Anatomic and Physiologic Classification of Congenital Heart Disease
David S. Majdalany
Francois Marcotte
INTRODUCTION AND CLASSIFICATIONS
Congenital heart diseases (CHD) comprise abnormalities in the cardiac anatomy that disrupt venous drainage, septation, and sequences of the cardiac segments, as well as valvular and great vessel function. The first comprehensive volume on congenital cardiac defects dates back to 1866, when Thomas B. Peacock published Malformations of the Human Heart. Subsequently, Maude Abbott’s Atlas of Congenital Heart Disease correlated the clinical and pathologic findings of the congenital cardiac defects.1,2 After the successful ligation of a patent ductus arteriosus (PDA) by Robert E Gross, in 1938, and further advancement in surgical palliation and repair of CHD, it became important to understand the nature and effects of a cardiac defect. The advent of multimodality imaging techniques and cardiac catheterization facilitated the early and accurate diagnosis of CHD.3
A number of classifications of CHD have been proposed, most notably the segmental approach described by Stella Van Praagh and the sequential approach described by Robert Anderson.4,5 Both classifications aim at simplifying the complexity of CHD by dividing complexity to conquer, one level at time, in accordance with the cardiac segments identifiable during embryology. In the Van Praagh nomenclature, the sidedness (situs) of the atria, ventricles, and great vessels are determined separately; moreover, each congenital heart abnormality is assigned a 3-letter notation in parentheses. Atrial sidedness may be solitus (S), ambiguous (A), or inversus (I). Ventricular sidedness is either D-loop or solitus (S), L-loop or inversus (L), or ambiguous (X). The sidedness of the great vessels can either be solitus (S), inversus (I), D-transposition (D), L-transposition (L), or ambiguous (A). For example TGA (S,L,L) would correspond to congenitally corrected transposition of the great vessels. In this chapter, the Andersonian approach would be followed.
Normal cardiac anatomy consists of three segments: the atria, the ventricles, and the great vessels. The segments are divided into a right and a left component and arranged such that deoxygenated blood is routed to the lungs through the pulmonary artery (PA) and oxygenated blood is circulated systemically through the aorta.6 The atrioventricular valves join the atria and the ventricles, whereas the semilunar valves serve as the connectors between the ventricles and the great vessels. For proper diagnosis of CHD, it is essential to identify the distinguishing features of the right- and left-sided structures.
CARDIAC POSITION AND AXIS
The first step in cardiac anatomic assessment is defining the heart location in the chest as well as the direction of the cardiac apex (Figure 102.1A). Normally, the heart is positioned in the left chest, which is referred to as levoposition. It can be altered by other associated CHD and abnormalities in the neighboring (ie, spine, lung, or diaphragmatic) structures. Dextroposition refers to the rightward shift of the heart, whereas midline shift is referred to as mesoposition.
The orientation of the base to the apex of the heart is referred to as the axis (Figure 102.1B). Normally, the heart is oriented inferiorly and to the left, and this is referred to as levocardia (left-sided). Dextrocardia (right-sided) refers to the orientation of the heart inferiorly and to the right, whereas mesocardia refers to the vertical and midline orientation of the heart.7,8
MORPHOLOGY OF THE CARDIAC SEGMENTS
Atria
The atrium is a receiving chamber lying between the systemic or pulmonary veins and the atrioventricular valves. Each atrium has a venous component, a vestibule, an appendage, and an atrial septum. The morphologic right atrium (RA) is characterized by connections to the vena cava and coronary sinus, a large pyramidal atrial appendage, numerous pectinate muscles, the crista terminalis, which is a muscular band that separates the pectinate portion from the rest of the atrium, and the limbus of the fossa ovalis (Figure 102.2A). On the other hand, the morphologic left atrium (LA) features a hook-shaped appendage, which may be multilobed, smooth walls with limited pectinate muscles, the valve of the fossa ovalis, pulmonary venous drainage, and the lack of a crista terminalis.7,9
Atrioventricular Valves
The atrioventricular valves (AV) connect the atria and the ventricles and separate them electrically. These valves travel with their respective ventricle. Hence, the mitral valve connects to the morphologic left ventricle (LV), whereas the tricuspid valve connects to the morphologic right ventricle (RV). A
very important landmark that can help distinguish the AV is the crux of the heart, where the ring of the tricuspid valve is more apically attached to the ventricular septum relative to the mitral valve annulus. Moreover, the tricuspid valve is associated with septal chordal attachments and separation from the semilunar valve by collar of muscle—the infundibulum—in contrast to the direct continuity of the mitral valve with the semilunar valve.7
very important landmark that can help distinguish the AV is the crux of the heart, where the ring of the tricuspid valve is more apically attached to the ventricular septum relative to the mitral valve annulus. Moreover, the tricuspid valve is associated with septal chordal attachments and separation from the semilunar valve by collar of muscle—the infundibulum—in contrast to the direct continuity of the mitral valve with the semilunar valve.7
 FIGURE 102.1 (A) Location of the heart: left-sided, midline, or right-sided. Cardiac position is determined only by the overall location of the heart relative to the anatomic midline (top). It has no relationship to the internal organization of the cardiac structures. If the majority of the heart is to the left, then the heart is in levoposition (left-sided). Conversely, if most of the heart is to the right of the midline, then we refer to the patient as having dextroposition (right-sided). When the heart is located centrally in the chest, the patient is said to have meso- or midline position. (B) Direction of ventricular apex. Determination of the cardiac axis requires knowledge of the internal arrangement of the heart. It refers to the right to left direction of the so-called base-to-apex axis. The apex of the heart is the ventricular apex, and the base is at the great artery origin(s). The normal base-to-apex axis is directed inferiorly and to the left (bottom right). This orientation is referred to as levocardia (left-sided). When the heart is vertically oriented and in the midline, the apex is directly inferior to the base. This situation is illustrated by the central diagram and is referred to as mesocardiac (midline). The diagram on the bottom right illustrates the concept of dextrocardia (right-sided), where the cardiac apex is inferior and to the right relative to the base. A, atrium; A-I, anterior-inferior; L, left; P-S, posterior-superior; R, right; V, ventricle. (Modified with permission from Eidem BW, O’Leary PW, Cetta F. Echocardiography in Pediatric and Adult Congenital Heart Disease. 2nd ed. Philadelphia, PA: Wolters Kluwer; 2014. Figure 2.10.) |
Ventricles
Normal ventricles are characterized by three components: inlet, trabecular, and outlet regions, with no discrete boundaries between these parts. The inlet region includes the AV valve, its apparatus, and papillary muscles. The trabecular region extends from the papillary muscles to the apex, whereas the outlet portion leads toward the great vessels. The morphologic RV is typically crescent shaped and thin walled with coarse trabeculations and a moderator band. It is characterized by low septal insertion of the tricuspid valve with its septal chordal attachments and the presence of an infundibulum with resultant discontinuity between the tricuspid valve and the semilunar valve. The morphologic LV is typically circular and thick-walled in short axis. It features fine apical trabeculations, more basal (“higher”) septal insertion of the mitral valve, which lacks
septal chordal attachments, and continuity between the mitral and semilunar valves. In the setting of a hypoplastic ventricle where anatomic features can be difficult to discern or are absent, the rudimentary ventricle that is positioned along the anterosuperior surface of the heart is typically the morphologic RV, whereas a small chamber that occupies the postero-inferior aspect of the heart is typically the morphologic LV.7,9
septal chordal attachments, and continuity between the mitral and semilunar valves. In the setting of a hypoplastic ventricle where anatomic features can be difficult to discern or are absent, the rudimentary ventricle that is positioned along the anterosuperior surface of the heart is typically the morphologic RV, whereas a small chamber that occupies the postero-inferior aspect of the heart is typically the morphologic LV.7,9
 FIGURE 102.2 Cardiac-sidedness. (A) In situs solitus, the morphologic right and left atria are located in their proper side. The right and left atria are differentiated by their features. The right atrium has a large pyramidal atrial appendage, numerous pectinate muscles, the crista terminalis, and the limbus of the fossa ovalis. The morphologic LA features a hook-shaped appendage, smooth walls with limited pectinate muscles, the valve of the fossa ovalis, pulmonary venous drainage, and the lack of a crista terminalis. (B) Situs inversus is the mirror image of situs solitus, with the reversed position of the atria and lungs. CT, crista terminalis; LA, left atrium; LAA, left atrial appendage; PM, pectinate muscles; RA, right atrium; RAA, right atrial appendage; VFO, valve of the fossa ovalis. (Reprinted with permission from Allen HD, Driscoll DJ, Shaddy RE, et al. Moss & Adams’ Heart Disease in Infants, Children, and Adolescents: Including the Fetus and Young Adult. 8th ed. Philadelphia, PA: Wolters Kluwer Health/Lippincott Williams & Wilkins; 2012. Figure 2.3.) |
Great Arteries
As the semilunar valves are normally fairly identical and trileaflet, the aorta and the PA are recognized by the branching patterns. The aorta typically arches to the left, traveling over the left bronchus, and gives rise to the coronary arteries as well as the head, neck, and upper extremity arteries before becoming the descending thoracic aorta. In contrast, a right aortic arch crosses over the right bronchus and is typically associated with mirror-imaging of the brachiocephalic arterial branching. The PA is recognized by its bifurcation into right and left branch PAs.7,9
SEQUENTIAL SEGMENTAL ANALYSIS
Cardiac Sidedness
The first step is to determine the venous return and the atrial arrangement. In situs solitus, the morphologic right and left atria are located in their proper side (Figure 102.2A). The superior and inferior vena cavae empty into the RA, whereas the pulmonary veins drain into the LA. Moreover, the lungs and bronchi are concordant with the trilobed right lung and short bronchus on the right side and the bilobed lung and long bronchus on the left side. Situs inversus is the mirror image of situs solitus, with the reversed position of the atria and lungs (Figure 102.2B).6,7
In some cases, there is no laterality, and thus the situs is ambiguous, with both atria and lungs exhibiting atriopulmonary isomerism, and this may be associated with polysplenia and asplenia syndromes with disordered arrangement of the abdominal organs (visceral heterotaxy). In right isomerism, both atria show a right morphology and imply missed development of the left morphology and are associated with asplenia, with total anomalous pulmonary venous return noted frequently. In left isomerism, both atria show a left morphology and are associated with polysplenia and an interrupted inferior vena cava with the azygous vein continuation draining into the superior vena cava.6,7,8,9
Atrioventricular Connections
Once atrial situs is established, the atrioventricular connections should be analyzed. AV connections can be biventricular, univentricular, or ambiguous. Ambiguous AV connections occur in the setting of right or left cardiac isomerism. Biventricular connections occur when each atrium is connected with one ventricle and can be further subdivided into concordant or discordant variants. Concordant AV junction refers to the appropriate atrium connecting to its morphologically appropriate ventricle. Discordant AV junction occurs when the RA connects to the LV and the LA connects to the RV—that is, ventricular inversion or L-looped ventricles (Figure 102.3A).7
Univentricular AV connections are characterized by both atria mostly (>75%) connecting to only one ventricle through two common or discrete AV valves. There are three patterns of univentricular AV connections: double-inlet ventricle, where two AV valves are present; single-inlet ventricle, where there is one AV valve; and common-inlet ventricle, where a common AV valve connects both atria to only one ventricle (Figure 102.3B). The main ventricular chamber in univentricular AV connections can either be of left, right, or indeterminate morphology. Moreover, the dominant ventricle is always associated with a rudimentary second ventricle—rudimentary morphologic RVs are typically found anterosuperiorly, whereas rudimentary morphologic LVs are located inferiorly.6,7,8,9
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