Autonomic control of ventricular refractoriness.

The effects of vagal and sympathetic stimulation on canine ventricular refractoriness were studied in vivo. Sympathetic stimulation reduced the left ventricular refractory period to an extent linearly related to the logarithm of nerve stimulation frequency. Vagal stimulation had no effect in the absence of sympathetic stimulation but produced a frequency-dependent attenuation of sympathetic effects when the two systems were stimulated simultaneously. The effects of combined vagal and sympathetic stimulation were best described by a multilinear regression model using the logarithm of vagal and sympathetic frequency as covariates. The magnitude of vagal attenuation of sympathetic effects did not show any regional variation at the five widely spaced sites (2 right ventricular, 3 left ventricular) studied.