Low-Level Vagosympathetic Nerve Stimulation Inhibits Atrial Fibrillation Inducibility: Direct Evidence by Neural Recordings from Intrinsic Cardiac Ganglia

Chronic Intermittent Low-Level Stimulation of Tragus Reduces Cardiac Autonomic Remodeling and Ventricular Arrhythmia Inducibility in a Post-Infarction Canine Model

OBJECTIVES

This study investigated whether chronic low-level tragus stimulation (LL-TS) inhibits cardiac sympathetic remodeling and reduces ventricular arrhythmia inducibility in a post-infarction canine model.

BACKGROUND

Low-level vagal stimulation has been shown to suppress cardiac sympathetic activity, which plays an important role in ventricular arrhythmia after myocardial infarction (MI). Our previous studies reported a noninvasive approach to deliver vagal stimulation by transcutaneous stimulation at the tragus, where the auricular branch of the vagus nerve is located.

METHODS

Twenty-two beagles were randomized to the normal control (n = 6), MI (left anterior descending coronary artery ligation without LL-TS [n = 8]), and TS (MI plus LL-TS [n = 8]) groups. LL-TS was delivered 2 h each day at 80% below the threshold which slowed sinus rate.

RESULTS

At 2-month follow-up, LL-TS was found to significantly reduce ventricular arrhythmia inducibility (arrhythmia score: 1.8 ± 0.8 vs. 3.6 ± 0.7, p < 0.01, compared to the MI group), decreased left stellate ganglion (LSG) activity (frequency: 32 ± 15 vs. 112 ± 29 impulses/s; and amplitude: 0.15 ± 0.12 mV vs. 0.38 ± 0.12 mV, compared to MI group), and attenuated cardiac sympathetic remodeling induced by chronic MI. The nerve growth factor (NGF) protein was down-regulated, whereas the small conductance calcium-activated potassium channel type2 (SK2) protein was up-regulated in the LSG by chronic LL-TS.

CONCLUSIONS

Chronic LL-TS could reduce the ventricular arrhythmia inducibility, LSG neural activity and sympathetic neural remodeling in a post-infarction canine model. Down-regulation of NGF protein and up-regulation of SK2 protein in the LSG contribute to the salutary effects of LL-TS.

Spinal cord stimulation suppresses focal rapid firing-induced atrial fibrillation by inhibiting atrial ganglionated plexus activity

OBJECTIVE

This study was designed to demonstrate that spinal cord stimulation (SCS) could suppress high-frequency stimulation (HFS)-induced focal atrial fibrillation (AF) at atrial and pulmonary vein (PV) sites by inhibiting atrial ganglionated plexus (GP) activity.

METHODS

Multielectrode catheters were attached to atria and all PV sites. SCS was performed at the T1-T5 spinal region for 1 hour. At the baseline state and the end of 1 hour of SCS, 40 milliseconds of HFS was delivered 2 milliseconds after atrial pacing to determine the AF threshold at each site. One electrode was attached to the superior left GP so that HFS to this site induced sinus rate slowing. Microelectrodes inserted into the anterior right GP recorded neural firing.

RESULTS

SCS induced a significant increase in AF threshold at all sites (all P < 0.05). The sinus rate slowing response induced by superior left GP stimulation was blunted by SCS (17% ± 3.6% vs. 39% ± 3.8%, P < 0.05). The frequency (32 ± 4 vs. 87 ± 6 impulses per minute, P < 0.05) and amplitude (0.16 ± 0.02 vs. 0.42 ± 0.04 mv, P < 0.05) of the neural activity recorded from the anterior right GP were markedly inhibited by SCS.

CONCLUSIONS

SCS may prevent episodic AF caused by rapid PV and non-PV firing through modulating GP activity.

Aging and magnetism: Presenting a possible new holistic paradigm for ameliorating the aging process and the effects thereof, through externally applied physiologic PicoTesla magnetic fields

A new holistic paradigm is proposed for slowing our genomic-based biological clocks (e.g. regulation of telomere length), and decreasing heat energy exigencies for maintenance of physiologic homeostasis. Aging is considered the result of a progressive slow burn in small volumes of tissues with increase in the quantum entropic states; producing desiccation, microscopic scarring, and disruption of cooperative coherent states. Based upon piezoelectricity, i.e. photon-phonon transductions, physiologic PicoTesla range magnetic fields may decrease the production of excessive heat energy through target specific, bio molecular resonant interactions, renormalization of intrinsic electromagnetic tissue profiles, and autonomic modulation. Prospectively, we hypothesize that deleterious effects of physical trauma, immunogenic microbiological agents, stress, and anxiety may be ameliorated. A particle-wave equation is cited to ascertain magnetic field parameters for application to the whole organism thereby achieving desired homeostasis; secondary to restoration of structure and function on quantum levels. We hypothesize that it is at the atomic level that physical events shape the flow of signals and the transmission of energy in bio molecular systems. References are made to experimental data indicating the aspecific efficacy of non-ionizing physiologic magnetic field profiles for treatment of various pathologic states.

Low-level transcutaneous electrical vagus nerve stimulation suppresses atrial fibrillation

BACKGROUND

Transcutaneous low-level tragus electrical stimulation (LLTS) suppresses atrial fibrillation (AF) in canines.

OBJECTIVES

This study examined the antiarrhythmic and anti-inflammatory effects of LLTS in humans.

METHODS

Patients with paroxysmal AF who presented for AF ablation were randomized to either 1 h of LLTS (n = 20) or sham control (n = 20). Attaching a flat metal clip onto the tragus produced LLTS (20 Hz) in the right ear (50% lower than the voltage slowing the sinus rate). Under general anesthesia, AF was induced by burst atrial pacing at baseline and after 1 h of LLTS or sham treatment. Blood samples from the coronary sinus and the femoral vein were collected at those time points and then analyzed for inflammatory cytokines, including tumor necrosis factor alpha and C-reactive protein, using a multiplex immunoassay.

RESULTS

There were no differences in baseline characteristics between the 2 groups. Pacing-induced AF duration decreased significantly by 6.3 ± 1.9 min compared with baseline in the LLTS group, but not in the control subjects (p = 0.002 for comparison between groups). AF cycle length increased significantly from baseline by 28.8 ± 6.5 ms in the LLTS group, but not in control subjects (p = 0.0002 for comparison between groups). Systemic (femoral vein) but not coronary sinus tumor necrosis factor (TNF)-alpha and C-reactive protein levels decreased significantly only in the LLTS group.

CONCLUSIONS

LLTS suppresses AF and decreases inflammatory cytokines in patients with paroxysmal AF. Our results support the emerging paradigm of neuromodulation to treat AF.

Device-based autonomic modulation in arrhythmia patients: the role of vagal nerve stimulation

OPINION STATEMENT

Vagal nerve stimulation (VNS) has shown promise as an adjunctive therapy for management of cardiac arrhythmias by targeting the cardiac parasympathetic nervous system. VNS has been evaluated in the setting of ischemia-driven ventricular arrhythmias and atrial arrhythmias, as well as a treatment option for heart failure. As better understanding of the complexities of the cardiac autonomic nervous system is obtained, vagal nerve stimulation will likely become a powerful tool in the current cardiovascular therapeutic armamentarium.

The role of the autonomic ganglia in atrial fibrillation

Recent experimental and clinical studies have shown that the epicardial autonomic ganglia play an important role in the initiation and maintenance of atrial fibrillation (AF). In this review, we present the current data on the role of the autonomic ganglia in the pathogenesis of AF and discuss potential therapeutic implications. Experimental studies have demonstrated that acute autonomic remodeling may play a crucial role in AF maintenance in the very early stages. The benefit of adding ablation of the autonomic ganglia to the standard pulmonary vein (PV) isolation procedure for patients with paroxysmal AF is supported by both experimental and clinical data. The interruption of axons from these hyperactive autonomic ganglia to the PV myocardial sleeves may be an important factor in the success of PV isolation procedures. The vagus nerve exerts an inhibitory control over the autonomic ganglia and attenuation or loss of this control may allow these ganglia to become hyperactive. Autonomic neuromodulation using low-level vagus nerve stimulation inhibits the activity of the autonomic ganglia and reverses acute electrical atrial remodeling during rapid atrial pacing and may provide an alternative non-ablative approach for the treatment of AF, especially in the early stages. This notion is supported by a preliminary human study. Further studies are warranted to confirm these findings.

Low-level baroreceptor stimulation suppresses atrial fibrillation by inhibiting ganglionated plexus activity

BACKGROUND

The autonomic nervous system (ANS) plays an important role in the initiation and maintenance of atrial fibrillation (AF), and modulation of the ANS function may contribute to AF control.

METHODS

Anesthetized dogs received either sham treatment (SHAM group, n = 8) or low-level carotid baroreceptor stimulation (LL-CBS) treatment (LL-CBS group, n = 8). The stimulation voltage was set at 80% below the threshold. To simulate focal AF, high-frequency stimulation (HFS) was applied to local nerves during the atrial refractory period. Multielectrode catheters were attached to the atria and all the pulmonary veins to determine the changes in the AF threshold (AF-TH), the atrial effective refractory period (AERP), and the window of vulnerability (WOV) during HFS in both groups. Microelectrodes were inserted into the anterior right ganglionated plexus (ARGP) to record neural firing.

RESULTS

HFS induced sinus rate (SR) slowing in the superior left ganglionated plexus (SLGP). LL-CBS induced a progressive increase in AF-TH and AERP at all sites and a significant decrease in the sum of WOV at 2 hours (all P < 0.05). LL-CBS inhibited the ability of SLGP stimulation to slow the SR and the mean values of frequency and amplitude of ARGP neural activity compared with the SHAM group (all P < 0.05).

CONCLUSIONS

LL-CBS suppressed AF inducibility by inhibiting the neural activity of ganglionated plexuses. LL-CBS may serve as a novel therapeutic modality to treat AF.

Low-level vagosympathetic trunk stimulation inhibits atrial fibrillation in a rabbit model of obstructive sleep apnea

BACKGROUND

Atrial fibrillation (AF) is highly associated with obstructive sleep apnea (OSA) in which AF is triggered by hyperactivity of the cardiac autonomic nervous system. Previous studies showed that low-level vagosympathetic trunk stimulation (LLVS), at voltages not slowing sinus rate or AV conduction, inhibits AF by suppressing the cardiac autonomic nervous system.

OBJECTIVE

The purpose of this study was to investigate whether LLVS delivered at the right vagosympathetic trunk suppresses AF in a rabbit model of OSA.

METHODS

Eleven rabbits received a tracheostomy under general anesthesia. The endotracheal tube was clamped at end expiration for 1 minute to simulate OSA. Over a period of 4 hours, OSA was delivered every 6 minutes. Effective refractory period (ERP), blood pressure, intraesophageal pressure, and blood gases (O2, CO2, pH) were measured before and after each episode of OSA. AF duration and ERP were measured by programmed stimulation. Group 1 rabbits (n = 6) received LLVS (50% below that which slowed the sinus rate) in the first 3 hours. Group 2 rabbits (n = 5) only received OSA.

RESULTS

Group 1 ERP began to lengthen progressively from the second hour compared to group 2. AF duration increased in the first hour for both groups but began to shorten progressively after the first hour in group 1 rabbits. Blood pH, O2 or CO2 level, intraesophageal pressure, and hypertensive response during OSA were not different between the 2 groups.

CONCLUSION

LLVS is capable of suppressing ERP shortening and AF induced by OSA. LLVS may serve as a new therapeutic approach to treat OSA-induced AF.

The use of low-level electromagnetic fields to suppress atrial fibrillation

BACKGROUND

Extremely low-level electromagnetic fields have been proposed to cause significant changes in neural networks.

OBJECTIVE

We sought to investigate whether low-level electromagnetic fields can suppress atrial fibrillation (AF).

METHODS

In 17 pentobarbital anesthetized dogs, bilateral thoracotomies allowed the placement of multielectrode catheters in both atria and at all pulmonary veins. AF was induced by rapid atrial pacing (RAP) or programmed atrial extrastimulation. At baseline and end of each hour of RAP, during sinus rhythm, atrial programmed stimulation gave both the effective refractory period (ERP) and the width of the window of vulnerability. The latter was a measure of AF inducibility. Microelectrodes inserted into the anterior right ganglionated plexi recorded neural firing. Helmholtz coils were powered by a function generator inducing an electromagnetic field (EMF; 0.034 μG, 0.952 Hz). The study sample was divided into 2 groups: group 1 (n = 7)-application of EMF to both cervical vagal trunks; group 2 (n = 10)-application of EMF across the chest so that the heart was located in the center of the coil.

RESULTS

In group 1, EMF induced a progressive increase in AF threshold at all pulmonary vein and atrial sites (all P < .05). In group 2, the atrial ERP progressively shortened and ERP dispersion and window of vulnerability progressively increased (P < .05 compared to baseline values) during 3 hours of RAP and then returned to baseline values during 3 hours of combined application of RAP and EMF (P < .05 compared to the end of the third hour of RAP). The frequency and amplitude of the neural activity recorded from the anterior right ganglionated plexi were markedly suppressed by EMF in both groups.

CONCLUSION

Pulsed EMF applied to the vagal trunks or noninvasively across the chest can significantly reverse AF inducibility.

Left renal nerves stimulation facilitates ischemia-induced ventricular arrhythmia by increasing nerve activity of left stellate ganglion

INTRODUCTION

Renal sympathetic nerve (RSN) activity plays a key role in systemic sympathetic hyperactivity. Previous studies have shown that cardiac sympathetic hyperactivity, especially the left stellate ganglion (LSG), contributes to the pathogenesis of ventricular arrhythmias (VAs) after acute myocardial infarction (AMI).

METHODS AND RESULTS

Twenty-eight dogs received 3 hours of continuous left-sided electrical stimulation of RSN (LRS; Group-1, n = 9), sham RSN stimulation (Group-2, n = 9), or LSG ablation plus 3 hours of LRS (Group-3, n = 10) were included. AMI was induced by ligating the proximal left anterior descending coronary artery. LRS was performed using electrical stimulation on the adventitia of left renal artery at the voltage increasing the systolic blood pressure (BP) by 10%. BP, heart rate variability (HRV), serum norepinephrine (NE) level, and LSG function were measured at baseline and the end of each hour of LRS. C-fos and nerve growth factor (NGF) protein expressed in the LSG were examined in Group-1 and Group-2. Compared with baseline, 3 hours of LRS induced a significant increase in BP, sympathetic indices of HRV, serum NE level, and LSG function. The incidence of VAs in Group-1 was significantly higher than other groups. The expression of c-fos and NGF protein in the LSG was significantly higher in Group-1 than Group-2.

CONCLUSION

Three hours of LRS induces both systemic and cardiac sympathetic hyperactivity and increases the incidence of ischemia-induced VAs.

Role of the autonomic nervous system in modulating cardiac arrhythmias

The autonomic nervous system plays an important role in the modulation of cardiac electrophysiology and arrhythmogenesis. Decades of research has contributed to a better understanding of the anatomy and physiology of cardiac autonomic nervous system and provided evidence supporting the relationship of autonomic tone to clinically significant arrhythmias. The mechanisms by which autonomic activation is arrhythmogenic or antiarrhythmic are complex and different for specific arrhythmias. In atrial fibrillation, simultaneous sympathetic and parasympathetic activations are the most common trigger. In contrast, in ventricular fibrillation in the setting of cardiac ischemia, sympathetic activation is proarrhythmic, whereas parasympathetic activation is antiarrhythmic. In inherited arrhythmia syndromes, sympathetic stimulation precipitates ventricular tachyarrhythmias and sudden cardiac death except in Brugada and J-wave syndromes where it can prevent them. The identification of specific autonomic triggers in different arrhythmias has brought the idea of modulating autonomic activities for both preventing and treating these arrhythmias. This has been achieved by either neural ablation or stimulation. Neural modulation as a treatment for arrhythmias has been well established in certain diseases, such as long QT syndrome. However, in most other arrhythmia diseases, it is still an emerging modality and under investigation. Recent preliminary trials have yielded encouraging results. Further larger-scale clinical studies are necessary before widespread application can be recommended.

Role of the autonomic nervous system in atrial fibrillation: pathophysiology and therapy

Autonomic nervous system activation can induce significant and heterogeneous changes of atrial electrophysiology and induce atrial tachyarrhythmias, including atrial tachycardia and atrial fibrillation (AF). The importance of the autonomic nervous system in atrial arrhythmogenesis is also supported by circadian variation in the incidence of symptomatic AF in humans. Methods that reduce autonomic innervation or outflow have been shown to reduce the incidence of spontaneous or induced atrial arrhythmias, suggesting that neuromodulation may be helpful in controlling AF. In this review, we focus on the relationship between the autonomic nervous system and the pathophysiology of AF and the potential benefit and limitations of neuromodulation in the management of this arrhythmia. We conclude that autonomic nerve activity plays an important role in the initiation and maintenance of AF, and modulating autonomic nerve function may contribute to AF control. Potential therapeutic applications include ganglionated plexus ablation, renal sympathetic denervation, cervical vagal nerve stimulation, baroreflex stimulation, cutaneous stimulation, novel drug approaches, and biological therapies. Although the role of the autonomic nervous system has long been recognized, new science and new technologies promise exciting prospects for the future.

The Role of the Atrial Neural Network In Atrial Fibrillation: The Metastatic Progression Hypothesis

With the advent of catheter ablation of atrial fibrillation (AF) there has been acceleration in our understanding of the mechanisms underlying the etiology of this common clinical arrhythmia. In this regard, the role of the intrinsic cardiac autonomic nervous system in the initiation and maintenance of AF began to receive attention in numerous experimental and clinical investigations. Up to now, the focus has been on the large ganglionated plexi (GP) which are located in the posterior left atrium mainly at the pulmonary vein-atrial junctions. As long term outcomes have been reported and single procedures have indicated diminished success rates particularly for persistent/long standing persistent AF, emphasis has begun to shift away from the pulmonary vein isolation (PVI) alone as well as GP ablation with or without PVI. An understanding of the atrial substrate represented by the extensions of the intrinsic cardiac autonomic system constituting the atrial neural network is beginning to evolve. In this review, the contribution of the intrinsic cardiac autonomic nervous system to the etiology of AF is addressed, particularly in regard to the greater prevalence of AF in the elderly. In addition, we emphasize the involvement of the atrial neural network in the "metastatic" progression of paroxysmal to persistent and long standing persistent forms of AF.

Effects of low-level autonomic stimulation on prevention of atrial fibrillation induced by acute electrical remodeling

Background. Rapid atrial pacing (RAP) can induce electrical and autonomic remodeling and facilitate atrial fibrillation (AF). Recent reports showed that low-level vagosympathetic nerve stimulation (LLVNS) can suppress AF, as an antiarrhythmic effect. We hypothesized that LLVNS can reverse substrate heterogeneity induced by RAP. Methods and Results. Mongrel dogs were divided into (LLVNS+RAP) and RAP groups. Electrode catheters were sutured to multiple atrial sites, and LLVNS was applied to cervical vagosympathetic trunks with voltage 50% below the threshold slowing sinus rate by ⩽30 msec. RAP induced a significant decrease in effective refractory period (ERP) and increase in the window of vulnerability at all sites, characterized by descending and elevated gradient differences towards the ganglionic plexi (GP) sites, respectively. The ERP dispersion was obviously enlarged by RAP and more significant when the ERP of GP-related sites was considered. Recovery time from AF was also prolonged significantly as a result of RAP. LLVNS could reverse all these changes induced by RAP and recover the heterogeneous substrate to baseline. Conclusions. LLVNS can reverse the electrical and autonomic remodeling and abolish the GP-central gradient differences induced by RAP, and thus it can recover the homogeneous substrate, which may be the underlying mechanism of its antiarrhythmic effect.

Inhibition of atrial fibrillation by low-level vagus nerve stimulation: the role of the nitric oxide signaling pathway

PURPOSE

We examined the role of the phosphatidylinositol-3 kinase (PI3K)/nitric oxide (NO) signaling pathway in low-level vagus nerve stimulation (LLVNS)-mediated inhibition of atrial fibrillation (AF).

METHODS

In 17 pentobarbital anesthetized dogs, bilateral thoracotomies allowed the attachment of electrode catheters to the superior and inferior pulmonary veins and atrial appendages. Rapid atrial pacing (RAP) was maintained for 6 h. Each hour, programmed stimulation was used to determine the window of vulnerability (WOV), a measure of AF inducibility, at all sites. During the last 3 h, RAP was overlapped with right LLVNS (50 % below that which slows the sinus rate). In group 1 (n = 7), LLVNS was the only intervention, whereas in groups 2 (n = 6) and 3 (n = 4), the NO synthase inhibitor N (G)-nitro-L-arginine methyl ester (L-NAME) and the PI3K inhibitor wortmannin, respectively, were injected in the right-sided ganglionated plexi (GP) during the last 3 h. The duration of acetylcholine-induced AF was determined at baseline and at 6 h. Voltage-sinus rate curves were constructed to assess GP function.

RESULTS

LLVNS significantly decreased the acetylcholine-induced AF duration by 8.2 ± 0.9 min (p < 0.0001). Both L-NAME and wortmannin abrogated this effect. The cumulative WOV (the sum of the individual WOVs) decreased toward baseline with LLVNS (p < 0.0001). L-NAME and wortmannin blunted this effect during the fifth (L-NAME only, p < 0.05) and the sixth hour (L-NAME and wortmannin, p < 0.05). LLVNS suppressed the ability of GP stimulation to slow the sinus rate, whereas L-NAME and wortmannin abolished this effect.

CONCLUSION

The anti-arrhythmic effects of LLVNS involve the PI3K/NO signaling pathway.

The intrinsic autonomic nervous system in atrial fibrillation: a review

The procedure of catheter ablation for the treatment of drug resistant atrial fibrillation (AF) has evolved but still relies on lesion sets intended to isolate areas of focal firing, mainly the myocardial sleeves of the pulmonary veins (PVs), from the rest of the atria. However the success rates for this procedure have varied inversely with the type of AF. At best success rates have been 20 to 30% below that of other catheter ablation procedures for Wolff-Parkinson-White syndrome, atrioventricular junctional re-entrant tachycardia and atrial flutter. Basic and clinical evidence has emerged suggesting a critical role of the ganglionated plexi (GP) at the PV-atrial junctions in the initiation and maintenance of the focal form of AF. At present the highest success rates have been obtained with the combination of PV isolation and GP ablation both as catheter ablation or minimally invasive surgical procedures. Various lines of evidence from earlier and more recent reports provide that both neurally based and myocardially based forms of AF can separately dominate or coexist within the context of atrial remodeling. Future studies are focusing on non-pharmacological, non-ablative approaches for the prevention and treatment of AF in order to avoid the substantive complications of both these regimens.

Antiarrhythmic effects of vasostatin-1 in a canine model of atrial fibrillation

BACKGROUND

We examined the antiarrhythmic effects of vasostatin-1, a recently identified cardioregulatory peptide, in canine models of atrial fibrillation (AF).

METHODS AND RESULTS

In 13 pentobarbital-anesthetized dogs bilateral thoracotomies allowed the attachment of multielectrode catheters to superior and inferior pulmonary veins and atrial appendages (AA). Rapid atrial pacing (RAP) was maintained for 6 hours. Each hour, programmed stimulation was performed to determine the window of vulnerability (WOV), a measure of AF inducibility, at all sites. During the last 3 hours, vasostatin-1, 33 nM, was injected into the anterior right (AR) ganglionated plexus (GP) and inferior right (IR) GP every 30 minutes (n = 6). Seven dogs underwent 6 hours of RAP only (controls). At baseline, acetylcholine, 100 mM, was applied on the right AA and AF duration was recorded before and after injection of vasostatin-1, 33 nM, into the ARGP and IRGP. In separate experiments (n = 8), voltage-sinus rate response curves (surrogate for GP function) were constructed by applying high-frequency stimulation to the ARGP with incremental voltages with or without vasostatin-1. Vasostatin-1 significantly decreased the duration of acetylcholine-induced AF (11.0 ± 4.1 vs 5.5 ± 2.6 min, P = 0.02). The cumulative WOV (the sum of individual WOVs) significantly increased (P < 0.0001) during the first 3 hours and decreased toward baseline in the presence of vasostatin-1 (P < 0.0001). Cumulative WOV in controls steadily increased. Vasostatin-1 blunted the slowing of sinus rate with increasing stimulation voltage of ARGP.

CONCLUSIONS

Vasostatin-1 suppresses AF inducibility, likely by inhibiting GP function. These data may provide new insights into the role of peptide neuromodulators for AF therapy.

Neuromodulation targets intrinsic cardiac neurons to attenuate neuronally mediated atrial arrhythmias

Our objective was to determine whether atrial fibrillation (AF) results from excessive activation of intrinsic cardiac neurons (ICNs) and, if so, whether select subpopulations of neurons therein represent therapeutic targets for suppression of this arrhythmogenic potential. Trains of five electrical stimuli (0.3-1.2 mA, 1 ms) were delivered during the atrial refractory period to mediastinal nerves (MSN) on the superior vena cava to evoke AF. Neuroanatomical studies were performed by injecting the neuronal tracer DiI into MSN sites that induced AF. Functional studies involved recording of neuronal activity in situ from the right atrial ganglionated plexus (RAGP) in response to MSN stimulation (MSNS) prior to and following neuromodulation involving either preemptive spinal cord stimulation (SCS; T(1)-T(3), 50 Hz, 200-ms duration) or ganglionic blockade (hexamethonium, 5 mg/kg). The tetramethylindocarbocyanine perchlorate (DiI) neuronal tracer labeled a subset (13.2%) of RAGP neurons, which also colocalized with cholinergic or adrenergic markers. A subset of DiI-labeled RAGP neurons were noncholinergic/nonadrenergic. MSNS evoked an ∼4-fold increase in RAGP neuronal activity from baseline, which SCS reduced by 43%. Hexamethonium blocked MSNS-evoked increases in neuronal activity. MSNS evoked AF in 78% of right-sided MSN sites, which SCS reduced to 33% and hexamethonium reduced to 7%. MSNS-induced bradycardia was maintained with SCS but was mitigated by hexamethonium. We conclude that MSNS activates subpopulations of intrinsic cardiac neurons, thereby resulting in the formation of atrial arrhythmias leading to atrial fibrillation. Stabilization of ICN local circuit neurons by SCS or the local circuit and autonomic efferent neurons with hexamethonium reduces the arrhythmogenic potential.

Interactions between atrial electrical remodeling and autonomic remodeling: how to break the vicious cycle

BACKGROUND

The mechanism(s) underlying the maintenance of atrial fibrillation (AF) during the first few hours after AF was initiated remains poorly understood.

OBJECTIVE

To investigate the roles of the intrinsic cardiac autonomic nervous system in the maintenance of AF at the early stage.

METHODS

In 10 anesthetized dogs, we attached multielectrode catheters on atria and pulmonary veins. Microelectrodes inserted into the anterior right ganglionated plexi recorded neural activity. At baseline, programmed stimulation determined the effective refractory period (ERP) and window of vulnerability (WOV), a measure of AF inducibility. For the next 6 hours, AF was simulated by rapid atrial pacing (RAP) and the same parameters were measured hourly during sinus rhythm. A circular catheter was positioned in the superior vena cava for high-frequency stimulation (20 Hz) of the adjacent vagal preganglionics. During 4-6 hours of RAP, we delivered low-level vagal stimulation in the superior vena cava (LL-SVCS), 50% below that which induced slowing of the sinus rate.

RESULTS

During the 6-hour RAP, there was a progressive decrease in the ERP and an increase in ERP dispersion, WOV, and neural activity. With LL-SVCS during 4-6-hour RAP, ERP, WOV, and neural activity returned toward baseline levels (all P <.05, compared with the third-hour RAP values).

CONCLUSIONS

RAP not only induces atrial electrical remodeling but also promotes autonomic remodeling. These 2 remodeling processes may form a vicious cycle and each may perpetuate the other. These findings may help to explain how AF maintains itself in its very early stage. LL-SVCS both reversed remodeling processes and can potentially break the vicious cycle of "AF begets AF" in the first few hours of AF.