Book - Contributions to Embryology Carnegie Institution No.32
The Sino-Ventricular Bundle : A Functional Interpretation Of Morphological Findings
By Robert Retzer,
Professor of Anatomy in the University of Pittsburgh.
With one plate.
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Introduction
In spite of the large amount of seientifif work that has been done on the subject, tlie problem of how the contraction wave passes from the venous to the arterial end of the heart still remains unsolved. When a muscular connection between atria and ventricles was discovered and it was found that the severance of this connection brought about arhythmia, many adherents of the myogenic theory felt that the burden of proof lay with the neurogenists. It was, however, not long before it was established that there were nerve fibers accompanying this muscular connection and the problem stood as it did before the discoveries of His and Kent. I have devoted the last fifteen years to anatomical studies bearing on this subject and during this time my views have undergone considerable change.* In the present papers I have undertaken to outline the possible interpretations of the facts as we now know them.
It seems that there is a lack of vmderstanding between the anatomist and the
physiologist, because neither seems to ajipreciate the value of the facts described
by the other. For instance, it should not be left out of account that the heart of
Linuihis (whicli is unquestionably neurogenic) has more resemblance to voluntary
than to cardiac musculature, considering its morphology. Again, the peculiarity
of the histologic structure of the muscular connection between the atria and ventricles and of the Purkinje fibers is left almost entirely out of consideration by those
who hold that the myogenic theory is the only correct one. It is this phase of the
question which is the subject of this paper.
The literature has been so thoroughly reviewed recently by others that
I propose to discuss only those articles that have a direct bearing no the subject at hand. The term "atrio-ventricular bundle" was given by His, jr. (1893)
to a strand of cardiac muscle which arises in the posterior wall of the right
atrium, near the atrial septum, is sui)erimposed on the superior edge of the ventricular septum with numerous interchange of fibers, and (passing forward) divides
near the aorta into a right and left branch, the latter ending in the aortic leaflet of
the mitral valve. It was later foinid that this bundle does not begin nor end in the
manner described by His, but that the region of origin represents the primitive sinus
region of the heart, and that it terminates in a complex network of fibers long
known as "Purkinje fibers." Imbued with the idea that this connection conducts
impulses from atria to ventricles, Tawara (1906) gave it the name of "Reizleitungs-system." This term is still used by manj' authors, but feeling that a morphological
one must be used as long as the question of function is still in doubt, in 1908 I
employed the name "sino-ventrioular l^undle." By this term we definitely
commit ourselves only to the fact that the bundle forms an anatomical connection
between the sinus region and the ventricles. The terms "conductive system" and
"atrio-ventricular bundle" still have their place, as I shall indicate later.
- Although a large part of this work was done during my association with Professor Mall. I should like also to record my indebtedness to Professor Keibel of Freiburg, and Professor Felix, of Zurich, for the courtesies extended to me while a guest in their laboratories; and to Professor Bensley for his kindly interest during my residence in Chicago.
It may be noted that most of our anatonaical text-books take little cognizance of the change of our knowledge on this subject and still persist in using the term "bundle of His." It has already been pointed out that Ilis's description is far from correct. I maj' add here that considerable skepticism as to the correctness of the observations of His existed in the mind of liis father and of other mature anatomists when I made my first observations under Professor Spalteholz, in 1903, and it was for this reason that the problem was undertaken again. Kent's (1893) original description is far more correct in the Ught of our modern investigations than was that of His, and the bundle has been named the "bundle of Kent" by some authors; but we should recognize the fact that it was His, who by exi^erimental methods, was the first to attempt to prove that all impulses from atria to ventricles pass by way of the bundle.
In my notes, made in 1903, when I began my studies on the subject, I find the following review of Kent's article:
- "In his figure on p. 244, it seems to me that he mistakes the Purkinje fibers for fibers
of the myocardium. His description of the cells standing between muscle and connective tissue reminds me also of these (Purkinje fibers)."
This note was made five years before the appearance of Tawara's monograph, which showed indisputably that the Purkinje fibers represented the end-ramifica- tion of the atrio-ventricular bundle. Recently I read the Proceedings of the Physiological' Society of November 12, 1892, which I had previoush^ overlooked, and I was much interested in the report of Kent's paper before the society:
"Between the auricle and ventricle and lying in the cimnective-tissue ring are modified muscle cells, usually spindle-shaped, nucleated, granular, becoming extremely narrow in parts and then swelling out again, transversely striated, branched, and usually connected into a network. These cells are somewhat rudimentary in the case of the rat and are verj' well developed in the monkey. In the latter animal they exist as a complete network, permeating the fibrous connective tissue of the groove and extending through from auricle to ventricle. Upon approaching the groove the normal cardiac fillers split up into similar fibers and become connected with the network of cells lying in the fibrous tissue."
This shows even more conclusively that Kent did recognize the difference in appearance between the bundle-fibers and the heart-muscle fibers and also saw the ventricular transitions between them, although he did not recognize that the end-ramifications of the bundle really represent the Purkinje fibers. His description, however, lacked the dogmatism which seems so essential for the general acceptance of a new idea. Thus he states in a summary:
- "It would appear* then, that the fact of two masses of muscle being joined together by fibrous tissue is in itself no argument agamst the muscular continuity of such masses,
- The italics are mine (R. R.)
Content to be added----
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Cite this page: Hill, M.A. (2024, April 19) Embryology Book - Contributions to Embryology Carnegie Institution No.32. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Contributions_to_Embryology_Carnegie_Institution_No.32
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