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

by Unknown

The alteration in the form and size of the right ventricle varies greatly according to the time at which the pulmonary obstruction originates. The ventricle seems to maintain its size, and even to become hypertrophied and dilated, when the pulmonary obstruction occurs before the closure of the septum: if the pulmonary artery is obliterated or exceedingly narrowed at a later period, the ventricle shrivels, because no blood is able to pass, and gradually more and more of the foetal current passes through the foramen ovale to the left side; if, however, the pulmonary defect is but slight, the right ventricle continues its function, becomes hypertrophied, and may dilate. In pulmonary obstruction the right ventricle changes its form somewhat in accordance with the seat of obstruction. Thus the primary obstruction may be in the pulmonary artery or its branches; or in other cases the malformation is found within the cavity of the right ventricle. The last group is spoken of as conus stenosis.

The malformations of the conus of the right ventricle may present themselves under three forms: they all act as constrictions, but alter the shape of the ventricle very variously; their effect on the circulation is practically the same, varying only with the closeness of the constriction. If an inflammatory process occur at the seat of the normal muscular constriction between the sinus and the conus, it may result in fibrous thickening and contraction; thus the normal division of the sinus from the conus becomes exaggerated and permanent. The narrowed portion may continue to exhibit evidences of endocarditis, or these may fade away, leaving a smooth surface. These narrowed parts seem to be especially liable to inflammation at a subsequent period as the bulk of the blood and the force of the circulation increase. Peacock describes a condition of narrowing due to muscular hypertrophy alone. It would seem in these cases that the hypertrophy was, in not a few of the instances, an acquired condition, and not congenital.

These cases present a heart having, as it were, a double or subdivided ventricle, comparable to that of the turtle. The condition has been described by some writers as a supernumerary ventricle. The form and size of the communication between the two portions of the ventricles vary very greatly: in some of the cases due to inflammation the passage merely admits of a large probe, and consists of a firm fibrous ring, or there may be two or more such openings. In constriction by muscular bands the opening is usually a large oval with smooth walls. In these cases the size and the condition of the walls of the so-called supernumerary ventricle present different appearances according to the degree of constriction and the size of the pulmonary opening; it is probable also that the condition of the ventricular septum influences the consecutive alteration in the parts. When the constriction is close and but little blood enters the conus, its walls are thin and flaccid, while in cases of less marked narrowing, provided the pulmonary artery remains nearly normal, the walls of the conus become hypertrophied, in conjunction with a similar development of the other parts of the right ventricle.

In other cases the entire conus may be uniformly narrowed: this change is due almost invariably to inflammatory lesions, and in many instances it is difficult to determine whether the condition is of foetal origin or whether it arose during the early months of extra-uterine life or even at a later period. Its occurrence in conjunction with other malformations would point to its origination during the developmental period. The conus may also present a constriction directly at or just beneath the valvular orifice of the pulmonary artery. This condition is almost invariably combined with some narrowing of the artery itself, and there is so constantly present evidence of inflammation of recent date that it is almost impossible to say whether the defect is not due to a myocarditis originating after the developmental period. With this condition the entire conus usually presents more or less shrinkage or collapse, becoming greater as the constriction at the orifice is more marked. This collapse of the conus is to be looked upon as secondary to the primary defect at the orifice.

Closure or narrowing of the pulmonary artery trunk may be traced to many conditions acting at several different points of the course of the blood. Nearly all these conditions are caused by inflammatory lesions which result in contractions of the arterial walls. In fact, pulmonary artery defects not dependent on inflammatory changes are very obscure and difficult of explanation. In adult life we know of only two conditions which lead to obliterations of vessels; first, inflammation of the lining membrane (endarteritis); and second, stoppage of the blood-current, usually through pressure directly applied to the vascular trunk. The clots of blood which occupy the vessels form both in advance and beyond the point of pressure; hence we can look for obstruction, causing closure of the pulmonary artery, at either extremity of the blood-course. Thus, we may think of a primary conus obstruction which may secondarily have the effect of reducing the size of the pulmonary artery, but it is never obliterated through this means; nearly always some blood passes in this direction, and blood also enters the pulmonary artery from the ductus arteriosus Botalli: both conditions necessarily tend to keep the artery from complete collapse; moreover, the artery, even in cases of very narrow conus, may remain of its usual size. The same effect may be produced by narrowing of the tricuspid orifice. This condition is a very rare one, and never could lead to complete closure of the pulmonary artery unless this orifice were entirely obliterated and the septum of the ventricles remained closed. Peacock speaks of premature occlusion of the ductus arteriosus Botalli as one of the causes of narrowing of the pulmonary artery. The obliteration of this portion of the branchial arches, by preventing the blood flowing in its usual course to the descending aorta, he thinks results in narrowing the calibre of the pulmonary artery. May not the condition be equally well interpreted in a different manner? May not it be that the obstruction of the artery was the cause of collapse of the ductus? One would think it possible, if an obstruction arose in the ductus arteriosus Botalli, for the blood-current in the pulmonary artery to maintain another branchial arch patulous for its accommodation, or, failing this, to dilate the pulmonary branches and thence return to the left side of the heart. In rare cases the pulmonary artery has been found deficient in size when the lungs are malformed, either by reduction in their size as a whole or by the absence of one or more lobes. Such a cause has very little opportunity of acting with much force on the pulmonary artery during foetal life. This cause and all the others in this group are to be looked upon as secondary in their effects.

In primary defects of the pulmonary artery trunk the vast majority afford indubitable evidences of an original inflammatory causation; others are due just as positively to a defective evolution of this vessel from the common arterial trunk. Instances are on record of the complete closure of the pulmonary artery and its conversion into a ligamentous cord: these cases are very rare. In a somewhat larger number a pretty uniform narrowing, sometimes to an extreme degree, and often exhibiting thickened walls, is found. It is much more frequent to see the obstruction of the artery, due to inflammatory changes, at its valvular orifice.

Peacock describes the narrowing at the pulmonary orifice in many cases to be due to disease of the pulmonary valves, whereby the number of cusps are reduced in number, or to a membrane stretched across with small openings in its central portion; or the obstruction may consist of a duplicature of the lining of the vessels, or even to bands of muscular fibres surrounding the orifice. Two valves of unequal size may be found at the orifice, giving evidence that the larger one has been formed by the adhesion of two of the normal cusps; the membranous obstruction is probably due to the union more or less complete of the three cusps. The curtains thus formed protrude into the course of the artery and form a deep circular sinus between the valves and the walls of the vessel. The opening between these adherent valves varies from a transverse slit to a tubular or barrel-shaped orifice—a tube within a tube. These diseased valves are thickened, very firm, fibrous, or even calcified. In other cases the obstruction consists of abundant warty elevations, so numerous that they are equally effective in preventing the passage of blood as the united valves. The size of the opening is sometimes extremely reduced, measuring only five millimeters in diameter. The pulmonary artery is most generally less in size than normal, but never becomes reduced to the same extent as its orifice, unless it has likewise suffered from inflammatory disease; otherwise its walls remain thin, resembling the venæ cavæ.

In addition to disease within the calibre of the vessel, Meyer, who strongly advocated the inflammatory cause for all these defects, pointed to pericarditis, occurring at the origin of the pulmonary artery and compressing the vessel, as a rare method of causation.

In a very large majority of the cases of pulmonary narrowing on record the septum ventriculorum is found to be more or less defective. In accordance with the usual principles, this defect of the septum, in conjunction with narrowing of the pulmonary artery, is held to indicate that the obstruction of the artery dates from a period of development anterior to the closure of the septum. This view was advanced by Hunter in 1783. But Peacock gives an account of many cases of pulmonary narrowing, combined with open septum ventriculorum, in which the obstruction was caused by adhesion of the pulmonary valves. It is, however, a fact that the development of the valvular apparatus is not effected until after the septum of the ventricles is completed. How, then, can we suppose valves to adhere so as to obstruct the pulmonary artery and prevent the closure of the septum when in reality the valves themselves have not developed? Does it not seem possible that in some rare cases the opening found in the septum ventriculorum is in reality a reopening? Another case is on record of open septum ventriculorum and narrowing of the pulmonary orifice in a child born of a mother who suffered a prolonged fright during the fifth month of utero-gestation. Strong mental impressions are accounted causes of malformation of the foetus, and in this case the fright, if it was the origin of the defective development of the septum, came more than two months too late.

In cases of pulmonary narrowing with open septum the aorta communicates freely with the right ventricle, or appears to arise from both ventricles, or more rarely from the right cavity alone (the deficient pulmonary artery remaining in its usual position). Many opinions have been held as to which one of the three defects is primary. Hunter's conclusion has most generally prevailed. The obstruction of the course of the pulmonary artery is looked upon as the primary defect. From the obstruction the right ventricle becomes distended, and the opening of the septum is due to the blood-pressure, which prevents the final closure. The blood-pressure also alters the direction of the septum and pushes it farther to the right. Thus the septum comes to stand directly under the aortic orifice, or by a further deviation to the left side brings that orifice wholly within the right cavity. In these simple cases the origin of the aorta from the right ventricle is not a real but merely an apparent transposition or transplantation of this vessel; the aorta has not been moved, but only the septum has been moved under its orifice, and the right ventricle has consequently become more extensive. In other cases the aorta seems to move more toward the right side, usually coming also more to the front, and in other cases there is an actual transposition of these vessels. The method of this transposition will be further described.