Comparative Morphology of the Cardiac Conduction Tissue in Animals*

Abstract

The gross distribution, histologic structure, blood supply, innervation, and physiologic implications of this unique fiber system has continued to attract the research interests of investigators from many disciplines of science. The resulting body of diverse information is a voluminous and indeed a fascinating scientific story.A complete survey of even the essential achievements is beyond the limited time and scope of this presentation. However, the interested reader can obtain an appreciation of advancements through a perusal of several morphologic studies that include extensive citations from the early and current literature.' ' The comparative histology of the cardiac conduction system in reptiles, birds, and mammals has also been presented and reviewed.' '" T h e macroscopic relations a n d distribution of t h e conduction system in man and other mammals have been revealed by high magnification dissection," l 3 three-dimensional reconstructions," l6 histochemical ~t a i n i n g , '~ and painting the endocardia1 surface with dyes." ' " For detailed studies of the SA and AV nodal areas of man and other mammals the reader is referred to the contributions of Widran and Lev," James,I7 ") Titus et al.," and Truex et ~1 .~ The ultrastructure of the same nodal areas also has been reported.6.21." I n recent years we have obtained and studied the hearts of several species of animals in an attempt to resolve some of the questions pertaining to the presence or absence of the various portions of the conduction system in different animals. By the use of several methods (e.g., injection, microdissection, radiographic visualization, serial histologic sections, and model reconstructions), we have examined parts, or all, of the cardiac conduction system elements in the animals shown on the right side of F I G U R E 1. Differential stain procedures included hematoxylin and eosin, variations of the Masson's trichrome, azophloxine, Bodian or Holme's silver methods. These comparative studies are, as yet, incomplete and many additional animals in each of the groups remain to be examined. The purposes of this brief communication are to summate only our current information on the morphology of the several conduction elements, and to emphasize several structural characteristics which may enhance the interpretation of the physiological papers which appear in this monograph. We present these preliminary anatomic observations with the full realization that they may,

Optical Mapping of the Isolated Coronary-Perfused Human Sinus Node

“…(6) Previous histological and immonohistochemical studies by James,(10;13;24) Truex et al,(11;25) and Schuessler et al(5;26) support our functional and structural data, which demonstrate that the canine and human SAN are electrically insulated from most of the nearby atrial myocardium except for several SEPs. This conduction barrier is formed by the sinus nodal coronary arteries, connective tissue, and fat, as well as an abrupt change in Cx43 expression between atrial and nodal cells.…”

Conduction barriers and pathways of the sinoatrial pacemaker complex: their role in normal rhythm and atrial arrhythmias

“…Anatomical (10,27,29,49,50) and functional (7,46) studies suggest that the canine SAN (23) is a more realistic model for the human SAN (21) than that of small mammals (9,22). Figure 1 represents a more recent view of the structure of SAN pacemaker complex in canine and human hearts that consists of several major pacemaker compartments (head, center, and tail) surrounded by coronary arteries, fibrous tissue, fat, and the atrial myocardium all situated along CT.…”

Archetype, adaptation and the mammalian heart

“…Moreover, with the exception of mitochondrial density which depends on heart size, all cardiac myocytes have the same size and morphology, making it difficult to distinguish the myocytes of one species from another [16–19]. The same is true for specialised cardiac tissue such as the His bundles responsible for the conduction of the electrical impulse from the atria to the ventricles [20, 21]. …”