FUNCTIONAL PROPERTIES OF SINOCAVAL CONDUCTION

Publisher Website
Google Scholar
Abstract
The sequence of spread of sinus node impulse to the vena cava and the mechanisms of delay at the sinocaval junctional areas were studied with microelectrode methods. The impulse from the pacemaker located in the sinus node spreads slowly in the nodal tissues (1-10 cm/sec) and excites the crista terminalis. Spread is rapid in the crista (50-120 cm/sec). Then the impulse spreads from the upper and lower ends of the crista through the sinocaval junctional areas (SC areas) to the right and left superior vena cava. Conduction velocity is decreased in the SC areas (10-25 cm/sec) and again increased in the superior vena cava (40-80 cm/sec). In the inferior vena cava, the conduction of impulse is always completely blocked in the vicinity of the ostium. The features of superior vena cava 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 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 3 different types of changes associated with the increased atrial rate: the decrease in the amplitude and rate of rise, the separation into 2 discrete spikes and the widening of the step-like prepotential. Several evidences were presented which suggest that the SC areas are the latent pacemakers.