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 {693} 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. Osler[7] 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.
[Footnote 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 {694} 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 {695} recorded as possessing a large size beyond the seat of
narrowing in cases of undoubted congenital origin.
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 {696} 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 {697} 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 {698} 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.