INTERACTION OF SYMPATHETIC AND PARASYMPATHETIC NERVOUS-SYSTEM ON VENTRICULAR REFRACTORINESS ASSESSED BY LOCAL FIBRILLATION INTERVALS IN THECANINE HEART

Objective: The aim was to assess the effects of autonomic nerve stimul ation on local ventricular refractoriness by measuring local ventricul ar fibrillation intervals. Methods: In 10 dogs on cardiopulmonary bypa ss, ventricular fibrillation intervals were recorded simultaneously at up to 32 sites before and after neural stimulation. In four dogs (gro up 1) the response to bilateral stellate ganglion stimulation was meas ured before and after bilateral cervical vagotomy. In three dogs (grou p 2) bilateral stellate ganglion stimulation, vagal nerve stimulation, and combined vagal and stellate ganglia stimulation were performed. I n three dogs (group 3) the same protocol was applied after total decen tralisation of the autonomic nervous system. Results: Bilateral stella te ganglion stimulation shortened the ventricular fibrillation interva l at 44-50% of myocardial sites before and after vagotomy, whereas pro longation of the interval was observed at 14-18% of the sites. At high er stimulus strength shortening of the interval was measured at 85% of the sites in the intact and decentralised groups. No prolongation was observed. The shortening was largest in the decentralised group (11.1 ms). Dispersion in refractoriness increased in hearts from all groups , but not in each individual heart. Left, right, or bilateral vagal st imulation was without effect at about 75% of the tested sites. The fac t that the response to autonomic nerve stimulation varies from site to site warrants our approach of simultaneous recordings at multiple sit es. Dispersion in refractoriness was not affected by vagal stimulation . Combined autonomic stimulation had approximately the same effect on dispersion in refractoriness as bilateral stellate ganglion stimulatio n alone. However, vagal stimulation attenuated the responses to bilate ral stellate ganglion stimulation by some 20% in the decentralised gro up. Conclusions: Vagal stimulation has minor effects on ventricular re fractoriness, but this is not due to sparse innervation, since vagal s timulation is able to mitigate the effects of sympathetic stimulation in decentralised hearts.