Spinal Cord Stimulation Causes Potentiation of Right Vagus Nerve Effects on Atrial Chronotropic Function and Repolarization in Canines

Abstract

Experimental evidence suggests that spinal cord stimulation (SCS) can cause augmentation of parasympathetic influences on the heart via enhanced vagus nerve (VgN) activity. Herein, we investigated whether this might lead to enhanced inducibility of vagally mediated atrial tachyarrhythmias (AT) and whether such actions depend on intact autonomic neural connections with central neurons. Epidural SCS electrodes were implanted at T1-T4 in anesthetized canines. Sinus cycle length prolongation, atrial repolarization changes (191 epicardial electrode sites), and AT inducibility in response to right VgN stimuli applied at the cervical level were determined before and during SCS. VgN-induced sinus cycle length prolongation was potentiated during SCS among the animals with intact neural connections or bilateral vagotomy proximal to the stimulation site, whereas such prolongation was unaffected by SCS among animals with bilateral decentralization of stellate ganglia. Likewise, the atrial surface area in which VgN-induced repolarization wave form changes were identified was significantly augmented during SCS among the former but not among the latter. AT facilitation occurred during SCS in the majority of animals with intact neural connections, particularly among those displaying relatively greater potentiation of vagally mediated sinus cycle length prolongation. The data indicate that SCS may cause potentiation of parasympathetic influences on the atria in response to cervical VgN stimulation. Such SCS effects appear to be mediated via decreased tonic inhibitory sympathetic influences in the presence of intact stellate ganglion connections to central neurons.