Function of the atrioventricular node considered on the basis of observed histology and fine structure.

From the hearts of 20 young dogs, the region of the atrioventricular (AV) node was studied in vitro utilizing direct perfusion of the AV node artery. Intracellular impalement with microelectrodes provided records of local transmembrane action potentials in all 20 dogs. These were correlated with serial section histologic studies in 7 of the 20 dogs to characterize a smaller region that served as an anatomic guide for electron microscopic examination in 4 other dog hearts.

Structure and function of specific regions in the canine atrioventricular node.

The functional subregions of the rabbit atrioventricular (AV) node have been examined in detail, but it has not been possible to subject the normal canine AV node to such rigorous scrutiny. Arterial perfusion and beveled microelectrodes have now allowed us to explore the anatomic and functional regions of the isolated canine AV node. The atria and AV junctional tissues of 20 young dogs were excised and selectively perfused with physiological solution through the nutrient arteries to the sinus node, AV node, and His bundle.

Segmental study of the terminal coronary vessels in coarctation of the aorta: a natural model for study of the effect of coronary hypertension on human coronary circulation.

An electron microscopic study of the coronary terminal circulation (starting with the small coronary arteries) was carried out on small pieces of myocardium operatively resected from the left ventricle on 11 patients with coarctation of the aorta. The patients were 4 to 20 years of age. Structural modifications were found in the small coronary arteries and arterioles.

Fine structure of cells and their histologic organization within internodal pathways of the heart: clinical and electrocardiographic implications.

The fine structure of the normal internodal pathways was studied in 1 human and 2 canine hearts and correlated with histologic observations on more than 100 human and 10 canine hearts. From the electron microscopic studies six different kinds of myocardial cells were classified from two locations: the Eustachian ridge (posterior internodal pathway) and the Bachmann bundle (anterior internodal pathway). Five of the six kinds of cells (working myocardial cells, Purkinje-like cells, either broad or slender transitional cells and P cells, all previously described) were present in both locations.

The human coronary microcirculation: an electron microscopic study.

The ultrastructure of the terminal vascular bed of human coronary arteries was studied in the myocardial tissue obtained at surgery from different locations in the heart in five patients. The following vessels were identified: (1) Arterioles; slender and prolonged endothelial cells, flat nuclei and two to three layers of smooth muscle cells. (2) Precapillary sphincters: short endothelial cells, large nuclei bulging into the lumen, close myoendothelial junctions and a single layer of circular smooth muscle.