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The influence of tonic sympathetic and parasympathetic nervous system activity on ventricular refractory period duration was studied in 13 mongrel dogs. Strength-interval curves were obtained from the apex of the right ventricular endocardium with a transvenous bipolar catheter. The effects of sympathetic activity were assessed by unilateral and bilateral stellectomies and tonic vagal effects were studied by inducing cholinergic blockade with atropine (0.2 mg/kg) and by sectioning the cervical vagi bilaterally. Right stellectomy shifted the strength-interval curve 3-5 msec earlier (P less than 0.005). In contrast, left stellectomy shifted the strength-interval curve 4-7 msec later (P less than 0.001). Thus, right and left unilateral stellectomy produced opposite effects. However, when the contralateral ganglion was removed, right and left stellectomy produced qualitatively similar effects, increasing refractoriness. The net effect of bilateral stellectomy was to shift the strength-interval curve 8-10 msec later (P less than 0.001) and this was primarily dependent on left stellectomy. Blockade of vagal efferent activity with atropine shifted the strength-interval curve 3-6 msec earlier (P = .001). Removal of vagal afferent activity by vagotomy during atropine blockade shifted the strength-interval curve 2-3 msec earlier (P = 0.03). It is concluded that both stellate ganglia exert qualitatively similar effects on cardiac refractoriness; however, the left ganglion dominates and unilateral right stellectomy produces a paradoxical decrease in refractoriness. The sympathetic effects are tonically antagonized by vagal activity.
Schwartz et al. (Wed,) studied this question.