was that the defect was primarily in the septum of the ventricles, due
to a want of formative energy, and the pulmonary artery closed itself,
as do other arteries, from want of use. Meyer showed that a defect of
the septum was incapable of causing narrowing of the pulmonary artery,
since the exit of blood is easier through the artery, from the form of
the right ventricle, than through the open septum; the passage of the
blood from right to left is opposed by the blood-mass in the left
cavity. Heine also thought the pulmonary-artery narrowing was a
secondary defect, but did not think the opening of the septum caused
the narrowing. He considered the primary malformation to be a deviation
of the septum to the left. The deviation of the partition before its
closure brought the aorta within the left cavity, and furnished a free
exit for the blood from this chamber shorter and more convenient than
through the pulmonary and the ductus arteriosus Botalli to the
descending aorta; the pulmonary artery collapsed for want of use,
similarly to other foetal blood-courses. Hence, Heine considered that
in all cases of open septum and apparent transposition of the aorta
which exhibited no evidences of inflammation as a conjectural cause of
narrowing or closure of the pulmonary artery the explanation was to be
found in a primary deviation of the septum ventriculorum.
The difficulty in Heine's theory lies in showing the mechanism of a
deviation of the septum without a primary obstruction of the flow of
blood through the pulmonary artery. The hypertrophy of the right
ventricle which Heine proposed as an explanation is almost certainly a
secondary effect of the obstruction, and therefore cannot be supposed
to originate a deviation of the septum; it is doubtful if hypertrophy
can be considered as a cause of increased blood-pressure within the
cavity of a ventricle under any circumstances, and certainly not as
exercising pressure in a direction to cause the supposed deviation of
the septum. An open septum without obstruction of the pulmonary
orifice, which rarely occurs, does not produce hypertrophy of the right
chamber.
The explanation of cases of open septum with obstruction of the
pulmonary artery seems entirely satisfactory by Hunter's theory, or by
what Kussmaul has named the engorgement theory. But when there is a
real transposition of the arteries, the pulmonary placed farther to the
left and behind and coming from the left cavity, the aorta in front and
to the right and arising from the right or pulmonary chamber, thus
changing their relative positions and their orifices exchanging
ventricles, the difficulty of explanation becomes great, and the cause
of the abnormal relations of the vessels cannot be traced to a simple
deviation of the septum ventriculorum.
For the explanation of these cases of complete transposition of the
vessels, as well as their transplantation relatively to the ventricles,
Rokitansky has traced respectively the development of the two arterial
trunks from the common trunk and of the septum ventriculorum. He
considers that the partitioning of the arterial trunks is the governing
factor in their formation, and that the ventricular septum is arranged
in conformity with the septum of arterial trunks. In tracing the
development of the circulatory apparatus in man there seems to be no
doubt that the heart develops exactly like that of other vertebrates.
The very first rudiment of the heart is a spindle-shaped thickening of
the intestinal fibrous layer of the fore part of the alimentary canal.
This spindle-shaped formation then becomes a hollow pouch, and
separates from the intestinal layer and lies free in the cardiac
cavity. The earliest condition {699} yet seen in the human being is
that from an embryo of about two weeks (Coste), in which the viscus
appeared as a simple tube in the shape of a letter S--the hollow
rounded pouch having slightly elongated and bent to this form, and
simultaneously turned spirally on an imaginary axis, so that the
posterior part of the tube rested on the dorsal surface of the anterior
part. The yelk-veins connect at its posterior part, while the arteries
form a continuation of its anterior extremity. The spiral turning and
curving increase, and simultaneously two shallow indentations appear in
the twisted pouch, transversely to its long axis, looking like kinks in
a flexible tube. These indentations mark the outline of the three
primitive portions of the central organ--viz. the first, with which the
veins communicate, represents the future auricles; the next, the
ventricles; the third portion, the common arterial trunk (aortic bulb
or truncus arteriosus communis). Early in development the first section
is the largest, but by the time the S is formed the middle or
ventricular portion exceeds in size the auricles and their appendages.
So far, the central organ remains a continuous tube, indented
transversely in its course at the points which mark its future
division; the blood moves through it as through a coiled tube, entering
by the veins and passing out by the aortic bulb to the vascular or
branchial arches; the venous entrance is posterior, the arterial exit
is anterior and is directed toward the future aortic arch. This is the
condition at the end of the second week. The future auricles and
ventricles now form a common cavity; the indentation between them,
called the auricular canal, represents the future auriculo-ventricular
orifice. The future fibrous ring forming this orifice is the first to
be developed of all the permanent structures of the heart; its
infolding to form the two auriculo-ventricular orifices comes early,
but at a later date than here spoken of. Its exact method of
development is not clearly described.
Between the second and fourth weeks is exhibited an indication of the
future most important step in development; this process does not really
step forth until the fourth week, although superficial traces of a
furrow antedate this time. This step is the division of three sections
of the tube into opposite halves, a right or venous, a left or arterial
half. This division results in the formation of the future septa
between the auricles and between the ventricles, and separates the
common arterial trunk (aortic bulb) into the future aorta and pulmonary
artery. This partition is spoken of as longitudinal; but it will be
seen, if the real lines of growth of the future auricular and
ventricular septa are carefully regarded, that the indentations which
mark their site are also transverse, as were the primitive ones for
division of the auricles from the ventricles. The proximal end of the
tube comes in contact with the distal portion by a further bending
movement, so that these two ends go to make the left half of the heart;
and the middle portion of tube, composed partly of auricle and partly
of ventricle, forms the right half of the heart. This secondary
indentation, commonly spoken of as longitudinal, is in reality
transverse, although, from the more markedly bent condition of the tube
which has come about, it does not advance in the same plane as the
primitive indentation of the tube. The mechanism of the division of the
aortic bulb will be described later.
This secondary indentation, which finally results in the formation of
the auricular and ventricular septa, appears earlier in the ventricular
cavity, about the fourth week, and later in the auricles, about the
eighth week. By about the twelfth week the process of formation for the
muscular partitions is completed; the septum ventriculorum normally is
gradually built up, and by this time has joined itself, at the base of
the heart, to the septum forming itself in the arterial bulb; thus the
right and left ventricles are finally separated. The septum in the
auricles is also finished in its muscular part, mostly built up from
the base and posteriorly toward the roof of the cavity, {700} leaving,
however, the foramen to be closed by the membrane some days after
birth.
The foetal heart from the fourth week onward becomes more and more
rounded in outline, and finally more or less rectangular. The auricular
appendages become conspicuous and overhang the ventricles. The future
left ventricle appears larger than the right, and the former projects
notably leftward and downward. The aortic bulb or common trunk appears
to arise wholly from the right ventricle, although the vessel
communicates with both cavities, since at this period the cavities are
undivided. The furrow which marks the line of the future septum
ventriculorum runs to the left of the root of the common trunk; and
until at least as late as the sixth week this trunk appears from the
exterior to be in connection only with the future right ventricle.
As early as the sixth week, possibly earlier, a distinct furrow is seen
on both sides of the common trunk running longitudinally from its root
at the ventricle to its first branch (branchial arch). This indentation
does not traverse directly to the ventricular furrow; in fact, at this
period the ventricular furrow is not conspicuous at the origin of the
trunk toward the base of the heart, the septum within not having risen
as yet to the base of the ventricles. During the formation of this
furrow the common trunk continues its slow partial rotation on its
axis; the rotation of the other parts of the cardiac tube has ceased;
the segments of the tube have come to a standstill--become, as it were,
fixed and adherent to each other, the proximal to the distal end, the
anterior surface to the posterior, through the previous bending of the
tube on itself.
Within the common trunk Rokitansky has described the changes, as seen
in cross-sections, which result in its division into a permanent aorta
and pulmonary artery, and also the adaptation of the septum arteriosus
trunci to the septum ventriculorum. He says that at an earlier period
than here described for the external furrow appearing, on the inner
surface of the truncus arteriosus communis (aortic bulb), to its left
side and somewhat posteriorly, above the starting-point of the anterior
limb of the septum ventriculorum, a little swelling appears, which
grows toward the right and slightly forward, so that the common trunk
is divided into an anterior rather left-hand, and a posterior right
portion, respectively the pulmonary artery and aorta. The growth does
not pass in a straight line through the lumen of the common trunk, but
so that the forming septum makes a concavity posteriorly toward the
aorta, and a convexity anteriorly toward the pulmonary; thus, on
cross-section the aorta has the outline of the gibbous moon--the
pulmonary, fitting into it, separated by the septum, of a new moon. The
septum ventriculorum, as seen starting at the base of the ventricles
from the fibrous ring of the auriculo-ventricular orifice (having
already been built upward from the future apex of the heart),
originates at a point on the posterior wall of the common ventricular
cavity in exact correspondence with the starting-point of the little
swelling on the inner surface of the common arterial trunk. The two
septa are thus formed in apposition. The septum ventriculorum, in
advancing forward to meet the other limb of the septum forming on the
opposite wall of the ventricular cavity, follows the septum trunci
arteriosus communis, surrounds the posterior vessel (the aorta) to its
front, then passes around it to its right; the pulmonary is on the
other side of the septum; the portion of the septum ventriculorum
between the orifices of the vessels is the pars membranacea of the
septum. The anterior portion of the septum ventriculorum forms one wall
of the arterial conus of the right ventricle. Thus it happens that by
the eighth week the common trunk is divided into aorta and pulmonary
artery; the structure of the septum ventriculorum is so far advanced
that these vascular trunks are connected with the proper ventricles,
but the {701} septum ventriculorum does not close completely until
about the twelfth week.
In explaining the occurrence of a transposition of the arterial trunks
in accordance with the facts of their normal development, Rokitansky
says, if the septum trunci, starting from the usual point of the little
swelling on the inner surface of the common trunk, turns abnormally
with its concavity forward (instead of backward as normally), and thus
passes through the trunk, there will be established an anterior left
aorta and a posterior right pulmonary, because the septum ventriculorum
in its growth conforms to the direction of the septum trunci. Thus,
another than the usual portion of the common trunk is partitioned off
and placed in communication with the respective ventricles. This
furnishes us with examples of transposition of the arterial trunks
relatively to each other, but not transposed in relation to the
ventricle into which they are implanted. The great majority of
specimens of this sort with which we are acquainted--and Rokitansky
knew no others--show an open septum. They are usually spoken of,
therefore, as instances of "both vessels arising from the same
ventricle (the right usually)," or of "aorta communicating with both
ventricles, the pulmonary artery normally placed." Rokitansky assigns
no reason for this deviation in the line of growth of the septum trunci
across the lumen of the common trunk; in fact, he never examined a
malformed heart during this stage of development. The deviation of the
septum trunci, the primitive factor in this malformation--since to it
the septum ventriculorum conforms its development--he accounts for by
chance (deviation of formative energy). It seems much more probable, as
it is always the pulmonary artery which must be reduced in size when
the concavity of the septum trunci presents anteriorly (the aorta
occupies the smaller area when the concavity of the septum is
posterior), that the deviation of the septum trunci is due to some one
of the many conditions (endo-myocarditis) which have already been
pointed out as the cause of pulmonary-artery narrowing or closure;
hence, another malformation of the heart can be thus traced to
pulmonary obstruction, the evident cause of so many other defects.
For examples of transposition of the vessels, both relatively to each
other and to the ventricles, with complete closure of the septum
ventriculorum, Rokitansky also gives a satisfactory explanation. It is
important to note the distinction between cases of closed and open
septum. Transposition of the vessels with open septum are, as already
shown, doubtful instances of transposition from one ventricle to the
other, although the vessels may be transposed in relation to each
other; furthermore, the mechanism which explains relative transposition
of the vessels does not explain the implantation of the vessels into
the improper ventricle. His explanation is that the starting-point of
the little swelling from which the septum trunci forms is shifted to a
point farther forward on the inner circumference of the common trunk,
and at the same time has its concavity anteriorly, and as in the
previous case decreasing also the area of the pulmonary artery; and
thus the aorta comes more forward and to the right, and the pulmonary
artery passes more to the left and backward. The septum ventriculorum,
in conforming itself to the abnormal starting-point and direction of
the septum trunci, must consequently pass across the common ventricular
cavity in such direction that the aorta comes in connection with the
pulmonary side of the heart, and the pulmonary artery with the systemic
heart. Consequently, Rokitansky traces both the relative and the actual
transposition of the arterial trunks to the deviation either of the
direction or of the starting-point of the septum trunci. The deviation
of the position of the little swelling on the inner surface of the
common trunk, which Rokitansky supposes, is probably not an actual
transference or misplacement of this point of formative energy, but in
reality a failure of the common trunk (aortic bulb) to continue its
axis-rotation, as it {702} normally does, after the other portions have
become fixed. This premature cessation of the rotation of the common
trunk would leave the starting-point of the septum trunci in a more
anterior position than normal, since the trunk rotates normally in a
direction to bring its left side, on which the starting-point of the
septum trunci is situated, more posteriorly. A pericardial inflammatory
adhesion, such as Meyer pointed out for certain cases of pulmonary
artery obstruction, would fix the common trunk, prevent its proper
rotation, and at the same time narrow the pulmonary orifice in certain
instances. In other cases, in which the pulmonary artery is found of
normal size, the septum trunci may be supposed to divide the vessel in
the usual direction (concavity posteriorly as normal), whilst the
septum trunci commenced to grow from an abnormal position, more
anteriorly and to the left than normal (through failure of rotation);
hence, as the septum ventriculorum conforms to its growth, the vessels
become connected with the improper ventricle; the pulmonary, however,
is not found permanently narrowed, and the septum ventriculorum is
completely closed. Here the cause is a failure of the common trunk to
rotate on its axis, probably from an external adhesion of its
periphery.
Malformations affecting primarily the Right Side of the Heart.
In classifying defects in the course of the pulmonary artery we come
to--
1. Closure or narrowing of the artery, with perfect ventricular septum.
Congenital obstruction of the pulmonary artery, with closed septum,
although more rare than with open septum, is nevertheless a frequent
defect. Unfortunately, it is very often impossible to distinguish with
certainty whether the stenosis is essentially congenital or is acquired
after birth. Complete closure is the least difficult to distinguish,
because this defect very soon causes death; the prognosis in a merely
narrowed orifice is much more favorable. The duration of life in
complete closure never extends beyond a full year, while in undoubted
congenital narrowing the age of sixty-five years has been attained.
From this atresia the most striking consequence is a reduction of size
of the right ventricle, increasing almost to closure. This result is so
common that Peacock thought it was the law that in atresia the right
ventricle reduced itself to closure, while in stenosis it dilated and
became hypertrophied. This is not the law, but only a rule of very
common occurrence. Instances of eccentric and concentric hypertrophy
are found among the records of these cases. Great reduction of the
right ventricle results probably only when the obstruction comes very
soon after the completion of the septum ventriculorum--thus at a time
when the ventricle is yet very small. The wasting of the right
ventricle can reach a very high degree, and when it becomes very great
the tricuspid orifice is also defective. The foramen ovale and the
ductus arteriosus Botalli are, in complete closure, usually found open.
The obstruction may come in the conus or at the valvular orifice, or
the artery is found converted into a cord.
In seven cases the duration of life varied from four days to nine
months.
When the stenosis does not reach a high grade, positive clinical signs
are often wanting for the determination of its existence, and the
difficulty becomes greater as the age of the person advances.
Clinically, we find congenital blueness with palpitation, dyspnoea,
together with the physical signs of pulmonary stenosis; these symptoms,
however, may make their first appearance only on the advent of some
acute disease. Sometimes they come in the first month or the first year
of life, or even much later. {703} If abundant congenital compensatory
changes are present, the symptoms may be postponed until further
compensatory alterations become impossible; or at the narrowed orifice
the development of a fresh endocarditis may determine the occurrence of
symptoms. The mere increase of the body and of the mass of the blood
may alter the relations of the circulation, and this disproportion may
show itself with suddenness. Febrile conditions may also suddenly
disorder the circulation.
The compensatory alterations which commonly are held to indicate a
congenital origin of stenosis of the pulmonary artery are patulousness
of the auricular septum and of the ductus arteriosus Botalli. When both
of these remain open there cannot be much doubt that the date of origin
is from the foetal state or in the first weeks of life. If only one of
the foetal passages remains open, the ductus gives a greater surety of
a foetal date than the foramen ovale. The closure of both foetal
passages does not exclude a congenital origin if the obstruction of the
pulmonary orifice is moderate. The patulousness of both foetal passages
indicates that the defect arose at least shortly after birth, because
these openings close within four or five weeks of this event. The
foramen ovale alone open indicates very little with certainty, as it is
so often found with one or more small openings without any probable
cause. Bézot found it partially unprotected in 44 cases out of 155;
Klob, 224 in 500; Wallmann, 130 in 300. Rokitansky has indicated that a
strong blood-pressure not unfrequently may press the fibrous valve of
the foramen strongly toward one auricle or the other, and thus lead to
its atrophy in part, forming larger or smaller openings of
communication between the two cavities. In doubtful cases of stenosis
of the pulmonary artery such small openings are not signs of much value
in determining the congenital origin of the stenosis. Unless there is a
marked defect in the septum atriorum, the congenital origin of the
pulmonary atresia or stenosis cannot be predicated on this ground.
Patency of the ductus arteriosus Botalli has been very rarely observed
as a primary malformation. A coincidence of this as primary defect with
post-natal stenosis of the pulmonary artery must necessarily be
extremely rare. In persistence of the ductus art. Botalli the current
passes from the aorta toward the pulmonary artery; the obstruction of
the pulmonary artery conditions a dilatation with hypertrophy of the
right ventricle. Reopening of the closed ductus is impossible.
The condition of the pulmonary valves as well as the diameter of the
pulmonary artery itself and its branches often afford valuable points
for the determination of the congenital origin of stenosis of this
orifice. The greater the narrowing, or the more extreme the thinning of
the wall, the earlier the coming of the obstruction.
Morgagni reported the first case of stenosis of the pulmonary
orifice--in fact, the first case of congenital malformation of the
heart--in a girl aged sixteen. He recognized the relationship of the
open foramen ovale and the dilatation of the right ventricle as
mechanical effects of the pulmonary stenosis.
2. Obstruction of the conus arteriosus dexter, with open ventricular
septum.
A. The separation of the conus in the form of a so-called supernumerary
third ventricle has been reported by Peacock in ten cases, and ten
others have been added by Kussmaul from various sources. The degree of
separation varies very greatly in individual cases: in some it is so
slight that the designation becomes doubtful, while in others it is so
great that the word stricture might with propriety be employed. In two
cases a goosequill-sized opening existed between the sinus of the right
ventricle and the conus; in others the communication between the two
was multiple. The size of the supernumerary ventricle varies greatly;
in one case of a girl of twelve years it would only contain a hazelnut.
{704} In most of the cases the partitioning probably commences by
hypertrophy of the muscular bands which are more or less marked in
normal hearts in this situation: to this, as the result of
endo-myocarditis, is added cicatricial contraction of the inflammatory
products, whereby the original partitioning becomes greatly increased.
The preponderating frequency of the seat of the stenosis directly at
the transition of the conus to the sinus increases the likelihood of
this explanation of its causation.