach: Analysis according to the heart’s three major developmental segments: (1) visceroatrial situs, (2) ventricular loop, and (3) conotruncus. The atrioventricular valves and the infundibulum are the two connecting cardiac segments.

The embryologic basis held responsible for atrioventricular discordance in congenitally corrected transposition resides in the l ventricular loop of the embryonic heart tube. When the heart tube bends to the left in situs solitus , the morphologic RV lies to the left of the morphologic left ventricle. The developing left atrium becomes aligned with the morphologic RV, and the developing right atrium becomes aligned with the morphologic left ventricle. Ventriculoarterial discordance has a less well-defined embryologic basis with one school of thought arguing that the developmental fault is in the infundibular segment of the embryonic heart tube, while the other school argues that the fault lies in the arterial segment of the embryonic heart tube.

Virtually all patients have coexisting cardiac malformations–ventricular septal defect, pulmonary stenosis, abnormalities of the left atrioventricular (AV) valve, and conduction defects. A ventricular septal defect is present in 78% of necropsy cases (see Fig. 6.3 ), is usually nonrestrictive perimembranous, and typically extends into the inlet and trabecular septum. The inlet septum is poorly aligned with the atrial septum, resulting in a malalignment gap that is sometimes filled by tissue from the membranous septum. Pulmonary stenosis or atresia occurs in 50% of cases and represents obstruction to outflow of the morphologic left ventricle ( Figs. 6.5 and 6.6 ). The stenosis is isolated in about 20% of cases and occurs with a ventricular septal defect in the remaining 80%. Fixed subpulmonary stenosis takes several forms: (1) a fibrous subpulmonary diaphragm attached to the mitral valve, analogous to fixed subaortic stenosis in hearts with noninverted ventricles, (2) an aneurysm or fibrous tissue tags that originate from the relatively large membranous septum, and (3) accessory mitral leaflet tissue. Subaortic stenosis (obstruction to outflow of the morphologic right ventricle ) is caused by anterior deviation of the infundibulum septum or by hypertrophied infundibular muscle bundles.

The coronary artery arrangement is an important morphological aspect of congenitally corrected transposition. Established convention proposes a means of relating the origins of the coronary arteries to the aortic sinuses from which they originate. The coronary arteries almost always arise from both, or one or the other, aortic sinuses that are adjacent to the pulmonary trunk, and are morphologically concordant with the ventricles (i.e., the right coronary artery perfuses the morphologic RV and the left coronary artery perfuses the morphologic left ventricle) ( Figs. 6.7 and 6.8 and see Chapter 29 ). ^, Coronary artery patterns have been shown to correlate with morphological aorto-pulmonary rotation. Epicardial distribution is a guide to ventricular inversion, because the course of the anterior descending artery establishes the location of the ventricular septum. Coronary artery abnormalities are common, especially a single coronary artery (see Chapter 29 ). There can also be an unexpected course of the coronary sinus with abnormal cardiac veins.

In congenitally corrected transposition of the great arteries, the anterior and leftward ascending aorta and the posterior and rightward pulmonary trunk are parallel and do not cross as in the normal heart (see Figs. 6.2–6.4 and 6.8 ). The aorta is either convex to the left or ascends vertically, but it is not border-forming on the right. A subaortic conus is responsible for the anterior and leftward position of the ascending aorta and the posterior and medial position of the pulmonary trunk. Anatomically corrected malposition refers to an anomaly in which the ascending aorta lies anterior and to the left of the pulmonary trunk in the presence of atrioventricular and ventriculoarterial concordance. ^,

Physiologic consequences

The physiologic anomalies associated with congenitally corrected transposition depend on the functional adequacy of a subaortic morphologic RV and on coexisting congenital malformations. ^{, ,} The thick-walled subaortic RV is concordant with a right coronary artery that is designed to perfuse a thin-walled, low-resistance RV. A normal subpulmonary RV is designed to serve the low-resistance pulmonary circulation, and its geometry remains unchanged when it is inverted to the subaortic position. Regional strain, twist, and radial wall motion in a subaortic RV differ considerably from a subaortic left ventricle. Global longitudinal systolic strain is significantly reduced in patients with a systemic RV, can be correlated with subpulmonary ventricular function, and appears to adversely impact outcomes.

An inverted subaortic RV has a high prevalence of myocardial perfusion defects and abnormalities of regional wall motion. A normal subpulmonary RV has a relatively high end diastolic volume, so normal stroke volumes are achieved (ejection fractions of 35% to 45%). ^, Ventricular septal defect, pulmonary stenosis, abnormalities of the left AV valve, and conduction defects have a considerable impact on the function of an inherently inadequate inverted RV. ^,

Abnormalities of the inverted left atrioventricular valve are present in over 90% of cases. The malformed valve usually functions normally in early life, but there is an age-related increase in regurgitation. The abnormalities resemble those of Ebstein’s anomaly of a right-sided tricuspid valve in hearts without ventricular inversion ( Fig. 6.9 ), ^{, ,} but the anterior leaflet of the inverted Ebstein valve is usually small and malformed, and the atrialized portion of the inverted RV is poorly developed. Left atrioventricular valve incompetence is not necessarily caused by an Ebstein-like malformation, and the valve is occasionally stenotic rather than incompetent ( Figs. 6.10 and 6.11 and see Chapter 11 ). Neonates with severe regurgitation of the inverted atrioventricular valve have an increased incidence of hypoplasia of the aortic arch, aortic atresia, and aortic coarctation. Function of the abnormal Ebstein-like malformation improve significantly after physiologic repair regardless of the occurrence of direct or indirect surgical intervention. Abnormalities of the right-sided inverted mitral valve have been reported in over half of necropsy specimens and consist of multiple cusps, multiple or compound papillary muscles, anomalous chordal attachments, and a cleft valve or a common valve.

The history

Male/female ratio is approximately 1.5:1. The occurrence of congenitally corrected transposition and complete transposition among first-degree relatives in different families is believed to represent monogenic transmission and implies a pathogenetic link between the two malformations. ^, Symptoms and clinical course depend chiefly on the presence and degree of coexisting malformations (see earlier), but longevity principally hinges on the vulnerability of the subaortic morphologic RV even when there are no coexisting malformations. Infant mortality is related to congestive heart failure. Survival is then relatively constant with an attrition rate of approximately 1% to 2% per year. Young patients with isolated congenitally corrected transposition are often overlooked because symptoms are absent and clinical signs are subtle. The diagnosis may come to light because of abnormalities in an x-ray ( Fig. 6.12 ) or an electrocardiogram ( Fig. 6.13 ), or because of symptomatic complete heart block ( Fig. 6.14 ) (see below). ^{, ,}

Survival to the sixth or seventh decade is infrequent, ^{, , ,} but two patients reached their eighth decade. ^, In isolated congenitally corrected transposition, failure of the subaortic RV is uncommon but not rare and may occur during pregnancy in previously asymptomatic women. Myocardial perfusion defects are prevalent. Angina pectoris is attributed to a supply-demand imbalance between a thick-walled systemic RV and its blood supply from a morphologic right coronary artery (see earlier).

The ventricular septal defect that accompanies congenitally corrected transposition is typically nonrestrictive with a clinical course analogous to a ventricular septal defect of analogous size in normally formed hearts (see Chapter 14 ). Pulmonary stenosis exerts a protective effect by curtailing excessive pulmonary blood flow. An inverted subpulmonary left ventricle adapts to the systemic systolic pressure incurred by a nonrestrictive ventricular septal defect. Isolated pulmonary stenosis varies from mild to severe and has a clinical course analogous to equivalent pulmonary stenosis in hearts without ventricular inversion (see Chapter 10 ).

Physical appearance

Retarded growth and development are reserved for infants with a large ventricular septal defect and congestive heart failure. Cyanosis and clubbing appear when pulmonary stenosis or pulmonary vascular disease reverses the shunt.