A system of practical medicine. By American authors. Vol. 3

by Unknown

The premature closure of the ductus arteriosus Botalli, which is spoken of by some authors, seems to be a rather unfair designation to apply to the condition. In most cases it is in reality an absence of the duct dependent on the defective development of certain of the branchial arches. In other cases the apparent premature closure is due to general uniform narrowing, almost closure, of the pulmonary orifice and vessels; in such cases the lungs are supplied by the enlarged bronchial arteries or other collateral branches. The ductus arteriosus Botalli remains patulous when the pulmonary artery is narrowed or closed; in these cases the blood from the right side of the heart to reach the lungs must pass either through an opening in the septum ventriculorum or through the patent foramen ovale. The duct is generally open in cases of transposition of the main arteries, or even in cases of obstruction of the aortic orifice, or of uniform narrowing of the descending aorta or its main branches. Its usual length and its point of origin from the pulmonary artery or its branches, as well as its junction with the aorta, may vary. Two ducts have been found—one from each pulmonary branch, one of them joining the aorta as usual, the other seeking one of its branches. A distinct duct has been found arising directly from the right ventricle. None of these defects are to be considered as primary malformation, but as the secondary results from alterations of the circulation occasioned by other malformations of the heart or of its great vascular trunks.

Fully bearing in mind the distinction which must be made between primary and secondary defects, and the fact that congenital lesions of the orifices and valves are mostly located on the right side of the heart, let us look at various causes which are capable of producing malformations. In many cases, from the condition of the parts, it is possible to say positively that the alterations are dependent on an inflammatory process commencing in the endo-myocardium at an early period of foetal existence; this is true even after excluding cases in which the inflammatory products present may fairly be considered to be the result of defective development and not its cause. Inflammation was, as has already been shown, long ago pointed out as the cause of these obstructive malformations. Rokitansky (1844) was followed in his views by many, who asserted, probably wrongly, that this condition was the sole cause of the misdirection of development. It was considered that while in very many cases the evidences of the inflammation remained indubitable, in others, through a greater lapse of time, the inflammatory products became less distinct or were wholly removed. Thus, all defects of development may be traced as the results of some obstruction of the pathways of the foetal blood, which, on the one hand, effects the closure of certain vessels or orifices, or on the other hand maintains patent others which normally should be obliterated. It is much easier to trace these causes when they operate during the later periods of development, after the heart and great vessels have assumed the general shape they maintain, than those which operate at the earlier periods of transition. It is plain to us that an obstruction of the pulmonary artery or its branches coming before the end of the third foetal month must, by preventing the flow of blood through it from the right ventricle, maintain an opening of greater or less size in the incomplete septum ventriculorum. It is much less easy—or, in fact, impossible—to be positive about an obstruction or other change which causes the transposition or an unequal division of the great vessels, or which prevents entirely the development of either septum. Nevertheless, we can believe that some obstruction of the foetal circulation causes the former defect as well as the latter, if we may judge of so dark a question by the analogies. In fact, what would present itself as a trifling obstacle in the third or fourth month of foetal life would in the sixth week be an impassable obstruction.

It has been urged against the view that some inflammatory process is the invariable cause of the obstacle, by those who support the development theory, that, as the heart remains in a rudimentary condition, the defects result from a want of formative or plastive activity of the parts. It seems, however, as difficult to account for the want of formative activity which prevents the development of the septum or causes an unequal division of great arterial trunks as to find the traces of an obstruction. Maternal impressions or shocks have doubtless caused many headless foetuses or otherwise misshapen the product of conception during the early months of development. The effect on the foetus from such shocks cannot of course be a direct nervous impression, such as those seen producing local disturbances of nutrition or of formative activity in the adult's own organism, but it is due to disturbances of the placental circulation, by which the blood-current is delayed in the foetal circuit. Such delay may result in a temporary obstruction of the blood in certain foetal vessels. A delay of the blood-current during a few hours in the early period of development of the foetus, when formation is excessively rapid, may result in changes which become permanent. The evidences of such obstruction may fade completely. Osler⁷ has recently urged that it is difficult to suppose an endocarditis limited to the pulmonary valves in an embryo not more than an inch in length, and whose heart could not be above a few millimeters in size. But is it not possible to suppose an endocardial inflammation which affects at the same time, for example, the vascular orifices and the line of the rudimentary septum? The septum may thus be prevented from further development, and the orifice suffer malformation by subsequent contraction. The evidences of the inflammation would greatly lessen as the size of the heart expanded. Cannot inflammation, syphilis, or other communicable disease, from which we know the foetus suffers, be substituted for the unknown "want of formative activity"? In respect to the extent of surface involved in the foetal heart in inflammatory or other morbid processes, can we not suppose that the area exhibiting evidences of disease in the minute heart would be as restricted as in the adult heart? In rheumatic endocarditis of the adult the cause which leads to the inflammation is a general one; the evidences we find of the morbid process, however, are confined to very narrow limits. The reasons for this restriction may be the same.

⁷ Montreal Gen. Hos. Reps., vol. ii.

The simple narrowing of a blood-track where direct evidence is wanting may be explained by the occurrence of a specific morbid process as satisfactorily as by an appeal to lack or excess of formative power. The real difficulty arises in the explanation of cases of transposition of the great vessels. The problem is in every way a most difficult one for solution under any supposition. If it were true that the formation of the pulmonary artery and the aorta was from the start by separate blood-channels, and these distinct vessels suffered a genuine transplantation and became attached to the wrong ventricle, the aorta to the right and the pulmonary to the left ventricle, then undoubtedly we should be compelled to accept the developmental theory as usually expressed. But it is not the case that these vessels are developed in distinct trunks: their development results from the division of a common trunk through an infolding of the walls or the gradual formation of a septum proceeding contemporaneously with the septum of the ventricles, the vessels at the same time making a half turn on their axis. A delay in the formation of either septum may result in the malapposition of the vessels to the ventricles. The septum which is probably delayed in formation is the vascular septum, since it is apparently the growth of this septum that applies the force which results in the axis rotation of the vessels. Are we again to explain the abortive formation of the vascular septum or any portion of the branchial arches by the unknown want of formative power? The want of formative power must have a cause; it does not come spontaneously. Are not inflammatory endarteritis and syphilitic lesions of the blood-channels probable causes of the contraction or obliteration of portions of the branchial arches?

Another question, dark and obscure, requires a short comment. It is commonly accepted, if an abnormal communication (speaking of small openings) exists between the two ventricles, that the septum has been prevented from closing by the blood-current being diverted from its usual course through narrowing of an arterial ostium, and compelled to flow into one or the other ventricle. The patency or the closure of the ventricular septum is held as a criterion of the date of origin of the primary malformation. We know that certain ulcerations of the endo-myocardium may result in forming openings between the two ventricles, but is it not possible that a perforation may be made in the ventricular septum after it has closed by a lesion originating at an arterial ostium of the same character as one that prevented the septum from closing? The muscular tissue of the heart from the third to the sixth foetal month, and even later, is of very soft character. A rapidly-coming closure, or even temporary obstruction, of one or the other great arterial trunks would greatly increase the blood-pressure within the corresponding ventricular cavity. The ventricular septum would become stretched and thin, and might readily be perforated, so delicate is the muscular tissue.

If such a possibility is consummated, it must alter the value which has hitherto been placed on the opening in the ventricular septum as a criterion of the date of origin of the primary lesions of the great vessels which ordinarily are the cause of the patent condition of this partition.

It is to be seen from a review of the recorded cases of malformation of the heart that defects of the arterial outlet of the right ventricle are the primary cause of the largest number of cases. It is impossible to state the proportion of these to those at other orifices or the great vessels, so incomplete are the records and so unlike are the opinions of the reporters. It is but natural that this the more active ventricle of foetal life should exhibit more frequently defects of development, since the left ventricle in adults suffers more commonly in its valvular apparatus during its more active period.

The position at which the defects resulting in obstruction of the blood-current through the pulmonary artery may occur have been mentioned. The degree of the narrowing is of much importance—much more than the seat of the obstruction; but of still greater consequence is the date of origin of the defect of development, since on its occurrence early or late in foetal life depend the condition of the septum ventriculorum and the perfection of secondary compensatory alterations which render the heart capable or incapable of a prolonged extra-uterine life.

Narrowing or closure of the course of the blood passing through the pulmonary artery may be divided into two classes: 1, those cases in which the septum ventriculorum is imperfect to a greater or less degree; and 2, those in which it is fully formed, the separation between the ventricles being complete. The date of their origin corresponds to different periods of the development of the foetus. The earlier the obstruction comes in the normal outlet of the ventricle, the more rudimentary is the ventricular septum. The size of the opening of the septum depends on the degree of narrowing of the pulmonary outlet as well as on the date of origin of the obstruction. If the arteries are transposed in relation to the ventricles, and one of them becomes obstructed, the effect on the septum is the same, although the direction of the current through the opening is reversed. Kussmaul and others have pointed to certain exceptions which may lead to errors. In a congenital opening of the ventricular septum, isolated from other defects, an endocarditis involving the pulmonary orifice may occur subsequent to the time of the usual closure of the septum, or even after birth. It would be difficult to distinguish such a case from one of pulmonary narrowing occurring before the third foetal month. The character of the inflammatory changes and the size of the pulmonary artery beyond the point of narrowing would assist in marking the distinction. It must be remembered, however, that the pulmonary artery is recorded as possessing a large size beyond the seat of narrowing in cases of undoubted congenital origin.