EXTERIORISATION OF THE HEART (ECTOPIA CORDIS)

It is maintained that the famous case of tetralogy of Fallot first reported by Nicolas Steno ¹ was the first report of an extrathoracic heart. ² Rashkind ³ has argued that such malformations were almost certainly recognised long before 1671. In his opinion, ³ they were recorded in the writings of the ancient Babylonians, although there is some dispute concerning the precise translation of the text on the tablet involved. Be that as it may, 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. The lesion is usually termed ectopia , but there are deficiencies in such usage. ⁴ The Greek word ektopos simply means away from a place. As such, a heart found in the right chest of an otherwise normal person is ectopic. Despite this semantic failing, which represents yet another example of deficient use of a classical term, and supports the use of the vernacular, ectopia is used universally to account for a heart located in part, or completely, outside the thoracic cavity.

Known cases of an extrathoracic heart have been reviewed extensively and well. ^4–6 In terms of categorisation, it was as long ago as 1845 that extrathoracic hearts were grouped according to their location, with description of cervical, thoracic and abdominal subsets. ⁷ Subsequently, it was suggested that the combined thoracoabdominal position made up a further distinct pattern, with a combined thoracocervical group then added to this list. ⁴ Cases encountered more recently continue to fall within these groupings.

When the heart is found in the neck, the sternum is usually intact. According to some, ⁴ this arrangement reflects a retention of the normal initial site of cardiac development. This subset was dismissed by other experts, ² who argued that it is found only in malformed fetuses. Examples have been recorded, nonetheless, 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. ⁸ This latter example, however, would probably be better placed in the 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. ² This seems to be unnecessarily divisive, since a heart within the neck is certainly not within the thorax, irrespective of whether or not the sternum is cleft. 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. Although 38 such hearts were catalogued in one series, ⁵ re-examination 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. ² The majority of cases, therefore, either protrude from the chest, or else extend through a diaphragmatic defect. All occupy a midline deficiency of the body wall, lying partly in the chest and partly within the abdomen. In the cases exteriorised from the chest, the hearts are usually covered by neither skin nor pericardium ( Fig. 48-1 ). 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 exteriorised hearts being covered with a contraption made of pliable osiers and linen, and anointed with wine and melted butter. ⁹ Hearts were also covered with a pasteboard cone, with oil used for the anointing agent, or else saline sponges. ⁶ Irrespective of the method employed, most patients survived for only a matter of hours or days.

A neonate with the heart exteriorised through the thoracic wall.

(Courtesy of Dr Marshall Jacobs, Temple University, Philadelphia, Pennsylvania.)

The difference between exclusively thoracic exteriorisation, and those cases grouped together because the heart is located partly in the thorax and partly in the abdomen ( Fig. 48-2 ), is that in the latter instances the heart is better covered by the body wall, having at least a covering of skin or membrane ( Fig. 48-3 ). It is this group of patients that fall within the syndrome unified by five anomalies, known as the pentalogy of Cantrell. These 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. ¹⁰ 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. ¹¹ Lesser forms of the pentalogy include the midline deficiencies shown in Figures 48-2 and 48-3 , and protrusions of ventricular diverticula through midline deficiencies of the body wall ( Fig. 48-4 ). Complete exteriorisation of the heart represents the extreme form of the syndrome. Treatment of the patients with the abdominothoracic type of exteriorisation has previously been more successful than for those having exclusively thoracic exteriorisation, although recent experience has shown that the exteriorised thoracic heart can successfully be placed back within the thorax ( Fig. 48-5 ).

This patient has the midline deficiencies of the pentalogy of Cantrell. The heart, occupying both the thorax and the abdomen, is covered by skin and a pericardial cavity.

(Courtesy of Dr Benson R. Wilcox, University of North Carolina, Chapel Hill.)

Opening the skin in the patient shown in Figure 48-2 revealed a midline heart with it apex also in the midline. There was isomerism of the right atrial appendages and the intracardiac anatomy of tetralogy of Fallot.

(Courtesy of Dr Benson R. Wilcox, University of North Carolina, Chapel Hill.)

This magnetic resonance image shows a left ventricular (LV) diverticulum protruding through a midline deficiency of the body wall ( arrow ). AO, aorta; L, left; R, right; RV, right ventricle.

(Courtesy of Dr Walter Duncan, University of British Columbia, Vancouver, British Columbia, Canada.)

The heart in the patient shown in Figure 48-1 was successfully replaced within the thorax.

(Courtesy of Dr Marshall Jacobs, Temple University, Philadelphia, Pennsylvania.)

Until recently, very few patients survived reparative surgery, although several persons with abdominal hearts who did not undergo surgery survived into adult life. An example is an old soldier who reputedly fought through several campaigns, and died of suppurative nephritis of the right kidney. ¹² 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 co-existence of a large omphalocoele. Recent experience, nonetheless, such as that shown in Figures 48-1 and 48-3 , and that of Morales and associates, ¹³ who reported four successful repairs encountered over a period of 6 years, suggests that the prognosis for those born with exteriorised hearts is now markedly improved, albeit conditioned by the severity of 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. A deficiency of this firm bag can also be found when the heart is in its anticipated intrathoracic position. According to Van Praagh and his colleagues, ² the anomaly was first observed by Columbus in 1559. Since then, about 150 cases have been described. Hence, the lesion is exceedingly rare. Only three examples were discovered amongst the 1716 hearts in the archive of Boston Children’s Hospital. ² We have knowingly observed only a single case at postmortem, this being a chance finding in a 68-year-old patient. ¹⁴ Cases can, therefore, 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 localised 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. 48-6 ). A large left-sided deficiency permits the entire heart to shift leftwards, with production of three rather than two knuckles on the left heart border as seen on the chest radiograph. 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. Additional imaging ( Fig. 48-7 ) can confirm herniation of the appendage if it is suspected. 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 enlargement of the defect, then incurring the small risk of losing the seat belt effect, or else by closure using a flap of mediastinal pleura.

The chest radiograph shows an extensive bulge in the left border of the cardiac silhouette ( arrows ). This is very suggestive of herniation of the left atrial appendage through a pericardial deficiency.

Magnetic resonance imaging in the patient shown in Figure 48-6 confirms the herniation of the left atrial appendage (LAA), albeit through a thinned area of pericardium rather than a true pericardial defect ( arrow ). Ao, aorta; LA, left atrium; PA, pulmonary trunk; RA, right atrium; RAA, right atrial appendage.

CONJOINED TWINS

A malformation in the process of monozygotic twinning, which usually produces separate but identical individuals by cleavage of the single fertilised 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. ¹⁵ 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 joined twins at autopsy.

In one case, 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 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, even though set in a common ventricular mass. The interconnections of the great veins, however, were complex in the extreme and would have precluded any attempt at surgical separation.

One of the other sets of twins studied was joined at atrial level in a fascinating fashion. The hearts were joined in the fashion of leaves of a book, rather than faces to face. Within this arrangement, the twins shared a midline morphologically right atrium ( Fig. 48-8 ). Consequently, while the one twin had usual atrial arrangement, the other exhibited isomerism of the right atrial appendages. ¹⁶ 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 its abdominal cavity. Several other examples of conjoined twins have been recorded where the one twin had usual arrangement of its organs and the other had right isomerism. Always it is the right-sided twin that is afflicted by the isomerism. Recent investigations suggest the concept of cross-talk between the conjoined embryos as the basis for failure of lateralisation. ¹⁷ The left-sided twin is hypothesised to synthesise an inhibitor of the gene sonic hedgehog , activin being proposed as the inhibitor. It is then 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 22 ).

The hearts from conjoined twins joined together at atrial and ventricular levels. In the right-sided heart, the right-sided appendage, although not well seen in the photograph, was of right morphology. There is a shared midline appendage, also of right morphology, whilst the left-sided appendage is of left morphology. Thus, the heart of the right-sided twin exhibits right isomerism, whilst the atrial appendages in the heart of the left-sided twin are usually arranged.

Clinical diagnosis of conjunction is not now likely to be a problem. Intra-uterine cross sectional ultrasonography is now likely to 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. Angiocardiography and echocardiography should always be performed, along with resonance imaging. 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 exteriorisation 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 . There are several reasons why the heart can be deviated from this position, or its apex be pointed in an unexpected direction. Although the abnormal position of the heart can be due the cardiac defect, it can also be secondary to a non-cardiac pathology. 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. The abnormally rightward position of the heart is typically seen in association with right pulmonary hypoplasia in scimitar syndrome and absence of the right pulmonary artery. The abnormal position is not in itself necessarily an abnormality of the heart. Normal individuals with mirror-imaged arrangement of the organs, for example, normally have a right-sided heart.

When assessing the significance of a right-sided heart, therefore, 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 aetiology? 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 usage of the terms dextrocardia, levocardia, dextroversion, evoversion, and dextroposition, particularly when combined with adjectives such as isolated, pivotal, or mixed ¹⁸ For these reasons, it is better not to use these cryptic conventions.

When describing the abnormally positioned heart, it is necessary first to account for its overall location. This can be accomplished by describing it as left-sided, central, or right-sided. Thereafter, it is necessary to account for the orientation of its apex. This also can be left-sided, central, or right-sided. All locations can be categorised 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. If, for example, the heart is described as lying mostly in the right chest, and with its apex orientated to the left, there can be little room for misunderstanding this arrangement, irrespective of the precise reason for the abnormal position.

Abnormal positioning of the heart, therefore, 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. Description of abnormal location is but one part of full sequential segmental analysis (see Chapter 1 ). Certain well-recognised lesions, or combinations of lesions, nonetheless, are associated with right-sided hearts, or left-sided hearts in those with mirror imagery. The heart is typically right-sided in association with hypoplasia of the right lung in the scimitar syndrome and its variants, known also as the broncho-pulmonary foregut malformation. ¹⁹ 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 39 ). At best, these are clues to the final diagnosis. The variety of lesions that can exist when the heart is abnormally positioned is protean.