Functional and morphological organization of the rabbit sinus node.

TLDR

The study used microelectrode recordings in isolated rabbit right atria to map sinus node activation, then correlated the electrophysiology with light and electron microscopy and compared criteria for defining the dominant pacemaker. A central cluster of at least 5,000 uniformly coupled nodal cells generates the impulse, and excitation propagates obliquely cranially toward the crista terminalis, a pattern explained by the tissue architecture rather than distinct conduction pathways.

Abstract

In isolated right atria of the rabbit heart, we studied the activation pattern within the sinus node, using the microelectrode technique. After the electrophysiological experiments, the preparations were subjected to a correlative morphological investigation, using light or electron microscopy. Different criteria for defining the dominant pacemaker were compared. A group of at least 5000 cells, located within the central part of the node where the most characteristic tissue architecture was found, was considered to be responsible for generation of the impulse. At the ultrastructural level, this leading cell group appeared to be part of a larger uniform cell group. The number of gap junctions observed suggests that all nodal cells are coupled by these structures. Toward the periphery, the excitation wave was propagated preferentially in an oblique cranial direction toward the crista terminalis. Neither morphologically nor electrophysiologically specific pathways were found for the conduction, but the preferential direction could be explained by the tissue architecture.