Comparative Anatomy

All large mammalian hearts are considered to have a very similar conduction system with the following main components: the sinoatrial node, the atrioventricular node, the bundle

Heart Section

Fig. 13. Histological section through the bundle of His in a canine heart. The section was prepared using a modified Masson's trichrome stain (collagen/nuclei stain blue, muscle/keratin/cytoplasm stain red). Ao, aorta; HB, His bundle; IVS, interventricular septum; LA, left atrium; LV, left ventricular endocardium; RA, right atrium endocardium; RV, right ventricle endocardium; TV, tricuspid valve.

Fig. 13. Histological section through the bundle of His in a canine heart. The section was prepared using a modified Masson's trichrome stain (collagen/nuclei stain blue, muscle/keratin/cytoplasm stain red). Ao, aorta; HB, His bundle; IVS, interventricular septum; LA, left atrium; LV, left ventricular endocardium; RA, right atrium endocardium; RV, right ventricle endocardium; TV, tricuspid valve.

Bundle His

Fig. 14. Histological section through the bundle of His in a canine heart. The region enlarged is noted by the dashed lines in the original histological section. Both sections were prepared using a modified Masson's trichrome stain (collagen/nuclei stain blue, muscle/keratin/ cytoplasm stain red). Ao, aorta; CFB, central fibrous body (provides structure and isolates the atrial from the ventricular tissues); HB, His bundle; IVS, interventricular septum; LA, left atrium; LV, left ventricular endocardium; RA, right atrium endocardium; RV, right ventricle endocardium; TV, tricuspid valve.

Fig. 14. Histological section through the bundle of His in a canine heart. The region enlarged is noted by the dashed lines in the original histological section. Both sections were prepared using a modified Masson's trichrome stain (collagen/nuclei stain blue, muscle/keratin/ cytoplasm stain red). Ao, aorta; CFB, central fibrous body (provides structure and isolates the atrial from the ventricular tissues); HB, His bundle; IVS, interventricular septum; LA, left atrium; LV, left ventricular endocardium; RA, right atrium endocardium; RV, right ventricle endocardium; TV, tricuspid valve.

of His, the right and left main bundle branches, and the Purkinje fibers. Yet, interspecies variations are well recognized (1,38-40). (For a summary of the major differences in the conduction systems between human, swine, canine, and ovine hearts, refer to Table 1, Chapter 5.)

More specifically, Bharati et al. (38) made a comparison of the electrophysiological properties of the swine and human heart (Table 3). In addition to significant differences in atrial (high right atrium-low right atrium) and atrial-ventricular conduction times (much shorter in the swine), the authors also found significantly more autonomic innervation within the atrioventricular node and penetrating bundle of the swine heart (thought to be both adrenergic and cholinergic). They concluded that this indicates a more important neurogenic component to the swine conduction system relative to the human heart. Because of this difference, they cautioned using swine as a model for assessing cardiac arrhythmias. Although the neurogenic differences between the human and swine are significant in vivo, isolation of such hearts results in denervation of the conduction systems and thus reduces or eliminates the relevance of this finding.

The canine is another commonly used model in biomedical device research. Information on atrial-to-ventricular timing in canines was published by Karpawich et al. (15). They placed tripolar electrodes on the right atrial epicardium near the noncoronary cusp of the aorta of canines; the resulting timing recorded was extracted from the article and is tabulated in Table 4.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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