Paper - Transposition of the ventricles and the arterial stems (1931)
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Walmsley T. Transposition of the ventricles and the arterial stems. (1931) J Anat. 65: 528-540. PMID 17104346
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Transposition of the Ventricles and the Arterial Stems
By Thomas Walmsley
Queen’s University, Belfast
The heart which is described here is that of a man who died of heart failure at 35 years of age; for at least 10 years previously there had been complete heart block, the pulse rate being about 40 per minute, but until a month before his death the man had followed the fairly heavy work of a clothpresser,
It was noted, during the removal of the heart, that at its commencement the aorta lay in front of the pulmonary artery and that the two vessels ran straight upwards, maintaining their position and without any spiral twisting on one another, to the upper limit of the pericardium. Outside of the pericardium the aortic arch passed backwards over the left pulmonary artery, and from its summit there arose a common stem for the right subclavian artery and the right and left common carotid arteries and, close to it, as a separate vessel, the left subclavian artery. The ligamentum arteriosum was impervious ; and the left recurrent laryngeal nerve had its usual relations. There was no transposition of any of the viscera. No notes were made of the position of the heart or of its relation to the chest wall.
The aorta and the pulmonary artery, in this specimen of transposition of the arterial stems, arise, it would seem, from their proper ventricles. The ventricle of the left side is continued upwards anteriorly and on the right into a short infundibular part from which the aorta takes origin (fig. 2); there is no infundibular part of the ventricle of the right side, the pulmonary artery which arises from it arising directly from the ventricular base. At their origin the aorta lies in front and to the left of the pulmonary artery in as nearly as possible a reversal of their usual positions; both orifices are of average size (fig. 1).
The heart is considerably enlarged, especially in its transverse axis, the maximum circumference reund the ventricles being 14-75 inches. It is much more rounded in its form than usual, approaching more closely the foetal than the normal adult form; the maximum transverse diameter of the ventricles (d) is 5-7 inches and the maximum ventricular height (h) is 4-6 inches, so that the h/d ratio is 0-82. The margo acutus is replaced by a rounded surface, the change in the form of the heart being largely due to the alteration in form of this region.
1 The clinical history, the electrocardiograph findings, and the details of the coronary artery distribution and of the histology of the a.-v. system will be described in a later paper.
2 See Zimmermann, “Uber die Form des Herzens in Abhangigheit von seiner Arbeit.” Anat. Anz. Bd. Lxrx, S. 466, 1930.
Fig. 2. The heart viewed from in front, above, and the right.
As viewed directly from the front the ventricular region appears symmetrical about the aorta. The anterior inter-ventricular groove commences on the right side of the aorta, runs downwards and to the left, and cuts the lower margin of the heart to the left of its lowest point. The posterior interventricular groove lies in the same relative position, so that the greater part of the ventricular region on both surfaces of the heart is occupied by the ventricle of the left side. The apex of the heart is about the middle of the lower border. The separation between the atria and the ventricles is more pronounced than usual, and when the heart is viewed from the front and in the conventional position, the aorta and the pulmonary artery being cut across above their valves, the anterior surface of the left atrium is more fully exposed than is normal (fig. 2). This is due partly to an increase in the size of the pre-atrial area of the ventricular base, especially on the left side, and partly to a vertical elongation of the atrial chambers, the long axis of both of which is vertical.
The orifice of the superior cava in the right atrium is farther forward than is normal; it lies immediately above the orifice of the atrial appendix (figs. 1 and 7), the crista terminalis alone intervening, and it is separated from the orifice of the inferior cava by the antero-posterior as well as by the vertical extent of the atrial septum. The sulcus terminalis thus runs backwards over the roof of the atrium. The left atrium is remarkable for the alteration in its shape, the direction of its long axis being vertical (fig. 2), and for its large and long atrial appendix which measures 4-75 inches in its axial length; it is the longest atrial appendix which I have seen1. The pulmonary veins open into the upper part of the left atrium. The line of the pericardial reflection crosses the front part of the roof (fig. 1).
The arrangement of the arterial cusps in the atrial roots is the normal arrangement4, and it is possible to identify the divided and undivided bulbar rudiments from which the cusps are derived (figs. 1 and 8). It is to be noted here that the left coronary artery of this heart arises opposite the non-septal cusp of the aortic valve, and, further, that the anterior inter-ventricular artery is a branch of the right coronary artery (fig. 4). The details of the coronary distribution® (fig. 4) demonstrate an almost exact reversal of the coronary fields on the front and back of the heart, and also, what is of significance, that the septal arteries, when viewed from behind (fig. 4), run downwards and to the left instead of downwards and to the right; and among them there can be distinguished, as a branch of the anterior inter-ventricular artery as is usual, the artery of the moderator band‘.
1 See Keith, J. Anat. vol. xvi, p. 211, 1911-12.
2 See Quain’s Anatomy, ‘“‘The Heart,” vol. Iv, pt. 3, p. 48, 1929.
3 See p. 528, footnote 1.
4 Alterations of the origin of the branches of the coronary arteries and in their distribution are common in all types of transposition of the arterial stems, but little attention has been paid to them and their classification seems hardly possible; but though in “uncorrected transposition” (see Spitzer, “Uber den Bauplan des normalen und missbilderen Herzens,” Virch. Arch. Bd. ccxii, 8. 174 u. 191, 1923) as in the normal heart (see Quain’s Anatomy, “The Heart,” vol. rv, pt. 3, p. 100, 1929) the posterior inter-ventricular artery may be a branch of the left coronary artery, there seems to be no record in these cases of the anterior inter-ventricular artery having been observed to be a branch of the right coronary artery. It is apparently also unknown in these cases (and there is no record of the coronary artery origin and distribution in the published cases of “corrected transposition’’) to find a coronary vessel arising, as in this case, opposite the nonseptal cusp of the aorta (see Keith, “Malformations of the heart,” Lancet, pt. 2, 1909; Symmers, “Accessory coronary arteries,” J. Anat. vol. Xt, p. 141).
Fig. 3. Diagram to show (a) the position of the arterial orifices; (6) the position and several parts of the ventricular septum 1-6; (c) the arrangement of the cusps of the a.-v. valves; (d) the position of the crista supraventricularis; and (e) the origin and distribution of the coronary arteries in (A) a case of “corrected transposition” and (B) the normal heart.
Fig. 4. X-ray photograph of injected coronary arteries in a case of “‘corrected transposition”; viewed from behind.
The arrangement of the coronary sinus and of the great veins of the heart wall, with the exception of the anterior inter-ventricular vein, is normal. The anterior inter-ventricular vein, which drains the front of both ventricles, turns to the right in the coronary sulcus, and after a short course in it crosses the right coronary artery and enters the right atrium on its lateral side and in front of the sulcus terminalis. No special significance need be attached, I believe, to this mode of termination of this vein for in the normal heart the small cardiac veins of the right ventricle terminate in this manner; but the direction of the stem of the anterior inter-ventricular vein is the reverse of normal and its separation from the coronary sinus may be a factor in the nonemancipation of the orifice of the coronary sinus from the sinus area to the atrial area of the right atrium? (vide infra).
The atrial and ventricular septa of this heart are complete. The foramen ovale is completely closed and the valve of the foramen ovale, as seen from the left atrium, is of a usual form. There are distinct evidences of the left venous valve in the form of a thin narrow membrane which lies along the septal margin of the inferior cava close to the lower edge of the septum ovale and extends backwards below the posterior limb of the annulus ovalis and forwards below the anterior limb; and from the membrane a rich though fine trabeculated network extends upwards on to the septum ovale. The Eustachian valve is continuous with the Thebesian valve, that is, it does not pass on to the septal side of the caval orifice but is continued straight on below the orifice of the coronary sinus; there is therefore no fold between the orifices of the inferior cava and coronary sinus, and by pulling on the Eustachian valve nothing in the nature of the ridge caused by the tendon of Todaro can be raised. The free edge of the left venous valve can easily be followed on the lower part of the atrial septum above the orifice of the coronary sinus; and by pulling on the common Eustachian-Thebesian valve a number of little ridges are raised which pass below the coronary orifice and join the remains of the left venous valve. The lower part of the sinus area can thus be readily defined and in it there is the orifice of the coronary sinus’.
1 See Griffith, J. Anat. vol. xxxvu, p. 251. The factors which govern the change in position of the orifice of the left horn of the sinus vinosus from the position and valvular relations it has as the left superior cava to the position and valvular relations it has when it forms the collecting stem of the cardiac veins have still to be determined. The dissociation of the anterior interventricular vein from the coronary sinus has been noted in situs inversus of the atria with normal ventricles; see Yater, Amer. J. Dis. of Children, vol. xxxvim, p. 118.
2 In a further communication the position of the a.-v. node will be described.
The pars membranacea septi is longer in its antero-posterior extent than usual for it extends backwards .between the a.-v. orifices along the upper edge of the posterior part of the ventricular septum, as far as their hinder parts (fig. 3 A). In relation to the arterial cusps its fore part is situated below the left cusp of the pulmonary artery, which position represents a reversal of its normal position below the right cusp of the posterior vessel—the aorta— in the normal heart (fig. 8); and, further, its atrio-ventricular part intervenes not between the right atrium and the left ventricle, as is normal, but between the left atrium and the ventricle of the right side. I have understood from this that the posterior part of the ventricular septum met and fused with the septum intermedium not close to the right atrio-ventricular orifice as in the normal heart (fig. 5 A) but close to the left orifice (fig. 5 B), and that it lay, in reference to the atrial canal, to the left of its usual position}.
Fig. 5. Diagram of the formation of the atrio-ventricular septum in (A) the normal heart, and (B) a case of “corrected transposition.” The arrow passes through the septum, which is considered to be a part of the septum intermedium.
The internal conformation of the ventricles of this heart is peculiar. In the ventricle of the left side (fig. 6) the trabeculation has the coarse form and the vertical arrangement which are normally characteristic of the right side, and there is also present the profuse apical trabeculation which is usually found in the right ventricle. There is a well-developed crista supraventricularis above and a moderator band formation below, so that the subdivision of the ventricle which is normally typical of the right ventricle is here present in the ventricle of the left side. The crista supraventricularis (figs. 6 and 8) is a broad flat muscular bundle on the roof of the ventricle, being much less elevated there than is often to be observed in normal hearts; but when followed downwards on to the septum (fig. 6 B) it is continued into a very prominent muscle mass which intervenes between the front and back parts of the ventricular cavity. The moderator band formation, which is of large size and which is continuous below with the apical trabeculae, is continued from the lower end of this mass to the lateral wall of the ventricle; the two parallel parts of which it has been said to consist (Spitzer) could not be defined. The anterior papillary muscle arises from its posterior aspect close to its lateral end. The infundibular (anterior) part of the ventricle is coarsely trabeculated on all its walls up to the bases of the arterial cusps, as is sometimes to be found in the infundibulum of the right ventricle of the normal heart; but the downward extension of this cavity below the moderator band? is represented only by a broken-up slit-like space among the trabeculae.
1 I would point out here—a full account will be given in a later paper—that to reach the ventricular septum the course of the stem of the a.-v. bundle through the fibrous tissue at the base of the ventricles must be much longer in the “transposed” than in the normal heart (fig. 5); and, after microscopic examination of the parts, I believe that the fibrosis which has occurred in the main stem—the right limb of the bundle being normal in its appearances—was the cause of the heart block.
Fig. 7. The interior of the right chambers of the heart. A, the septal parts, and B, the lateral parts.
The left a.-v. valve (figs. 83 A and 6) consists of three cusps and these are so placed that the valve more closely represents a reversed tricuspid valve? than a division of the posterior cusp of a normal mitral valve into the two parts of which it is formed. The anterior cusp is the largest and strongest. It is incised near its medial end, indicating a partial non-union of the two anterior elements (see references in footnote 2 below) of which it is formed. It receives entirely on its ventricular surface the subdivisions of six large chordae tendineae from the anterior papillary muscle and at its edges smaller chordae from the posterior papillary muscle and from the septum; and it is distinguished from an aortic mitral cusp by the fact that some of these chordae reach nearly to its base before they are inserted into its substance. The septal papillary muscles, the chordae tendineae of which are attached to its medial part, are two in number; and their bases are attached to the septum along the anterior edge of the septal extension of the crista supraventricularis, as is usual in the normal right ventricle*. The front part of the base of the septal cusp of the valve crosses the fore part of the septum membranaceum, dividing it, as the septal cusp of the tricuspid usually does, into atrio-ventricular and ventricular parts. The chordae tendineae of this cusp arise directly from the septum and from the more medial of the two small posterior papillary muscles. The papillary muscles of this ventricle have thus the form, size, and position which are characteristic of the muscles of the right’ ventricle.
1 The author believes this part of the right ventricle to be a specific part of the chamber, formed, as it were, by a process of excavation from above downwards in the anterior wall. It is very variable in its size, and when it is absent—as is sometimes to be observed in the human heart and as is so marked a feature in birds—the moderator band formation is incorporated in, and forms part of, the anterior wall. :
2 The tricuspid condition of the left a.-v. valve which has been described to occur in specimens of “corrected transposition” of the arterial stems, such as this case is, is not—at least as it is figured by Vierordt (Nothnagel’s System, 1898) and Abbot (Osler and McCrae, System of Medicine, vol. 1v, 1908)—a reversal of the normal right tricuspid valve as is present in this specimen and shown in fig. 3 A, but might be explained as a division of the posterior cusp of a normal mitral valve. It is true that the observations of Mall (‘“‘The development of the heart,” Amer. J. Anat. vol. xm, 1912) and Shiro Sato (“Uber die Entwickelung der Atrioventricularklappen,” Anat. Hefte, Bd. t, 1914) on the developmental history of the a.-v. valves detract from the significance of the a.-v. valve form in determining the nature of the ventricle, but the reversal of both sides is here so definite that I believe I am justified in using it as is done later in the discussion.
3 Spitzer (“Uber den Bauplan des normalen und missbildeten Herzens,” Virch. Arch. Bd. coxLq1, 1923) distinguishes in the right ventricle a region—the conus of the right aorta (fig. 3 B)—between the anterior cusp of the tricuspid valve and the crista supraventricularis, and in discussing the morphology of the crista holds that it intervenes not between an ingoing and an outgoing part but between two outgoing parts of the ventricle, the pulmonary orifice in front and the right aortic region behind. He does not consider the position of the origin of the septal papillary muscles, which, as it is described here, would not readily form part of his interpretation.
In the ventricle of the right side (fig. 7) the trabeculation is fine, like that which is usual in the left ventricle, but the upper half of the septum is smooth; and this smooth area is bounded above by a limbus marginalis (His) as is usually found on the left ventricle. There is no crista supraventricularis and no moderator band formation. It is possible to identify on the septum a formation and a distribution of the a.-v. bundle limb which are normal in the left ventricle; that is, it is possible to identify (and the identification was confirmed by histological examination) a broad flat band of a.-v. tissue on the upper part of the septum and to follow it downwards to its division into anterior and posterior branches and to trace these branches to their distribution among the apical trabeculae1. There are two cusps in the atrio-ventricular valve, which are arranged as is shown in fig. 3. The cusp which intervenes between the a.-v. and pulmonary orifices is much longer and thicker than the posterior cusp, and shows no tendency to the subdivision which is shown on the posterior cusp; its basal attachment is wholly above the membraneous septum. The chordae tendineae of the cusps arise from large anterior and posterior papillary muscles, which in their size, position, and form resemble those which are normally present in the left ventricle (fig. 7).
As measured on the anterior walls near the base of the ventricles, the wall of the right ventricle is 0-35 inch and that of the left ventricle 0-55 inch in thickness,
This heart is an example of the very rare condition which was named ‘corrected transposition” by Rokitansky*, and the description of it in his terms would be that the relation of the arterial vessels to one another had been altered by an abnormal deviation of the aortico-pulmonary septum so that the trunks had been transposed, and that the transposition had been “corrected” by a reverse deviation of the ventricular septum from its normal position, in that it now surrounds the posterior vessel on its left instead of its right wall (fig. 3 A), so that the vessels arise from their proper ventricles. It has long been recognised that though Rokitansky’s general explanation of the transposition of the arterial stems is a masterly elucidation of an obscure subject, this description of “‘ corrected transposition” is incomplete, and several modifications of it and additions to it have been proposed; but as examples
1 Cp. fig. 56, p. 83, Quain’s Anatomy, vol. Iv, pt. 3. This reversal of the form of the a.-v. limbs has already been noted in a case of “corrected transposition” by Shiro Sato (“Uber die Entwickelung der Atrioventricularklappen,” Anat. Hefte, 151 Hefte, Bd. 1, Hefte 2, S. 244, 1914). A similar case of transposition of the a.-v. limbs was described by Ménckeberg (Verh. d. Deutsch. path. Gesellschaft, Marburg, 1913) in a complicated malformation of the ventricular septum. I have not yet been able to identify the left limb, that is, it is not present in a recognisable form in the moderator band.
2 Rokitansky, Die Defekte der Scheidewdnde des Herzens, Wien, 1875.
of the condition are uncommon}, and as in the descriptions of some of the earlier cases references to the important features have been omitted, some of the newer matter is very largely theoretical. In the six examples collected by Abbot? the aorta and pulmonary artery are reversed in their relation to one another (as in the case described here, fig. 3 A) and they arise from their proper ventricles; in all of them there is a defect of the inter-ventricular septum at its base (there is no defect in the present specimen); and in all of them the a.-v. valve formations are transposed as in this case (but see p. 535, footnote 2), the mitral formation being in the ventricle of the right side and the tricuspid formation in the ventricle of the left side. It is obvious that the reversal of the a.-v. cusp formations, which is a common character of all the recorded examples, cannot be accounted for by a simple deviation of the septum. Lochte?, having described his specimens, especially the second, in great detail, put forward as the explanation of the condition the occurrence of a left to right twisting of the left ventricle round the right ventricle, instead of the normal right to left twisting of the right round the left ventricle, with a corresponding deviation of the ventricular septum which brings about the transposition of the a.-v. valves; and the anomalous position of the arteries he considers to be due to an impeded torsion of the bulbus. But though this condition of ventricular torsion may occur’, its interpretation presents great
1 Spitzer (1923) has made the following analysis of the 16 cases which are described in the literature as examples: (1) and (2) Two cases by Rokitansky in infants (four months and eleven months old). (3) A case of Rokitansky’s cited as such by Vierordt; but it belongs to the opposite type of “uncorrected transposition.” (4) A case reported by Gamage, New England Jour. of Med. and Surg. vol. tv, 1818. (5) Rauchfuss, in Gerhardt’s Handb. d. Kinderkrankheiten, Bd. tv. Abt. 1, 1878. (6) Ténnies, “Uber eine seltene Missbildung des Herzens,” Inaug. Diss. Géttingen, 1884. (7) Mann, Bettrdge z. path. Anat. Bd. xvi, 1889. (8) Grunmach, Berl. klin. Wochenschr. 1890. (9) Graanboom, Zeitsch. f. klin. Med. Bd. xvm, 1891; this is really an example of “uncorrected transposition” with situs inversus of the atria. (10) and (11) Two cases by Lochte, Beitrdge z. path. Anat. Bd. xvi, 1894 and Bd. xxrv, 1898. (12) and (13) Two cases by Geipel, Arch. fiir Kinderheilk. Bd. xxxv, 1903. (14) and (15) Two cases are mentioned, without description, by Keith, Lancet, vol. Lxxxvu, pt. 2, 1909. (16) Shiro Sato, Anat. Hefte, Bd. L, 1914.
In addition to these cases there are two mentioned by Abbot which occurred in Thérémin’s series (Etudes sur les affections congénitales du ceur, Paris, 1895) and there should also be included two cases described by Young and Robinson (Med. Chron. Manchester, Nov. 1907). The six cases described by Abbot are the two cases of Thérémin, the two of Rokitansky, and those of Rauchfuss and Ténnies
2 See footnote above.
3 T have been fortunate enough to see this condition. It occurred in a human embryo of 5-5 mm. C.R. length belonging to Prof. C. J. Patten, and I am much indebted to him for the permission he gave me to model the heart and to include a reference to it here. The embryo showed a very great dorsal concavity and a considerable straightening of the head region; and these abnormalities had prevented, I believe, the normal expansion of the dorsal wall of the pericardium. The ventricular loop lies almost in a sagittal plane on the right side of the heart, the descending limb of the loop being in front and the ascending limb behind and resting on the dorsal wall of the pericardium. At its upper end the ascending limb turns downwards (caudalwards) and forms a loop with the convexity towards the head and then passes backwards to pierce the dorsal wall of the pericardium at about one-third its proper distance from the area of the septum transversum from which the sinus venosus emerges. This looped part lies behind and to the right of the atrial canal, which has been displaced to the left. The atrial part of the heart is small in size, especially the right part which has been unable to expand behind the ascending limb of the ventricular loop.
difficulties for it must be accompanied by irregularities in the hinder parts of the heart which are not referred to by Lochte; and it is obvious that it would require considerable readjustments of development to bring the ventricular bulbus region, which during the early stages lies on the posterior part of the heart, to occupy the most ventral position of the adult heart.
The only other explanation! that there is in this condition a situs inversus of the ventricular loop, the descending limb of the loop being on the right side and forming what is here the right ventricle and the ascending limb on the left and forming the ventricle of the left side, is strongly supported by the arrangements of the ventricles of this specimen; and as the primary anomaly of this heart it would be sufficient, I believe, to account for the reversal of the a.-v. valve formations, the reversal of the internal conformation of the ventricles, the incidence of the atrio-ventricular part of the pars membranacea septi, the reversal of the form of the limbs of the a.-v. bundle, and the reversal of coronary artery fields. This explanation postulates an independence of the ventricular loop from the other parts of the cardiac tube during the early stages of development. Such an independence is easily conceived, and that it does occur seems to be proved by those cases of total transposition of the viscera, including the atria of the heart, in which, however, the ventricles are not transposed?; and the recognition of the ventricles by their internal features, as has been claimed in this account, is the more certainly correct if it be noted that in no case of complete situs inversus of the viscera (including the ventricles of the heart) has there been any doubt of the inversion of the ventricles on account of anomalies in the structure of these chambers.
The primary anomaly of this heart is then, I believe, an inversion of the ventricular loop, so that what is here the ventricle of the right side is the descending limb of the loop and morphologically the left ventricle, and what is the ventricle of the left side is the ascending limb and morphologically the right ventricle. This explanation would account for the structural features of the specimen and also for the left-sided position of the ventricular septum ; and further it would produce a rotation of the ventricular septum and of the proximal bulbar septum in a direction the reverse of normal, that is in a left-winding in place of a right-winding spiral (fig. 8), and the infundibulum, formed from the anterior part of the proximal bulbus as usual, will be included in the ventricle of the left side. Now in all the cases of “corrected transposition” in which the facts have been recorded the aorta forms a normal left aortic arch, and at its termination the pulmonary artery occupies its normal position behind the aorta. I wish therefore to suggest that in these cases the aortico-pulmonary and distal bulbar septa have rotated normally, there being no inversion of these parts, and that, therefore, the anterior arterial stem is, as normally, continued into the right orifice at the base of the heart and the posterior stem into the left orifice (fig. 8 A, 1-8 and B, 1-8)!.
1 This explanation has been suggested by Robertson (“The comparative anatomy of the bulbus cordis,” J. Path. vol. xxv, 1913-14), Shiro Sato, and Spitzer, and is referred to, with modifications, by Bremer (“‘An interpretation of the development of the heart,” Amer. J. Anat. vol. xiu, 1928).
2 Such cases have been reported by Keith and MacDonnell (“Case of transposition of the viscera showing a potentially bicameral heart,’ Proc. Roy. Soc. Med. vol. x1v, 1921) and Yater (“Congenital heart block,” Amer. J. Dis. of Children, vol. xxxvut, 1929); in the latter paper the literature is reviewed.
3 In situs inversus of the ventricular loop the proper anterior surface of the ascending limb and of the bulbus will remain on the anterior surface, just as the anterior surface of the inverted stomach is the proper anterior surface. Transposition of the Ventricles and the Arterial Stems 539
Fig. 8. Diagrams to illustrate the course of the ventriculo-bulbar and aortico-pulmonary septa in A, the normal heart, and B, a heart with transposed ventricles.
1 See the diagrams by Keith (“Malformations of the heart,” Lancet, 1909, pt. 2, and “The fate of the bulbus cordis,” Lancet, 1924, pt. 2). 540 Thomas Walmsley
Below this position, however, the rotation of the ventricular and proximal bulbar septum being the reverse of normal in the transposed heart, the posterior arterial stem will continue its course from the left orifice in the direction the reverse of normal. It will pass again, therefore, to the posterior aspect of the anterior vessel (fig. 8 B, 4-7), instead of to its anterior aspect, but it will be continued, as is normal, into the ventricle of the right side; and the anterior arterial stem, from its position on the right at the base of the heart, will be continued into the ventricle of the left side, which as already indicated will include the infundibulum. I would suggest, therefore, that the transposition of the arterial stems is the direct result of the transposition of the ventricles combined with a normal rotation of the aortico-pulmonary septum!; that is, that the only anomalous condition which is present in “corrected transposition” is the situs inversus of the ventricular loop, and that the straight course of the aorta and pulmonary artery relative to one another is the simple straightening out of two opposite spiral curves?. In the specimen which is described here these opposite rotations have occurred perfectly and the septation of the heart is complete; in this respect it is a unique heart.
1 I have not thought it necessary to enter into the explanation advanced by Spitzer. This is founded on two premises: (1) that transposition of the arterial stems not being a condition of any stage of normal development cannot be due to purely ontogenetic factors; and (2) that the mammalian heart is in direct evolutionary series with the existing reptilian heart. On these premises Spitzer has founded the conclusion that “uncorrected transposition” of the stems is due to the gradual opening up of the right aorta of the reptilian heart (see fig. 3 B), an opening of the conus region alone producing a “riding aorta” with a basal defect of the ventricular septum, and a total suppression of the left aorta producing a condition in which both pulmonary artery and right aorta will arise from the right ventricle. He also postulates, however, a mal-rotation of the bulbus which brings the aorta in front of the pulmonary artery; and, in an extremely suggestive section on the constitution of the ventricular septum, holds that the anterior part of the ventricular septum (fig. 3 B, 1-2) in the more advanced abnormalities is really the very greatly developed crista supraventricularis, and that what is the crista supraventricularis is the true but greatly regressed anterior part of the septum.
The premises of these descriptions do not seem to me to be sound, and the descriptions themselves, I think, require to be re-examined, but when they are applied to “corrected transposition,” in which condition Spitzer believes they occur with a situs inversus of the ventricular loop, it is certain they do not agree with the facts; for as is shown in figs. 3 A and 3 B the “transposed” heart is the mirror image of the normal heart and not of a heart with a right aorta, the only difference of the image being the stem of origin of the coronary arteries. Further, if Spitzer’s account were correct, and if what is named here the crista supraventricularis (fig. 3 A) were the proper anterior part of the septum, then the crista supraventricularis (what is named here the anterior part of the septum (fig. 3 A, 1-2)) is in an unreversed position; and this would render it impossible to name the arterial orifices at all.
2 It is this straight course of the vessels which has given rise to the very common description that there has been an absence of rotation.
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