Non-pharmacological, non-ablative approaches for the treatment of atrial fibrillation: experimental evidence and potential clinical implications

Clinical Effects of "Selective Drug" Regulating Vagus Nerve Signal Pathway in Vagally-Mediated Atrial Fibrillation

Background

The cardiac autonomic nervous system plays a crucial role in genesis and development of atrial fibrillation (AF) through the G protein signal transduction pathway. Therefore, intervening in the G protein signal transduction pathway may be a new “selective drug” method to regulate autonomic nerve activity to prevent vagally-mediated AF.

Material/Methods

Seventeen adult beagles were randomized into 3 groups: shame-operation control group (group A, n=5), empty vector gene control group (group B, n=6), and Gα_i2ctp gene experimental group (group C, n=6). Group A was injected with normal saline into the anterior atrial wall, and group B and group C animals were injected with recombinant adenovirus with empty vector or Gα_i2ctp vector in the same region. AF was induced by the method of rapid atrial pacing in groups B and C. To determine the clinical effect of vagal modulation, the effective refractory periods (ERP) and field action potential duration (FAPD) were evaluated by electrophysiological study. The expression levels of tyrosine hydroxylase (TH) and choline acetyl transferase (CHAT) in different parts were determined with immunohistochemistry.

Results

After successful Gα_i2ctp gene transfer, in group B, the ERP and FAPD significantly decreased (P<0.05), and TH and CHAT expression observably increased (P<0.05), while those differences were absent between groups A and C (P>0.05).

Conclusions

Recombinant adenovirus-mediated overexpression of Gα_i2ctp in canine myocardial cells can interfere with the activity of the vagus nerve, reverse the development and progression of electrical remodeling, and reduce the incidence of AF.

Vagal stimulation targets select populations of intrinsic cardiac neurons to control neurally induced atrial fibrillation

Mediastinal nerve stimulation (MNS) reproducibly evokes atrial fibrillation (AF) by excessive and heterogeneous activation of intrinsic cardiac (IC) neurons. This study evaluated whether preemptive vagus nerve stimulation (VNS) impacts MNS-induced evoked changes in IC neural network activity to thereby alter susceptibility to AF. IC neuronal activity in the right atrial ganglionated plexus was directly recorded in anesthetized canines (n = 8) using a linear microelectrode array concomitant with right atrial electrical activity in response to: 1) epicardial touch or great vessel occlusion vs. 2) stellate or vagal stimulation. From these stressors, post hoc analysis (based on the Skellam distribution) defined IC neurons so recorded as afferent, efferent, or convergent (afferent and efferent inputs) local circuit neurons (LCN). The capacity of right-sided MNS to modify IC activity in the induction of AF was determined before and after preemptive right (RCV)- vs. left (LCV)-sided VNS (15 Hz, 500 μs; 1.2× bradycardia threshold). Neuronal (n = 89) activity at baseline (0.11 ± 0.29 Hz) increased during MNS-induced AF (0.51 ± 1.30 Hz; P < 0.001). Convergent LCNs were preferentially activated by MNS. Preemptive RCV reduced MNS-induced changes in LCN activity (by 70%) while mitigating MNS-induced AF (by 75%). Preemptive LCV reduced LCN activity by 60% while mitigating AF potential by 40%. IC neuronal synchrony increased during neurally induced AF, a local neural network response mitigated by preemptive VNS. These antiarrhythmic effects persisted post-VNS for, on average, 26 min. In conclusion, VNS preferentially targets convergent LCNs and their interactive coherence to mitigate the potential for neurally induced AF. The antiarrhythmic properties imposed by VNS exhibit memory.

Continuous low-level vagus nerve stimulation reduces stellate ganglion nerve activity and paroxysmal atrial tachyarrhythmias in ambulatory canines

BACKGROUND

We hypothesize that left-sided low-level vagus nerve stimulation (LL-VNS) can suppress sympathetic outflow and reduce atrial tachyarrhythmias in ambulatory dogs.

METHODS AND RESULTS

We implanted a neurostimulator in 12 dogs to stimulate the left cervical vagus nerve and a radiotransmitter for continuous recording of left stellate ganglion nerve activity, vagal nerve activities, and ECGs. Group 1 dogs (N=6) underwent 1 week of continuous LL-VNS. Group 2 dogs (N=6) underwent intermittent rapid atrial pacing followed by active or sham LL-VNS on alternate weeks. Integrated stellate ganglion nerve activity was significantly reduced during LL-VNS (7.8 mV/s; 95% confidence interval [CI] 6.94 to 8.66 versus 9.4 mV/s [95% CI, 8.5 to 10.3] at baseline; P=0.033) in group 1. The reduction was most apparent at 8 am, along with a significantly reduced heart rate (P=0.008). Left-sided low-level vagus nerve stimulation did not change vagal nerve activity. The density of tyrosine hydroxylase-positive nerves in the left stellate ganglion 1 week after cessation of LL-VNS were 99 684 μm(2)/mm(2) (95% CI, 28 850 to 170 517) in LL-VNS dogs and 186 561 μm(2)/mm(2) (95% CI, 154 956 to 218 166; P=0.008) in normal dogs. In group 2, the frequencies of paroxysmal atrial fibrillation and tachycardia during active LL-VNS were 1.4/d (95% CI, 0.5 to 5.1) and 8.0/d (95% CI, 5.3 to 12.0), respectively, significantly lower than during sham stimulation (9.2/d [95% CI, 5.3 to 13.1]; P=0.001 and 22.0/d [95% CI, 19.1 to 25.5], P<0.001, respectively).

CONCLUSIONS

Left-sided low-level vagus nerve stimulation suppresses stellate ganglion nerve activities and reduces the incidences of paroxysmal atrial tachyarrhythmias in ambulatory dogs. Significant neural remodeling of the left stellate ganglion is evident 1 week after cessation of continuous LL-VNS.