The aim of the present study was to advance our knowledge regarding the anatomy of the purkinje fibres from their origin, at the bundle branches, till their termination within the myocardium. Indian ink injections of the purkinje fibres were carried out in the left ventricle of 25 fresh sheep hearts and in the right ventricle of 20 hearts. Numerous samples were taken from the walls and papillary muscles of the two ventricles for histological analysis and determination of the mode of termination of the fibres. The ventricular conduction system could be injected as far proximally as the bundle branches, thus illustrating the bifascicular nature of the left bundle branch, with numerous interfascicular communications. The purkinje fibres were observed to form an extensive subendocardial network, forming a polygonal arrangement in the left ventricle with a characteristic pattern around the papillary muscles. Deep myocardial branches took origin from this network which penetrated the ventricular wall to reach the epicardium. Histological analysis demonstrated the characteristic features of the purkinje cells, and confirmed the presence ofa perifascicular sheath of connective tissue which surrounded the purkinje fibres until their transition with working cardiomyocytes. The perifascicular connective tissue sheath is important in organising the contraction of the myocardium by preventing lateral spread of conduction and by permitting transmission of the impulse only at the termination of the purkinje fibre. The sheath may also protect the fibres from the stresses and strains originating from contraction of the surrounding myocardium.
The anatomy of the atrioventricular conduction system was first described nearly a hundred years ago. Since then, it has been an occasional subject of controversy mainly through a lack of adherence to the original definitions based on histology. The gross landmarks for locating the atrial component of the conduction system are found in the right atrium. The components and structure of the system in human are comparable to that found in commonly used laboratory animals. The conduction system is composed of specialized myocytes. Its atrial component, the atrioventricular node, is in contact with atrial myocardium. Having penetrated the atrioventricular insulating plane, the major ventricular bundles are encased in fibrous sheaths that separate the specialized myocytes from the ordinary myocardium. Only at the distal ramifications of the bundle branches do the fibrous sheaths disappear, allowing continuity with ventricular myocardium. Being the only muscular pathway connecting atrial with ventricular myocardium, knowledge of its structure can help in developing potential therapies for some forms of cardiac arrhythmias.
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