Subdiaphragmatic vagal nerve stimulation attenuates the development of hypertension and alters nucleus of the solitary tract transcriptional networks in the spontaneously hypertensive rat

Augmented vagal signaling may be therapeutic in hypertension. Most studies to date have used stimulation of the cervical vagal branches. Here, we investigated the effects of chronic intermittent electric stimulation of the ventral subdiaphragmatic vagal nerve branch (sdVNS) on long-term blood pressure, immune markers, and gut microbiota in the spontaneously hypertensive rat (SHR), a rodent model of hypertension characterized by vagal dysfunction, gut dysbiosis, and low-grade inflammation. We evaluated the effects of sdVNS on transcriptional networks in the nucleus of the solitary tract (NTS), a major cardioregulatory brain region with direct gut vagal projections. Male juvenile SHRs were implanted with radiotelemetry transmitters and vagal nerve cuffs for chronic intermittent electric sdVNS, applied three times per day for 7 consecutive weeks followed by 1 wk of no stimulation. Blood pressure was measured once a week using telemetry in the sdVNS group as well as age-matched sham-stimulated SHR controls. At the endpoint, colonic and circulating inflammatory markers, corticosterone, and circulating catecholamines were investigated. Bacterial 16 s sequencing measured gut bacterial abundance and composition. RNA sequencing evaluated the effects of sdVNS on transcriptional networks in the NTS. SHRs that received sdVNS exhibited attenuated development of hypertension compared with sham animals. No changes in peripheral inflammatory markers, corticosterone, or catecholamines and no major differences in gut bacterial diversity and composition were observed following sdVNS, apart from decreased abundance of Defluviitaleaceale bacterium detected in sdVNS SHRs compared with sham animals. RNA sequencing revealed significant sdVNS-dependent modulation of select NTS transcriptional networks, including catecholaminergic and corticosteroid networks.NEW & NOTEWORTHY We show that stimulation of the ventral subdiaphragmatic vagal nerve branch may be a promising potential approach to treating hypertension. The data are especially encouraging given that rodents received only 30 min per day of intermittent stimulation therapy and in view of the potential of long-term blood pressure effects that are not stimulus-locked.

The Effect of Cold Application to the Lateral Neck Area on Peripheral Vascular Access Pain: A Randomised Controlled Study

INTRODUCTION

Various types of vagus nerve stimulation are employed in the treatment of a range of conditions, including depression, anxiety, epilepsy, headache, tinnitus, atrial fibrillation, schizophrenia, and musculoskeletal pain. The objective of this study was to apply vagal stimulation to the neck area using standardised cold, and then analyse the level of vascular access discomfort experienced by individuals who underwent venous cannulation from the dorsal side of the hand prior to anaesthesia.

MATERIALS AND METHODS

A total of 180 patients, aged 18-75, who were scheduled to undergo elective surgery, were categorised into three distinct groups: the Sham group (Group S), the Control group (Group K), and the Cold group (Group M), with each group consisting of 60 individuals. Bilateral cold application to the lateral side of the neck was performed prior to the commencement of vascular access in Group M patients, followed by the subsequent opening of vascular access. The alterations in heart rate among patients was assessed subsequent to the application of cold and following the establishment of vascular access. The participants were instructed to assess their level of vascular access pain on a numerical pain scale (NRS) ranging from 0 to 10.

RESULTS

A statistically significant difference (p = 0.035) was seen when comparing the pain ratings of patients during vascular access. The study revealed that the NRS values exhibited a statistically significant decrease in Group M compared to both Group K (p = 0.038) and Group S (p = 0.048). Group M had a higher prevalence of individuals experiencing mild pain compared to other groups, and the difference was statistically significant (p = 0.029). In Group M, the average heart rate following vagal stimulation exhibited a statistically significant decrease compared to the average heart rate observed at the beginning of the study (p < 0.05). Upon comparing the original heart rate measurements with the heart rate values following vascular access, it was observed that there was an elevation in heart rate for both Group S and Group K. Conversely, Group M exhibited a decrease in heart rate after vascular access when compared to the initial heart rate values.

CONCLUSIONS

In the present investigation, it was discovered that the application of cold to the neck region resulted in a drop in heart rate among the patients, which persisted throughout the process of vascular access. Furthermore, the level of pain experienced by these individuals was reduced during vascular access procedures.

Is it feasible to avoid suction before spontaneous breathing is established?

BACKGROUND

Suctioning of the posterior pharynx immediately after birth during neonatal resuscitation can produce a vagal response resulting in bradycardia or apnea. The feasibility of delaying any airway suctioning and avoiding deep suctioning has not been studied.

OBJECTIVES

To test the hypothesis that newborn resuscitation is feasible with the following two guidelines: 1) avoiding any suctioning until the infant establishes spontaneous respiration, and 2) avoiding the use of deep suction with catheters.

STUDY DESIGN

A quality improvement project was implemented using these two guidelines. Infants' mouth was cleaned with a dry cloth. No suction was started until infants establish spontaneous breathing. Then, bulb suction was used to clear secretions from the sides of the mouth and the nose without reaching the back of the pharynx. Deep suction using catheters was not used. Neonatal staff and physicians received biweekly training to support these changes. Resuscitation data before and after the practice change were compared.

RESULTS

A total of 999 sequential cases were compared; of them 501 and 498 infants were resuscitated before and after the implementation of the new practice, respectively. Suction before spontaneous breathing occurred in 12.4% in the first cohort. There were no differences between groups except for less use of oxygen with the new guidelines (12.4% vs 4.4%, P < 0.001).

CONCLUSION

Avoidance of any suction prior to spontaneous breathing and not applying deep suction with catheters are feasible during newborn resuscitation. These practices are associated with decreased exposure to oxygen in the delivery room.

Device-Based Approaches Targeting Cardioprotection in Myocardial Infarction: The Expanding Armamentarium of Innovative Strategies

Coronary reperfusion therapy has played a pivotal role for reducing mortality and heart failure after acute myocardial infarction. Although several adjunctive approaches have been studied for reducing infarct size further, both ischemia-reperfusion injury and microvascular obstruction are still major contributors to both early and late clinical events after acute myocardial infarction. The progress in the field of cardioprotection has found several promising proof-of-concept preclinical studies. However, translation from bench to bedside has not been very successful. This comprehensive review discusses the importance of infarct size as a driver of clinical outcomes post-acute myocardial infarction and summarizes recent novel device-based approaches for infarct size reduction. Device-based interventions including mechanical cardiac unloading, myocardial cooling, coronary sinus interventions, supersaturated oxygen therapy, and vagal stimulation are discussed. Many of these approaches can modify ischemic myocardial biology before reperfusion and offer unique opportunities to target ischemia-reperfusion injury.

Effect of Adropin on Pancreas Exocrine Function in a Rat Model: A Preliminary Study

The aim was to investigate the potential effect of adropin (ADR) on pancreatic−biliary juice (PBJ) secretion (volume, protein content, trypsin activity) in a rat model. The animals were divided into control and five experimental groups: adropin, CCK-8 (CCK-8 stimulation), capsaicin (capsaicin deactivation of afferents), vagotomy (vagotomy procedure), and vagal stimulation (vagal nerve stimulation). The experiment consisted of four phases, during which vehicle (0.9% NaCl) and three ADR boluses (5, 10, and 20 µg/kg BW) were administered i.v. every 30 min. PBJ samples were collected from each rat at 15 min intervals after boluses. Exogenous ADR failed to affect the pancreatic responses after vagotomy and the capsaicin pretreatment and reduced the PBJ volume, protein outputs, and trypsin activity in the adropin, CCK-8, and vagal stimulation groups in a dose-dependent manner. In all these groups, volume of PBJ was reduced only by the highest dose of ADR (p < 0.001 for adropin group and p < 0.01 for CCK-8 and vagal stimulation groups), and the protein outputs were reduced by the administration of ADR 10 µg/kg BW (adropin and CCK-8 groups, p < 0.01 in both cases) and 20 µg/kg BW (p < 0.001 for adropin and CCK-8 groups, p < 0.01 for vagal stimulation group). The 10 µg/kg BW dose of ADR reduced the trypsin output in the CCK-8 group (p < 0.01), and the highest ADR dose reduced the trypsin output in the CCK-8 (p < 0.001) and vagal stimulation (p < 0.01) groups. In conclusion, adropin in the analyzed doses exhibits the negative feedback pathway. This mechanism seems to participate in the regulation of pancreatic juice secretion via an indirect vagal mechanism.

Electrical properties and synaptic transmission in mouse intracardiac ganglion neurons in situ

The intrinsic cardiac nervous system represents the final site of signal integration for neurotransmission to the myocardium to enable local control of cardiac performance. The electrophysiological characteristics and ganglionic transmission of adult mouse intrinsic cardiac ganglion (ICG) neurons were investigated using a whole-mount ganglion preparation of the excised right atrial ganglion plexus and intracellular microelectrode recording techniques. The passive and active electrical properties of ICG neurons and synaptic transmission including synaptic response strength and efficacy as a function of stimulation frequency were examined. The resting membrane potential and input resistance of ICG neurons were -47.9 ± 4.0 mV and 197.2 ± 81.5 MΩ, respectively. All neurons had somatic action potentials with overshoots of >+15 mV and after-hyperpolarizations having an average of 10 mV amplitude and ~45 ms half duration. Phasic discharge activities were recorded from the majority of neurons studied and several types of excitatory synaptic responses were recorded following inputs from the vagus or interganglionic nerve trunk(s). Most postganglionic neurons (>75%) received a strong, suprathreshold synaptic input and reliably followed high-frequency repetitive nerve stimulation up to at least 50 Hz. Nerve-evoked synaptic transmission was blocked by extracellular Cd2+ , ω-conotoxin CVIE, or α-conotoxin RegIIA, a selective α3-containing nicotinic acetylcholine receptor antagonist. Synaptic transmission and the electrical properties of murine ICG neurons contribute to the pattern of discharge which regulates chronotropic, dromotropic, and inotropic elements of cardiac function.

Microvolt T-Wave Alternans Is Modulated by Acute Low-Level Tragus Stimulation in Patients With Ischemic Cardiomyopathy and Heart Failure

Aims: Microvolt T-wave alternans (TWA), an oscillation in T-wave morphology of the electrocardiogram (ECG), has been associated with increased susceptibility to ventricular tachy-arrhythmias, while vagus nerve stimulation has shown promising anti-arrhythmic effects in in vivo and ex vivo animal studies. We aimed to examine the effect of non-invasive, acute low-level tragus stimulation (LLTS) on TWA in patients with ischemic cardiomyopathy and heart failure.

Methods: 26 patients with ischemic cardiomyopathy (left ventricular ejection fraction <35%) and chronic stable heart failure, previously implanted with an automatic implantable cardioverter defibrillator (ICD) device with an atrial lead (dual chamber ICD or cardiac resynchronization therapy defibrillator), were enrolled in the study. Each patient sequentially received, (1) Sham LLTS (electrode on tragus, but no stimulation delivered) for 5 min; (2) Active LLTS at two different frequencies (5 and 20 Hz, 15 min each); and (3) Active LLTS, during concomitant atrial pacing at 100 bpm at two different frequencies (5 and 20 Hz, 15 min each). LLTS was delivered through a transcutaneous electrical nerve stimulation device (pulse width 200 μs, frequency 5/20 Hz, amplitude 1 mA lower than the discomfort threshold). TWA burden was assessed using continuous ECG monitoring during sham and active LLTS in sinus rhythm, as well as during atrial pacing.

Results: Right atrial pacing at 100 bpm led to significantly heightened TWA burden compared to sinus rhythm, with or without LLTS. Acute LLTS at both 5 and 20 Hz, during sinus rhythm led to a significant rise in TWA burden in the precordial leads (p < 0.05).

Conclusion: Acute LLTS results in a heart-rate dependent increase in TWA burden.

Low-Level Tragus Stimulation Modulates Atrial Alternans and Fibrillation Burden in Patients With Paroxysmal Atrial Fibrillation

Background

Low‐level tragus stimulation (LLTS) has been shown to significantly reduce atrial fibrillation (AF) burden in patients with paroxysmal AF. P‐wave alternans (PWA) is believed to be generated by the same substrate responsible for AF. Hence, PWA may serve as a marker in guiding LLTS therapy. We investigated the utility of PWA in guiding LLTS therapy in patients with AF.

Methods and Results

Twenty‐eight patients with AF were randomized to either active LLTS or sham (earlobe stimulation). LLTS was delivered through a transcutaneous electrical nerve stimulation device (pulse width 200 μs, frequency 20 Hz, amplitude 10–50 mA), for 1 hour daily over a 6‐month period. AF burden over 2‐week periods was assessed by noninvasive continuous ECG monitoring at baseline, 3 months, and 6 months. A 5‐minute control ECG for PWA analysis was recorded during all 3 follow‐up visits. Following the control ECG, an additional 5‐minute ECG was recorded during active LLTS in all patients. At baseline, acute LLTS led to a significant rise in PWA burden. However, active patients receiving chronic LLTS demonstrated a significant reduction in both PWA and AF burden after 6 months (P<0.05). Active patients who demonstrated an increase in PWA burden with acute LLTS showed a significant drop in AF burden after 6 months of chronic LLTS.

Conclusions

Chronic, intermittent LLTS resulted in lower PWA and AF burden than did sham control stimulation. Our results support the use of PWA as a potential marker for guiding LLTS treatment of paroxysmal AF.

Occipitoatlantal decompression and noninvasive vagus nerve stimulation slow conduction velocity through the atrioventricular node in healthy participants

CONTEXT

Management of atrial fibrillation includes either rhythm control that aims at establishing a sinus rhythm or rate control that aims at lowering the ventricular rate, usually with atrioventricular nodal blocking agents. Another potential strategy for ventricular rate control is to induce a negative dromotropic effect by augmenting cardiac vagal activity, which might be possible through noninvasive and nonpharmacologic techniques. Thus, the hypothesis of this study was that occipitoatlantal decompression (OA-D) and transcutaneous auricular vagus nerve stimulation (taVNS) not only increase cardiac parasympathetic tone as assessed by heart rate variability (HRV), but also slow atrioventricular conduction, assessed by the PQ-interval of the electrocardiogram (EKG) in generally healthy study participants without atrial fibrillation.

OBJECTIVES

To test whether OA-D and/or transcutaneous taVNS, which have been demonstrated to increase cardiac parasympathetic nervous system activity, would also elicit a negative dromotropic effect and prolong atrioventricular conduction.

METHODS

EKGs were recorded in 28 healthy volunteers on three consecutive days during a 30 min baseline recording, a 15 min intervention, and a 30 min recovery period. Participants were randomly assigned to one of three experimental groups that differed in the 15 min intervention. The first group received OA-D for 5 min, followed by 10 min of rest. The second group received 15 min of taVNS. The intervention in the third group that served as a time control group (CTR) consisted of 15 min of rest. The RR- and PQ-intervals were extracted from the EKGs and then used to assess HRV and AV-conduction, respectively.

RESULTS

The OA-D group had nine participants (32.1%), the taVNS group had 10 participants (35.7%), and the CTR group had nine participants (32.1%). The root mean square of successive differences between normal heartbeats (RMSSD), an HRV measure of cardiac parasympathetic modulation, tended to be higher during the recovery period than during the baseline recording in the OA-D group (mean ± standard error of the mean [SEM], 54.6 ± 15.5 vs. 49.8 ± 15.8 ms; p<0.10) and increased significantly in the taVNS group (mean ± SEM, 28.8 ± 5.7 vs. 24.7 ± 4.8 ms; p<0.05), but not in the control group (mean ± SEM, 31.4 ± 4.2 vs. 28.5 ± 3.8 ms; p=0.31). This increase in RMSSD was accompanied by a lengthening of the PQ-interval in the OA-D (mean ± SEM, 170.5 ± 9.6 vs. 166.8 ± 9.7 ms; p<0.05) and taVNS (mean ± SEM, 166.6 ± 6.0 vs. 162.1 ± 5.6 ms; p<0.05) groups, but not in the control group (mean ± SEM, 164.3 ± 9.2 vs. 163.1 ± 9.1 ms; p=0.31). The PQ-intervals during the baseline recordings did not differ on the three study days in any of the three groups, suggesting that the negative dromotropic effect of OA-D and taVNS did not last into the following day.

CONCLUSIONS

The lengthening of the PQ-interval in the OA-D and taVNS groups was accompanied by an increase in RMSSD. This implies that the negative dromotropic effects of OA-D and taVNS are mediated through an increase in cardiac parasympathetic tone. Whether these findings suggest their utility in controlling ventricular rates during persistent atrial fibrillation remains to be determined.

Cardiac parasympathetic modulation in the setting of radiofrequency ablation for atrial fibrillation

The cardiac autonomic nervous system plays an important role in the genesis and maintenance of atrial fibrillation. Although, pulmonary vein isolation is the cornerstone in today's approach to atrial fibrillation ablation, a considerable proportion of patients will recur with atrial arrhythmias following this procedure, especially in the non-paroxysmal forms. The pulmonary vein isolation indirectly targets and ablate the ganglionated plexi. This might ultimately enhance the efficacy of the procedure, but an optimal ablation strategy and a reliable method to confirm and quantify the efficacy of vagal denervation following the procedure might be necessary, thus leading to significantly better results.

Is vagal stimulation or inhibition benefit on the regulation of the stomach brain axis in obesity?

Objective: Possible effects of the vagus inhibition and stimulation on the hypothalamic nuclei, myenteric plexes and the vagus nerve were investigated.Methods: The female rats divided to the inhibition (INH), stimulation (STI) and, sham (SHAM) groups were fed with high fat diet (including 40% of energy from animal fat). After nine weeks, the rats were allowed to recover for 4 weeks in INH group. In STI group, the left vagus nerve stimulated (30 Hz/500 msn/30 sec.) starting 2nd post operative day for 5 minutes during 4 weeks. Healthy female rats used as control (CONT). Then, tissue samples were analyzed by biochemical, histological and stereological methods.Results: The mean number of the neurons in the arcuate nucleus of the INH group was significantly less; but, that is significantly more in the STI group compared to the other groups. The neuronal density of ventromedial nucleus in the STI group was higher; while the density in the INH group was lower than the other groups. In the dorsomedial nucleus, neuron density of the INH group was lower than the other groups. In terms of the myenteric plexus volumes, that of the INH group was lowest. The myelinated axon number in the INH group was significantly highest. The myelin sheath thickness and axon area of the INH group was significantly lower than the other groups.Discussion: The results of the study show that the vagal inhibition is more effective than the vagal stimulation on the weight loss in the obesity.

Applying sinus node function testing to evaluate perioperative management for patients suffering from tachycardia-bradycardia syndrome before atrial fibrillation ablation

Sinus node (SN) function is an important prognostic factor of atrial fibrillation (AF). However, AF ablation guideline has not recommended SN function test before ablation. SN function testing before AF ablation in patients with tachycardia-bradycardia syndrome should be beneficial to determine further therapy strategies and prognosis.

Vagal baro- and chemoreceptors in middle internal carotid artery and carotid body in rat

The glossopharyngeal nerve, via the carotid sinus nerve (CSN), presents baroreceptors from the internal carotid artery (ICA) and chemoreceptors from the carotid body. Although neurons in the nodose ganglion were labelled after injecting tracer into the carotid body, the vagal pathway to these baro- and chemoreceptors has not been identified. Neither has the glossopharyngeal intracranial afferent/sensory pathway that connects to the brainstem been defined. We investigated both of these issues in male Sprague-Dawley rats (n = 40) by injecting neural tracer wheat germ agglutinin-horseradish peroxidase into: (i) the peripheral glossopharyngeal or vagal nerve trunk with or without the intracranial glossopharyngeal rootlet being rhizotomized; or (ii) the nucleus of the solitary tract right after dorsal and ventral intracranial glossopharyngeal rootlets were dissected. By examining whole-mount tissues and brainstem sections, we verified that only the most rostral rootlet connects to the glossopharyngeal nerve and usually four caudal rootlets connect to the vagus nerve. Furthermore, vagal branches may: (i) join the CSN originating from the pharyngeal nerve base, caudal nodose ganglion, and rostral or caudal superior laryngeal nerve; or (ii) connect directly to nerve endings in the middle segment of the ICA or to chemoreceptors in the carotid body. The aortic depressor nerve always presents and bifurcates from either the rostral or the caudal part of the superior laryngeal nerve. The vagus nerve seemingly provides redundant carotid baro- and chemoreceptors to work with the glossopharyngeal nerve. These innervations confer more extensive roles on the vagus nerve in regulating body energy that is supplied by the cardiovascular, pulmonary and digestive systems.

Shift of leading pacemaker site during reflex vagal stimulation and altered electrical source-to-sink balance

KEY POINTS

Vagal reflexes slow heart rate and can change where the heartbeat originates within the sinoatrial node (SAN). The mechanisms responsible for this process - termed leading pacemaker (LP) shift - have not been investigated fully. We used optical mapping to measure the effects of baroreflex, chemoreflex and carbachol on pacemaker entrainment and electrical conduction across the SAN. All methods of stimulation triggered shifts in LP site from the central SAN to one or two caudal pacemaker regions. These shifts were associated with reduced current generation capacity centrally and increased electrical load caudally. Previous studies suggest LP shift is a rate-dependent phenomenon whereby acetylcholine slows central pacemaker rate disproportionately, enabling caudal cells that are less acetylcholine sensitive to assume control. However, our findings indicate the LP region is defined by both pacemaker rate and capacity to drive activation. Shifts in LP site provide an important homeostatic mechanism for rapid switches in heart rate.

ABSTRACT

Reflex vagal activity causes abrupt heart rate slowing with concomitant caudal shifts of the leading pacemaker (LP) site within the sinoatrial node (SAN). However, neither the mechanisms responsible nor their dynamics have been investigated fully. Therefore, the objective of this study was to elucidate the mechanisms driving cholinergic LP shift. Optical maps of right atrial activation were acquired in a rat working heart-brainstem preparation during baroreflex and chemoreflex stimulation or with carbachol. All methods of stimulation triggered shifts in LP site from the central SAN to caudal pacemaker regions, which were positive for HCN4 and received uniform cholinergic innervation. During baroreflex onset, the capacity of the central region to drive activation declined with a decrease in amplitude and gradient of optical action potentials (OAPs) in the surrounding myocardium. Accompanying this decline, there was altered entrainment in the caudal SAN as shown by decreased conduction velocity, OAP amplitude, gradient and activation time. Atropine abolished these responses. Chemoreflex stimulation produced similar effects but central capacity to drive activation was preserved before the LP shift. In contrast, carbachol produced a prolonged period of reduced capacity to drive and altered entrainment. Previous studies suggest LP shift is a rate-dependent phenomenon whereby acetylcholine slows central pacemaker rate disproportionately, enabling caudal cells that are less acetylcholine sensitive to assume control. Our findings indicate that cholinergic LP shifts are also determined by altered electrical source-to-sink balance in the SAN. We conclude that the LP region is defined by both rate and capacity to drive atrial activation.

Optimization of Vagal Stimulation Protocol Based on Spontaneous Breathing Rate

Controlled breathing maneuver is being widely applied for cardiovascular autonomic control evaluation and cardiac vagal activation through reduction of breathing rate (BR). However, this maneuver presented contradictory results depending on the protocol and the chosen BR. These variations may be related to the individual intrinsic profile baseline sympathetic tonus, as described before by others. In this study, we evaluated the effect of controlled breathing maneuver on cardiovascular autonomic control in 26 healthy subjects allocated into two protocols: (1) controlled breathing in three different rates (10, 15, and 20 breaths/min) and (2) controlled breathing in rates normalized by the individual spontaneous breathing rate (SBR) at 100, 80, 70, and 50%. Our results showed autonomic responses favorable to vagal modulation with the lower BR maneuvers. Nevertheless, while this activation was variable using the standard protocol, all participants of the normalized protocol demonstrated an increase of vagal modulation at 80% BR (HFnu 80 = 67.5% vs. 48.2%, p < 0.0001). These results suggest that controlled breathing protocols to induce vagal activation should consider the SBR, being limited to values moderately lower than the baseline.

Failing Hearts Are More Vulnerable to Sympathetic, but Not Vagal Stimulation-Induced, Atrial Fibrillation-Ameliorated with Dantrolene Treatment

BACKGROUND

Both vagal (VS) and sympathetic (SS) stimulations can increase atrial fibrillation (AF) inducibility, with VS being known as more arrhythmogenic in normal hearts. Heart failure (HF) results in autonomic dysfunction (characterized by sympathetic activation and vagal withdrawal) and is associated with an increased AF incidence. This study investigated whether failing hearts, compared with normal control hearts, respond differently to autonomic stimulation-induced AF arrhythmogenesis and the effect of dantrolene on SS-enhanced AF in HF.

METHODS AND RESULTS

A rat myocardial infarction (MI) HF model was used. In experiment 1, AF inducibility was compared in 9 MI-HF rats versus 10 sham-control animals at baseline, during VS, and during SS with isoproterenol infusion. In experiment 2, dantrolene treatment (n = 8) was compared with placebo-control (n = 9) on SS-induced AF inducibility in HF. Compared with the sham-control, baseline AF inducibility was higher in the MI-HF group. AF inducibility was augmented in both groups by autonomic stimulation. However, under VS the increased magnitude was less in the MI-HF group (49% ± 11% vs 80% ± 10%; P = .029), but under SS was significantly more (53% ± 8% vs 6% ± 7%; P < .001), compared with sham-control. Dantrolene significantly attenuated SS-enhanced AF in HF (69% ± 6% vs 29% ± 9%; P = .006).

CONCLUSIONS

Failing hearts are less sensitive to VS, but more vulnerable to SS-induced AF compared with normal-control hearts. Dantrolene can significantly attenuate SS-enhanced AF in HF, indicating that cardiac ryanodine receptor dysfunction may play a critical role in SS-enhanced AF in HF, and stabilizing leaky ryanodine receptor with the use of dantrolene may be a new treatment option in this condition.

Vagal stimulation after acute coronary occlusion: The heart rate matters

BACKGROUND

There is a well documented causal link between autonomic imbalance and cardiac elec-trical instability. However, the mechanisms underlying the antiarrhythmic effect of vagal stimulation are poorly understood. The vagal antiarrhythmic effect might be modulated by a decrease in heart rate.

METHODS

The proximal anterior interventricular artery was occluded in 16 pigs by clamping under general anaesthesia. Group 1: heart rates remained spontaneous (n = 6; 12 occlusions); Group 2: heart rates were fixed at 190 bpm with atrial electrical stimulation (n = 10; 20 occlusions). Each pig received two occlusions, 30 min apart, one without and one with vagal stimulation (10 Hz, 2 ms, 5-20 mA). The antiarrhythmic effect of vagal activation was defined as the time to the appearance of ventricular fibrillation (VF) after occlusion.

RESULTS

In Group 1, vagal stimulation triggered a significant decrease in basal heart rate (132 ± 4 vs. 110 ± 17 bpm, p < 0.05), and delayed the time to VF after coronary occlusion (1102 ± 85 vs. 925 ± ± 41 s, p < 0.05). In Group 2, vagal stimulation did not modify the time to VF (103 ± 39 vs. 91 ± 20 s). Analyses revealed that heart rate and the time to VF were positively linearly related.

CONCLUSIONS

Maintaining a constant heart rate with atrial electrical stimulation in pigs prevented vagal stimulation from modifying the time to VF after acute coronary occlusion.

Effect of botulinum toxin on inducibility and maintenance of atrial fibrillation in ovine myocardial tissue

BACKGROUND

Aberrant vagal stimulation may promote the generation and propagation of atrial fibrillation (AF). Researchers have suggested that botulinum toxin (BTX), a neurotoxin that decreases neural vagal stimulation, may decrease the incidence of postoperative AF. The exact electrophysiologic mechanism underlying the observations and histopathologic alterations associated with BTX are unclear.

OBJECTIVE

To investigate the electrophysiologic, functional, and histopathologic effects of BTX on fibrillation induction in ovine atria.

METHODS

Eight sheep underwent BTX injections into their pulmonary veins, atrial fat pads, and ventricular walls. Electrophysiology with pacing was performed at baseline and 7 days after injection to evaluate the atrial effective refractory period (ERP) and vulnerability to AF with and without vagal stimulation. Echocardiography was performed at baseline and day 7. After euthanasia, histopathologic analysis was performed.

RESULTS

Seven sheep completed the study. For both atria, there was significant shortening in the ERP with vagal stimulation versus no stimulation on day 0 but not on day 7. More aggressive pacing was required to induce AF in the left atrium on day 7 than on day 0. Echocardiography on day 7 showed no significant changes in ejection fraction or new wall-motion abnormalities of the left and right ventricle. Histopathologic analysis showed no significant adverse effects.

CONCLUSION

The subacute BTX effect reduced the vulnerability of atrial tissue to AF induction and reduced the vagal influence on atrial ERP shortening compared to baseline levels. Direct BTX injection did not cause myocardial dysfunction or histologic adverse effects.

Atrioventricular Node Slow-Pathway Ablation Reduces Atrial Fibrillation Inducibility: A Neuronal Mechanism

Background

Radiofrequency ablation (RFA) for atrioventricular nodal reentrant tachycardia appears to reduce atrial tachycardia, which might relate to parasympathetic denervation at cardiac ganglionated plexuses.

Methods and Results

Compared to 7 control canines without RFA, in 14 canines, RFA at the bottom of Koch's triangle attenuated vagal stimulation–induced effective refractory periods prolongation in atrioventricular nodal and discontinuous atrioventricular conduction curves but had no effect on the sinoatrial node. RFA attenuated vagal stimulation–induced atrial effective refractory periods shortening and vulnerability window of atrial fibrillation widening in the inferior right atrium and proximal coronary sinus but not in the high right atrium and distal coronary sinus. Moreover, RFA anatomically impaired the epicardial ganglionated plexuses at the inferior vena cava‒inferior left atrial junction. This method was also investigated in 42 patients who had undergone ablation of atrioventricular nodal reentrant tachycardia, or 12 with an accessory pathway (AP) at the posterior septum (AP‐PS), and 34 patients who had an AP at the free wall as control. In patients with atrioventricular nodal reentrant tachycardia and AP‐PS, RFA at the bottom of Koch's triangle prolonged atrial effective refractory periods and reduced vulnerability windows of atrial fibrillation widening at the inferior right atrium, distal coronary sinus and proximal coronary sinus but not the high right atrium. In patients with AP‐free wall, RFA had no significant atrial effects.

Conclusions

RFA at the bottom of Koch's triangle attenuated local autonomic innervation in the atrioventricular node and atria, decreased vagal stimulation–induced discontinuous atrioventricular nodal conduction, and reduced atrial fibrillation inducibility due to impaired ganglionated plexuses. In patients with atrioventricular nodal reentrant tachycardia or AP‐PS, RFA prolonged atrial effective refractory periods, and narrowed vulnerability windows of atrial fibrillation.

Vagus nerve stimulation attenuates myocardial ischemia/reperfusion injury by inhibiting the expression of interleukin-17A

Interleukin (IL)-17A has an important role in myocardial ischemia/reperfusion (I/R) injury, and vagal stimulation (VS) has been demonstrated to exert cardioprotective effects. The present study aimed to investigate the effects of VS on a rat model of myocardial I/R injury, and detected an association between VS and IL-17A. Anesthetized rats underwent VS (2 msec; 10 Hz) or were treated with anti-IL-17A neutralized monoclonal antibodies (mAbs) (200 µg; iv), and subjected to ischemia for 30 min prior to 4 h reperfusion. The following parameters were measured: Infarct size; lactate dehydrogenase (LDH), creatine kinase (CK), malondialdehyde (MDA), superoxide dismutase (SOD) and caspase-3 activity levels; tumor necrosis factor (TNF)-α and IL-6 expression levels; and the percentage of terminal deoxynucleotidyl-transferase mediated dUTP nick-end labeling (TUNEL) positive cells. High mobility group box 1 protein (HMGB1) and IL-17A expression levels were assessed by immunoblotting. Following 4 h reperfusion, VS was able to significantly decrease the infarct size and the activity levels of LDH and CK (P<0.05). Furthermore, VS administration significantly suppressed the increased MDA and decreased SOD activity levels, and significantly reduced caspase-3 activity and the percentage of TUNEL-positive cells (P<0.05). Treatment with anti-IL-17A mAbs demonstrated the same effects as VS. Furthermore, VS was able to significantly inhibit the increased expression levels of TNF-α, IL-6, HMGB1 and IL-17A induced by I/R (P<0.05). The results of the present study suggested that VS may attenuate myocardial I/R injury by reducing the expression of inflammatory cytokines, oxidative stress and the apoptosis of cardiomyocytes. Furthermore, VS may induce cardioprotective effects, which may be associated with the inhibition of IL-17A expression.

Vagus Nerve Stimulation During Rehabilitative Training Improves Forelimb Recovery After Chronic Ischemic Stroke in Rats

BACKGROUND AND OBJECTIVE

Stroke is a leading cause of long-term disability. Currently, there are no consistently effective rehabilitative treatments for chronic stroke patients. Our recent studies demonstrate that vagus nerve stimulation (VNS) paired with rehabilitative training improves recovery of function in multiple models of stroke. Here, we evaluated the ability of VNS paired with rehabilitative training to improve recovery of forelimb strength when initiated many weeks after a cortical and subcortical ischemic lesion in subjects with stable, chronic motor deficits.

METHODS

Rats were trained to perform an automated, quantitative measure of voluntary forelimb strength. Once proficient, rats received injections of endothelin-1 to cause a unilateral cortical and subcortical ischemic lesion. Then, 6 weeks after the lesion, rats underwent rehabilitative training paired with VNS (Paired VNS; n = 10), rehabilitative training with equivalent VNS delivered 2 hours after daily rehabilitative training (Delayed VNS; n = 10), or rehabilitative training without VNS (Rehab, n = 9).

RESULTS

VNS paired with rehabilitative training significantly improved recovery of forelimb function compared with control groups. The Paired VNS group displayed an 86% recovery of strength, the Rehab group exhibited 47% recovery, and the Delayed VNS group exhibited 42% recovery. Improvement in forelimb function was sustained in the Paired VNS group after the cessation of stimulation, potentially indicating lasting benefits. No differences in intensity of rehabilitative training, lesion size, or MAP-2 expression were observed between groups.

CONCLUSION

VNS paired with rehabilitative training confers significantly greater recovery of forelimb function after chronic ischemic stroke in rats.

Treatment of Atrial and Ventricular Arrhythmias Through Autonomic Modulation

This paper reviews the contribution of autonomic nervous system (ANS) modulation in the treatment of arrhythmias. Both the atria and ventricles are innervated by an extensive network of nerve fibers of parasympathetic and sympathetic origin. Both the parasympathetic and sympathetic nervous system exert arrhythmogenic electrophysiological effects on atrial and pulmonary vein myocardium, while in the ventricle the sympathetic nervous system plays a more dominant role in arrhythmogenesis. Identification of ANS activity is possible with nuclear imaging. This technique may provide further insight in mechanisms and treatment targets. Additionally, the myocardial effects of the intrinsic ANS can be identified through stimulation of the ganglionic plexuses. These can be ablated for the treatment of atrial fibrillation. New (non-) invasive treatment options targeting the extrinsic cardiac ANS, such as low-level tragus stimulation and renal denervation, provide interesting future treatment possibilities both for atrial fibrillation and ventricular arrhythmias. However, the first randomized trials have yet to be performed. Future clinical studies on modifying the ANS may not only improve the outcome of ablation therapy but may also advance our understanding of the manner in which the ANS interacts with the myocardium to modify arrhythmogenic triggers and substrate.

Can we Modulate the Autonomic Nervous System to Improve the Life of Patients with Heart Failure? The Case of Vagal Stimulation

An imbalance of the autonomic nervous system, with reduced vagal and increased sympathetic activity, contributes to pathogenesis and clinical deterioration in heart failure (HF). Experimental studies have demonstrated that vagal stimulation (VS) has an antifibrillatory effect that has proved beneficial in animal models of HF. The potential value of chronic VS in man was first investigated with an implantable neuro-stimulator capable of delivering low current pulses with adjustable parameters to stimulate the right vagus. The results of a pilot study and a small multicentre clinical trial of VS in HF patients appeared to show a favourable clinical effect, and feasibility and safety data were encouraging. An ongoing pivotal clinical trial will provide a definitive assessment of the efficacy and usefulness of chronic VS in HF patients.This approach represents a new and exciting possibility for the management of HF that will provide clinicians with a novel tool to modulate non-pharmacologically the autonomic nervous system in patients with moderate-to-advanced HF.

Device-Based Approaches to Modulate the Autonomic Nervous System and Cardiac Electrophysiology

Alterations in resting autonomic tone can be pathogenic in many cardiovascular disease states, such as heart failure and hypertension. Indeed, autonomic modulation by way of beta-blockade is a standard treatment of these conditions. There is a significant interest in developing non-pharmacological methods of autonomic modulation as well. For instance, clinical trials of vagal stimulation and spinal cord stimulation in the treatment of heart failure are currently underway, and renal denervation has been studied recently in the treatment of resistant hypertension. Notably, autonomic stimulation is also a potent modulator of cardiac electrophysiology. Manipulating the autonomic nervous system in studies designed to treat heart failure and hypertension have revealed that autonomic modulation may have a role in the treatment of common atrial and ventricular arrhythmias as well. Experimental data on vagal nerve and spinal cord stimulation suggest that each technique may reduce ventricular arrhythmias. Similarly, renal denervation may play a role in the treatment of atrial fibrillation, as well as in controlling refractory ventricular arrhythmias. In this review, we present the current experimental and clinical data on the effect of these therapeutic modalities on cardiac electrophysiology and their potential role in arrhythmia management.

Effect of the cholinesterase inhibitor donepezil on cardiac remodeling and autonomic balance in rats with heart failure

In an earlier study we demonstrated the beneficial effect of direct vagal electrical stimulation on cardiac remodeling and survival. In the study reported here, we attempted to reproduce the effect of vagal enhancement through the administration of an acetylcholinesterase inhibitor, donepezil. A rat model of heart failure following extensive healed myocardial infarction was used. Compared to their nontreated counterparts, rats given donepezil (5 mg/kg/day) in their drinking water had a smaller biventricular weight (3.40 +/- 0.13 vs. 3.02 +/- 0.21 g/kg body weight, P < 0.05), and maximal rate of rise (3256 +/- 955 vs. 3822 +/- 389 mmHg/s, P < 0.05) and the end-diastolic value (30.1 +/- 5.6 vs. 23.2 +/- 5.7 mmHg, P < 0.05) of left ventricular pressure were improved. Neurohumoral factors were suppressed in donepezil-treated rats (norepinephrine 1885 +/- 1423 vs. 316 +/- 248 pg/ml, P < 0.01; brain natriuretic peptide 457 +/- 68 vs. 362 +/- 80 ng/ml, P < 0.05), and the high-frequency component of heart rate variability showed a nocturnal increase. These findings indicated that donepezil reproduced the anti-remodeling effect of electrical vagal stimulation. Further studies are warranted to evaluate the clinical usefulness of donepezil in heart failure.