Introduction

It might reasonably be thought that those who diagnose and treat patients with congenitally malformed hearts would, by now, have reached consensus concerning the most appropriate way of describing the malformations with which they are confronted. It is certainly the case that nomenclature is far less contentious now than in the previous millennium. It would be a brave person, nonetheless, who stated that the field of description and categorization was now fully resolved. It is not our intention, in this chapter, to extend these polemics. Rather, we describe our own system for description, leaving the readers to decide whether this is satisfactory for their needs. By and large, there is no right or wrong way of describing hearts, simply different ways. Even these different ways have been mitigated to considerable extent by the cross-mapping of existing systems. The ongoing differences should now be resolved simply by describing the abnormal anatomy as it is observed.

The need for a standardized approach reflects the fact that the number of individual lesions that can coexist within malformed hearts is considerable. Add to this the possibilities for combinations of lesions, and the problem of providing “pigeon holes” for each entity becomes immense. Straightforward lesions, such as septal deficiencies or valvar stenoses, are typically encountered in hearts that are otherwise structurally normal. It is when the hearts containing the lesions are themselves built in grossly abnormal fashion that difficulties are produced. If these alleged complex lesions are approached in a simple and straightforward fashion, none need be difficult to understand and describe.

The simplicity is provided by recognizing that the heart has three basic building blocks, namely the atriums, ventricular mass, and arterial trunks ( Fig. 1.1 ). The system for description and categorization based on recognition of the limited potential for variation in each of these cardiac segments was developed independently in the 1960s by two groups: one based in the United States and led by Richard Van Praagh, and the other from Mexico City, headed by Maria Victoria de la Cruz. Both of these systems concentrated on the different topologic arrangements of the components within each cardiac segment. When Van Praagh and colleagues introduced the concept of concordance and discordance between atriums and ventricles, they were concerned primarily with the harmony or disharmony to be found between the topologic arrangements of the atrial and ventricular components. At this time, they placed less emphasis for description on the fashion in which the atrial and ventricular chambers were joined together across the atrioventricular junctions. A similar approach, concentrating on arterial relationships, had been taken by de la Cruz et al. when they formulated their concept of arterioventricular concordance and discordance. These approaches were understandable because it was often difficult, at that time, to determine precisely how the adjacent structures were linked together.

The essence of sequential segmental analysis depends on recognition of the topologic arrangement of the three cardiac segments and combines this with analysis of the fashions in which the segments are joined, or are not joined, to each other.

All was changed by the advent of cross-sectional echocardiography. Since the mid-1970s, it has been possible with precision to determine how atriums are, or are not, joined to ventricles, and similarly to establish the precise morphology found at the ventriculoarterial junctions. Our preferred system evolved concomitantly with the development of echocardiography and concentrates on the variations possible across the atrioventricular and ventriculoarterial junctions. We call this system sequential segmental analysis (see Fig. 1.1 ). In making such analysis, we do not ignore the segments themselves. Indeed, junctional connections cannot be established without knowledge of segmental topology.

Our system, throughout its evolution, has followed the same basic and simple rules. From the outset, we have formulated our categories on the basis of recognizable anatomic facts, avoiding any speculative embryologic assumptions. Again, from the start, we have emphasized the features of the morphology of the cardiac components, the way they are joined or not joined together, and the relations between them, as three different facets of the cardiac make-up. The clarity of the system depends upon its design. Some argue that brevity is an important feature and have constructed formidable codifications to achieve this aim. However, in the final analysis, clarity is more important than brevity. Therefore we do not shy from using words to replace symbols, even if this requires several words. Wherever possible, we strive to use words that are as meaningful in their systematic role as in their everyday usage. In our desire to achieve optimal clarity, we have made changes in our descriptions over the years, most notably in our use of the term “univentricular heart.” We make no apologies for these changes because their formulation, in response to valid criticisms, has eradicated initially illogical points from our system to its advantage. It is our belief that the system now advocated is entirely logical, and we hope it is simple.

Basic Concepts of Sequential Segmental Analysis

The system we advocate depends first upon the establishment of the arrangement of the atrial chambers. Thereafter, attention is concentrated on the anatomic nature of the junctions between the atrial myocardium and the ventricular myocardial mass. This feature, which we describe as a type of connection, is separate from the additional feature of the morphology of the valve or valves that guard the junctions. There are two junctions in the normally constructed heart, and usually they are guarded by two separate valves. The two atrioventricular junctions can be guarded, on occasion, by a common valve. If we are to achieve this analysis of the atrioventricular junctions, we must also determine the structure, topology, and relationships of the chambers within the ventricular mass. Having dealt with the atrioventricular junctions, the ventriculoarterial junctions are also analyzed in terms of the way the arterial trunks are joined to the ventricular mass and the morphology of the arterial valves guarding their junctions. Separate attention is directed to the morphology of the outflow tracts and to the relationships of the arterial trunks. A catalog is made of all associated cardiac and, where pertinent, noncardiac, malformations. Included in this final category are such features as the location of the heart, the orientation of its apex, and the arrangement of the other thoracic and abdominal organs.

Implicit in the system is the ability to distinguish the morphology of the individual atriums and ventricles and to recognize the types of arterial trunk taking origin from the ventricles. This is not as straightforward as it may seem; often, in congenitally malformed hearts, these chambers or arterial trunks may lack some of the morphologic features that most obviously characterize them in the normal heart. The most obvious feature of the morphologically left atrium in the normal heart is the connection to it of the pulmonary veins. In hearts with totally anomalous pulmonary venous connection, these veins connect in extracardiac fashion. In spite of this, it is still possible to identify the left atrium. It is considerations of this type that prompted the concept we use for recognition of the cardiac chambers and great arteries. Dubbed by Van Praagh and his colleagues the “morphologic method” and based on the initial work of Lev, the principle states that structures should be recognized in terms of their own intrinsic morphology and that one part of the heart, which is itself variable, should not be defined on the basis of another variable structure. When this eminently sensible concept is applied to the atrial chambers, the connections of the great veins are obviously disqualified as markers of morphologic rightness or leftness because, as discussed previously, the veins do not always connect to their anticipated atriums. Fortunately, there is another component of the atrial chambers that, in our experience, has been almost universally present and that, on the basis of the morphology of its junction with the remainder of the chambers, has enabled us always to distinguish between morphologically right and left atriums. This is the appendage. The morphologically right appendage has the shape of a blunt triangle and joins over a broad junction with the remainder of the atrium. The junction is marked externally by the terminal groove and internally by the terminal crest. Its most significant feature is that the pectinate muscles lining the appendage extend around the parietal atrioventricular junction to reach the cardiac crux ( Fig. 1.2A ).

(A) Short-axis view of the right atrioventricular junction from above, the atrium having been opened with a cut parallel to the atrioventricular junction, and with subsequent reflection of the wall of the appendage. Note that the pectinate muscles within the appendage extend all around the vestibule of the tricuspid valve. (B) Short-axis view of the left atrioventricular junction photographed from above from the same heart. The pectinate muscles are confined within the tubular appendage, so that the inferior wall of the atrium is smooth. This contains the coronary sinus within the morphologically left atrioventricular junction. Note also the typical appearance of the morphologically left side of the septum.

The morphologically left appendage, in contrast, is much narrower and tubular. It has a narrow junction with the remainder of the atrium, the junction being marked neither by a terminal groove nor by a muscular crest. The pectinate muscles are confined within the morphologically left appendage, with the walls of the remainder of the atrium being smooth as they extend to the cardiac crux (see Fig. 1.2B ).

The morphologic method also shows its value when applied to the ventricular mass, which extends from the atrioventricular to the ventriculoarterial junctions. Within the ventricular mass as thus defined, there are almost always two ventricles. Description of ventricles, no matter how malformed they may be, is facilitated if they are analyzed as possessing three components. The first is the inlet, extending from the atrioventricular junction to the distal attachment of the atrioventricular valvar tension apparatus. The second part is the apical trabecular component. The third is the outlet component, supporting the leaflets of the arterial valve ( Fig. 1.3 ).

(A) Three component parts of the morphologically right ventricle, which extends from the atrioventricular to the ventriculoarterial junctions (dotted lines). The coarse apical trabeculations are the most constant of these features. (B) Three component parts of the morphologically left ventricle of the same heart. The ventricular cavity again extends from the atrioventricular to the ventriculoarterial junctions (dotted lines). The fine apical trabeculations are its most constant feature.

Of these three components, the apical trabecular component is most universally present in normal, as well as in malformed and incomplete, ventricles. Furthermore, it is the pattern of the apical trabeculations that differentiates morphologically right from left ventricles (see Fig. 1.3 ). This is the case even when the apical components exist as incomplete ventricles, lacking either inlet or outlet components, or sometimes both of these components ( Fig. 1.4 ).

Heart illustrating a double inlet to, and double outlet from, a dominant left ventricle. The aorta and pulmonary trunk are seen arising in parallel fashion from the left ventricle, with the aorta anterior and to the left. However, on the anterior and right-sided shoulder of the dominant left ventricle, there is still a second chamber to be seen, fed through a ventricular septal defect. This chamber is the apical trabecular component of the right ventricle (RV), identified because of its coarse trabeculations.

When the morphology of individual ventricles is identified in this fashion, all hearts with two ventricles can be analyzed according to the way that the inlet and outlet components are shared between the apical trabecular components. To fully describe any ventricle, account must also be taken of its size. It is necessary further to describe the way that the two ventricles themselves are related within the ventricular mass. This feature is described in terms of ventricular topology because two basic patterns are found that cannot be changed without physically taking apart the ventricular components and reassembling them. The two patterns are mirror images of each other. They can be conceptualized in terms of the way that, figuratively speaking, the palmar surface of the hands can be placed upon the septal surface of the morphologically right ventricle. In the morphologically right ventricle of the normal heart, irrespective of its position in space, only the palmar surface of the right hand can be placed on the septal surface such that the thumb occupies the inlet and the fingers fit into the outlet ( Fig. 1.5 ).

Diagram showing how the palmar surface of the right hand can be placed on the septal surface of the normal morphologically right ventricle with the thumb in the inlet component and the fingers extending into the ventricular outlet. (A) The essence of right hand ventricular topology, also known as a d-ventricular loop. The palmar surface of the left hand fits in comparable fashion within the morphologically left ventricle, but the right hand is taken as the arbiter for the purposes of categorization. (B) The mirror-imaged normal heart. In this setting, the palmar surface of the left hand can be placed on the septal surface of the morphologically right ventricle with the thumb in the inlet and the fingers in the outlet.

Therefore the usual pattern can be described as right hand ventricular topology. The other pattern, the mirror image of the right hand prototype, is described as left hand ventricular topology. In this left hand pattern, seen typically in the mirror-imaged normal heart, or in the variant of congenitally corrected transposition found with usual atrial arrangement, it is the palmar surface of the left hand that fits on the septal surface of the morphologically right ventricle with the thumb in the inlet and the fingers in the outlet. This is the essence of left hand topology, or the “l-ventricular loop” (see Fig. 1.5 ). These two topologic patterns can always be distinguished irrespective of the location occupied in space by the ventricular mass itself. Therefore a left hand pattern of topology is readily distinguished from a ventricular mass with right hand topology in which the right ventricle has been rotated to occupy a left-sided position. Component make-up, trabecular pattern, topology, and size are independent features of the ventricles. On occasion, all may need separate description to remove any potential for confusion.

Only rarely will hearts be encountered with a solitary ventricle. Sometimes this may be because a right or left ventricle is so small that it cannot be recognized with usual clinical investigatory techniques. Nonetheless, there is a third pattern of apical ventricular morphology that is found in hearts possessing a truly single ventricle. This is when the apical component is of neither right nor left type but is very coarsely trabeculated and crossed by multiple large muscle bundles. Such a solitary ventricle has an indeterminate morphology ( Fig. 1.6 ).

Heart opened in clamshell fashion to show that both atrioventricular valves enter the same ventricular chamber, which also gives rise to both outflow tracts. We were unable to find a second ventricular chamber in this example. The exceedingly coarse apical trabeculations and the absence of the second chamber identify this heart as having a solitary ventricle of indeterminate morphology. This is the only true “single” ventricle.

Analysis of ventricles on the basis of their apical trabeculations precludes the need to use illogically the terms “single ventricle” or “univentricular heart” for description of those hearts with one big and one small ventricle. These hearts may produce a functionally univentricular arrangement, but all chambers that possess apical trabecular components can be described as ventricles, be they big or small and be they incomplete or complete. Any attempt to disqualify such chambers from ventricular state must lead to a system that is artificial. Only hearts with a truly solitary ventricle need be described as univentricular, albeit that the connections of the atrioventricular junctions can be univentricular in many more hearts.

When determining the morphology of the great arteries, no intrinsic features enable an aorta to be distinguished from a pulmonary trunk or from a common or solitary arterial trunk. Nonetheless, the branching pattern of the trunks themselves is sufficiently characteristic to permit these distinctions ( Fig. 1.7 ).

The branching pattern of arterial trunks permits their distinction. The solitary arterial trunk is described when the intrapericardial pulmonary arteries are absent because in this setting it is impossible to determine, had they been present, whether they would have taken origin from the heart, making the trunk an aorta, or from the trunk itself, in which case there would have been a common arterial trunk with pulmonary atresia.

The aorta gives rise to at least one coronary artery and the bulk of the systemic arteries. The pulmonary trunk gives rise directly to both, or one or other, of the pulmonary arteries. A common trunk supplies directly the coronary, systemic, and pulmonary arteries. A solitary arterial trunk exists in the absence of the proximal portion of the pulmonary trunk. In such circumstances, it is impossible to state with certainty whether the persisting trunk is common or aortic. Even in the rare cases that have transgressed one of these rules, examination of the overall branching pattern has always permitted us to distinguish the nature of the arterial trunk.

Atrial Arrangement

The cornerstone of any system of sequential analysis must be accurate establishment of atrial arrangement because this is the starting point for subsequent analysis. When arrangement of the atriums is assessed according to the morphology of the junction of the appendages with the rest of the atriums, There are only four possible patterns of arrangement ( Fig. 1.8 ) because all hearts have two atrial appendages, each of which can only be morphologically left or right.

When analyzed on the basis of the extent of the pectinate muscles relative to the atrioventricular vestibules (see Fig. 1.2 ), there are only four possible ways in which the two atrial appendages can be arranged. However, note that the venoatrial connections can show marked variation, particularly in the isomeric settings, also known collectively as visceral heterotaxy.

The most common is the usual arrangement, also called situs solitus, in which the morphologically right appendage is right-sided and the morphologically left appendage is left-sided. The second arrangement, which is very rare, is the mirror image of the usual. It is often called situs inversus, even though the atrial chambers are not upside down. In these two arrangements, the appendages are lateralized, with the morphologically right appendage being to one side, and the morphologically left appendage to the other. The two other arrangements do not show such lateralization. Instead, there is isomerism of the atrial appendages. In these patterns, the two appendages are mirror images of each other, with morphologic characteristics at their junctions with the rest of the atriums on both sides of either right type or left type.

Recognition of Atrial Arrangement

The arrangement of the appendages, ideally, is recognized by direct examination of the extent of the pectinate muscles round the vestibules (see Fig. 1.2 ). It has been questioned for some time as to whether these features can be distinguished in the clinical setting. With modern-day equipment, it is our belief that the arrangements should now be recognizable using cross-sectional echocardiography, particularly from the transesophageal window. The extent of the pectinate muscles can be demonstrated by using computed tomography. However, in most clinical situations, it is rarely necessary to rely only on direct identification. This is because the morphology of the appendages is almost always in harmony with the arrangements of the thoracic and abdominal organs. In patients with lateralized arrangements, that is, the usual and mirror-imaged patterns, it is exceedingly rare for there to be disharmony between the location of the organs ( Fig. 1.9 ).

Usual and mirror-imaged arrangements of the organs, which are lateralized. Almost always there is harmony between the arrangement of the right and left atrial appendages and the remaining thoracoabdominal organs. The numbers show the three lobes of the morphologically right and the two lobes of the morphologically left lungs. LAA, Left atrial appendage; RAA, right atrial appendage.

When the appendages are isomeric, in contrast, usually the abdominal organs are typically jumbled up, although the lungs and bronchuses are typically isomeric ( Fig. 1.10 ).

Typical features of the thoracoabdominal organs in so-called visceral heterotaxy. The abdominal organs are jumbled up, but the lungs and atrial appendages are usually isomeric, having the same morphologic features on the right and left sides. It is usual for right isomerism to be associated with absence of the spleen and left isomerism with multiple spleens, but these associations are far from constant. Thus different pictures emerge when so-called heterotaxy is subdivided on the basis of isomerism as opposed to splenic morphology. However, cardiac assessment should start with analysis of atrial morphology based on the structure of the atrial appendages.

Even when there is abdominal heterotaxy, the lungs and bronchial tree are almost always symmetric. It is rare for the bronchial arrangement to show disharmony with the morphology of the appendages. The presence of isomerism therefore can almost always be inferred from the bronchial anatomy. The morphologically left bronchus is long. It branches only after it has been crossed by its accompanying pulmonary artery, making the bronchus hyparterial. In contrast, the morphologically right bronchus is short and is crossed by its pulmonary artery after it has branched, giving an eparterial pattern of branching. The four patterns of bronchial branching are almost always in harmony with the arrangement of the atrial appendages. Similar inferences to those provided from bronchial arrangement can also usually be obtained noninvasively by using cross-sectional ultrasonography to image the abdominal great vessels. These vessels bear a distinct relation to each other, and to the spine, which generally reflects bodily arrangement, although not as accurately as does bronchial anatomy. The vessels can be distinguished ultrasonically according to their pattern of pulsation. When the atriums are lateralized, almost without exception the inferior caval vein and aorta lie to opposite sides of the spine, with the caval vein on the side of the morphologically right appendage. When there is isomerism, the great vessels usually lie to the same side of the spine, with the caval vein in anterior position in those with isomerism of the right atrial appendages, and posterior, or with the azygos vein posterior, in those having isomerism of the left atrial appendages.

In general, isomerism of the right atrial appendages is associated with absence of the spleen, whereas isomerism of the left atrial appendages is associated with multiple spleens. Patients with isomerism of the atrial appendages therefore are frequently grouped together, from the cardiac standpoint, under the banner of the “splenic syndromes.” This approach is much less accurate than describing the syndromes directly in terms of isomerism of the atrial appendages because the correlation between isomerism of the right atrial appendages and absence of the spleen, and between isomerism of the left atrial appendages and multiple spleens, is far from perfect.