MISPLACEMENTS of the heart are of rare occurrence, and the more important of them are merely part of a general malformation of the body. The heart may be transposed, that is to say, placed in a position on the right side of the chest corresponding with that which it normally occupies on the left. With this there is usually transposition of the viscera, but it sometimes occurs alone. Again, the heart may occupy the middle line, as it does in early foetal life. It may be placed outside the thorax altogether (Ectopia cordis), but in this case there are other congenital malformations, and that of the heart only forms a part.

Malformations Of The Pericardium

Absence of the pericardium is a rare congenital malformation, and is mostly associated with ectopia cordis. There are, however, cases of absence of the pericardium in persons otherwise well formed. The sac may be entirely absent or there may be traces of it at the base.

Diverticulum of the pericardium is an unusual malformation. It occurs in the form of a sac with a narrow neck, which communicates with the pericardium. When distended the sac is about the size of a pigeon's egg. (See cases by Bristowe, Path, trans., xx., 101, and by author in Catalogue of Western Infirmary Museum).

Malformations Of The Heart And Great Vessels

These for the most part represent survivals of foetal conditions. The heart at an early period consists of two cavities, an auricle and a ventricle. The simple auricle receives the two ventse cavae, and the ventricle gives origin to the common arterial trunk. The ventricle, the auricle, and the common arterial trunk subsequently undergo subdivision each into two. This separation in the ventricle begins near the apex; the septum gradually rises towards the base, its completion at the base being delayed after the rest of the septum has been formed. Kokitansky distinguishes two parts in the ventricular septum, namely, an anterior (septum anterius) which divides the orifices of the aorta and pulmonary artery, and a posterior (septum posterius) which comes between the two auriculo-ventricular openings. The undefended space (pars membranacea) is at the union of the anterior and posterior septa, and will be the last part to close. This portion of the septum remains throughout life devoid of muscular tissue, being composed of the two layers of endocardium from the two ventricles. It is situated at the base of the septum, just beneath the aortic valve. There is sometimes a minute aperture persisting in adult life. The common arterial trunk begins to show signs of division by a septum about the time that the inter-ventricular septum is approaching the base. A septum passing from both sides of the artery meets and divides the vessel into what are subsequently the pulmonary artery and the aorta. These are so adjusted as to connect with the right and left ventricles respectively. The division of the nitrides does not begin till the ventricular septum is nearly completed, namely, about the ninth week, and after being fully formed the septum remains partially open during the whole of intra-uterine life.

The foetal circulation, so far as the heart and great vessels are concerned, differs from that of the adult chiefly in two respects, namely, in the existence of the foramen ovale and in the patency of the ductus arteriosus. The Foramen ovale forming a communication between the two auricles closes more or less completely at birth. The Ductus arteriosus connects the pulmonary artery with the descending aorta, and in the foetus it conveys most of the blood going to the abdomen and lower limbs, as well as that to the umbilical arteries. The left ventricle and aortic arch thus supply in the foetus the upper part of the body and the upper limbs, whilst the right ventricle and pulmonary artery through the ductus arteriosus supply the lower parts. There is a small part of the aorta between the origin of the subclavian artery and the opening of the ductus arteriosus, which is thus almost out of use in the foetus. It is called the Isthmus aortae, and is important in connection with subsequent lesions.

Consistently with the larger amount of work thrown on the right ventricle in the foetus as compared with the adult, the wall of this ventricle is similar in thickness to that of the left ventricle.

Causation Of Malformations Of The Heart

A large proportion of cases of malformation are related to narrowness or Stenosis of the pulmonary artery. This has been variously ascribed to inflammation during foetal life, and defective formation of the parts in the fœtus.

By some (Peacock, Meyer) inflammation occurring in early foetal life has been assigned as the cause of the stenosis. We shall see afterwards that inflammation of the endocardium frequently leads to valvular lesions, which result in obstruction of the orifices. In the adult it mostly occurs in the valves of the left side of the heart, and this is usually ascribed to the fact that the systemic arteries are liable to greater variations in blood-pressure and greater strain than the pulmonary vessels. In the foetus it is otherwise; a much larger proportion of the circulation is dependent on the right ventricle, the abdominal aorta and umbilical arteries being fed by this ventricle. The umbilical arteries, again, are, from their position, exposed to variations in pressure, and this may tell on the pulmonary artery at its origin.

On the other hand, Rokitansky seeks to ascribe the frequency of defect of the pulmonary artery to deficiency in the original formation of the septum dividing the primary common arterial trunk. This is probably the more correct explanation, as there are seldom traces of inflammation visible in the endocardium at birth, and, besides, the lesion is not simply one of the valves, which inflammation produces, but frequently a real narrowing or defect in the artery, as if in the division of the primary arterial stem the greater part had been monopolized by the aorta.

The stenosis of the pulmonary artery is commonly associated with defects in the septa, and these may be ascribed to a mechanical interference with the complete closure of the septa. Let us suppose that the common arterial trunk, instead of dividing in the normal way into pulmonary artery and aorta, does so imperfectly, and so there is a large aorta and a small pulmonary artery, or even an entire absence of the latter. In the case last mentioned the blood from the right ventricle, as well as that from the left, would pass into the aorta, and the constant recurrence of this passage of blood at each systole of the ventricle would prevent the closure of the septum at the base, and cause the aorta to take permanent origin from the right ventricle as well as from the left. On a similar principle the obstruction of the pulmonary artery will, by raising the pressure of the blood in the right auricle, interfere with the closure of the foramen ovale.

Instead of stenosis of the pulmonary artery, we may have a similar condition of the aorta. The consequence of this will be defect of the septa and alterations in the circulation, the latter differently located to those already mentioned.

Forms Of Malformation. 1. Defects Of The Septum Ventriculorum

As already indicated, this usually goes along with defect of the great vessels. When the stenosis is in the pulmonary artery, as is mostly the case, it is chiefly the anterior part of the septum which is defective;while in the case of aortic stenosis it is the posterior (Rokitansky). The defect, if limited in extent, is usually in or near the undefended space (see Fig. 200). The defect may be so great as that there is virtually no septum, the ventricle being composed of a single cavity, or it may present various degrees of divergence from this extreme.

Fig. 200. - Defect of inter-ventricular septum. The gap is situated at the base, in the position of the undefended space in the normal heart. (Peacock).