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Architectural Basis of Heart Macroscopical Structure
A-. Four anatomical facts
The pattern described was found in all birds and mammal examined, including man. Although the findings relate to human heart, many of the dissections were performed on bovine hearts, which are freely available, but the same morphological features have been amply demonstrated in human hearts.
Four fundamental anatomical facts are first shown in the order in which they were demonstrated.
a) Left ventricle : apical half.
The apex of the heart belongs to the left ventricle. Figure 1 illustrates how starting from the epicardial surface and
pulling on any group of superficial fibres, a laminar trajectory is evidenced with a
corresponding contingent of myocardium, usually called muscular layer, which always took a
helical path. In figure 2 are evidenced
several laminar trajectories, with correspondent muscular
layers, runing from the periphery to the center ; there the sub-epicardial fibres,
undergoing a twist, turned into sub-endocardial fibres around a central tunnel, a virtual
one, closed on the outside by the epicardium and on the inside by the endocardium.
Another way of demonstrating this
arrangement was by dissecting alternate groups of fibres ; then, after being removed the
superficial fibres, that virtual tunnel, or orifice, of the apex became a real one, as
seen in figure 3, defined by the circularly
overlapping muscular layers.
b) Left ventricle : basal half.
A constant architectural order also
characterised the arrangement of the fibres in the basal region of the free wall of the
left ventricle. There, blunt dissection revealed an indefined number of laminar
trajectories, with their correspondent muscular layers, which took a helical path from the
periphery towards the centre (fig. 4). It was
similar in structure to
that observed in the apex and, as
there, another way of demonstrating this arrangement of circularly overlapping muscular
layers was by dissecting alternate groups of fibres to give grooves defined by the intact
adjacent fibres (fig. 5). It could be observed
how the fibres passed beneath, but were not inserted into, the mitral ring (in fig. 5 the mitral ring has been excised).
c) Right ventricle : apical half.
By dissecting alternate groups of
fibres, in the apical border of the free wall of the right ventricle, it was again
revealed a series of overlapping muscular layers separated by correpondent laminar
trajectories (fig. 6).
d) Right ventricle : basal half.
Dissection showed that, at the base,
the myocardial arrangement of the free wall of the right
ventricle (fig. 7)
corresponded with that found previously in the base of left ventricle and in the apical
regions.
It was stablished, by the four anatomical facts described above, that a constant architectural pattern, represented by overlapping or imbricated muscular layers, was common to the basal and apical myocardium.
a) A difference.
But, nevertheless, there was a difference between the basal and the apical regions structure since the fibres, in their helical course from the epicardium to the endocardium, run in opposite sense, as showed by the muscular trajectories when comparing the base and the apex (figs. 3, 5, 6 and 7).
b) A rope model.
Only a rope model, as the one shown in figure 8, can explain that difference, which is evident when
comparing each one of the segments of the rope model with the corresponding anatomical
preparation (fig. 9). It can be seen then
that, being quite parallel the muscular trajectories and the rope bundles, at the base the
fibres go deeper, becoming subendocardial, runing from right to left (see C
and D in the same figure) whereas
at the the apex they become deeper runing from left to right.
Then it was seen also the reason of another difference, the thickness of the ventricular walls ; the left free wall, made up of two loops, is more thick than the right free wall, constituted by only one loop (fig. 9).
c) A muscular band.
The above described four anatomical
facts suggest, when
compared
with the rope model (fig. 9), that the ventricular myocardium
consists of a single band of muscle twisted on itself and curled in two helical loops. But
in such conception, on the ventricular myocardium structure, no one reference was made on
the beginning and the end of that band.
d) The beginning and the end of the ventricular myocardial band.
After establishing that four anatomical facts descibed previously, I had to identify the beginng and end of the single ventricular muscle band. After some unsuccesful years of work I tried to solve the problem with the help of phylogenetics studies since, because of the difficulties of obtaining fetal hearts, I could not develop any study on ontogenetics.
I started with the following basis :
1. In worms (nemertina, annelida) the circulatory system consists of one circular tube divided in
two stretchs, the venous (VS) and the arterial (AS), by a pulmonary and a systemic capillary bed (fig. 10 a). The blood flow is the result of the peristaltic form contactions of the vascular musculature of this primitive circulatory system, which forms a single circle.
2. In a later phylogenetic step, to fishes (b), a simple heart appears in the venous side (SV). It is made up of a single sinus venosus, an atrium and a ventricle. This circulatory system still consists of a single circle.
3. When passing from fishes to amphibia and reptilia (e), the heart is constituted by a single ventricle and two atria. In this circulatory system, however, there are now two circles, a pulmonary and a systemic one. The explanation of these differences, between fishes and reptilia, only can be achieved accepting that there is a looping (c and d) of the arterial stretch (AS) to produce a single common ventricle. This is also the reason on how the two circles appear in amphibia and reptilia.
4. In the next phylogenetic step, to birds and ammals (f), not only do we find two atria but also two ventricles and, of course, two circles, the pulmonary and the systemic. The appearance of two ventricles comes when is completed the looping of the arterial stretch (As) of dorsal aorta. It appears then clear that the atria of the amphibia, reptilia, birds and mammals, represented the vestige of the fish heart .
In this way I reached the conclusion that the origin and the end of the ventricular myocardial band, which makes up, by means of two loops (fig. 9), the ventricles, had to be looked for in the roots of the pulmonary artery and the aorta, respectively, and, in fact, I found them to be where I predicted.
By means of dissection it was confirmed that the pulmonary artery was the point of departure of the ventricular myocardial band whereas the aorta represented its final destination.
After achieving that
results I realize than the rope model (fig. 8 C) should be
transformed in the way shown in figure 11(schemes
A to C).