Selective in situ parasympathetic control of the canine sinoatrial and atrioventricular nodes

The autonomic nervous system and the origins of neurocardiology

Following new concepts by Bichat in the early 19th century, of organic and animal life centered around the ganglionic nervous system, over 100 years of anatomic studies and physiologic experimentation eventually resulted in Gaskell's 1916 book entitled "The Involuntary Nervous System" and Langley's 1921 book entitled "The Autonomic Nervous System." Neurology and cardiology emerged as specialties of medicine in the early 20th century. Although neurology made several prominent discoveries in neurophysiology during the first half of the 20th century, cardiology developed coronary care units and cardiac catheterization in the 1960s. Programmed electrical stimulation of the heart and noninvasive ambulatory monitoring provided new methodologies to study clinical cardiac arrhythmias. Experimentally, direct cardiac nerve stimulation of sympathetic nerve endings, as well as parasympathetic control of the atrioventricular node, provided the background to new detailed autonomic studies of the heart. Neurocardiology, perhaps initially more directed towards our understanding of sudden cardiac death, ultimately embraced an even significantly more complex scheme of local circuit neurons and near-endless loops of interconnecting neurons in the heart. Intrathoracic extracardiac and intracardiac ganglia have been recharacterized, both anatomically and physiologically, laying the groundwork for potential new therapies of cardiac neuromodulation.

Improvement in Atrioventricular Conduction Using Cardioneuroablation Performed Immediately after Pulmonary Vein Isolation

In patients with atrial fibrillation (AF) recurrences after pulmonary vein isolation (PVI), concomitant treatment using anti arrhythmic drugs (AADs) can lead to clinical success. However, patients with atrioventricular (AV) block may not be good candidates for concomitant AAD therapy due to the risk of further worsening of conduction abnormalities. Cardioneuroablation (CNA), as an adjunct to PVI, may offer a solution to this problem. We present a case of a 74-year-old male with paroxysmal AF and first degree AV block in whom CNA following PVI led to PR normalization. The presented case describes an example of CNA utilization in patients with AF undergoing PVI who have concomitant problems with AV conduction and shows that CNA can be sometimes useful in older patients with functional AV block.

The vagus nerve in cardiovascular physiology and pathophysiology: From evolutionary insights to clinical medicine

The parasympathetic nervous system via the vagus nerve exerts profound influence over the heart. Together with the sympathetic nervous system, the parasympathetic nervous system is responsible for fine-tuned regulation of all aspects of cardiovascular function, including heart rate, rhythm, contractility, and blood pressure. In this review, we highlight vagal efferent and afferent innervation of the heart, with a focus on insights from comparative biology and advances in understanding the molecular and genetic diversity of vagal neurons, as well as interoception, parasympathetic dysfunction in heart disease, and the therapeutic potential of targeting the parasympathetic nervous system in cardiovascular disease.

Endocardial ablation of epicardial ganglionated plexi: history, open questions and future prospects of cardioneuroablation

Neurocardiogenic syncope is the most common cause of transient loss of consciousness and considerably reduces quality of life. Pharmacological and pacing therapy may not be fully efficacious and complications related to implanted hardware must be considered. In this context, cardioneuroablation (CNA) has been proposed to attenuate the vagal reflex with elimination of cardioinhibition. It has been shown that CNA is able to eliminate recurrences of syncope in over 90% of cases and no major complications are reported in the current literature. Despite these encouraging findings, CNA is only mentioned in current guidelines as a possible alternative treatment and has no real indication class. The diversity of mapping techniques, the absence of direct denervation control, the lack of a precise endpoint, the possible placebo effect, the short follow-up, and the question of the learning curve represent the major limitations of this promising procedure. The aim of this review was to look over the existing literature, analysing the novelties, the limitations, the unresolved issues and the outcome of CNA.

From Mice to Mainframes: Experimental Models for Investigation of the Intracardiac Nervous System

The intracardiac nervous system (IcNS), sometimes referred to as the "little brain" of the heart, is involved in modulating many aspects of cardiac physiology. In recent years our fundamental understanding of autonomic control of the heart has drastically improved, and the IcNS is increasingly being viewed as a therapeutic target in cardiovascular disease. However, investigations of the physiology and specific roles of intracardiac neurons within the neural circuitry mediating cardiac control has been hampered by an incomplete knowledge of the anatomical organisation of the IcNS. A more thorough understanding of the IcNS is hoped to promote the development of new, highly targeted therapies to modulate IcNS activity in cardiovascular disease. In this paper, we first provide an overview of IcNS anatomy and function derived from experiments in mammals. We then provide descriptions of alternate experimental models for investigation of the IcNS, focusing on a non-mammalian model (zebrafish), neuron-cardiomyocyte co-cultures, and computational models to demonstrate how the similarity of the relevant processes in each model can help to further our understanding of the IcNS in health and disease.

Autonomic modulation of the arrhythmogenic substrate in the evolution of atrial fibrillation and therapeutic approaches

The autonomic nervous system (ANS) plays an important role in atrial arrhythmogenesis and is one of the factors responsible for the initiation and maintenance of atrial fibrillation (AF). Over the past few decades, neuromodulation has been shown to help in the management of AF. This review focuses on the correlation between AF and the ANS and how different approaches to identifying and modulating the autonomic substrate impact outcomes in AF. The authors conclude that the ANS is one of the key components in the development of AF and that modulation of autonomic nerve function may contribute to the management of AF. Therapeutic approaches such as catheter ablation of ganglionated plexi (GP), renal denervation and transcutaneous vagus nerve stimulation are viable treatment options that need further confirmation in larger randomised controlled trials. In addition, new imaging technologies were able to identify GPs accurately and reproducibly, which promises exciting prospects for the future.

Innervation and Neuronal Control of the Mammalian Sinoatrial Node a Comprehensive Atlas

[Figure: see text].

Cellular and Molecular Mechanisms of Functional Hierarchy of Pacemaker Clusters in the Sinoatrial Node: New Insights into Sick Sinus Syndrome

The sinoatrial node (SAN), the primary pacemaker of the heart, consists of a heterogeneous population of specialized cardiac myocytes that can spontaneously produce action potentials, generating the rhythm of the heart and coordinating heart contractions. Spontaneous beating can be observed from very early embryonic stage and under a series of genetic programing, the complex heterogeneous SAN cells are formed with specific biomarker proteins and generate robust automaticity. The SAN is capable to adjust its pacemaking rate in response to environmental and autonomic changes to regulate the heart's performance and maintain physiological needs of the body. Importantly, the origin of the action potential in the SAN is not static, but rather dynamically changes according to the prevailing conditions. Changes in the heart rate are associated with a shift of the leading pacemaker location within the SAN and accompanied by alterations in P wave morphology and PQ interval on ECG. Pacemaker shift occurs in response to different interventions: neurohormonal modulation, cardiac glycosides, pharmacological agents, mechanical stretch, a change in temperature, and a change in extracellular electrolyte concentrations. It was linked with the presence of distinct anatomically and functionally defined intranodal pacemaker clusters that are responsible for the generation of the heart rhythm at different rates. Recent studies indicate that on the cellular level, different pacemaker clusters rely on a complex interplay between the calcium (referred to local subsarcolemmal Ca²⁺ releases generated by the sarcoplasmic reticulum via ryanodine receptors) and voltage (referred to sarcolemmal electrogenic proteins) components of so-called "coupled clock pacemaker system" that is used to describe a complex mechanism of SAN pacemaking. In this review, we examine the structural, functional, and molecular evidence for hierarchical pacemaker clustering within the SAN. We also demonstrate the unique molecular signatures of intranodal pacemaker clusters, highlighting their importance for physiological rhythm regulation as well as their role in the development of SAN dysfunction, also known as sick sinus syndrome.

Pleiotropic activity of nerve growth factor in regulating cardiac functions and counteracting pathogenesis

Cardiac innervation density generally reflects the levels of nerve growth factor (NGF) produced by the heart—changes in NGF expression within the heart and vasculature contribute to neuronal remodelling (e.g. sympathetic hyperinnervation or denervation). Its synthesis and release are altered under different pathological conditions. Although NGF is well known for its survival effects on neurons, it is clear that these effects are more wide ranging. Recent studies reported both in vitro and in vivo evidence for beneficial actions of NGF on cardiomyocytes in normal and pathological hearts, including prosurvival and antiapoptotic effects. NGF also plays an important role in the crosstalk between the nervous and cardiovascular systems. It was the first neurotrophin to be implicated in postnatal angiogenesis and vasculogenesis by autocrine and paracrine mechanisms. In connection with these unique cardiovascular properties of NGF, we have provided comprehensive insight into its function and potential effect of NGF underlying heart sustainable/failure conditions. This review aims to summarize the recent data on the effects of NGF on various cardiovascular neuronal and non‐neuronal functions. Understanding these mechanisms with respect to the diversity of NGF functions may be crucial for developing novel therapeutic strategies, including NGF action mechanism‐guided therapies.

Recording Intrinsic Nerve Activity at the Sinoatrial Node in Normal Dogs With High-Density Mapping

BACKGROUND

It is known that autonomic nerve activity controls the sinus rate. However, the coupling between local nerve activity and electrical activation at the sinoatrial node (SAN) remains unclear. We hypothesized that we would be able to record nerve activity at the SAN to investigate if right stellate ganglion (RSG) activation can increase the local intrinsic nerve activity, accelerate sinus rate, and change the earliest activation sites.

METHODS

High-density mapping of the epicardial surface of the right atrium including the SAN was performed in 6 dogs during stimulation of the RSG and after RSG stellectomy. A radio transmitter was implanted into 3 additional dogs to record RSG and local nerve activity at the SAN.

RESULTS

Heart rate accelerated from 108±4 bpm at baseline to 125±7 bpm after RSG stimulation (P=0.001), and to 132±7 bpm after apamin injection (P<0.001). Both electrical RSG stimulation and apamin injection induced local nerve activity at the SAN with the average amplitudes of 3.60±0.72 and 3.86±0.56 μV, respectively. RSG stellectomy eliminated the local nerve activity and decreased the heart rate. In ambulatory dogs, local nerve activity at the SAN had a significantly higher average Pearson correlation to heart rate (0.72±0.02, P=0.001) than RSG nerve activity to HR (0.45±0.04, P=0.001).

CONCLUSIONS

Local intrinsic nerve activity can be recorded at the SAN. Short bursts of these local nerve activities are present before each atrial activation during heart rate acceleration induced by stimulation of the RSG.

Long-Term Evaluation of the Vagal Denervation by Cardioneuroablation Using Holter and Heart Rate Variability

Background:

Several disorders present reflex or persistent increase in vagal tone that may cause refractory symptoms even in a normal heart patient. Cardioneuroablation, the vagal denervation by radiofrequency ablation of the neuromyocardial interface, was developed to treat these conditions without pacemaker implantation. A theoretical limitation could be the reinnervation, that naturally grows in the first year, that could recover the vagal hyperactivity. This study aims to verify the vagal denervation degree in the chronic phase after cardioneuroablation. Additionally, it intends to investigate the arrhythmias behavior after cardioneuroablation.

Methods:

Prospective longitudinal study with intrapatient comparison of 83 very symptomatic cases without significant cardiopathy, submitted to cardioneuroablation, 49 (59%) male, 47.3±17 years old, having vagal paroxysmal atrial fibrillation 58 (70%) or neurocardiogenic syncope 25 (30%), New York Heart Association class<II and absence of significant comorbidities. Cardioneuroablation was performed in both atria by interatrial septum puncture, with irrigated conventional catheter and electroanatomic reconstruction. Ablation targeted the neuromiocardial interface by fragmentation mapping (AF-Nests) using the velocity fractionation software, conventional recording, and anatomic localization of the ganglionated plexi. Heart rate variability (time and frequency domain) and arrhythmias were compared by 24h-Holter, before, and 1 year and 2 years after cardioneuroablation. In a 40 month follow-up, 80% of patients were asymptomatic.

Results:

Time- and frequency-domain heart rate variability demonstrated significant decrease in all autonomic parameters, showing an important parasympathetic and sympathetic activity reduction at 2-year post-cardioneuroablation ( P <0.001). There was no difference in heart rate variability between the 1-year and 2-year post-cardioneuroablation ( P >0.05) suggesting that the reinnervation has halted. There was also an important reduction in all bradyarrhythmias and tachyarrhythmias pre-cardioneuroablation versus post-cardioneuroablation ( P <0.01).

Conclusions:

There is an important and significant vagal and sympathetic denervation after 2 years of cardioneuroablation with a significant reduction in bradyarrhythmia and tachyarrhythmia in the whole group. There were no complications.

Relation of Fractionated Atrial Potentials With the Vagal Innervation Evaluated by Extracardiac Vagal Stimulation During Cardioneuroablation

BACKGROUND

Vagal hyperactivity is directly related to several clinical conditions as reflex/functional bradyarrhythmias and vagal atrial fibrillation (AF). Cardioneuroablation provides therapeutic vagal denervation through endocardial radiofrequency ablation for these cases. The main challenges are neuromyocardium interface identification and the denervation control and validation. The finding that the AF-Nest (AFN) ablation eliminates the atropine response and decreases RR variability suggests that they are related to the vagal innervation.

METHOD

Prospective, controlled, longitudinal, nonrandomized study enrolling 62 patients in 2 groups: AFN group (AFN group 32 patients) with functional or reflex bradyarrhythmias or vagal AF treated with AFN ablation and a control group (30 patients) with anomalous bundles, ventricular premature beats, atrial flutter, atrioventricular nodal reentry, and atrial tachycardia, treated with conventional ablation (non-AFN ablation). In AFN group, ablation delivered at AFN detected by fragmentation/fractionation of the endocardial electrograms and by 3-dimensional anatomic location of the ganglionated plexus. Vagal response was evaluated before, during, and postablation by 5 s noncontact vagal stimulation at the jugular foramen, through the internal jugular veins (extracardiac vagal stimulation [ECVS]), analyzing 15 s mean heart rate, longest RR, pauses, and atrioventricular block. All patients had current guidelines arrhythmia ablation indication.

RESULTS

Preablation ECVS induced sinus pauses, asystole, and transient atrioventricular block in both groups showing a strong vagal response (P=0.96). Postablation ECVS in the AFN group showed complete abolishment of the cardiac vagal response in all cases (pre/postablation ECVS=P<0.0001), demonstrating robust vagal denervation. However, in the control group, vagal response remained practically unchanged postablation (P=0.35), showing that non-AFN ablation promotes no significant denervation.

CONCLUSIONS

AFN ablation causes significant vagal denervation. Non-AFN ablation causes no significant vagal denervation. These results suggest that AFNs are intrinsically related to vagal innervation. ECVS was fundamental to stepwise vagal denervation validation during cardioneuroablation. Visual Overview A visual overview is available for this article.

Is Vagal Response During Left Atrial Ganglionated Plexi Stimulation a Normal Phenomenon?

Background:

Ganglionated plexi (GPs) play an important role in both the initiation and maintenance of atrial fibrillation (AF). GPs can be located by using continuous high-frequency stimulation (HFS) to elicit a vagal response, but whether the vagal response phenomenon is common to patients without AF is unknown.

Methods:

HFS of the left atrial GPs was performed in 42 patients (aged 58.0±10.2 years) undergoing ablation for AF and 21 patients (aged 53.2±12.8 years) undergoing ablation for a left-sided accessory pathway. The HFS (20 Hz, 25 mA, 10-ms pulse duration) was applied for 5 seconds at 3 sites within the presumed anatomic area of each of the 5 major left atrial GPs (for a total of 15 sites per patient). We defined vagal response to HFS as prolongation of the R-R interval by >50% in comparison to the mean pre-HFS R-R interval averaged over 10 beats and active-GP areas as areas in which a vagal response was elicited.

Results:

Overall, more active-GP areas were found in the AF group patients than in the non-AF group patients, and at all 5 major GPs, the maximum R-R interval during HFS was significantly prolonged in the AF patients. After multivariate adjustment, association was established between the total number of vagal response sites and the presence of AF.

Conclusions:

The significant increase in vagal responses elicited in patients with AF compared with responses in non-AF patients suggests that vagal responses to HFS reflect abnormally increased GP activity specific to AF substrates.

Sympathetic responses induced by radiofrequency catheter ablation of atrial fibrillation

Radiofrequency catheter ablation (RFCA) is a frequently performed procedure in patients with atrial fibrillation. Prior studies have shown that the RFCA may directly stimulate vagal afferents during the procedure, whereas the vagal tone assessed by heart rate variability (HRV) is lowered weeks after the RFCA procedure. The effects of RFCA performed in the left atrium on sympathetic nerve activity have not been assessed. In the present study, we hypothesized that RFCA would lower muscle sympathetic nerve activity (MSNA) during ablation and would raise MSNA 1 day postablation. A total of 18 patients were studied. In protocol 1 ( n = 10), electrocardiogram, blood pressure, and MSNA in the peroneal nerve were recorded through the RFCA procedure performed in the electrophysiology laboratory. In protocol 2, eight patients were studied before the procedure and 1 day postablation. RFCA led to a decrease in MSNA immediately after the procedure (25.4 ± 3.2 to 17.2 ± 3.8 bursts/min, P < 0.05). Cardiac parasympathetic activity was determined using indexes of HRV and increased during the procedure. One day postablation, MSNA was above baseline values (21.3 ± 3.7 to 35.7 ± 2.6 bursts/min, P < 0.05). HRV indexes of cardiac parasympathetic activity fell, and the HRV index of sympathovagal balance was not significantly altered. The results show that RFCA raised cardiac parasympathetic activity and decreased MSNA during the procedure. One day postablation, MSNA rose and cardiac parasympathetic activity fell. In addition, RFCA evokes differentiated sympathetic responses directed to the heart and skeletal muscles. NEW & NOTEWORTHY The effects of radiofrequency catheter ablation performed in the left atrium on muscle sympathetic nerve activity (MSNA) have not been assessed. The results of this study show that radiofrequency catheter ablation raised cardiac parasympathetic activity and decreased MSNA during the procedure. One day postablation, MSNA rose and cardiac parasympathetic activity fell. We speculate that the partial autonomic afferent denervation induces these effects on autonomic activity.

A novel approach to mapping the atrial ganglionated plexus network by generating a distribution probability atlas

Introduction

The ganglionated plexuses (GPs) of the intrinsic cardiac autonomic system are implicated in arrhythmogenesis. GP localization by stimulation of the epicardial fat pads to produce atrioventricular dissociating (AVD) effects is well described. We determined the anatomical distribution of the left atrial GPs that influence atrioventricular (AV) dissociation.

Methods and Results

High frequency stimulation was delivered through a Smart‐Touch catheter in the left atrium of patients undergoing atrial fibrillation (AF) ablation. Three dimensional locations of points tested throughout the entire chamber were recorded on the CARTO™ system. Impact on the AV conduction was categorized as ventricular asystole, bradycardia, or no effect. CARTO maps were exported, registered, and transformed onto a reference left atrial geometry using a custom software, enabling data from multiple patients to be overlaid. In 28 patients, 2108 locations were tested and 283 sites (13%) demonstrated (AVD‐GP) effects. There were 10 AVD‐GPs (interquartile range, 11.5) per patient. Eighty percent (226) produced asystole and 20% (57) showed bradycardia. The distribution of the two groups was very similar. Highest probability of AVD‐GPs (>20%) was identified in: inferoseptal portion (41%) and right inferior pulmonary vein base (30%) of the posterior wall, right superior pulmonary vein antrum (31%).

Conclusion

It is feasible to map the entire left atrium for AVD‐GPs before AF ablation. Aggregated data from multiple patients, producing a distribution probability atlas of AVD‐GPs, identified three regions with a higher likelihood for finding AVD‐GPs and these matched the histological descriptions. This approach could be used to better characterize the autonomic network.

Subthreshold Stimulation for His Bundle Pacing

One of the drawbacks of permanent His bundle pacing has been the relatively high pacing thresholds. The present experimental study was proposed to address this issue. In this article the authors present preliminary evidence that His bundle pacing can be achieved with subthreshold stimulation, thereby providing for increased battery life and consequently longer replacement intervals. Possible mechanisms underlying the paradoxical effects of subthreshold stimulation before and after the onset of complete atrioventricular block are also discussed.

Acetylcholine-Atropine Interactions: Paradoxical Effects on Atrial Fibrillation Inducibility

Atropine (ATr) is well known as a cholinergic antagonist, however, at low concentrations ATr could paradoxically accentuate the parasympathetic actions of acetylcholine (ACh). In 22 pentobarbital anesthetized dogs, via a left and right thoracotomy, a leak-proof barrier was attached to isolate the atrial appendages (AAs) from the rest of the atria. In group 1 (Ach+ATr+Ach), ACh, 100 mM, was placed on the AA followed by the application of ATr, 2 mg/mL. The average atrial fibrillation (AF) duration was 17 ± 7 minutes. After ATr was applied to the AA and ACh again tested, the AF duration was markedly attenuated (2 ± 2 minutes, P < 0.05). In group 2 (ATr+Ach), ATr was initially applied to the AA followed by the application of ACh, 100 mM. There was no significant difference in AF duration (16 ± 4 minutes vs. 18 ± 2 minutes, P = NS). The inhibitory effect of ATr on induced HR reduction (electrical stimulation of the anterior right ganglionated plexi and vagal nerves) was similar between groups 1 and 2. These observations suggest that when ATr is initially administered it attaches to the allosteric site of the muscarinic ACh receptor (M2) leaving the orthosteric site free to be occupied by ACh. The M3 receptor that controls HR slowing does not show the same allosteric properties.

Increase of Autonomic Nerve Factors in Epicardial Ganglionated Plexi During Rapid Atrial Pacing Induced Acute Atrial Fibrillation

Background

The cardiac autonomic nervous system plays an essential role in epicardial ganglionated plexi (GP) regulation of atrial fibrillation onset and progression. To date, the activity of GP and the function of the cardiac autonomic nervous system are not well understood. The aim of this study was to determine alterations in epicardial GP cholinergic nerve, adrenergic nerve, and nerve growth factor expression using rapid atrial pacing to induce atrial fibrillation in canines.

Material/Methods

Nine healthy adult beagles were divided into two groups: the pacing experimental group (n=6) and the sham-operation control group (n=3). For the pacing group, high frequency pacing of the left atrial appendage was performed for eight hours. In the control group, electrodes were implanted without rapid atrial pacing. Immunocytochemistry was used to identify neurons positively expressing tyrosine hydroxylase, choline acetyl transferase, nerve growth factor and neurturin.

Results

After successfully establishing a rapid atrial pacing of the left atrial appendage induced atrial fibrillation model, we found that expression of choline acetyl transferase, tyrosine hydroxylase, nerve growth factor, and neurturin was significantly higher in the rapid atrial pacing group than the control group (p<0.05).

Conclusions

In our model, incremental excitability of both the adrenergic and cholinergic nerves led to frequent incidents of atrial fibrillation, which were possibly due to an imbalance of autonomic nerve factors in the epicardial GP during acute atrial fibrillation.

Is the Atrial Neural Plexis a Therapeutic Target in Atrial Fibrillation?

Circumferential pulmonary vein isolation is the mainstay of atrial fibrillation (AF) ablation, but alternative approaches and techniques have been developed to improve the outcomes. One of these additional ablation targets are ganglionated plexi of the intrinsic cardiac autonomic system that contain a variety of sympathetic and parasympathetic neurons that communicate with the extrinsic cardiac autonomic nervous system. The ganglionated plexi of the heart do not serve as a simple relay station but could modulate the autonomic interaction between the extrinsic and intrinsic cardiac autonomic system. Intrinsic cardiac autonomic nerve activity is an invariable trigger of paroxysmal atrial tachyarrhythmia, including atrial fibrillation. Although multiple studies have shown that ganglionated plexi play an important role in initiating atrial fibrillation, there is no consensus on a standardized protocol for selecting target sites and determining how ganglionated plexi ablation can best be accomplished. Recent clinical trials have demonstrated the feasibility and efficacy of ganglionated plexi ablation in addition to pulmonary vein isolation, but novel technologies and strategies are necessary to improve the current ablation techniques in managing patients with atrial fibrillation. This review focuses on the relationship between atrial ganglionated plexi and atrial fibrillation and the potential benefits and limitations of ganglionated plexi ablation in the management of atrial fibrillation.

Atrial autonomic denervation for the treatment of long-standing symptomatic sinus bradycardia in non-elderly patients

PURPOSE

Multiple lead and generator replacement and related complications often complicate the decision of pacemaker implantation in non-elderly patients with symptomatic bradycardia. This study sought to investigate the efficacy and safety of atrial autonomic denervation for treating the symptomatic long-standing sinus bradycardia (SB) in non-elderly patients.

METHODS AND RESULTS

Eleven non-elderly patients (mean age, 45.9 ± 10.9 years; eight men) with a long history of SB (106.2 ± 43.7 months; range, 60-189) were enrolled. Five atrial ganglionated plexies (GPs), identified by anatomic distribution and high-frequency stimulation, were targeted and ablated. The end point was elimination of the vagal response at ablation sites. The symptoms of SB and Holter were followed up at 3 days, 6, and 12 months and, thereafter, over a period of 18 months. Six patients were under 50 years old (group I) and 5 patients were between 50 and 60 years old (group II). There were 3.1 ± 0.7 GPs with positive vagal response and 11.3 ± 2.7 ablation sites in each patient. During the 18.4 ± 6.2 (range, 12-25) months of follow-up, all patients reported significant symptom improvement with a significant decrease of the SB-related symptoms score. The total heartbeats, mean, and minimum heart rate significantly increased that persisted for 12 months. Compared with patients in group II, those in group I had more increases in total heartbeats and mean heart rate (HR).

CONCLUSION

Atrial autonomic denervation increases sinus rate and improves symptoms in non-elderly patients with symptomatic long-standing SB, thus, potentially serving as an alternative to pacemaker implantation.

Contact force mapping and voltage thresholds during high-frequency stimulation of human cardiac ganglionated plexuses†

AIMS

The intrinsic cardiac nervous system consists of ganglionated plexuses (GPs) localized epicardially to specific regions of the left atrium (LA). The relation between voltage thresholds and endocardial contact force associated with autonomic effects during stimulation of GPs has not previously been evaluated.

METHODS AND RESULTS

Sixteen patients with symptomatic atrial fibrillation (AF) underwent mapping of GPs prior to radiofrequency ablation of AF. Pre-acquired computed tomographic images were merged with 3D non-fluoroscopic electroanatomic mapping of the LA. Using high-frequency stimulation (HFS), the voltage thresholds of GPs was obtained while patients received conscious sedation. At each location, the contact force measurement from the catheter was correlated with the voltage applied during HFS at 5, 10, or 15 V to obtain an autonomic effect, usually associated with asystole, or marked bradycardia. There were 192 applications of HFS, resulting in GP identification in all patients (mean 3.4 per patient, range 1-5). During HFS, an autonomic response was significantly more likely to occur at 10 V as compared with 5 V (P < 0.008). There was no significant relation between the measured contact force and the likelihood of obtaining an autonomic response. When performing HFS at 15 V, a sudden overshoot with maximal values of contact force of up to 100 g was also observed. High-frequency stimulation was well tolerated, without associated adverse events.

CONCLUSION

An autonomic response during HFS was significantly more likely to occur at 10 V as compared with 5 V. Although the GPs are epicardial structures, significant contact force was not required for their localization.

Features of intrinsic ganglionated plexi in both atria after extensive pulmonary isolation and their clinical significance after catheter ablation in patients with atrial fibrillation

BACKGROUND

The features of intrinsic ganglionated plexi (GP) in both atria after extensive pulmonary vein isolation (PVI) and their clinical implications have not been clarified in patients with atrial fibrillation (AF).

OBJECTIVE

The purpose of this study was to assess the features of GP response after extensive PVI and to evaluate the relationship between GP responses and subsequent AF episodes.

METHODS

The study population consisted of 216 consecutive AF patients (104 persistent AF) who underwent an initial ablation. We searched for the GP sites in both atria after an extensive PVI.

RESULTS

GP responses were determined in 186 of 216 patients (85.6%). In the left atrium, GP responses were observed around the right inferior GP in 116 of 216 patients (53.7%) and around the left inferior GP in 57 of 216 (26.4%). In the right atrium, GP responses were observed around the posteroseptal area: inside the CS in 64 of 216 patients (29.6%), at the CS ostium in 150 of 216 (69.4%), and in the lower right atrium in 45 of 216 (20.8%). The presence of a positive GP response was an independent risk factor for AF recurrence (hazard ratio 4.04, confidence interval 1.48-11.0) in patients with paroxysmal, but not persistent, AF. The incidence of recurrent atrial tachyarrhythmias in patients with paroxysmal AF with a positive GP response was 51% vs 8% in those without a GP response (P = .002).

CONCLUSION

The presence of GP responses after extensive PVI was significantly associated with increased AF recurrence after ablation in patients with paroxysmal AF.

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.

Experimental model of focal atrial tachycardia: clinical correlates

BACKGROUND

The mechanisms underlying focal atrial tachycardia (AT) are unclear.

METHODS

In 14 pentobarbital anesthetized dogs, a right thoracotomy allowed electrical stimulation (ES) of the anterior right ganglionated plexi (ARGP). After ES was applied to the ARGP at baseline, atropine, 1 mg/cc, was injected into the ARGP and repeat stimulation applied. After a left thoracotomy (n = 8), a similar procedure was followed by atropine injected into the superior left (SL) GP.

RESULTS

ES (0.6-3.2 V) applied to the ARGP and SLGP caused an average reduction in sinus rate from 151 ± 14/min to 60 ± 11/min. At ≥4.5 V atrial fibrillation (AF) was induced (duration 48 ± 14 seconds). After injection of atropine into the ARGP or SLGP, ES applied to these GP induced no slowing of the sinus rate. Runs of AT were induced at an average voltage of 10 ± 2 V in 14 experiments (duration ≥4 minutes). AT was localized by ice mapping or by 3D noncontact mapping to the crista terminalis (n = 6), AV junction (n = 2) or a focal site at the left superior pulmonary vein (6). In AT lasting <4 minutes (n = 2), epinephrine injected into the GP significantly increased the AT duration. In 4/4 experiments, sustained AT could be terminated by intravenous esmolol.

CONCLUSIONS

Atropine injected into the ARGP or SLGP promotes ES-induced AT whose duration is increased by adrenergic agonists and terminated by beta blockade. Presumably cholinergic blockade and accentuated release of adrenergic neurotransmitters provide the AT mechanism. The induced AT was found to be localized at sites similar to those reported clinically.

Nerves projecting from the intrinsic cardiac ganglia of the pulmonary veins modulate sinoatrial node pacemaker function

AIMS

Pulmonary vein ganglia (PVG) are targets for atrial fibrillation ablation. However, the functional relevance of PVG to the normal heart rhythm remains unclear. Our aim was to investigate whether PVG can modulate sinoatrial node (SAN) function.

METHODS AND RESULTS

Forty-nine C57BL and seven Connexin40+/EGFP mice were studied. We used tyrosine-hydroxylase (TH) and choline-acetyltransferase immunofluorescence labelling to characterize adrenergic and cholinergic neural elements. PVG projected postganglionic nerves to the SAN, which entered the SAN as an extensive, mesh-like neural network. PVG neurones were adrenergic, cholinergic, and biphenotypic. Histochemical characterization of two human embryonic hearts showed similarities between mouse and human neuroanatomy: direct neural communications between PVG and SAN. In Langendorff perfused mouse hearts, PVG were stimulated using 200-2000 ms trains of pulses (300 μs, 400 µA, 200 Hz). PVG stimulation caused an initial heart rate (HR) slowing (36 ± 9%) followed by acceleration. PVG stimulation in the presence of propranolol caused HR slowing (43 ± 13%) that was sustained over 20 beats. PVG stimulation with atropine progressively increased HR. Time-course effects were enhanced with 1000 and 2000 ms trains (P < 0.05 vs. 200 ms). In optical mapping, PVG stimulation shifted the origin of SAN discharges. In five paroxysmal AF patients undergoing pulmonary vein ablation, application of radiofrequency energy to the PVG area during sinus rhythm produced a decrease in HR similar to that observed in isolated mouse hearts.

CONCLUSION

PVG have functional and anatomical biphenotypic characteristics. They can have significant effects on the electrophysiological control of the SAN.

Postoperative Atrial Fibrillation: Year 2011 Review of Predictive and Preventative Factors of Atrial Fibrillation Post Cardiac Surgery

Background: Post cardiac surgery atrial fibrillation is common after cardiac surgery. Despite the advances in medical and surgical treatment, its incidence remains high and unchanged for decades. The aim of this review was to summarize studies published in 2011 on identifying factors, prevention strategies, treatment and effect of post operative atrial fibrillation (POAF) on the outcome after cardiac surgery. Methods: A review was performed on Medline, Embase and Chocrane on all of the English-language, peer-reviewed published clinical studies on POAF; studies investigating the mechanism of developing POAF, prevention, treatment and outcome were all included and analyzed. Case reports, studies on persistent/preoperative atrial fibrillation (AF), POAF after cardiac transplant, congenital cases and nonclinical studies were all excluded. We have also valuated these studies based on the type of the study, their originality, impact factor of the journal and their limitations. Results: Overall 62 studies were reviewed and analyzed; 26 on POAF predictive factors, 31 on preventative strategies and 6 on the outcome of POAF. Of these studies only two were original and the remaining were either performed in AF in general population (n=10) or had been studied and reported several times before in cardiac surgery (n=50). The average impact factor of the journals that POAF was published in was only 2.8 ranging between 0.5 and 14.5. Conclusion: Post cardiac surgery atrial fibrillation is a multi-factorial and complex condition. Cardiac surgery may be a risk factor for developing POAF in patients already susceptible to this condition and may not be a complication of cardiac surgery. Future studies should mainly focus on histological changes in the conductive tissue of atrium and related treatment strategies rather than predictive factors of POAF and more funding should be made available to study this condition from new and entirely different perspectives.

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.

Neural control of ventricular rate in ambulatory dogs with pacing-induced sustained atrial fibrillation

BACKGROUND

We hypothesize that inferior vena cava-inferior atrial ganglionated plexus nerve activity (IVC-IAGPNA) is responsible for ventricular rate (VR) control during atrial fibrillation (AF) in ambulatory dogs.

METHODS AND RESULTS

We recorded bilateral cervical vagal nerve activity (VNA) and IVC-IAGPNA during baseline sinus rhythm and during pacing-induced sustained AF in 6 ambulatory dogs. Integrated nerve activities and average VR were measured every 10 seconds over 24 hours. Left VNA was associated with VR reduction during AF in 5 dogs (from 211 bpm [95% CI, 186-233] to 178 bpm [95% CI, 145-210]; P<0.001) and right VNA in 1 dog (from 208 bpm [95% CI, 197-223] to 181 bpm [95% CI, 163-200]; P<0.01). There were good correlations between IVC-IAGPNA and left VNA in the former 5 dogs and between IVC-IAGPNA and right VNA in the last dog. IVC-IAGPNA was associated with VR reduction in all dogs studied. Right VNA was associated with baseline sinus rate reduction from 105 bpm (95% CI, 95-116) to 77 bpm (95% CI, 64-91; P<0.01) in 4 dogs, whereas left VNA was associated with sinus rate reduction from 111 bpm (95% CI, 90-1250) to 81 bpm (95% CI, 67-103; P<0.01) in 2 dogs.

CONCLUSIONS

IVC-IAGPNA is invariably associated with VR reduction during AF. In comparison, right or left VNA was associated with VR reduction only when it coactivates with the IVC-IAGPNA. The vagal nerve that controls VR during AF may be different from that which controls sinus rhythm.

The Autonomic Nervous System and Atrial Fibrillation:The Roles of Pulmonary Vein Isolation and Ganglionated Plexi Ablation

After the sequential successes of catheter ablation for the treatment of pre-excitation syndromes (WPW), junctional reentry (AVNRT) atrial flutter (AFL) and ventricular arrhythmias, clinical electrophysiologists have focused on the myocardial basis of atrial fibrillation (AF). Thus, the strategy for ablation of drug and cardioversion refractory AF was to isolate the myocardial connections from the focal firing pulmonary veins (PVs) in addition to altering the atrial substrate maintaining AF. However, the overall success rates have not achieved those of the other types of ablation procedures. In this review we have summarized the favorable aspects and drawbacks of pulmonary vein isolation (PVI). As for the role of the Intrinsic Cardiac Autonomic Nervous System (ICANS), both basic and clinical evidence has shown that ganglionated plexi (GP) stimulation promotes initiation and maintenance of AF, and that GP ablation reduces recurrence of AF following catheter or surgical ablation of these structures. Based on these findings, the GP Hyperactivity Hypothesis has been proposed to explain, at least in part, the mechanistic basis for the focal form of AF. For example, PV isolation may not always be necessary for elimination of AF, as in the early stages of paroxysmal AF. GP ablation alone, in these cases, may suffice for focal AF termination. In the persistent and long standing persistent forms the substrate for AF may be more extensive and therefore require GP ablation plus PV isolation and/or CFAE ablations. Clinical reports, both catheter based as well as minimally invasive surgical procedures, which include PVI plus GP ablation have shown relatively long-term success rates much closer to or equal to those achieved by myocardial ablation procedures in patients with WPW, AVNRT and AFL.

Spatially divergent cardiac responses to nicotinic stimulation of ganglionated plexus neurons in the canine heart

Ganglionated plexuses (GPs) are major constituents of the intrinsic cardiac nervous system, the final common integrator of regional cardiac control. We hypothesized that nicotinic stimulation of individual GPs exerts divergent regional influences, affecting atrial as well as ventricular functions. In 22 anesthetized canines, unipolar electrograms were recorded from 127 atrial and 127 ventricular epicardial loci during nicotine injection (100 mcg in 0.1 ml) into either the 1) right atrial (RA), 2) dorsal atrial, 3) left atrial, 4) inferior vena cava-inferior left atrial, 5) right ventricular, 6) ventral septal ventricular or 7) cranial medial ventricular (CMV) GP. In addition to sinus and AV nodal function, neural effects on atrial and ventricular repolarization were identified as changes in the area subtended by unipolar recordings under basal conditions and at maximum neurally-induced effects. Animals were studied with intact AV node or following ablation to achieve ventricular rate control. Atrial rate was affected in response to stimulation of all 7 GPs with an incidence of 50-95% of the animals among the different GPs. AV conduction was affected following stimulation of 6/7 GP with an incidence of 22-75% among GPs. Atrial and ventricular repolarization properties were affected by atrial as well as ventricular GP stimulation. Distinct regional patterns of repolarization changes were identified in response to stimulation of individual GPs. RAGP predominantly affected the RA and posterior right ventricular walls whereas CMVGP elicited biatrial and biventricular repolarization changes. Spatially divergent and overlapping cardiac regions are affected in response to nicotinic stimulation of neurons in individual GPs.

Comparison of atrial fibrillation inducibility by electrical stimulation of either the extrinsic or the intrinsic autonomic nervous systems

OBJECTIVES

To study the effects of bilateral vagosympathetic nerve stimulation (VNS) and ganglionated plexi stimulation (GPS) on atrial refractoriness and inducibility of atrial fibrillation (AF).

METHODS

Studies were performed in fourteen adult mongrel dogs anesthetized with Na-pentobarbital, 30 mg/kg. VNS was achieved by insertion of wires into the left and right VN trunks. An octapolar catheter was attached to contact the right superior pulmonary vein (RSPV) and other octapolar catheter electrodes were sutured to the right atrial (RA) free wall and appendage (RAA). GPS was performed via a plaque electrode sutured to the fat pad containing the anterior right (AR) GP. VNS and GPS were matched to decrease heart rate by approximately 50%. Programmed stimulation delivered from the RSPV or RAA at 2x, 4x and 10x threshold (TH) allowed the determination of atrial refractory period (ARP) and the AF inducibility. The latter was quantitated by the cumulative window of vulnerability (WOV), i.e., the longest minus the shortest coupling interval during which AF was induced at 2x, 4x, 10x, TH combined.

RESULTS

Programmed electrical stimulation at the RSPV showed that the ARP was significantly shorter for both VNS and GPS than baseline (baseline, 113 +/- 22 ms; VNS, 94 +/- 26 ms; GPS, 85 +/- 31 ms) but there was no significant difference in ARP between VNS and GPS. In contrast, the cumulative WOV was significantly wider with GPS (39 +/- 36 ms) than either the baseline state (1 +/- 1 ms) or with VNS (14 +/- 26 ms), p < 0.05. Moreover, pacing from RAA showed a significantly greater cumulative WOV for VNS (33 +/- 36 ms) vs both baseline and GPS (1 +/- 4 ms and 15 +/- 26 ms, respectively, p < 0.05). The heart rate slowing caused by GPS and VNS was not significantly different, 82 +/- 11/min vs 82 +/- 7/min.

CONCLUSIONS

These data indicate a distinct functional separation of autonomic nerve innervation to the atria from the extrinsic and intrinsic nervous systems. AF is more liable to occur due to intrinsic nerve stimulation at the PVs whereas peripheral atrial sites are more readily inducible for AF due to the extrinsic neural input.

Post-operative atrial fibrillation management by selective epicardial vagal fat pad stimulation

PURPOSE

Post-operative atrial fibrillation (POAF) is a common complication after cardiac surgery and often leads to poorly tolerated fast ventricular rates. Negative dromotropic drugs are not always effective and may not be well tolerated in heart failure patients. Aim of this study is to verify if high-frequency stimulation of the right inferior fat pad (RIFPS) allows an effective decrease in ventricular rate (VR) during POAF.

METHODS

We enrolled 32 consecutive patients submitted to bypass; during surgery, a temporary heart wire was implanted in a site where RIFPS evoked a functional AV block. During POAF, RIFPS was delivered from the heart wire to decrease VR.

RESULTS

Intra-operative RIFPS evoked complete AV block in 29 patients (91%). Fourteen patients (44%) developed POAF (mean VR 127 +/- 12 bpm). In these patients, RIFPS achieved a 25% reduction of VR and complete AV block with 6.0 +/- 1.9 and 7.5 +/- 1.8 V (duration 0.2 ms, frequency 50 Hz), respectively.

CONCLUSION

Epicardial RIFPS represents an effective and feasible technique to decrease VR during POAF.

Antifibrillatory properties of mivacurium in a canine model of atrial fibrillation

The electrophysiologic actions of the competitive neuromuscular blocker mivacurium (0.05-0.8 mg/kg IV; N = 10) and atropine sulfate [0.01-0.16 mg/Kg intravenously (IV), N = 6] were determined under control conditions, during right vagus nerve stimulation, and during anterior right ganglionated plexus stimulation. Both drugs suppressed shortening of right atrial monophasic action potential (MAP) duration, right atrial refractoriness, and right superior pulmonary vein sleeve refractoriness produced by vagus nerve or ganglionated plexus stimulation and suppressed the induction of atrial fibrillation. Suppression of atrial fibrillation by atropine was accompanied by improved sinus and atrioventricular (AV) nodal function, increasing the ventricular heart rate observed during sinus rhythm and atrial fibrillation and eliminating the depressant actions of vagus nerve stimulation on sinoatrial (SA) and AV nodal function. Unlike atropine, mivacurium selectively antagonized the effects of vagus nerve and ganglionated plexus stimulation on atrial and pulmonary vein sleeve myocardium (shortening of action potential duration/refractoriness and increased atrial vulnerability) without altering sinus or AV nodal function under control conditions or during vagus nerve stimulation. The selective inhibition of parasympathetic nervous system effects in atrium versus sinus and AV nodes by mivacurium may represent a selective mechanism for the suppression of atrial fibrillation without altering SA and AV nodal function.

Gradients of Atrial Refractoriness and Inducibility of Atrial Fibrillation due to Stimulation of Ganglionated Plexi

INTRODUCTION

The mechanism(s) whereby atrial ectopy induces atrial fibrillation (AF) is still poorly understood.

METHODS AND RESULTS

In 12 dogs, we determined the refractory period (RP) along the right atrium (RA) and right superior pulmonary vein (RSPV), and AF inducibility with and without concurrent stimulation of the anterior right ganglionated plexi (ARGP) at the base of the RSPV. Multielectrode catheters were attached to the RSPV and RA with the distal electrodes close to ARGP. The RP and window of vulnerability (WOV), i.e., the longest S1-S2 minus the shortest S1-S2 at which AF was induced, were measured before and during incremental levels of ARGP stimulation. Mapping of the onset of AF was performed using the EnSite mapping system (St. Jude Medical, St. Paul, MN, USA) positioned in the RA. A single premature depolarization (PD) from the RSPV that did not induce AF without ARGP stimulation could do so with ARGP stimulation. The onset of AF consistently arose at the myocardium subtending the ARGP. With GP stimulation, the average WOV at the RSPV-atrial junction was significantly wider than at the RA appendage (65 +/- 27 vs. 8 +/- 17 msec, P < 0.05) or further along the RSPV sleeve (48 +/- 39 vs. 10 +/- 20 msec, P < 0.05). Even without GP stimulation, high intensity (10-20 mA) premature stimuli delivered at the RA appendage induced AF, originating from atrial tissue subtending the ARGP, presumably due to axonal conduction that activated the ARGP.

CONCLUSION

GP stimulation, subthreshold for atrial excitation, converts isolated PDs into AF-inducing PDs, suggesting that autonomic tone may play a critical role in the initiation of paroxysmal AF.