Influence of vagal tone on stellectomy-induced changes in ventricular electrical stability

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Abstract
The effects of vagotomy and stellectomy on ventricular vulnerability were studied in 50 chloralose-anesthetized dogs. The repetitive extrasystole (RE) threshold was employed to assess vulnerability. Left or right cervical vagotomy resulted in significant decreases in RE threshold. Blcokade of efferent vagus activity with atropine (0.3 mg/kg) was without significant effect on RE threshold. In dogs with intact vagi, unilateral stellectomy did not alter the vulnerable period. In vagotomized animals, left, but not right stellectomy, significantly increased the threshold (27% above control). The effect of bilateral stellectomy was similar to that of left stellectomy. The RE threshold resulting from unilateral or bilateral stellectomy did not differ from the value observed prior to vagotomy. In both neurally intact and bilaterally stellectomized dogs, .beta.-adrenergic blockade with propranolol (0.25 mg/kg) significantly increased the RE threshold. Tonic afferent vagal activity exerts a protective effect upon ventricular vulnerability. This effect is thought to be mediated via reflex inhibition of sympathetic outflow by sensory fibers in the vagosympathetic trunk. The protective effect of stellectomy is evident only upon removal of the tonic inhibitory influence of afferent vagal activity. .beta.-Adrenergic blockade is more effective in increasing the vulnerable period threshold than is bilateral stellectomy, presumably due to blockade of circulating catecholamines.

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