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Anatomically Corrected Malposition of the Great Arteries
Definition
Anatomically corrected malposition is an anomaly in the position of the great arteries but not in cardiac connections. Thus, there is atrioventricular (AV) and ventriculoarterial (VA) concordant connection as in the normal heart, but the aortic origin lies to the left and usually anterior to the pulmonary trunk origin when there is situs solitus (Van Praagh's S,D,L; see “Symbolic Convention of Van Praagh” in Chapter 1 ) and to the right of the pulmonary trunk origin when there is situs inversus (I,L,D). The circulatory pathways remain in series.
Historical Note
Anatomically corrected malposition of the great arteries was first reported by Theveanin in 1895 (cited by Van Praagh and Van Praagh ) and was first termed anatomically corrected transposition of the great arteries by Harris and Farber in 1939. It is possible similar cases were described earlier under a variety of names. This confusion is exemplified by the case of Raghib and colleagues, described in 1966 with the phrase isolated bulbar inversion in corrected transposition . The Van Praaghs, who had doubted its existence, described three cases in 1967 using the term anatomically corrected transposition of the great arteries . At that time, Abbott's influential 1927 definition of transposition, according to which any abnormality in the relationship of the great arteries or between the great arteries and the ventricles was called transposition, was still accepted. This confusion was clarified when Van Praagh and colleagues redefined transposition in 1971 as the origin of the aorta from the morphologically right ventricle and the pulmonary trunk from the morphologically left ventricle (i.e., VA discordant connection) and proposed that other positional and connection abnormalities be included in the definition of malposition . The present condition was thus renamed anatomically corrected malposition of the great arteries .
Morphology and Morphogenesis
Morphology
When there is situs solitus of the atria, usually the right atrium is connected to the right ventricle 1 (D-loop), which lies to the right, and the left atrium is connected to the left ventricle, which lies to the left (S,D,L arrangement). Structure of the sinus portions of both ventricles is normal. However, although the aorta arises from the left ventricle and the pulmonary trunk from the right ventricle, there are abnormalities of the outlet, or infundibulum, in both ventricles. The left ventricle probably always exhibits a subaortic conus (infundibulum) with a well-formed conal septum, and muscle exists between aortic and mitral valve anuli. Aortic origin is accordingly displaced superiorly and anteriorly. The right ventricle may also have an infundibulum, but it may be less well developed than normal and in some cases is absent. In the latter case, there is pulmonary-tricuspid fibrous continuity. The aorta lies to the left and usually anterior to the pulmonary trunk, and both arteries are parallel. Rarely, there may be situs inversus with an I,L,D arrangement.
1 The adjectives left and right used to modify atrium or ventricle mean morphologically left or right. Position of the chamber is referred to as right-sided or left-sided .
Hearts with similar types of infundibular development but AV discordant connection, although originally included in this category by both the Van Praaghs and Anderson and colleagues, are not called anatomically corrected malposition in this text but are included as variants of isolated ventricular inversion (see Section II of Chapter 55 ).
Morphogenesis
Van Praagh argues that all forms of abnormally related great arteries relate to maldevelopment of the subsemilunar conal free walls—an abnormality of what he terms the embryonic aortic switch procedure . In anatomically corrected malposition of the great arteries, the ventricles have looped in one direction, which the great arteries have twisted in the opposite direction, carrying with them the subsemilunar conal free wall. Although the great arteries are normally related (aligned), Van Praagh notes that the VA connection is very abnormal because of the abnormality in subsemilunar conal resorption.
Associated Anomalies
All reported cases of anatomically corrected malposition have been associated with other congenital cardiac anomalies. A large ventricular septal defect (VSD) is commonly present, usually conoventricular but occasionally elsewhere, as would be anticipated with abnormal subarterial conal connections to the ventricles; VSDs may be multiple. When the VSD is subpulmonary, the pulmonary trunk may override onto the left ventricle such that the condition merges with double outlet left ventricle (see Morphology in Chapter 54 ). When the VSD is subaortic, the aorta may override onto the right ventricle such that the condition merges with double outlet right ventricle (see Morphology in Chapter 53 ). In a recent report of six cases from one institution, VSD was absent in three, although a literature review of 53 cases reported absence of VSD in only three.
Pulmonary stenosis is usual, often infundibular in association with the subpulmonary conus, but occasionally valvar. Subaortic stenosis may occur from narrowing of the muscular subaortic conus. Tricuspid atresia or tricuspid valve hypoplasia has been noted in half the reported cases, accompanied by right ventricular hypoplasia. A right aortic arch is common, as is leftward juxtaposition of the atrial appendages and dextrocardia.
Aortic coarctation and arch hypoplasia has been reported in five cases. Two of these had associated severe subaortic stenosis and left ventricular hypoplasia, and three had no physiologic left ventricular outflow tract obstruction and a normally developed left ventricle.
Clinical Features And Diagnostic Criteria
Clinical features depend on associated anomalies such as VSD or pulmonary stenosis. Correct diagnosis may first be suspected from the characteristic appearance of L-malposition in the chest radiograph ( Fig. 57-1 ). Two-dimensional echocardiography usually establishes the diagnosis, confirming abnormalities of ventricular outflow tracts, concordant AV and VA connections, situs, positions of cardiac chambers and great vessels, and associated intracardiac defects. Additional studies such as cineangiography ( Fig. 57-2 ), magnetic resonance imaging ( Fig. 57-3 ), or computed tomography ( Fig. 57-4 ) are confirmatory or diagnostic if echocardiography fails to fully characterize the lesion. Occasionally, correct diagnosis is made only at operation. The diagnosis may remain ambiguous when there is a conoventricular VSD and one of the great arteries is overriding.
Possible diagnoses other than anatomically corrected malposition in patients with atrial situs solitus and L-malposition of the aorta include complete transposition with L-malposition (see Chapter 52 ), AV concordant connection with double outlet right ventricle and L-malposition (see Chapter 53 ), AV concordant connection with double outlet left ventricle (see Chapter 54 ), congenitally corrected transposition of the great arteries (see Chapter 55 ), AV discordant connection with double outlet right or left ventricle (see Chapter 55 ), and several forms of univentricular AV connection, most commonly those associated with double inlet left ventricle, rudimentary left-sided right ventricle, and VA discordant connection (see Chapter 56 ).
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