In rabbit atriocaval preparations, conduction velocity decreased in the sinocaval junctional areas (10-25 cm/sec) compared to the crista terminalis and superior venae cavae, with high atrial rates producing localized delay and block.
This preclinical study maps the electrophysiological properties of sinocaval conduction, identifying the sinocaval junctional areas as transitional zones with latent pacemaker potential.
The sequence of spread of sinus node impulse to the venae cavae and the mechanisms of delay at the sinocaval junctional areas were studied with the microelectrode methods.The impulse from the pacemaker located in the sinus node spreads slowly in the nodal tissues (1-10cm/sec) and excites the crista terminalis. Spread is rapid in the crista (50-120cm/sec). Then the impulse spreads from theupper and lower ends of the crista through the sinocaval junctional areas (SC areas) to the right and left superior venae cavae. Conduction velocity is decreased in the SC areas (10-25cm/sec) and again increased in the superior venae cavae (40-80cm/sec). In the inferior vena cava, the conduction of impulse is always completely blocked in the vicinty of the ostium.The features of superior vena caval action potentials are closely similar to those of cardiac action potentials, showing the constant diastolic level, the rapid upstroke, the high amplitude, the clear plateau and the rapid conduction.The fibers in the SC areas apparently show a transitional stage from the nodal fibers to the superior vena caval fibers. The action potentials of the SC areas are intermediate in the amplitude and rate of rise between those of sinus nodal and superior vena caval action potentials, and often reveal a step on the upstroke. The activation of right atrium at high rate produced a delay and block localized to the SC areas. The action potentials of the SC areas show three different types of changes associated with the increased atrial rate: I) the decrease in the amplitude and rate of rise, II) the separation into two discrete spikes and III) the widening of the step-like prepotential.Several evidences were presented which suggest that the SC areas are the latent pacemakers.
Ito et al. (Sun,) reported a other. High rate atrial stimulation was evaluated on Conduction velocity and action potential characteristics in sinocaval areas. In rabbit atriocaval preparations, conduction velocity decreased in the sinocaval junctional areas (10-25 cm/sec) compared to the crista terminalis and superior venae cavae, with high atrial rates producing localized delay and block.