Mesenchymal tissue of the interventricular septum

Summary Light and electron microscopic studies of frontal and sagittal sections of embryonic chick hearts (Stages 25, 28–29), reveal mesenchymal tissue in the cephalic portion of the interventricular septum. The endocardium of this cephalic portion contains reoriented and invaginated cells with pseudopodia; in addition there are cells immediately subjacent to the endocardium. Similar cellular events take place during the formation of mesenchymal tissue in the atrioventricular and conotruncal regions. In these regions the mesenchymal tissue originates by means of an endocardial activation process.The structural characteristics of the formation of the cephalic portion of the interventricular septum suggest that local mesenchymal tissue is contributed by the endocardium. However, based upon the close anatomic relationship observed by us between the mesenchymal tissues of the atrioventricular canal, conotruncal region and the cephalic portion of the interventricular septum; we do not discard a contribution by migration of cells from atrioventricular and conotruncal regions to the interventricular septum.     

The membranous part of the human interventricular cardiac septum

The arrangement of collagen and elastic fibers of the membranous part of the interventricular septum (PMS) was studied in hearts from adult humans. Connective bundles formed a network of fairly independent tendons arranged in two layers. The tendinous bundles consisted essentially of type I collagen fibers while type III fibers were visible as a thin network with transversely and longitudinally oriented meshes around the muscle bundles. Cranial and caudal to the PMS were narrow and irregular bands of collagen fibers that apparently represented zones of low resistance to the high blood pressures acting from the left to the right heart chambers. The predominance of fiber bundles arranged in an approximately transverse direction with regard to the arterial cone axis suggests a resistance to enlargement resulting from high aortic blood pressure. Elastic fibers were observed in the transitional zone between the cardiac muscle and the PMS. They were continuous with elaunin fibers and these with oxytalan fibers closely intermingled with the narrow network of type I collagen fibers of the PMS. The successive transformation of elastic fibers, which were very numerous in the muscle-tendon transition, into elaunin and these into oxytalan fibers toward the central portions of the PMS suggests a functional sequence characterized by a high elasticity and consequent mobility of the transition region itself and by a progressive increase of resistance in this portion.     

室间隔膜部的应用解剖学研究

目的阐明成年人心室间隔膜部的形态、位置、毗邻关系,为医学影像诊断提供形态学基础。方法成年人离体心脏64例,大体解剖观察室间隔膜部的形态、位置、毗邻结构。胸部断层标本观察室间隔膜部的原位解剖学特征。结果离体心室间隔膜部:①形态可见不规则形、三角形、半月形、圆形、卵圆形、四边形和楔形。②左侧面位于主动脉前半月瓣环和右后半月瓣环相对缘与肌性室间隔嵴之间,上缘紧邻主动脉前半月瓣环和右后半月瓣环及其瓣间三角;右侧面位于三尖瓣前内侧连合处,房室隔最前端,与三尖瓣前内侧连合、室上嵴、主动脉隆凸、Koch三角尖端和右纤维三角相邻。经四心腔横断层,MPIS占室间隔的后1/3,自左前斜向右后与矢状面、冠状面约呈45°角;经升主动脉冠状断层,MPIS自肌性室间隔嵴斜向右上方达主动脉半月瓣环的下方,与正中矢状面呈45°角。结论MPIS形态多样,左、右侧面的位置和毗邻各异;横断层和冠状断层能很好地显示MPIS的形态、位置和毗邻关系。     

Pulmonary artery stenosis with an intact interventricular septum

15 hearts with pulmonary artery stenosis with an intact interventricular septum (PAS with IIVS) were studied morphologically and morphometrically. The results were evaluated separately according to the type of the defect: with a noncomplicated valvular stenosis of pulmonary artery (PA); with a combined valvular and infundibular stenosis of PA. Every of these types of PAS with IIVS has characteristic features of morphological structure and all possess common anatomical signs: constriction at one of the levels of circulation from the right ventricle to the lesser circulation, normal geometric structure of the cone and myocardial hypertrophy of the right ventricle. Leading cause of the obstruction of the right ventricle effluent part, regardless of the PAS with IIVS type, is a hypertrophy of the supraventricular crest and its parietal projection. As distinct from the defects on the conus-truncus, complex of PAS with IIVS is characterized by a normal spatial orientation of the supraventricular crest.     

Role of the left interventricular sulcus in formation of the interventricular septum and crista supraventricularis in normal human cardiogenesis

Serial sections of normal human embryos were studied and three-dimensional images reconstructed to determine the early development of the interventricular septum. The position of the interventricular septum is determined in stage 9 of normal development by the formation of the left interventricular sulcus. As a result of unknown properties of the cells of the myocardial layer, the left interventricular sulcus persists while the right disappears, producing the initial lateral asymmetry of the primary heart tube. By stage 14, the left interventricular sulcus forms a spiral which is continuous with the developing interventricular septum. The dorsal limb of the spiral passes to the right between the atrioventricular canal and the origin of the outflow tract, and is lost in the wall of the trabeculated right ventricle. It appears that this dorsal limb of the spiral is the precursor of part of the cirsta supraventricularis. The midportion of the sulcus, the bulboventricular groove, becomes the socalled fibrous continuity between the aortic and mitral valves. The ventral limb of the spiral passes caudally in the anterior interventricular groove and then dorsally and cranially toward the dorsal cushion of the atrioventricular canal. The ventral limb of the spiral is continuous with the crest of the muscular interventricular septum, which develops by apposition of tissue from the expanding right and left ventricles. From stage 14 to stage 19, the muscular interventricular septum, the atrioventricular endocardial cushions, and the ventricular end of the spiral ridges of the outflow tract appose and fuse. Subsequent formation of the membranous interventricular septum completes the physical separation of the right and left ventricles.     

Morphological changes of interventricular septum in long-term follow-up cases]

In patients who could be followed by echocardiography for a long period, the clinical significance of sigmoid septum and basal septal hypertrophy including long-term changes was investigated in patients with hypertension. The subjects were 66 patients (24 males and 42 females, mean age: 53 +/- 12 years old) who underwent repeated echocardiography, and the initial examination and observation after long-term follow-up (mean duration of follow-up: 10.8 +/- 1.4 years) were compared. Sigmoid septum was more advanced at the time of initial examination in the hypertensive group than in the normotensive group, but it was similarly advanced after the long-term follow-up in both groups. There was no significant difference in basal septal hypertrophy between the hypertensive and normotensive groups at the time of initial examination, but significant increases in thickening were observed in the hypertensive group after the long-term follow-up. The above findings suggested that morphological changes in the interventricular septum reflect the severity of arteriosclerosis that is expected to be more advanced in hypertensive patients than in normotensive patients.     

Role of the left interventricular sulcus in formation of interventricular septum and crista supraventricularis in normal human cardiogenesis.

Serial sections of normal human embryos were studied and three-dimensional images reconstructed to determine the early development of the interventricular septum. The position of the interventricular septum is determined in stage 9 of normal development by the formation of the left interventricular sulcus. As a result of unknown properties of the cells of the myocardial layer, the left interventricular sulcus persists while the right disappears, producing the initial lateral asymmetry of the primary heart tube. By stage 14, the left interventricular sulcus forms a spiral which is continuous with the developing interventricular septum. The dorsal limb of the spiral passes to the right between the atrioventricular canal and the origin of the outflow tract, and is lost in the wall of the trabeculated right ventricle. It appears that this dorsal limb of the spiral is the precursor of part of the cirsta supraventricularis. The midportion of the sulcus, the bulboventricular groove, becomes the so-called fibrous continuity between the aortic and mitral valves. The ventral limb of the spiral passes caudally in the anterior interventricular groove and then dorsally and cranially toward the dorsal cushion of the atrioventricular canal. The ventral limb of the spiral is continuous with the crest of the muscular interventricular septum, which develops by apposition of tissue from the expanding right and left ventricles. From stage 14 to stage 19, the muscular interventricular septum, the atrioventricular endocardial cushions, and the ventricular end of the spiral ridges of the outflow tract appose and fuse. Subsequent formation of the membranous interventricular septum completes the physical separation of the right and left ventricles.     

Catenoidal shape of the interventricular septum acquired secondary to myocardial infarction

A catenoidal, or saddle-shaped, configuration of the interventricular septum, concave toward the left ventricular cavity in the transverse plane, but convex toward the left ventricular cavity in the apex to base plane, occurs in idiopathic hypertrophic subaortic stenosis and possibly may lead to septal hypertrophy and immobility. The authors also have observed catenoidal shape of the interventricular septum in hearts with myocardial infarcts. They reviewed 1,415 hearts examined after postmortem arteriography and fixation in distention from patients autopsied at The Johns Hopkins Hospital. Among 586 hearts with myocardial infarcts, there were 54 (9%) with a catenoidal shape of the interventricular septum. The infarcts, 45 anterior septal and 9 inferior and lateral, appeared to account for the reversal of normal apex to base curvature, although coexistent idiopathic hypertrophic subaortic stenosis could not be excluded in 3 patients. There was moderate or marked infarct expansion in 25/54 (46%) and septal or free wall rupture in 8 (15%) hearts. Reduced average net septal curvature in the 54 hearts, highly significant compared with that in 80 hearts without infarcts (P less than 0.001), would reduce the septum's contribution to left ventricular function and may contribute to the observed postinfarct congestive failure, 30/54 (56%), and hypoperfusion, 7/54 (13%). The results suggest that some myocardial infarcts may produce a catenoidal shape of the interventricular septum that could reduce the functional activity of the surviving uninfarcted basilar portion of the septum and thereby contribute to postinfarction cardiac dysfunction.     

室间隔膜部瘤破裂与室间隔缺损伴发的膜部瘤

室间隔缺损与膜部瘤的关系日益受到重视，主要包括两种情况：即室间隔膜部瘤破裂与室间隔缺损伴发的膜部瘤，前者被称为真性膜部瘤，后者则为假性膜部瘤。有文献报道膜周部室间隔缺损伴有膜部瘤者达30％～60％，作者在对膜周部室间隔缺损进行介入治疗研究中，发现有48．75％的患者合并有膜部瘤。张玉顺等报告的膜周部室间隔缺损伴膜部瘤形成者高达86％。     

Architectonic characteristics of the heart ventricles in a perimembranous defect of the interventricular septum

The results of quantitative morphological macro-, micro-, and ultrastructural (myocardial biopsies) studies of the ventricles with perimembranous septal defect in 135 infants under the age of one year have been compared. In newborns there appeared ventricular myocardial hyperplasia and low absolute and relative values of all the myocardial parameters versus normal control. At the age of 3 months the parameters were similar to or above the control ones exceeding them considerably by the age of 10-12 months. The comparison of the parameters of the septal parts showed predominant abnormality of the sinus part indicating that the perimembranous ventricular septal defect entity is a sinus one.     

The membranous portion of the interventricular septum in neonates An anatomic study in neonatal cadavers

Summary The membranous portion of the interventricular septum (MPIS) has been described as a small, oval portion of the cardiac septum that lies immediately below the aortic valve. Its location and relationship with the aortic valve are very important in surgical interventions. Several studies have been reported in adults but few in neonates. For this reason, studies of the MPIS were made in the hearts of 26 (12 male, 14 female) fullterm neonates. The left side of the MPIS was photographed with transillumination from the right ventricle. The shapes of the septum were assessed from the photographic images. In addition, in accordance with the ruler in the photographs a millimetric scale was prepared on the tracing paper and the surface area of the MPIS and its distance from the superior border of the aortic valve were measured. In these 26 cases, the following shapes of MPIS were found: semilunar, 7 (26.92%); triangular, 6 (23.07%); quadrangular, 5 (19.23%); oval, 4 (15.38%); circular, 2 (7.69%); irregular, 2 (7.69%). Its surface area varied from 2–21 mm² (mean 5.84 mm²). The superior border of MPIS was in close relationship with the aortic valve. In 10 cases (38.46%) the MPIS was in direct continuity with the attachments of both the right and posterior aortic cusps, in 8 (30.76%) only with the posterior aortic cusp, in 5 (19.23%) only with the right aortic cusp, while in 3 (11.53%) the superior border of MPIS was below the attached portion of both cusps. The distance between the superior border of the MPIS and the attachment of the right or posterior aortic cusps did not exceed 3.5 mm. There were no statistically significant sex-related differences in shape, surface area and relationship with the aortic valve.

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La partie membranacée du septum interventriculaire du nouveau-né. Étude anatomique sur des cadavres de nouveau-nés

Résumé La partie membranacée du septum interventriculaire (PMSI) a été décrite comme une petite partie ovale du septum du coeur, située immédiatement au-dessous de la valve aortique. Sa situation et ses rapports avec la valve aortique sont très importants lors des interventions chirurgicales. Plusieurs études ont été publiées chez l'adulte, mais peu concernent les nouveau-nés. Pour cette raison, la PMSI a été étudiée sur les coeurs de 26 nouveau-nés à terme (12 garçons et 14 filles). Le versant gauche de la PMSI a été photographié après transillumination à partir du ventricule droit. Les formes du septum ont été appréciées à partir des images photographiques. De plus, grâce à une règle apparente sur les photographies, une échelle millimétrique a été préparée sur du papier calque, la superficie de la PMSI et la distance la séparant du bord supérieur de la valve aortique ont été mesurées. Parmi ces 26 cas, la PMSI avait les formes suivantes : semi-lunaire 7 fois (26,94 %), triangulaire 6 fois (23,07 %), quadrangulaire 5 fois (19,23 %), ovale 4 fois (15,38 %), circulaire 2 fois (7,69 %), irrégulier 2 fois (7,69 %). Sa superficie variait de 2 à 21 mm² (moyenne 5,89 mm²). Le bord supérieur de la PMSI était en relation étroite avec la valve aortique. Dans 10 cas (38,46 %), la PMSI était en continuité directe avec le bord d'attache des cuspides aortiques droite et postérieure, dans 8 cas (30,76 %) avec la seule cuspide aortique postérieure, dans 5 cas (19,23 %) avec la seule cuspide aortique droite, alors que dans 3 cas (11,53 %) son bord supérieur était situé un peu au-dessous du bord d'attache de ces deux cuspides. La distance séparant le bord supérieur de la PMSI et le bord d'attache des cuspides aortiques droite et/ou postérieure n'excédait pas 3,5 mm. Il n'y avait pas de différence statistiquement significative entre les deux sexes concernant la forme, la superficie et les rapports avec la valve aortique.

     

Development of the outflow tract and closure of the interventricular septum in the normal human heart

The majority of congenital heart malformations in humans involve defects in the atrioventricular valves, the crest of the interventricular septum, and/or the outflow tract, but the position and timing of these structures during cardiac development is controversial. We examined all 622 staged, serially sectioned normal human embryos and fetuses in the Carnegie Embryological Collection, and obtained a statistical tabulation of the appearance of the endocardial cushion components and surrounding structures for 382 embryos in good condition between stages 9 and 23 inclusive, when the heart normally develops. Accurately scaled drawings of ventral and lateral views of the hearts of seven embryos from stage 13 through 22 were prepared from graphic reconstructions in order to visualize the relationships of the structures under consideration. We found that development of the outflow tract septum follows the apparent functional separation of both the left and right ventricles and the blood streams leaving them. Elevations of the endocardial cushion material are continuous throughout the outflow tract and develop as a consequence of the elliptical configuration imposed on the circular cross section of the outflow tract. The membranous interventricular septum is formed of cushion material in the space bounded by the outflow tract septum, interventricular septum, and the fused AV cushion and right outflow tract cushion. The results of this study are consistent with the assertion that functional separation of the aortic and pulmonary outflow tracts precedes anatomic septation, and that anatomic septation is brought about by mechanical modeling of developing myocardium and endocardial cushion material.