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Congenital Heart Disease

ventricle, blood, artery, aorta, foramen, pulmonary, auricle, ovale and lungs

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CONGENITAL HEART DISEASE.

other parts of the body the heart is subject to malformations from arrest of development. These vary in importance according to the period of intrauterine life in which they occur ; but all, since they affect the centre of the circulatory system, materially hamper the distribution of the blood-current and therefore interfere with the due discharge of all the nutritive functions of the body.

In its progress from the simplicity of its rudimentary state to the com plex machinery of the fully developed organ, the heart passes through a variety of changes. At first a mere tube doubled upon itself, it soon be comes divided into three cavities—a simple auricle, a simple ventricle, and the arterial bulb. At this stage the organ resembles a horse-shoe in shape, the ventricle occupying the position of the curve. This cavity then begins to bulge out more conspicuously at its lower part so as to suggest by its appearance the later form of the heart ; and at the same time the auricle and the bulb approach more closely together. Next, the auricle and ventricle become each divided into parts by a septum ; and the bulbus arteriosus is also divided into two channels which are the future aorta and pulmonary artery. The auricular and ventricular septa are each at first incomplete, so that the cavities severally communicate ; and the opening in the auricular septum—the foramen ovale—remains open until birth.

Just before the completion of intrauterine existence the course of the blood-current is as follows :—Starting from the placenta, in which it has been to a certain extent purified and recharged with oxygen, the blood enters the body of the foetus through the umbilical vein and is conveyed to the under service of the liver. At this point a portion passes directly into the inferior vena cava by the ductus venosus ; the remainder joins the blood in the portal vein and circulates through the liver before it reaches the inferior vena cava and is conveyed with the first portion to the right auricle. Here it meets with the blood returning from the head and neck by the superior vena cava. The two currents do not, however, mix. That coming from the head passes, as it would do in the adult, through the auriculo-ventricular orifice to the right ventricle. From this point a small quantity reaches the lungs through the pulmonary artery ; but the larger portion is directed through the ductus arteriosus into the aorta below the origin of the great vessels, and passes to the lower part of the body and the placenta. The blood reaching the right auricle by the inferior vena cava, instead of entering the right ventricle, is directed by the Eustachian valve through the foramen ovale into the left auricle. Consequently,

this portion of the blood also escapes the passage through the lungs, and is distributed by the left ventricle to the head and body generally through the aorta.

At birth, the lungs, which had been previously inactive, come into play, and blood is drawn into them through the pulmonary artery. As a necessary consequence, the foramen ovale 1 and ductus arteriosus—the channels by means of which the passage through the lungs had been avoided, become useless. The arterial duct contracts and ceases to be pervious ; while the foramen ovale also closes and the separation of the auricles is henceforth complete.

The arrest of development of the heart, which is the cause of the con genital malformation, may occur at any of the stages which have been referred to. The heart may retain its nearly primitive form of a double cavity with only rudimentary divisions between the two sides, and the aorta and pulmonary artery may be still undeveloped from the original arterial trunk. This form is not common, but examples have been no ticed. In the earliest of these, placed on record by Mr. Wilson in 1788, the infant survived its birth seven days.

If the arrest take place at a later period, the septa dividing the cavities are more nearly complete, and the aorta and pulmonary artery are distinct vessels. This condition is far more common than the preceding. Its prominent feature, in addition to the still imperfect state of the partitions, is a displacement or even a transposition of the great vessels. The aorta is displaced to the right, arising iu part from the right ventricle ; or it springs completely from that cavity and the pulmonary artery takes its origin from the left ventricle. When the aorta is merely displaced to the right, without malposition of the pulmonary artery, we usually find some obstruction to the passage of blood from the right ventricle through the lat ter vessel. The artery is too small, or its valves are incomplete, or the blood is prevented from passing freely into it by some constriction of the ventricle near the outlet, or its channel may be even entirely obliterated. In all such cases the foramen ovale must remain open or the circulation could no longer be carried on. The blood being unable to find its way in sufficient quantity to the left side of the heart through the lungs, con tinues to follow its original course through the opening in the auricular septum, and the foramen ovale is prevented from closing. If, however, in such a case the aorta arise sufficiently to the right to allow of the escape of blood through it from the right ventricle, the foramen ovale and ductus arteriosus may cease to be pervious.

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