Morphological and functional characteristics of the crista terminalis in the rabbit right atrium.

The structural and electrophysiological characteristics of the crista terminalis (CT) in the right atrium of the rabbit have been analyzed. The myocardial cells of the CT show a longitudinal and parallel arrangement corresponding to the long axis of the CT and can be divided into two distinct groups, i.e.: (1) smaller cells, that resemble those of the atrial common myocardium and constitute a thin superficial (subendocardial) layer; (2) larger clear cells, that are organized in a homogeneous thick and deeper row and display an extended T-tubular system. The action potentials of the surface of the whole CT preparation were heterogeneous and could be grouped into three main types. Such heterogeneity was possibly related to electrotonic coupling between atrial cells. The action potentials recorded from the deep cells of the CT were homogeneous, displaying high amplitude, very high maximum rate of rise and relatively long duration. The above data supply a correlation between morphological and electrophysiological findings. They suggest that the deep layer of the CT could be responsible for the high conduction rate.