Left-sided Noninvasive Vagus Nerve Stimulation Suppresses Atrial Fibrillation by Upregulating Atrial Gap Junctions in Canines

BACKGROUND: We have previously shown that right-sided low-level tragus nerve stimulation (LL-TS) is an effective approach for the treatment of atrial fibrillation (AF) induced by rapid atrial pacing (RAP) and acts by preventing the loss of atrial connexins (Cxs). Whether a left-sided approach would achieve the same effect remains unknown. OBJECTIVE: We hypothesized that left-sided LL-TS would inhibit AF by preserving atrial Cxs as effectively as right-sided LL-TS. METHODS: Bilateral thoracotomies allowed the attachment of multielectrode catheters to the pulmonary vein and non-pulmonary vein sites in 32 anaesthetized beagles. The dogs were randomly divided into 3 groups: RAP group (9 hours of RAP at the left appendage, n = 10), LL-TS group (9-hour RAP plus LL-TS, n = 12), and control group (sham RAP without LL-TS, n = 10). Alligator clips were clipped on the tragus of the left ear for electrical stimulation (20 Hz, 1 millisecond square waves). A voltage of stimulation setting at 80% below the threshold that slowed the sinus rate was defined as LL-TS. Electrophysiological parameters were measured at baseline and 9 hours after pacing. Connexin proteins from atrial tissues were measured at the end of the protocol. RESULTS: RAP induced a significant reduction in the effective refractory period and an increase in AF inducibility (P < 0.05). However, left-sided LL-TS reversed the effective refractory period reduction induced by RAP and the increase in AF inducibility. It also shortened the AF duration and prolonged the AF cycle length, which are associated with Cx40 and Cx43 upregulation (P < 0.05). CONCLUSIONS: We propose that left-sided LL-TS exerts its anti-AF effects through upregulation of Cxs as effectively as right-sided LL-TS, suggesting that LL-TS for AF suppression is not unique to the right tragus nerve.