Effect of stimulation of somatic nerves on the ventricular fibrillation threshold in dogs

Abstract

Summary The data indicate that activation of somatic afferent fibers can produce a change in cardiac sympathetic activity which may influence development of arrhythmias under certain conditions. In this study, the VFT was lowered significantly by stimulation of somatic afferent fibers belonging to Groups II to IV. The decrease in VFT was probably due to increased sympathetic activity to the heart, since β-adrenergic blockade prevented the change in VFT during nerve stimulation. Recently, Theroux and associates 28 have shown that premedication of conscious dogs with morphine prevents the occurrence of ventricular fibrillation in the first few minutes following abrupt coronary artery occlusion. It was thought that morphine prevented the excitement reaction (which was characterized by marked agitation and struggling) in response to the ischemic pain associated with the coronary occlusion. According to the present study, morphine may have interrupted the somatosympathetic reflux associated with the pain and excitement and prevented the reflex increase in sympathetic activity to the heart. These observations deserve further, study, especially with regard to the effect of morphine on somatosympathetic reflexes. An alternate explanation is that morphine may have produced an increase in vagal efferent activity, which has been shown to antagonize the influence of the sympathetic nervous system on the heart 3 .