Introduction
An abnormally positioned heart is not in itself a malformation of major significance. Such abnormal positioning, for example, can be secondary to a deformity or defect of the chest wall, such as pectus excavatum or carinatum. The exceptions are the extreme examples of exteriorization of the heart, usually described as ectopia cordis, or union of parts of the heart in the setting of conjoined twins. A heart unusually positioned within the chest, an abnormal orientation of the cardiac apex, or the finding of unexpected relationships of structures within the heart, nonetheless, can all lead to considerable diagnostic problems. In the past, such situations created significant confusion. Our philosophy and approach to these situations have been outlined in Chapter 1 . Those who have not studied this chapter in detail should, perhaps, return for refreshment concerning our ground rules. This chapter seeks to synthesize the value of our concepts in the setting of abnormally positioned hearts, along with the finding of unexpected intracardiac relationships. We start by discussing the situation encountered in the setting of absence or clefting of the sternum, which can be considered a variant of “ectopia.” We then address the much more significant problems produced by a truly extrathoracic position of the heart, or “classic” ectopia cordis in its various degrees. We follow this with a brief account of congenital absence of the pericardium. We then summarize the cardiac problems encountered in the setting of conjoined twins. The location of the heart in an unexpected part of the thoracic cavity, or the orientation of its apex in a disharmonious fashion, the next topics for consideration are best dealt with simply by description. Having suggested such simple descriptions, we then discuss the problems produced by, and the anomalies associated with, juxtaposition of the atrial appendages. We conclude with a consideration of the arrangements variously described as criss-cross or twisted hearts, superoinferior ventricles, or the topsy-turvy arrangement.
Exteriorization of the Heart (Ectopia Cordis)
It is maintained that the allegedly initial description of tetralogy of Fallot provided by Steno was also the first report of an extrathoracic heart. Rashkind, however, argued that such malformations were almost certainly recognized long before 1671, providing evidence that they were recorded in the writings of the ancient Babylonians. Hearts positioned in part, or completely, out of the thorax fortunately remain very rare. Until recently, with relatively few exceptions, such occurrences proved uniformly fatal. Although the lesion is usually termed “ectopia,” there are deficiencies in such usage, since the Greek word “ektopos” simply means away from a place. It follows that a heart found in the right chest of an otherwise normal person would be ectopic. Ectopia, nonetheless, is more usually used to account for a heart located in part, or completely, outside the thoracic cavity. The heart, with or without its pericardial covering, is completely exteriorized through a deficiency of the skin in approximately three quarters of the reported cases. In the remaining cases, the heart is seen pulsating through the intact skin, with this variant also known as partial ectopia cordis.
The hearts have traditionally been grouped according to their location, with initial descriptions of cervical, thoracic, and abdominal subsets. It is convenient, nonetheless, to add a combined thoracoabdominal variant, along with a combined thoracocervical group. Cases encountered more recently continue to fall within these groupings.
When the heart is found in the neck, the sternum is usually intact. This arrangement reflects a retention of the normal initial site of cardiac development. Examples have been recorded when an infant survived for a few hours with a cervical heart, while one patient with this anomaly was reputed to have survived to adult life. This latter example, however, would probably be better placed in the combined thoracocervical group. Those dismissing the existence of the cervical subset have suggested the need to distinguish between a cleft to the sternum and an extrathoracic heart. Congenital absence or clefting of the sternum is always associated with abnormal positioning of the heart and arterial trunks to some extent, albeit with the overlying skin and pericardium remaining intact ( Fig. 49.1 ). Rarely, premature fusion of the manubriosternal joint and the sternal segments may produce a high carinate deformity of the chest, along with a short sternum. This is the so-called Currarino-Silverman syndrome, which is frequently associated with congenital heart disease. Irrespective of such niceties, hearts of the cervical type are by far the rarest. There is also a question mark over the group with the heart allegedly contained within the abdomen. A large series of such hearts was combined to produce this grouping, but reexamination of the original reports suggested that, in all but one, part of the heart was retained within the chest, thus making it better to group them within the combined abdominothoracic subset. Therefore the majority of all cases either protrude from the chest or extend through a diaphragmatic defect. All occupy a midline deficiency of the body wall, lying partly in the chest and partly either within the abdomen or the neck. In the cases exteriorized from the chest, the hearts are usually covered by neither skin nor pericardium ( Fig. 49.2 ). In the past, various means had been employed to provide the lack of moisture ensuing from the absence of a pericardial cavity. Thus, quaint accounts survive from the 18th century, describing exteriorized hearts being covered with a contraption made of pliable osiers and linen, and anointed with wine and melted butter. Hearts were also covered with a pasteboard cone, with oil used for the anointing agent, or else saline sponges. Irrespective of the method employed, most patients survived for only a matter of hours or days.
The cases making up the combined thoracoabdominal subset differ from those with exclusively thoracic exteriorization in that the heart is better covered by the body wall, having at least a covering of skin or membrane ( Fig. 49.3 ). These patients all fall within the syndrome unified by five anomalies, which is usually known as the pentalogy of Cantrell. The anomalies are a midline deficiency of the abdominal wall, a defect of the lower part of the sternum, a deficiency of the pericardial sac, a deficiency of the diaphragm, and an intracardiac congenital lesion. Not all patients with extrathoracic hearts extending into the abdomen have all of these features. Indeed, the cases can themselves be grouped according to the number of the five features that are present. Lesser forms of the pentalogy include the midline deficiencies shown in Fig. 49.3 , along with protrusions of ventricular diverticulums through midline deficiencies of the body wall ( Fig. 49.4 ). Complete exteriorization of the heart represents the extreme form of the syndrome. Treatment of the patients with the abdominothoracic type of exteriorization has previously proved more successful than for those having exclusively thoracic exteriorization, although the patient with the exteriorized thoracic heart shown in Fig. 49.2 was treated successfully. Nonetheless, until recently, very few patients survived reparative surgery, although several people with abdominal hearts who did not undergo surgery have been described as surviving into adult life. The surgical problems encountered in restoring the heart to the body are considerable, including the small size of the deficient thoracic cavity, the excessive length of the venous and arterial connections to the extrathoracic heart, and the frequent coexistence of a large omphalocele. Therefore the prognosis for those born with exteriorized hearts is now markedly improved, albeit conditioned by the severity of the associated intracardiac defects.
Congenital Deficiency of the Pericardium
An integral part of the various forms of extrathoracic heart is a gross deficiency of the fibrous pericardial sac. Such deficiencies can also be found when the heart is in its anticipated intrathoracic position, although the lesion is exceedingly rare. We have knowingly observed only a single case at postmortem, a chance finding in a 68-year-old patient. Therefore cases can be entirely asymptomatic. Alternatively, such patients may have chest pain that can resemble angina. When associated with other anomalies, such as diaphragmatic hernia or lesions of the heart, it is the associated malformations that dominate the clinical picture. The biggest intrinsic problems occur with relatively localized left-sided deficiencies of the pericardium. Either the ventricles or the left atrial appendage can become herniated through a small opening, with strangulation and, in extreme cases, death. Limited deficiency of the fibrous sac on the right side can result in herniation of the lung into the pericardial cavity, with subsequent obstruction of the superior caval vein. The diagnosis is often made, or at least suggested, from the chest radiograph ( Fig. 49.5 ). Complete absence of the left pericardium is characterized by leftward displacement of the heart in the absence of pectus excavatum ( Fig. 49.6 ). In this setting, there is increased mobility and increased change in volume of all the cardiac chambers in systole and diastole. Although the margin of the deficient pericardium cannot be identified, the diagnosis can safely be made when a part of the left lung is interposed between the pulmonary trunk and aortic root (see Fig. 49.6D ). When the defect is small and there is herniation of the left appendage, the heart is normally positioned, but the malpositioned appendage produces an exaggerated bulge in the region of the pulmonary knob (see Fig. 49.5 ). Additional imaging ( Fig. 49.7 ) can confirm suspected herniation of the appendage. Only the small defects require surgical treatment, although large deficiencies may not be entirely benign. This is because the pericardial sac functions as the cardiac seat belt. The heart is more prone to traumatic injury when the pericardium is deficient. Surgical treatment of small defects is done either by enlarging the defect, incurring the small risk of losing the seat-belt effect, or by closure using a flap of mediastinal pleura.
Conjoined Twins
A malformation in the process of monozygotic twinning, which usually produces separate but identical individuals by cleavage of the single fertilized egg, can result in the twins becoming incompletely divided. This produces the rare examples of conjoined twins that, for centuries, have fascinated both medical and lay persons. The incidence is calculated at approximately 1 conjunction in every 50,000 births. The fanciful accounts of monsters and prodigies that appeared in centuries past are not that far removed from reality. The possibilities and sites for conjunction are legion. Accordingly, the categories provided for classification are formidable. The famous Siamese twins, Eng and Chang, who survived into old age, were joined only at the abdomen, sharing no more than a common cord of liver substance. Twins with cardiac involvement are all joined at the chest, although not necessarily with common cardiac chambers. Indeed, those with separate hearts in a common thoracic cavity have the best chance of survival. Even when the hearts themselves are quite separate, there can be extensive intermingling of the circulations between the twins. We have had the opportunity to study three sets of conjoined twins at autopsy.
In one set, the twins faced each other and were joined at the thorax and abdomen with a common rib cage, with a sternum at each side common to both twins. The right side of one twin faced the left side of the other, and each had its organs arranged in the usual fashion. There were separate lungs, but a common liver. Each twin possessed a spleen in its own left side. The hearts were joined at ventricular and atrial level, even though each heart had two atriums and two ventricles. The latter were unconnected, although contained in a common ventricular mass. However, the interconnections of the great veins were complex in the extreme and would have precluded any attempt at surgical separation.
The second set of twins studied was joined at the atrial level in a fascinating manner. The hearts were joined in the fashion of leaves of a book, rather than face to face. Within this arrangement, the twins shared a midline morphologically right atrium ( Fig. 49.8 ). Consequently, while the one twin had usual atrial arrangement, the other exhibited isomerism of the right atrial appendages. In keeping with the right isomerism, the right-sided twin also had lungs and bronchuses bilaterally of right morphology, and there was no spleen in the abdominal cavity. Several other examples of conjoined twins have been recorded where the one twin had the usual arrangement of its organs and the other had right isomerism. It is always the right-sided twin that is afflicted by the isomerism. Recent investigations have suggested the concept of cross-talk between the conjoined embryos as the basis for the failure of lateralisation. The left-sided twin is hypothesized to synthesize an inhibitor of the gene sonic hedgehog , activin being proposed as the inhibitor. It is suggested that diffusion of the inhibitor to the right-sided twin prevents the induction of nodal , this latter gene being considered necessary for the formation of morphologically left structures (see also Chapter 26 ).
Clinical diagnosis of conjunction is not now likely to be a problem. Intrauterine cross-sectional ultrasonography will reveal the diagnosis in the majority of cases. Although analysis will be difficult, an assessment can be made of the degree of cardiac involvement. If surgical separation is to be attempted, a full investigation will be needed after birth. Echocardiography should always be performed, along with resonance imaging or computed tomography. It is questionable if angiography is now required for diagnosis. Interpretation of the images, considered difficult in the past, should now be very much easier. Even in potentially suitable cases, survivors of attempted separation have thus far been rare. As with exteriorization of the heart, the situation must be anticipated rapidly to improve, depending of course on the degree of fusion of the cardiac structures, and the severity of the intracardiac lesions in each twin.
Abnormal Positioning of the Heart
The heart is normally located in the mediastinum, with one-third of its bulk to the right, and two-thirds to the left of the midline. With this arrangement, the apex usually points inferiorly and to the left. This combined pattern is traditionally described as “levocardia.” The heart can be deviated from this position, or its apex be pointed in an unexpected direction, for various reasons, and not always because of a congenital cardiac malformation. For example, the heart can be pushed to the right by a space-occupying lesion in the left lung or left pleural cavity, such as hyperinflation of the left lung, or pleural effusion and pneumothorax involving the left pleural cavity. The heart can also be pulled to the right when the right lung is underdeveloped or collapsed. An abnormal rightward position of the heart is also typically seen in association with right pulmonary hypoplasia in scimitar syndrome, ligamentous or ductal origin of right pulmonary artery, or atresia of stenosis of the right pulmonary vein. Nonetheless, the abnormal position in itself does not necessarily imply an abnormality of the heart. Normal individuals with mirror-imaged arrangement of the organs usually have a right-sided heart. Therefore when assessing the significance of a right-sided heart or a heart with its apex pointing to the right, it is necessary to take account of all these various features. Several questions should be asked. What is the overall arrangement of the organs? Is there an abnormality of the lungs or the thoracic contents? If present, is it of congenital or acquired etiology? Is the heart itself abnormally structured, or are its chambers grotesquely enlarged? Only when these questions have been posed, and answered, can the significance of an abnormally positioned heart be fully appreciated. Attempts to compress all this information into short phrases or single words have led to complex and confusing terms, such as dextrocardia, levocardia, dextroversion, levoversion, and dextroposition. Our preference is to avoid using these cryptic conventions.
A much simpler approach when considering the abnormally positioned heart, is first to account for its overall location. This can be left-sided, central, or right-sided. It is necessary to account for the orientation of its apex, which can similarly be left-sided, central, or right-sided. All locations can be categorized solely in terms of the position of the heart, and the orientation of its apex. This information, of course, must be placed in the context of the overall arrangement of the thoracic and abdominal organs, and the presence of acquired or congenital disease of either the heart or the lungs. Therefore abnormal positioning of the heart should no longer be regarded as a diagnosis in its own right. Finding a right-sided heart, for example, gives no clue as to what is happening inside the organ. The heart itself may be entirely normal. The description of an abnormal location is but one part of full sequential segmental analysis (see Chapter 1 ). Nonetheless certain well-recognized lesions, or combinations of lesions, are associated with right-sided hearts, or left-sided hearts in those with mirror imagery. As already emphasized, the heart is typically right-sided in association with hypoplasia of the right lung in the scimitar syndrome and its variants, which is also known as the bronchopulmonary foregut malformation. Rightward displacement of the heart is also seen in association with ligamental ductal origin of the right pulmonary artery, with unilateral absence of the right pulmonary artery, and with unilateral atresia or stenosis of the right pulmonary veins. The heart is also right-sided in well over a third of individuals who have an isomeric arrangement of their organs (see Chapter 22 ). The single lesion most associated with a right-sided heart, or left-sided heart with mirror-imaged arrangement, is congenitally corrected transposition (see Chapter 38 ). At best, these are clues to the final diagnosis. The variety of lesions that can exist when the heart is abnormally positioned is protean.
Juxtaposition of the Atrial Appendages
Juxtaposition of the atrial appendages is a potentially confusing feature of a congenitally malformed heart. In the normally constructed heart, the appendages lie one to each side of the arterial pedicle. It is the morphologic nature of each appendage that determines the arrangement of the atrial chambers (see Chapter 1 ). Juxtaposition of the appendages is seen when both the appendages are to the same side of the arterial pedicle. Such juxtaposition does not interfere with recognition of the structure of each appendage, since this feature is assessed on the basis of the extent of the pectinate muscles. Therefore juxtaposition can occur in the person with the usual atrial arrangement ( Fig. 49.9 ), in the individual with a mirror-imaged arrangement, or in the presence of isomeric appendages ( Fig. 49.10 ). In the presence of the usual atrial arrangement, juxtaposition occurs most frequently when the right appendage is deviated leftward through the transverse sinus so that it lies above the left appendage ( Figs. 49.11 and 49.12 , see also Fig. 49.9 ). This is conventionally called left juxtaposition. It tends to be associated with relatively complex anatomic lesions. Noteworthy associated malformations are tricuspid atresia, hypoplasia of the right ventricle, and abnormal ventriculoarterial connections, such as double-outlet right ventricle.
