Ultrastructural study of specialized conducting and working myocytes in the sinoatrial region of the human heart. I. Qualitative analysis

A qualitative ultrastructural analysis of specialized conducting and working myocytes in the sinoatrial region of the human heart was made using autopsied and biopsied material from 45 men and women. Autopsied material was prepared not later as than 3 hours after the death. Biopsied material was taken during the operation for surgical correction of disturbances of cardiac rhythm and conduction. Cell contacts of light and dark myocytes within the sinus node, and of working myocytes of the right atrium were evaluated. The ratio of light to dark myocytes in the sinus node were estimated from both dead people and patients. The principles of correct ultrastructural classification of conducting and working myocytes in human heart are discussed.     

Embryonic histogenesis of the atrioventricular segment of the heart conduction system of swine (Sus porcus L.)]

Histological, histochemical and neurochemical methods were used in order to study the features of the histogenesis of structures of the atrioventricular area of the conducting system of the heart and the formation of their cholinergic innervation in the postnatal period of the hog. Under study were 175 hearts of embryos of the hog at the age of 3, 4, 5, 6, 8, 10, 12, 14 and 15 weeks and 22 hearts of adult hogs. The formation of different areas of this system was shown to be asynchronous. The atrioventricular fascicle is formed during the 4th week, the atrioventricular node -- during the 6th week and the conducting muscle fibres--during the 8th week of embryogenesis. The fascicle and the node have a complicated structure and different cellular composition. In the process of prenatal ontogenesis the increased amount of glycogen and increased activity of phosphorylase were noted in the cytoplasm of myocytes of the atrioventricular area of the conducting system of the heart. The cholinergic nerve fibres grow up to the structures of the atrioventricular area of the conducting system of the heart during the 6th week of embryogenesis, and by the end of the prenatal development they form a thick network in all its structures.     

Cardiac conducting system of Gallus domesticus with special reference to the atrial bundles

Gross anatomy and histology of the cardiac conducting system of Gallus domesticus has been studied. Detailed histology of the atrium revealed for the first time, in the avian heart, the presence of three atrial bundles which communicate between the sinuatrial node and the atrioventricular node. Purkinje fibres in the subendocardium of the right atrium are observed. An atrioventricular segment comprising of the posterior end of the interatrial septum and the atrioventricular nodal region has been reported in which the three atrial bundles converge. The role of the atrial bundles in the cardiac contraction has been discussed.     

Enzyme histochemical studies on the conducting system of the human heart

Summary In this communication, the results of applying various histochemical techniques for the localization of oxidoreductases, transferases, hydrolases and isomerases in the human heart are presented. The Purkinje fibres of the atrioventricular conducting system of the human heart differ from the myocardium proper in containing a slightly higher activity of most of the glycolytic and gluconeogenetic enzymes investigated. The relatively higher activity of 6-phosphofructokinase, the key enzyme in anaerobic carbohydrate metabolism, is especially noteworthy. On the other hand, the activities of some of the enzymes that play a part in the aerobic energy metabolism is slightly less than those in the myocardium fibres.As for the activity of the NADPH regenerating enzymes, the activity of 6-phosphogluconate dehydrogenase and malate dehydrogenase (oxaloacetate-decarboxylating) is somewhat higher, and the activity of glucose-6-phosphate dehydrogenase similar, in the Purkinje fibres compared to that in the myocardial fibres. The activity of myosin ATPase is similar for both types of fibre. Likewise, the fibres of the conducting system and of the myocardium show a similar activity of acid phosphatase, -glucuronidase, non-specific naphthylesterase and peroxidase. The neurogenic function of the conducting system of the human heart was demonstrated by the high activity of acetylcholinesterase in the Purkinje fibres and in the atrioventricular node. All these histochemical findings in Purkinje fibres are similar at widely differing levels of the conducting system.     

An immunocytochemical study of the sinuatrial node and atrioventricular conducting system of the rat for atrial natriuretic peptide distribution

Summary Immunocytochemical studies of the adult rat heart show that specific heart granules and atrial natriuretic peptide immunoreactivity are absent from the majority of the myocytes of the specialized nodes, atrioventricular bundle and bundle branches. Immunoreactive granules are present in a small proportion of the transitional sinuatrial and atrioventricular nodal myocytes but, in these regions, they are smaller than their counterparts in the general atrial myocytes. A rarer type of cell profile, identical to general atrial myocytes but lacking immunoreactive granules, is also present at the periphery of the sinuatrial node. A very small proportion of myocytes in the ventricular myocardium, generally in the subendocardial layers subjacent to the terminal ramifications of the bundle branches, contain a few immunoreactive granules.     

Levels of DNA and sex chromatin bodies in the myocyte nuclei of different sections of the human heart

Nuclei of ventricular, atrial and atrioventricular node myocytes of normal and hypertrophied human heart were studied on squash preparations and on 12 micron sections after the Feulgen staining. The cytophotometric DNA measurements have shown a distinction in the degree of polyploidization of nuclei in different heart compartments. In contrast to ventricular and atrial myocardia, in which polyploid nuclei predominate, the conduction system myocytes contain 77-88% of diploid nuclei. A correlation between DNA content and the number of sex chromatin bodies was observed for myocyte nuclei from all the compartments under investigation.     

A comparative enzyme histochemical study of glucose metabolism in the conduction system of mammalian hearts.

A histochemical study of some enzymes of glucose metabolism was performed on the heart conduction system of rat, dog, rabbit, pig, calf and lamb. Histochemical activities revealed a higher rate of anaerobic metabolism and a lower rate of aerobic metabolism in the conducting cells in comparison with the working myocardial fibres. An increase of the histochemical activities from the atrioventricular node to the distal portions of bundle branches was noted. The importance of the high glycogen content and the high phosphorylase activity in the heart conduction system was discussed.     

Morphology of the principal divisions of heart conducting system of rats]

Light optic and electron microscopic investigation of the sinuauricular node node (spu), atrioventricular node (pzhu) and bundle of His (pzhp) has been carried out in 23 hearts of intact non-inbred male rats. Original techniques of oriented embedding of elements of the conductive system for their electron microscopic identification have been suggested. A morphological classification of specialized cardiac myocytes has been worked out basing on differences in their form and size, number of myofibrils and degree of their regulation. On its base three type of specialized myofibrils have been revealed in the conductive system. Topography of these cells has been described within spu, pzhu and pzhp. The suggested ultrastructural classification of specialized cardiac myocytes is compared with the data obtained for the cardiac conductive system in other types of mammals.     

Vascularization of the conducting system in the human heart

On 200 randomized specimens of the human heart, of either sex, from 20 to 80 years of age, we investigated the vascularization of the conducting system of the heart in relation to the type of coronary ramification, by the dissection, injection-corrosive, radiographic and coronarographic method. The symmetrical type of arterial vascularization was established in 24%, the right type in 63% and the left type in 13% of the cases investigated. The sinoatrial node is vascularized in 60% by the right and in 40% of the cases by the left coronary artery. The atrioventricular node and the stem of the atrioventricular bundle are vascularized by the right coronary artery in 85% of the cases investigated, in 13% by the left and in 2% by both arteries. The right fasciculus of the atrioventricular bundle is vascularized by the left artery, the left fasciculus by both arteries. The vascularization of the posterior strand in both ventricles is conformable to the type of arterial vascularization of the heart.     

An extra atrioventricular node in an anomalous heart of a calf

An extra atrioventricular node in a double outlet ventricle with a quite normal inflow septum in a calf is described. The anomaly resembles the topography of the conducting system in the calf heart in the embryonic stages from 13.5 mm-90 mm.     

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.     

Location and functional characterization of the right atrioventricular pacemaker ring in the adult avian heart

Previous histological studies showed that in addition to a sinus node, an atrioventricular (AV) node, an AV bundle, left and right bundle branches, birds also possess a right AV‐Purkinje ring that is located in the atrial sheet of the right muscular AV‐valve along all its base length. The functionality of the AV‐Purkinje ring is unknown. In this work, we studied the topology of pacemaker myocytes in the atrial side of the isolated chicken spontaneously contracting right muscular AV‐valve using the method of microelectrode mapping of action potentials. We show that AV‐cells having the ability to show pacemaking reside in the right muscular AV‐valve. Pacemaker action potentials were exclusively recorded close to the base of the valve along its whole length from dorsal to the ventral attachment to the interventricular septum. These action potentials have much slower rate of depolarization, lower amplitude, and higher diastolic depolarization than action potentials of Purkinje (conducting) cells. We conclude the right AV‐valve has a ring bundle of pacemaker cells (but not Purkinje cells) in the adult chicken heart. J. Morphol. 277:363–369, 2016. © 2015 Wiley Periodicals, Inc.     

Ultrastructure of the DNA-synthesizing cells of the sinoatrial node in mouse embryos according to electron microscopic autoradiographic data

By means of electron microscopic autoradiography with 3H-thymidine a study was made of the differentiation degree of DNA synthesizing muscle cells in the sinoatrial node (SAN) of the heart conductive system of the 18 day old mouse embryos. Clear myocytes (CM), predominating in the SAN at this stage, are irregular in shape, with interdigitating protrusions. Nuclei are clear, spherical or ellipsoidal. One hour following 3H-thymidine injection, about 6% of CM display labeled nuclei; this index is considerably lower than in working ventricular myocardium. Like unlabeled myocytes, CM being in phase S contain sparse, randomly located thin myofibrilles. In some areas of the sarcoplasm, only myofilament bundles and Z-disk material can be seen. The number of CM myofibrilles is always considerably less than in the working ventricular myocytes. Accumulations of intermediate (8--11 nm) filaments are present. Mitochondria with a few cristae are not numerous. The sarcoplasmic reticulum and Golgi apparatus being relatively well developed, multivesicular bodies, centrioles, and occasional cilia are often seen. Near the centrioles (basal bodies), striated filamentous bundles are found sometimes showing periodic dense lines separated by 50--70 nm. Specialized contacts between CM are rare, being presented only by desmosomes and primitive intercalated discs. Besides CM, sparse small dark cells occur filled with myofibrilles and mitochondria. In the peripheral regions of the node "transitional" cells are seen. The SAN of the 18 day old embryo mouse heart grown due to proliferation of CM with a poorly developed myofibrillar apparatus.     

Age characteristics of the projections of the heart and its foramina on the anterior thoracic wall in newborn infants and children younger than 7 years of age

Projections of the heart borders and its orifices on the anterior thoracic wall have been studied in 122 corpses of newborns and children up to 7 years of age by means of visiography, dioptrography and preparation methods. In parallel with changes occurring in the cardiac borders, projections of the vena cava, the pulmonary trunk orifices, as well as projections of both atrioventricular orifices change, too. The level of their projections is gradually going down. For example, in the pulmonary trunk orifices from the II rib level drops down to the III rib, the aortic orifices--from the II rib level down to the IV rib, the right atrioventricular orifice--from the III rib level down to the V rib, and the left one--from the III rib level down to the IV intercostal level. While the child is growing, the heart is turning around the sagittal, vertical and frontal axis. Department of Operative Surgery and Topographic Anatomy, M. I. Kalinin Medical Institute, Andizhan.     

Cumulative indices of DNA synthesizing myocytes in different compartments of the working myocardium and conductive system of the rat’s heart muscle following extensive left ventricle infarction

Ten successive³H-thymidine injections at 12h intervals (which is a little shorter than the adult heart myocyte S phase) were performed for labeling of the majority of cardiac myocytes synthesizing DNA at any moment of such a 5 days experiment. In the hearts of control unoperated rats ten-fold repeated³H-thymidine administration results in labeling of 2–3% myocyte nuclei, in both atria, ca. 1% of the specialized muscle cell nuclei in the atrioventricular conductive system, only occasional muscle cells being labeled in the working ventricular myocardium. When ten successive³H-thymidine injections were made between the 5th and 10th days following extended left ventricle infarction, the percentage of labeled myocytes in left and right atria reaches, respectively, 51.4±4.4% and 34.7±3.6%. In the left ventricle labeled muscle nuclei are accumulated predominantly (9.3±2.1%) within the thin subepicardial layer of the surviving myofibers, while myofibers located in other perinecrotic areas contained only 1.3±0.5% labeled muscle nuclei. The number of these nuclei in the atrioventricular system remains at the level observed in control hearts (up to 2%), approaching closely the zero level in the working myocardium of both the ventricles and interventricular septum, located at the considerable distance from the infarcted region. When similar experiments with ten-fold repeated³H-thymidine injections were performed between 15th and 20th post-infarction days the number of labeled myocyte nuclei was found to be reduced 4–6 times in atria, being changed rather a little in the perinecrotic ventricular myocardium and in the specialized myocardium of the atrioventricular system. Some possible reasons of the observed differences in the proliferative behaviour of cardiac myocytes in terms of their topology and/or specialization are discussed     

Similarity of the effects of first-generation antiarrhythmia agents and decreased extracellular concentration of sodium ions on action potentials of atrial myocytes]

In rabbit right atria beating in a spontaneous sinus rhythm, myocytes of two types were studied, which differ by the initial form of action potentials. First-class antiarrhythmics and a gradual decrease in extracellular Na+ concentration induced qualitatively similar and unidirectional changes in the form of action potentials of myocytes. In some myocytes of the "conducting system" type, a slow diastolic depolarization was observed after repolarization, and the form of their action potentials became similar to that of the pacemaker cells. An enhancement of the action caused short-time arrhythmias.     

Essential features of endocardial and myocardial morphology: SEM and TEM studies

The conducting pathway of the ferret's myocardium and endocardium was studied under the electron and scanning microscope. Comparisons between the two methods showed that the scanning microscope is well suited for those dimensional demonstration of biological material. Contrary to a relative absence of interspecific differences in endocardial morphology, there is a strong variation of this morphology related to the intracardiac localization of the endocardial cells. The following findings were obtained. S.e. microscopically, it was observed that the endocardium of the sino-atrial node region is not smooth, and that, more likely, it shows rough surfaced profiles. The electron microscopic study shows that the cells of the S-A node are elongated. The S-A node is located at the junction of the superior vena cava with the right atrial wall. It consists of nodal fibres which are embedded in a richinterstitial connective tissue (Figs 1-8). The Purkinje fibres originate from large bundles in the region of the right and left atrioventricular valve in the area where heart muscle fibres were originally described by Purkinje (Purkinje, 1845); these fibres, meanwhile, have become synonymous with cells of the generalized conducting system. The Purkinje fibres consist of a poorly developed contractile apparatus and contain unorganized, fine, filamentous material (Illustration 1). The SR is poorly developed, transverse tubules are absent. S.e. microscopically, one can visualize the trabecular system and the sinusoids. The trabeculae obtain muscle fibres rich in contractile material and transverse tubules. The trabeculae appear to be tendonous (chordae tendineae), especially when they freely traverse the ventricular cavity (Fig. 16). The interventricular septum (the muscle fibres from this region) takes its origin from large bundles in the region of the right and left atrioventricular valves. The endocardium of the interventricular septum is filled with large numbers of plasma-lemma folds (Figs 17, 18). The endocardium which covers the papillary muscle has a thickness of 0.5 micron. The endocardial cells lie on the myocardium so close and so thin that the surface relief and part of the atriation of the myocardium are visible (Figs 13-15).