Arterial vascularization of the sino-atrial and atrio-ventricular nodes and frequency of coronary artery branches in Papio Erxleben, 1777

The arterial blood supply to the sino-atrial (S-A) and atrio-ventricular (A-V) nodes was studied in 63 baboon hearts (Papio cynocephalus and Papio hamadryas). The arterial coronary injection was made with latex neoprene (23 hearts), a latex and lead oxide mixture (30 hearts) and polyester resin (10 hearts) for dissection, radiographic and corrosion cast studies, respectively. The S-A artery is a long recurrent left coronary branch (92.1%) or an ascendant less long right coronary branch (7.9%). The A-V arteries were 2 or 3 small branches of the interventricular posterior artery originating from the right or the left with the same frequency as in man. The percent distribution of the other coronary branches was similar to that observed in man.     

The development of the conduction system in the mouse embryo heart: IV. Differentiation of the atrioventricular conduction system

The development of the atrioventricular conduction system in the mouse heart has been studied by light and electron microscopy from the time of the completion of ventricular septation to fetal stage II, 13–16 days postcoitum. At the beginning of this period the already established atrioventricular node (AVN) enlarges rapidly into the dorsal AV cushion from the primitive AV tract, reaching almost its full fetal size when septation is complete. The development of the atrionodal interconnections is a slow and complex process. The dorsal atrial myocardium develops on both sides of the node, establishing a muscular overlay over its proximal aspect, and also incorporating the former AV tract. At this time also, the developing muscular interatrial septum grows downward to establish contact with the node, the sinus venosus, and the myocardium of the right and left atrial walls. The distally proceeding differentiation of the ab initio continuous conduction pathway along the AVN, His bundle, and bundle branches demonstrates a progressive and sequential development of high cellular glycogen content. Progressive isolation of the atrioventricular conduction system leading to (still incomplete) insulation by connective tissue, has been observed.     

Blood supply and the atrioventricular conduction system of the dog heart

In 30 experiments in order to specify the blood supply and conducting system in the dog heart, coronal arteries were injected with a contrasting mass that was followed by roentgenography and preparation of the coronal arteries. The topography and blood supply of the atrioventricular conducting system with application of prevital blood supply, and the left coronal artery is the main source of blood supply for all the parts of the cardiac atrioventricular conducting system.     

Effect of cimetidine on the heart conduction system]

An effect of cimetidine on ECG records has been investigated in a group of 40 patients with gastric or duodenal ulcers and coexisting circulatory disorders. For this purpose ECG has been recorded with Holter's technique (Medilog 2000) together with ECG-recording using high amplifying technique. An intravenous injection of 200 mg of cimetidine produced in some of patients inhibition of the sinus rhythm atrio-ventricular conduction disturbances as well as changes in the end phase of ECG ventricular image. The authors suggest, that intravenous administration of cimetidine to patients with cardiac diseases should be monitored with ECG recording.     

The conduction system in the human heart at midgestation-immunohistochemical demonstration of the intermediate filament protein skeletin

Summary The intermediate filaments have during recent years increasingly attracted attention and new information on the distribution of the subunits of the filaments has become available by the use of specific antibodies. In the present study human fetal hearts at midgestation were studied with immunofluorescence microscopy for a demonstration of the intermediate filament subunit skeletin. In the ordinary ventricular and atrial myocytes the fluorescence was moderate, mainly concentrated to the Z disk levels. The proximal parts of the conduction system also showed a moderate fluorescence, while the fluorescence was intense in the cells in the peripheral parts. The shift from moderate to intense fluorescence occurred in the very proximal part of the left bundle branch and in the distal part of the intramural right bundle branch. We conclude that the conduction cells attain Purkinje fibre-like characteristics at these levels, as evidenced by the content of skeletin. Furthermore, the human fetal Purkinje fibres are more easily distinguished with the technique used herein than with conventional histological techniques. The observed differences in content of skeletin are discussed in terms of the cytoskeletal function of intermediate filaments and the embryology of the conduction system.     

The development of the conduction system in the mouse embryo heart: I. The first embryonic A-V conduction pathway

In the 8-, 9-, and 10-day-old mouse embryos, the primitive atria are interconnected with the ventricles via the atrioventricular (A-V) canal. Due to the twisting process of the tubular heart, the wall of the A-V canal establishes continuity not only with the left ventricle but also with the bulbus and truncus arteriosus. At this stage of heart development, the A-V node and bundle have not yet appeared, and, thus, the atrial impulse must be conveyed to the ventricle by the muscle tissue of the wall of the A-V canal, in which two muscle cell layers have been observed. The inner layer extends deep into the left ventricular cavity and is interconnected with both the trabecular system and the ventricular (IV) septum, which begins to develop on the tenth day. In the inner dorsal wall of the A-V canal, the cells are large (～ 20 μm in diameter) and show a strong PAS reaction. It is likely that these large glycogen-rich cells from which the A-V node primordium develops on the eleventh day play the main role in the A-V impulse conduction. The muscle cells at the ventrolateral walls of the canal are small and form a loose spongy myocardium into which the connective tissue cells begin to penetrate on the tenth day, ultimately to form the annulus fibrosus. At the same time, the outer cell layer of the dorsal wall begins to deteriorate; the cells show vacuolar degeneration, myolysis, and shrinkage necrosis. This process appears to represent a programmed cell death, as was described in the bird heart (Pexieder, 1975). On the basis of morphological data, the sequence of atrioventricular activation before the appearance of the A-V node and bundle is discussed.     

The development of the early atrioventricular conduction system in the embryonic heart

Recent electrophysiological evidence indicates that periodic spontaneous depolarizations occur in the primordial heart of the bird (and presumably mammal) even before the myocardial cells can contract, and these are initiated in the primordial sinoatrial region. As contractions are generated, these then establish a peristaltic wave. From that time on, during ontogenesis, the contractile sequence follows a regular pattern of development. As chambers form they contract sequentially in the direction of blood flow, even though, in the twisted configuration, myocardial continuities suggest the possibility of short-circuiting the electrical conduction pathways from atrium to bulbus. This implies that, even at these early stages, the electrical properties of the myocardium are not isotropic, and that specialized conduction pathways must exist. To the present time, electrophysiological techniques have limited the direct evidence that can be obtained on these delicate electrically specialized pathways. However, microscopical techniques have permitted studies on the morphological development of the tissue and of the cells in the various regions of the myocardium. The present paper traces the development of cell morphology in these regions, including the development of structural nodes and proximal ventricular fibre pathways, and from these observations, the manner in which the electrical conduction pathways are believed to develop is suggested.     

Electron microscopic study of the innervation of the heart conduction system in rats]

A systemic quantitative electron microscopic analysis on innervation of the sinus node, the atrioventricular node, the bundle of His and its pedicles within the interventricular septum has been performed in intact hearts of mature rats. The data have been obtained on the size of nonmyelinated and myelinated nerve fibres, efferent and afferent terminals within different parts of the cardiac conductive system, their interconnection with specialized cardiomyocytes have been described. Application of certain methods for electron microscopic investigation on the innervation of mammalian cardiac conductive system has been discussed.