[ Scientific Activity - Actividad Científica ] [ Brief Communications - Temas Libres ]

Abstract
Introduction: The sinus node is a small mass of specialized cardiac muscular fibers localized in the junction of the vena cava superior with the walls of the right atrium near to the superior extremity of the terminal sulcus.
Objective: The objective of this work went begin the study of the conducting system in hamster's hearts, until then unknown, describing the topography and morphology of the sinus node, of its innervation and irrigation in hearts of hamsters.
Material and Methods: Twenty animals were utilized in all. After the fixation. After this stage, the piece was included in paraffin, obtaining seriate cuts of all the piece. The sequential cuts were stained by hematoxylin eosin technique.
Results: The sinus node showed itself morphologically as a mass of specialized cardiac muscular cells, with very similar aspect to the normal cardiac fibers. The directions of these cells were very irregular and were often found with many orientations. The cells of the sinus node, show them with an eosinophilic aspect, less reactive that the normal cardiac striated muscular cells. Presence of autonomous nervous ganglion, intermingled to the node cells. Presence of a membrane of fibrous connective tissue, that envolves almost all the set formed by node, ganglions and vessels and a arteriola of a big relative caliber, in the junction of the sinus node with the myocardial wall. Sinus node, when analysed in a topographic view presented itself, as an only fusiform mass, tridimensional, adjacent accompaning the anatomy of the superior cava vein. Such description could be evidenced from the seriate cuts in the area of the sinus complex.
Discussion: To leave of that work it was described the anatomy of the sinus node in the hamster's heart for the first time.
Conclusion: The sinus node of the hamster's heart resembles each other to the human heart.

Introduction:

Efficiency of the heart, as a double pump depends on the synchronic contraction of the right and left hearts, and of the consecutive stage of the cardiac cycle succeeded each other in the appropriate sequence. The rhythmic coordination depends on the passage of the excitation wave by the heart through its conductive system of impulse. This system is constituted of cardiac muscular cells specialized in start impulses to the contraction and conduct them by the heart (Ham, 1991).
The conducting human system is very well defined, being constituted by sinus and atrioventricular nodes, atrioventricular bundles and the subendocardium plexus of Purkinje's fibers (Gardner, 1988; Gray, 1988).
The sinus node is a small mass of specialized cardiac muscular fibers, contained in a substantial quantity of fibroelastic connective tissue highly vascularized, it measures from 10 to 20 mm length (Hurst and cols. ,1990), 3mm of width and 1mm of density (Truex, Smythe, Taylor, 1967).
It localizes in the junction of the vena cava superior with the walls of the right atrium near to the superior extremity of the terminal sulcus (Bloom and Fawcett, 1986). The fibers of the sinus node are narrower than the rest of the cardiac tissue, in addition, it contains less myofibrillae than the common cardiac muscular fibers (Ham, 1991).
From the sinus node, the wave of despolarization is conducted through the functions of Gap type along the three atrial internodal pathways (by Bachman, medium and posterior), up to a second node of specialized cells denominated atrioventricular node (James, 1963, 1971, 1972).
Atrioventricular node situates in the inferior part of the septum interatriale, it is anatomically smaller than the sinus node, it is located below the endocardium of the right atrium, in the part of the septum interatriale that forms or that continues the right fibrous trigonom immediately above the ostium of the coronary sinus, in the fixation of the cuspis septalis of the valva tricuspidalis (Gardner, 1988). It contains small number of muofibrillae (Ham, 1991). Both of the nodes can also be localized orientating themselves by the pathway of the artéria that irrigate them (Ryback, Mizeres, 1965).
The atrioventricular bundle or Hiss bundle is constituted by specialized cardiac muscular fibers (Ham, 1991). It penetrates in the fibrous part that separates the atrial and the ventricular musculare and entres in the septum interventricular, where it is subdivided in the right and left branches (Junqueira and Cols., 1985). Right branch is a rounded bundle that continues forward to the apical region, penetrates the trabecula septomarginalis and reaches the ventricular wall and the anterior papillary muscle. Its fibers, so, form a subendocardic complex of Purkinje's fibers in the papillaries muscles and on the wall of the right ventricle (Moore, 1994; Hurst and cols., 1990). The left branch goes towards to the apical region. It occurs immediately below the endocardium that covers the left face of the muscular part of the septum (Gardner, 1988; Gray, 1988).
The Purkinje's fibers are slightly higher and stain a little less than the originary cardiac muscular fibers, being its grooves less evident in slides of a standard staining in hematoxylin eosin (Kühnel, 1991). They can be accompanied up to the cardiac muscular fibers (Truex, Copenhaver, 1947; Kugler, Parkin, 1956; Ross and Rowrell, 1993; Becok and Pauleti, 1979).

Objectives:

Heart's conducting system has a fundamental importance in the comprehension of the rhythmic contraction mechanism, in the interpretation of electrocardiogram and diagnosis of cardiopathies, that's why it has been very well studied in the last years. Hamster is an animal of a wide utilization in the scientific milieu, by it's easy creation, maintenance and magnitude of presented results, being a theme of multiple researches. Some of these, aiming the comprehension of the cardiovascular dynamic and the current implications. In addition, hamsters has a immune system very similar to the human system. In despite of its importance, nothing is reported in the scientific literature about the conducting in hearts of hamsters. Knowing better the anatomy of hamster's conducting system, we can establish comparative studies with pathologies that affect the system or even the heart in front of great similarity among the hamster and human immune responses.
Also, one might develop experimental works having as a base a describe anatomy. Therefore, with the aim of contributing to a better knowledge of this system, we made a study describing the morphology e topography to the sinus node, of its irrigation and innervation.

Material and Methods:

Hamsters (Mesocricetus auratus), sirius race, adults (at about 100 days), of a medium weight of 105g, were used. Twenty animals were utilized in all, which were maintained in collective cages since their birth, in groups of three, in room temperature and humidity, being fed with standard of the biotério ration of the vivarium and Ad libitun water. The animals were weighted and inspected about the general state (behavior, body temperature and heart rate), conditions of the skin and hair.
Hamster was sacrificed after inhalation anesthesia by ether. Afterwars they were perfused with physiologic serum, to the removing of the bloo. Hearts were transversally sectioned in the hight of the atrioventricular valvulae to better fixation. Immediately after the withdrawal of the heart of each animal, it was dived in Bouin's fluid for 36 hours for fixation. After this stage, the piece was included in paraffine. Obtaining seriate cuts of all the piece with átrio about 5 micrometers of density. The sequential cuts were stained by hematoxylin eosin technique. Right away, they were examinated, catalogued and photographed in Zeiss photomicroscope.
Sinus node evaluation followed an order:
1 - morphologic evaluation (classification the found tissues, description of its aspects, tinctorial behavior, location, nucleus-cytoplasm relationship and cellular predominances).
2 - Study of anatomo-functional structures related to the system (from the classification of the tissues, the existent anatomo-functional relationships were established).
3 - Topographic evaluation (once carried out seriate cuts of the entire sinus node, it was possible to describe its structural characteristic).
Twenty animals were used to the study, in respect of the possible anatomic variations.
We also used, for this, the double-blind resource ( study of each animal of an independent form and without previous correlations with the obtained results in the other animals). At the end, it was compared the other results of all animals in order to have the anatomic and topographic pattern of the sinus node, of its irrigation and innervation in the hearts of hamsters.

Results:

All animals had the same anatomical, morphologic and topographical profile. The sinus node showed itself morphologically as a mass of specialized cardiac muscular cells, with very similar aspect, in its structural disposition, to the normal cardiac fibers.
Analyzed in a traversal cut it was observed that the directions of these cells are very irregular and are often found with many orientations, in the same area of the microscopic preparation, being like a tridimensional citoplasmic net. As a basic differential factor, cells of the sinus node, just like the Purkinje's fibers themselves, show them with an eosinophilic aspect, less reactive that the normal cardiac striated muscular cells (whitish aspect).
Another finding was the few quantity of myofribrillae characteristic of the conduction system.
Related to the morphologic disposition of the adjacent structures and according to the system, we verified:
1. Presence of autonomous nervous ganglion, intermingled to the node cells:
    1.1 Tinctorial basophilic aspect in the periphery relatively dense and neutrophilic in its inner where one can verify the presence of cellular body with an eccentric nucleus. The basophilic periphery is constituted by satellite cells forming an unique layer of lining.
    1.2 With tinctorial aspect intensely neutrophilic with a tenuous basophilic peripheric layer.
2. Presence of a membrane of fibrous connective tissue, a bit eosinophil, that envolves almost all the set formed by node, ganglions and vessels.
3. Presence of blood vessels:
    3.1 Arteriola of a big relative caliber, in the junction of the sinus node with the myocardial wall, the artery of the node, branch of the right coronary artery.
    3.2 Vessels of a smaller caliber.
Component structures of the heart normal anatomy as belonging to the epicardium myocardium and endocarium are also visualized. Related to the epicardium we have in its free surface an only layer of simple epithelial cell identified as mesothelial membrane. Immediately underlying it is verified a tenuous layer of fibroelastic tissue pertaining of its composition. Following this, superior to the vena cava one can observe, in a long extension, a thick layer of areolar tissue interposed between the vein and the myocardial wall, in which one can observe vessels and dispersed nerves.
Being a question of a cut in a superior and atrial level, we can verify the presence of the conucting system branch composed of a bunle of Purkinje's fibers, little reactive immediately underlying the mesothelium and epicardium.
Sinus node, when analysed in a topographic view presented itself, from transverse initials and superior cuts, as an only fusiform mass, tridimensional, adjacent accompaning the anatomy of the superior cava vein. Such description could be evidenced from the seriate cuts, which showed a progressive increase of the quantify of cells and consequently of the fusiform area of the sinoatrial complex. This results are view by the pictures L01, L02, L03, L04.

L01                                                                                         L02

Bibliography: