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

Autonomic Effects of Pulsed Field vs Thermal Ablation for Treating Atrial Fibrillation: Subanalysis of ADVENT

BACKGROUND

Autonomic denervation is an ancillary phenomenon during thermal ablation of atrial fibrillation (AF), that may have synergistic effects on symptomatic improvement and long-term freedom from AF. Pulsed field ablation (PFA), a nonthermal ablation modality, was noninferior to thermal ablation in treating AF; however, PFA's relative myocardial selectivity may minimize autonomic effects.

OBJECTIVES

This study sought to compare heart rate (HR) and heart rate variability (HRV) metrics as markers of autonomic function after ablation using PFA vs thermal ablation.

METHODS

ADVENT (The FARAPULSE ADVENT PIVOTAL Trial PFA System vs SOC Ablation for Paroxysmal Atrial Fibrillation) was a randomized pivotal study comparing PFA (pentaspline catheter) with thermal ablation (radiofrequency [RF] or cryoballoon [CB]) for treating paroxysmal AF. Baseline HR was acquired from a pre-ablation 12-lead electrocardiogram, whereas follow-up HRs, as well as HRV (standard deviation of all normal to normal RR intervals, standard deviation of 5-minute average RR intervals) metrics, were derived from 72-hour Holter monitors at 6 and 12 months.

RESULTS

This study included 379 paroxysmal AF patients undergoing PFA (n = 194) or thermal ablation (n = 185; n = 102 RF, n = 83 CB) completing 6- and 12-month Holter monitoring. Compared with PFA, thermal patients had significantly greater increases in HR from baseline to 6 months (ΔHR; 10.1 vs 5.9 beats/min; P = 0.02) and 12 months (ΔHR; 8.8 vs 5.2 beats/min; P = 0.03). This increase in HR at 6 and 12 months was similar between CB and RF (P = 0.94 and 0.83, respectively). HRV, both standard deviation of all normal to normal RR intervals and standard deviation of 5-minute average RR intervals, were significantly lower at both 6 and 12 months after thermal ablation compared with PFA (P < 0.01).

CONCLUSIONS

PFA's effect on the autonomic nervous system was attenuated compared with thermal ablation. Whether this affects long-term freedom from AF or symptomatic bradycardia/pauses after AF ablation requires further study.

2024 European Heart Rhythm Association/Heart Rhythm Society/Asia Pacific Heart Rhythm Society/Latin American Heart Rhythm Society expert consensus statement on catheter and surgical ablation of atrial fibrillation

In the last three decades, ablation of atrial fibrillation (AF) has become an evidence-based safe and efficacious treatment for managing the most common cardiac arrhythmia. In 2007, the first joint expert consensus document was issued, guiding healthcare professionals involved in catheter or surgical AF ablation. Mounting research evidence and technological advances have resulted in a rapidly changing landscape in the field of catheter and surgical AF ablation, thus stressing the need for regularly updated versions of this partnership which were issued in 2012 and 2017. Seven years after the last consensus, an updated document was considered necessary to define a contemporary framework for selection and management of patients considered for or undergoing catheter or surgical AF ablation. This consensus is a joint effort from collaborating cardiac electrophysiology societies, namely the European Heart Rhythm Association, the Heart Rhythm Society (HRS), the Asia Pacific HRS, and the Latin American HRS.

2024 European Heart Rhythm Association/Heart Rhythm Society/Asia Pacific Heart Rhythm Society/Latin American Heart Rhythm Society expert consensus statement on catheter and surgical ablation of atrial fibrillation

In the last three decades, ablation of atrial fibrillation (AF) has become an evidence-based safe and efficacious treatment for managing the most common cardiac arrhythmia. In 2007, the first joint expert consensus document was issued, guiding healthcare professionals involved in catheter or surgical AF ablation. Mounting research evidence and technological advances have resulted in a rapidly changing landscape in the field of catheter and surgical AF ablation, thus stressing the need for regularly updated versions of this partnership which were issued in 2012 and 2017. Seven years after the last consensus, an updated document was considered necessary to define a contemporary framework for selection and management of patients considered for or undergoing catheter or surgical AF ablation. This consensus is a joint effort from collaborating cardiac electrophysiology societies, namely the European Heart Rhythm Association, the Heart Rhythm Society, the Asia Pacific Heart Rhythm Society, and the Latin American Heart Rhythm Society.

2024 European Heart Rhythm Association/Heart Rhythm Society/Asia Pacific Heart Rhythm Society/Latin American Heart Rhythm Society expert consensus statement on catheter and surgical ablation of atrial fibrillation

In the last three decades, ablation of atrial fibrillation (AF) has become an evidence-based safe and efficacious treatment for managing the most common cardiac arrhythmia. In 2007, the first joint expert consensus document was issued, guiding healthcare professionals involved in catheter or surgical AF ablation. Mounting research evidence and technological advances have resulted in a rapidly changing landscape in the field of catheter and surgical AF ablation, thus stressing the need for regularly updated versions of this partnership which were issued in 2012 and 2017. Seven years after the last consensus, an updated document was considered necessary to define a contemporary framework for selection and management of patients considered for or undergoing catheter or surgical AF ablation. This consensus is a joint effort from collaborating cardiac electrophysiology societies, namely the European Heart Rhythm Association, the Heart Rhythm Society, the Asia Pacific Heart Rhythm Society, and the Latin American Heart Rhythm Society .

The frequency of atrial fibrillatory waves is modulated by the spatiotemporal pattern of acetylcholine release: a 3D computational study

In atrial fibrillation (AF), the ECG P-wave, which represents atrial depolarization, is replaced with chaotic and irregular fibrillation waves (f waves). The f-wave frequency, F f, shows significant variations over time. Cardiorespiratory interactions regulated by the autonomic nervous system have been suggested to play a role in such variations. We conducted a simulation study to test whether the spatiotemporal release pattern of the parasympathetic neurotransmitter acetylcholine (ACh) modulates the frequency of atrial reentrant circuits. Understanding parasympathetic involvement in AF may guide more effective treatment approaches and could help to design autonomic markers alternative to heart rate variability (HRV), which is not available in AF patients. 2D tissue and 3D whole-atria models of human atrial electrophysiology in persistent AF were built. Different ACh release percentages (8% and 30%) and spatial ACh release patterns, including spatially random release and release from ganglionated plexi (GPs) and associated nerves, were considered. The temporal pattern of ACh release, ACh(t), was simulated following a sinusoidal waveform of frequency 0.125 Hz to represent the respiratory frequency. Different mean concentrations ( A C h ¯ ) and peak-to-peak ranges of ACh (ΔACh) were tested. We found that temporal variations in F f, F f(t), followed the simulated temporal ACh(t) pattern in all cases. The temporal mean of F f(t), F ¯ f , depended on the fibrillatory pattern (number and location of rotors), the percentage of ACh release nodes and A C h ¯ . The magnitude of F f(t) modulation, ΔF f, depended on the percentage of ACh release nodes and ΔACh. The spatial pattern of ACh release did not have an impact on F ¯ f and only a mild impact on ΔF f. The f-wave frequency, being indicative of vagal activity, has the potential to drive autonomic-based therapeutic actions and could replace HRV markers not quantifiable from AF patients.

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.

Cardioneuroablation Using Epicardial Pulsed Field Ablation for the Treatment of Atrial Fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia affecting millions of people worldwide. The cardiac autonomic nervous system (ANS) is widely recognized as playing a key role in both the initiation and propagation of AF. This paper reviews the background and development of a unique cardioneuroablation technique for the modulation of the cardiac ANS as a potential treatment for AF. The treatment uses pulsed electric field energy to selectively electroporate ANS structures on the epicardial surface of the heart. Insights from in vitro studies and electric field models are presented as well as data from both pre-clinical and early clinical studies.

Intrinsic Cardiac Neuromodulation in the Management of Atrial Fibrillation- A Potential Missing Link?

Atrial fibrillation (AF) is the most common supraventricular arrhythmia that is linked with higher cardiovascular morbidity and mortality. Recent evidence has demonstrated that catheter-based pulmonary vein isolation (PVI) is not only a viable alternative but may be superior to antiarrhythmic drug therapy for long-term freedom from symptomatic AF episodes, a reduction in the arrhythmia burden, and healthcare resource utilization with a similar risk of adverse events. The intrinsic cardiac autonomic nervous system (ANS) has a significant influence on the structural and electrical milieu, and imbalances in the ANS may contribute to the arrhythmogenesis of AF in some individuals. There is now increasing scientific and clinical interest in various aspects of neuromodulation of intrinsic cardiac ANS, including mapping techniques, ablation methods, and patient selection. In the present review, we aimed to summarize and critically appraise the currently available evidence for the neuromodulation of intrinsic cardiac ANS in AF.

Neuromodulation therapy for atrial fibrillation

Atrial fibrillation has a multifactorial pathophysiology influenced by cardiac autonomic innervation. Both sympathetic and parasympathetic influences are profibrillatory. Innovative therapies targeting the neurocardiac axis include catheter ablation or pharmacologic suppression of ganglionated plexi, renal sympathetic denervation, low-level vagal stimulation, and stellate ganglion blockade. To date, these therapies have variable efficacy. As our understanding of atrial fibrillation and the cardiac nervous system expands, our approach to therapeutic neuromodulation will continue evolving for the benefit of those with AF.

Impact of Catheter Ablation on Brain Microstructure and Blood Flow Alterations for Cognitive Improvements in Patients with Atrial Fibrillation: A Pilot Longitudinal Study

Atrial fibrillation (AF) predisposes patients to develop cognitive decline and dementia. Clinical and epidemiological data propose that catheter ablation may provide further benefit to improve neurocognitive function in patients with AF, but the underlying mechanism is poorly available. Here, we conducted a pilot prospective study to investigate whether AF ablation can alter regional cerebral blood flow (rCBF) and brain microstructures, using multimodal magnetic resonance imaging (MRI) technique. Eight patients (63 ± 7 years) with persistent AF underwent arterial-spin labeling (ASL) perfusion, 3D T1-structural images and cognitive test batteries before and 6 months after intervention. ASL and structural MR images were spatially normalized, and the rCBF and cortical thickness of different brain areas were compared between pre- and 6-month post-treatment. Cognitive–psychological function was improved, and rCBF was significantly increased in the left posterior cingulate cortex (PCC) (p = 0.013), whereas decreased cortical thickness was found in the left posterior insular cortex (p = 0.023). Given that the PCC is a strategic site in the limbic system, while the insular cortex is known to play an important part in the central autonomic nervous system, our findings extend the hypothesis that autonomic system alterations are an important mechanism explaining the positive effect of AF ablation on cognitive function.

Is Increased Resting Heart Rate after Radiofrequency Pulmonary Vein Isolation a Predictor of Favorable Long-Term Outcome of the Procedure?

Background: Increased resting heart rate (RHR) after pulmonary vein isolation (PVI) for treatment of atrial fibrillation (AF) is a common observation, possibly resulting from ganglionated plexus modification during ablation. Previous trials have suggested that an increase in RHR after ablation might be related to higher efficacy of the procedure. The aim of this study was to determine whether or not higher increase in RHR after radiofrequency (RF) PVI might predict better long-term outcome of the procedure in a real-life cohort of patients in whom index ablation for paroxysmal AF was performed. Material and methods: The health records of patients who underwent index point-by-point or drag lesion RF PVI for paroxysmal AF in our department between January 2014 and November 2018 were analyzed. Resting heart rate (RHR) was determined from 12-lead ECG recorded prior to the ablation and before discharge to evaluate changes in RHR after PVI. Only patients in sinus rhythm before the procedure and at discharge were included in the analysis. Telephone follow-up was collected for evaluation of arrhythmia recurrence status. Results: A total of 146 patients who underwent PVI for paroxysmal AF were included. Mean follow-up time was 3.5 years. RHR increased from 64 [58.5−70], prior to procedure, to 72 [64.25−80] bpm at discharge (p < 0.001). Higher increase in RHR was not protective from arrhythmia recurrence in long-term observation in both univariable HR = 1.001 (CI 0.99−1.017, p = 0.857) and multivariable analyses HR = 1.001 (CI 0.99−1.02, p = 0.84). Conclusions: RHR after PVI increased in comparison to baseline in our cohort. However, we did not observe higher increase in RHR to be associated with more favorable long-term effectiveness of the procedure.

Blocking Intermediate-Conductance Calcium-Activated Potassium Channels in the Macrophages Around Ganglionated Plexi Suppresses Atrial Fibrillation Vulnerability in Canines With Rapid Atrial Pacing

Previous studies have indicated that ganglionated plexi (GP) function influences atrial fibrillation (AF) vulnerability, and intermediate-conductance calcium-activated potassium channels (SK4) have a close relationship with cardiomyocyte automaticity and the induction of AF. However, the effects of the SK4 inhibitor on GP function and AF vulnerability are unknown. Eighteen beagles were randomly divided into a control group (n = 6), rapid atrial pacing (RAP) group (n = 6), and triarylmethane-34 (TRAM-34, an SK4 inhibitor) group (n = 6). TRAM-34 (0.3 ml, 15 mmol/L) and saline were locally injected into GPs in the TRAM-34 group dogs and dogs from the other groups, respectively. After that, dogs in the RAP and TRAM-34 groups were subjected to RAP, and the neural activity of anterior right GP (ARGP) and atrial electrophysiology were measured. The levels of inflammatory cytokines and function of macrophages in the ARGP were measured in the three groups. At 10 min after TRAM-34 injection, ARGP activity and atrial electrophysiology did not significantly change. The atrial pacing shortened effective refractory period (ERP) values at all sites and increased the AF vulnerability and ARGP neural activity, while TRAM-34 reversed these changes. The levels of CD68 + cells, induced nitric oxide synthase (iNOS), interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α in the ARGP tissues were higher in the RAP group and TRAM-34 group than they were in the control group. Furthermore, the levels of the CD68 + cells, iNOS, and inflammatory cytokines in the ARGP tissues were higher in the pacing group than those in the TRAM-34 group. Based on these results, administration of TRAM-34 into the atrial GP can suppress GP activity and AF vulnerability during atrial pacing. The effects of TRAM-34 might be related to macrophage polarization and the inflammatory response of GP.

Calcium-Induced Autonomic Denervation in Patients With Post-Operative Atrial Fibrillation

BACKGROUND

Post-operative atrial fibrillation (POAF) is associated with worse long-term cardiovascular outcomes.

OBJECTIVES

This study hypothesized that injecting calcium chloride (CaCl₂) into the major atrial ganglionated plexi (GPs) during isolated coronary artery bypass grafting (CABG) can reduce the incidence of POAF by calcium-induced autonomic neurotoxicity.

METHODS

This proof-of-concept study randomized 200 patients undergoing isolated, off-pump CABG to CaCl₂ (n = 100) or sodium chloride (sham, n = 100) injection. Two milliliters of CaCl₂ (5%) or sodium chloride (0.9%) was injected into the 4 major atrial GPs during CABG. All patients received 7-day continuous telemetry and Holter monitoring. The primary outcome was incidence of POAF (≥30 s) in 7 days. Secondary outcomes included length of hospitalization, POAF burden, average ventricular rate during AF, plasma level of inflammatory markers, and actionable antiarrhythmic therapy to treat POAF.

RESULTS

The POAF incidence was reduced from 36% to 15% (hazard ratio: 0.366; 95% confidence interval: 0.211 to 0.635; p = 0.001). Length of hospitalization did not differ between the 2 groups. POAF burden (first 7 post-operative days), the use of amiodarone or esmolol, and the incidence of atrial couplets and nonsustained atrial tachyarrhythmias were significantly reduced in the CaCl₂ group. Heart rate variability data showed a decrease in both high-frequency and low-frequency power in the CaCl₂ group with a preserved low-frequency/high-frequency ratio, suggesting that the sympathetic/parasympathetic balance was not perturbed by CaCl₂ injection.

CONCLUSIONS

Injection of CaCl₂ into the 4 major atrial GPs reduced the POAF hazard by 63%. Inhibition of GP function by Ca-mediated neurotoxicity may underlie the therapeutic effect. (Calcium Autonomic Denervation Prevents Postoperative Atrial Fibrillation; ChiCTR1800019276).

Ligament of Marshall ablation for persistent atrial fibrillation

Beyond pulmonary vein isolation, the two main additional strategies: Cox-Maze procedure or targeting of electrical signatures (focal bursts, rotational activities, meandering wavelets), remain controversial. High-density mapping of these arrhythmias has demonstrated firstly that a patchy lesion set is highly proarrhythmogenic, favoring macro-re-entry through conduction slowing and providing pivots for localized re-entry. Secondly, discrete anatomical structures such as the Vein or Ligament of Marshall (VOM/LOM) and the coronary sinus (CS) have epicardial muscular bundles that are more frequently involved in re-entry than previously thought. The Marshall Bundle can be ablated at any point along its course from the mid-to-distal coronary sinus to the left atrial appendage. If necessary, the VOM may be directly ablated using ethanol infusion to eliminate PV contributions and produce conduction block across the mistral isthmus. Ethanol ablation of the VOM, supplemented with RF ablation, may be more effective in producing conduction block at the mitral isthmus than repeat RF ablation alone.

Atrial fibrillation and autonomic nervous system: A translational approach to guide therapeutic goals

The autonomic nervous system (ANS) is known to play an important role in the genesis and maintenance of atrial fibrillation (AF). Biomolecular and genetic mechanisms, anatomical knowledges with recent diagnostic techniques acquisitions, both invasive and non-invasive, have enabled greater therapeutic goals in patients affected by AF related to ANS imbalance. Catheter ablation of ganglionated plexi (GP) in the left and right atrium has been proposed in varied clinical conditions. Moreover interesting results arise from renal sympathetic denervation and vagal nerve stimulation. Despite all this, in the scenario of ANS modulation translational strategies we necessary must consider the treatment or correction of dynamic factors such as obesity, obstructive sleep apnea, lifestyle, food, and stress. Finally, new antiarrhythmic drugs, gene therapy and "ablatogenomic" could be represent exciting future therapeutic perspectives.

Ganglionated Plexi Ablation for the Treatment of Atrial Fibrillation

Atrial fibrillation (AF) is the most common type of cardiac arrhythmia and is associated with significant morbidity and mortality. The autonomic nervous system (ANS) plays an important role in the initiation and development of AF, causing alterations in atrial structure and electrophysiological defects. The intrinsic ANS of the heart consists of multiple ganglionated plexi (GP), commonly nestled in epicardial fat pads. These GPs contain both parasympathetic and sympathetic afferent and efferent neuronal circuits that control the electrophysiological properties of the myocardium. Pulmonary vein isolation and other cardiac catheter ablation targets including GP ablation can disrupt the fibers connecting GPs or directly damage the GPs, mediating the benefits of the ablation procedure. Ablation of GPs has been evaluated over the past decade as an adjunctive procedure for the treatment of patients suffering from AF. The success rate of GP ablation is strongly associated with specific ablation sites, surgical techniques, localization techniques, method of access and the incorporation of additional interventions. In this review, we present the current data on the clinical utility of GP ablation and its significance in AF elimination and the restoration of normal sinus rhythm in humans.

The ligament of Marshall and arrhythmias: A review

The ligament of Marshall (LOM) is a remnant of the embryonic sinus venosus and left cardinal vein, and contains fat and fibrous tissues, blood vessels, muscle bundles, nerve fibers, and ganglia. The complexity of LOM's structure makes it as a source of triggers and drivers as well as substrates of re-entry for atrial arrhythmias, especially for atrial fibrillation (AF). LOM also serves as a portion of left atrial macro-re-entrant circuit, especially peri-mitral isthmus re-entrant circuit. Experimental studies demonstrate that the LOM acts as a sympathetic conduit between the left stellate ganglion and the ventricles, and participates in the initiation and maintenance of ventricular arrhythmias. Endocardial or epicardial catheter ablation or ethanol infusion into the vein of Marshall may serve as an important adjunct therapy to pulmonary vein isolation in patients with advanced stage of AF, and may help alleviate ventricular arrhythmias as well.

Interactions between metabolism regulator adiponectin and intrinsic cardiac autonomic nervous system: A potential treatment target for atrial fibrillation

BACKGROUND

Previous studies indicated that inhibiting the cardiac autonomic nervous system (CANS) suppressed atrial fibrillation (AF). Clinical research revealed serum adiponectin (APN) exerted a beneficial influence on sympathetic and vagal tone in patients with type 2 diabetes. However, the effects of APN on CANS is unknown. This study aims to investigate whether APN could regulate CANS and suppress rapid atrial pacing (RAP)-induced AF.

METHODS

Eighteen beagles were divided into the control group (saline plus sham RAP, N = 6), the RAP group (saline plus RAP, N = 6) and the APN + RAP group (APN plus RAP, N = 6). APN (10 μg, 0.1 μg/μL) or saline was microinjected into 4 major ganglionated plexi (GP) prior to RAP. Atrial electrophysiological parameters, anterior right GP (ARGP) function, neural activity and GP tissues were detected.

RESULTS

Compared with the control treatment, RAP shortened effective refractory period (ERP) values at all sites and increased cumulative window of vulnerability (ΣWOV), ARGP function and neural activity, whereas APN injection reversed these changes. Mechanistically, APN ameliorated RAP-induced inflammatory response and down-regulated the expression of c-fos protein and nerve growth factor. Moreover, the APN receptors 1 and APN receptors 2 were detected both in neurons and in non-neuronal cells. APN pretreatment activated downstream adenosine monophosphate-activated protein kinase (AMPK) signaling, inhibited nuclear factor-kappa B signaling and promoted macrophage phenotype switching from proinflammatory to anti-inflammatory state.

CONCLUSIONS

This study demonstrates that administration of APN into GP can suppress RAP-induced AF by regulating the CANS. APN signaling may provide a potential therapeutic target to AF.

A high-performance 8 nV/√Hz 8-channel wearable and wireless system for real-time monitoring of bioelectrical signals

BACKGROUND

It is widely accepted by the scientific community that bioelectrical signals, which can be used for the identification of neurophysiological biomarkers indicative of a diseased or pathological state, could direct patient treatment towards more effective therapeutic strategies. However, the design and realisation of an instrument that can precisely record weak bioelectrical signals in the presence of strong interference stemming from a noisy clinical environment is one of the most difficult challenges associated with the strategy of monitoring bioelectrical signals for diagnostic purposes. Moreover, since patients often have to cope with the problem of limited mobility being connected to bulky and mains-powered instruments, there is a growing demand for small-sized, high-performance and ambulatory biopotential acquisition systems in the Intensive Care Unit (ICU) and in High-dependency wards. Finally, to the best of our knowledge, there are no commercial, small, battery-powered, wearable and wireless recording-only instruments that claim the capability of recording electrocorticographic (ECoG) signals.

METHODS

To address this problem, we designed and developed a low-noise (8 nV/√Hz), eight-channel, battery-powered, wearable and wireless instrument (55 × 80 mm2). The performance of the realised instrument was assessed by conducting both ex vivo and in vivo experiments.

RESULTS

To provide ex vivo proof-of-function, a wide variety of high-quality bioelectrical signal recordings are reported, including electroencephalographic (EEG), electromyographic (EMG), electrocardiographic (ECG), acceleration signals, and muscle fasciculations. Low-noise in vivo recordings of weak local field potentials (LFPs), which were wirelessly acquired in real time using segmented deep brain stimulation (DBS) electrodes implanted in the thalamus of a non-human primate, are also presented.

CONCLUSIONS

The combination of desirable features and capabilities of this instrument, namely its small size (~one business card), its enhanced recording capabilities, its increased processing capabilities, its manufacturability (since it was designed using discrete off-the-shelf components), the wide bandwidth it offers (0.5-500 Hz) and the plurality of bioelectrical signals it can precisely record, render it a versatile and reliable tool to be utilized in a wide range of applications and environments.

The cardiac autonomic nervous system: A target for modulation of atrial fibrillation

The cardiac autonomic nerve system (CANS) is a potentially potent modulator of the initiation and perpetuation of atrial fibrillation (AF). In this review, we focus on the relationship between the autonomic nervous system (ANS) and the pathophysiology of AF and the potential benefit and limitations of neuromodulation in the management of this arrhythmia from eight aspects. We conclude that Activation and Remodeling of CANS involved in the initiation and maintenance of AF. The network control mechanism, innervation regions, and sympathetic/parasympathetic balance play an important role in AF substrate. And the formation of Complex Fractional Atrial Electrograms also related to CANS activity. In addition, modulating CANS function by potential therapeutic applications include ganglionated plexus ablation, renal sympathetic denervation, and low‐level vagal nerve stimulation, may enable AF to be controlled. Although the role of the ANS has long been recognized, a better understanding of the complex interrelationships of the various components of the CANS will lead to improvement of treatments for this common arrhythmia.

Time-dependent cervical vagus nerve stimulation and frequency-dependent right atrial pacing mediates induction of atrial fibrillation

Objective:

This study aimed to investigate the effects of right cervical vagus trunk simulation (RVTS) and/or right atrial pacing (RAP) on the induction of atrial fibrillation (AF).

Methods:

Twenty-four healthy adult dogs were randomly divided into four groups: RAP groups comprising RAP₅₀₀ (RAP with 500 beats/min) and RAP₁₀₀₀ (RAP with 1000 beats/min) and RVTS groups comprising RVTS and RAP₅₀₀+RVTS. All dogs underwent 12-h intermittent RAP and/or RVTS once every 2 h. The AF induction rate, AF duration, atrial effective refractory period (ERP), and dispersion of ERP (dERP) were compared after every 2 h of RAP or/and RVTS.

Results:

All groups had successful AF induction. The RAP₁₀₀₀ group had the highest AF induction rate and the longest AF duration. The RAP₁₀₀₀ group also had a shortened ERP in comparison to the other groups as well as the maximum dERP. Compared to the RAP₅₀₀ group, RAP₅₀₀+RVTS had an increased capacity to induce AF as measured by the AF induction rates, AF duration, ERP, and dERP.

Conclusion:

Increased tension in the vagus nerve and the intrinsic cardiac autonomic nervous system plays an important role in AF induction through different potential mechanisms. Interventions involving the vagus nerve and/or intrinsic cardiac autonomic nervous system can be a future potential therapy for AF.

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.

Towards a Mechanistic Understanding and Treatment of a Progressive Disease: Atrial Fibrillation

Atrial fibrosis appears to be a key factor in the genesis and/or perpetuation of atrial fibrillation (AF). The pathological distribution of atrial fibrosis is geographically consistent with the attachments between the posterior left atrium and the pericardium along the reflections where wall stiffness is increased and structural changes are found. While there is a wide range of complex etiological factors and electrophysiological mechanisms in AF, there is evidence for a common pathophysiological pathway that could account for deliberate substrate formation and progression of AF. Anatomical stresses along the atrium, mediated by the elastic modulus mismatch between atrial tissue and the pericardium, result in inflammatory and fibrotic changes which create the substrate for atrial fibrillation. This may explain the anatomical predominance of pulmonary vein triggers earlier in the development of atrial fibrillation and the increasing involvement of the atrium as the disease progresses. Ablative treatments that address the progressive nature of atrial fibrillation and fibrosis may yield improved success rates.

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.

Ganglionated plexi stimulation induces pulmonary vein triggers and promotes atrial arrhythmogenecity: In silico modeling study

BACKGROUND

The role of the autonomic nervous system (ANS) on atrial fibrillation (AF) is difficult to demonstrate in the intact human left atrium (LA) due to technical limitations of the current electrophysiological mapping technique. We examined the effects of the ANS on the initiation and maintenance of AF by employing a realistic in silico human left atrium (LA) model integrated with a model of ganglionated plexi (GPs).

METHODS

We incorporated the morphology of the GP and parasympathetic nerves in a three-dimensional (3D) realistic LA model. For the model of ionic currents, we used a human atrial model. GPs were stimulated by increasing the IK[ACh], and sympathetic nerve stimulation was conducted through a homogeneous increase in the ICa-L. ANS-induced wave-dynamics changes were evaluated in a model that integrated a patient's LA geometry, and we repeated simulation studies using LA geometries from 10 different patients.

RESULTS

The two-dimensional model of pulmonary vein (PV) cells exhibited late phase 3 early afterdepolarization-like activity under 0.05μM acetylcholine (ACh) stimulation. In the 3D simulation model, PV tachycardia was induced, which degenerated to AF via GP (0.05μM ACh) and sympathetic (7.0×ICa-L) stimulations. Under sustained AF, local reentries were observed at the LA-PV junction. We also observed that GP stimulation reduced the complex fractionated atrial electrogram (CFAE)-cycle length (CL, p<0.01) and the life span of phase singularities (p<0.01). GP stimulation also increased the overlap area of the GP and CFAE areas (CFAE-CL≤120ms, p<0.01). When 3 patterns of virtual ablations were applied to the 3D AF models, circumferential PV isolation including the GP was the most effective in terminating AF.

CONCLUSION

Cardiac ANS stimulations demonstrated triggered activity, automaticity, and local reentries at the LA-PV junction, as well as co-localized GP and CFAE areas in the 3D in silico GP model of the LA.

Fitting local repolarization parameters in cardiac reaction-diffusion models in the presence of electrotonic coupling

BACKGROUND

Repolarization gradients contribute to arrhythmogenicity. In reaction-diffusion models of cardiac tissue, heterogeneities in action potential duration (APD) can be created by locally modifying an intrinsic membrane kinetics parameter. Electrotonic coupling, however, acts as a confounding factor that modulates APD dispersion.

METHOD

We developed an algorithm based on a quasi-Newton method that iteratively adjusts the spatial distribution of a membrane parameter to reproduce a pre-defined target APD map in a coupled tissue. The method assumes that the relation between the adjustable parameter and APD is bijective in an isolated cell. Each iteration of the algorithm involved simulating the cardiac reaction-diffusion system with the updated parameter profile for one beat and extracting the APD map. The algorithm was extended to simultaneous estimation of two parameter profiles based on two APD maps at different repolarization thresholds.

RESULTS

The method was validated in 1D, 2D and 3D atrial tissues using synthetic target APD maps with controllable total variation and maximum APD gradient. The adjustable parameter was local acetylcholine concentration. The iterations converged provided that APD gradients were not too steep. Convergence was found to be faster 2-5 iterations) when the maximal gradient was less steep, when APD range was smaller and when tissue conductivity was reduced.

CONCLUSION

This algorithm provides a tool to automatically generate arrhythmogenic substrates with controllable repolarization gradients and possibly incorporate experimental APD maps into computer models.

Impact of Anatomically Guided Ganglionated Plexus Ablation on Electrical Firing from Isolated Pulmonary Veins

BACKGROUND

The mechanisms underlying atrial fibrillation (AF) initiation and pulmonary vein isolation (PVI) effectiveness remain unclear. Ganglionated plexus (GPs) have been implicated in AF initiation and maintenance. In this study, we evaluated the impact of GP ablation in patients with pulmonary vein (PV) firing after PVI.

METHODS

Patients with drug-refractory paroxysmal AF undergoing radiofrequency catheter ablation therapy with PVI were screened. Among 840 cases over a 3.75-year period, 12 cases were identified with persistent PV firing (left = 4 and right = 8) after PVI was achieved and left atrial sinus rhythm restored. Adjacent GP ablation was performed anatomically and followed if necessary by additional PV ablation.

RESULTS

In eight patients, PV firing was terminated during GP ablation outside of the circumferential ablation line. In one patient, additional PV ablation resulted in cessation of PV firing and in the remaining three patients, firing could not be terminated by GP ablation or additional PVI.

CONCLUSION

GP ablation outside of wide antral circumferential line frequently results in the cessation of rapid firing from electrically isolated PVs. These observations suggest that interactions between left atrium and PV beyond electrical conduction warrant consideration in AF mechanisms.

Autonomic Remodeling: How Atrial Fibrillation Begets Atrial Fibrillation in the First 24 Hours

BACKGROUND

The mechanism(s) of how atrial fibrillation (AF) sustains itself in the first 24 hours is not well understood.

OBJECTIVE

We sought to investigate the role of autonomic remodeling in the first 24 hours of AF simulated by rapid atrial pacing (RAP).

METHODS

Forty-eight rabbits were divided into 6 groups. One group (n = 8) was euthanized after baseline recordings. Another group (n = 8) did not receive RAP during the 24-hour period to serve as controls. In the other 4 groups, rabbits were euthanized after RAP for 4, 8, 12, or 24 hours (n = 8 for each). Before and after designated hours of RAP, atrial effective refractory period, heart rate variability, and left vagal and sympathetic nerve activity (VNA and SNA, respectively) were determined. The right and left atrial tissues were obtained for immunocytochemical analysis for growth-associated protein 43 (GAP43), tyrosine hydroxylase (TH), and choline acetyltransferase (ChAT).

RESULTS

RAP resulted in progressively shortened atrial effective refractory period and slower heart rate. In the first 12 hours of RAP, both SNA and VNA progressively increased. Then, VNA remained stably elevated but SNA began to attenuate. The high-frequency component and low-frequency/high-frequency ratio of heart rate variability followed the trend of VNA and SNA, respectively. The density of GAP43-positive, ChAT-positive, and TH-positive neural elements in the right and left atria was progressively higher with RAP.

CONCLUSIONS

AF resulted in progressive autonomic remodeling, manifesting as nerve sprouting, sympathetic and vagal hyperinnervation. Autonomic remodeling may play an important role in sustaining AF in the first 24 hours.

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.

Novel Percutaneous Epicardial Autonomic Modulation in the Canine for Atrial Fibrillation: Results of an Efficacy and Safety Study

BACKGROUND

Endocardial ablation of atrial ganglionated plexi (GP) has been described for treatment of atrial fibrillation (AF). Our objective in this study was to develop percutaneous epicardial GP ablation in a canine model using novel energy sources and catheters.

METHODS

Phase 1: The efficacy of several modalities to ablate the GP was tested in an open chest canine model (n = 10). Phase 2: Percutaneous epicardial ablation of GP was done in six dogs using the most efficacious modality identified in phase 1 using two novel catheters.

RESULTS

Phase 1: Direct current (DC) in varying doses (blocking [7-12 μA], electroporation [300-500 μA], ablation [3,000-7,500 μA]), radiofrequency ablation (25-50 W), ultrasound (1.5 MHz), and alcohol (2-5 mL) injection were successful at 0/8, 4/12, 5/7, 3/8, 1/5, and 5/7 GP sites. DC (500-5,000 μA) along with alcohol irrigation was tested in phase 2. Phase 2: Percutaneous epicardial ablation of the right atrium, oblique sinus, vein of Marshall, and transverse sinus GP was successful in 5/6 dogs. One dog died of ventricular fibrillation during DC ablation at 5,000 μA. Programmed stimulation induced AF in six dogs, preablation and no atrial arrhythmia in three, flutter in one, and AF in one postablation. Heart rate, blood pressure, effective atrial refractory period, and local atrial electrogram amplitude did not change significantly postablation. Microscopic examination showed elimination of GP, and minimal injury to atrial myocardium.

CONCLUSION

Percutaneous epicardial ablation of GP using DC and novel catheters is safe and feasible and may be used as an adjunct to pulmonary vein isolation in the treatment of AF in order to minimize additional atrial myocardial ablation.

Inducibility of human atrial fibrillation in an in silico model reflecting local acetylcholine distribution and concentration

Vagal nerve activity has been known to play a crucial role in the induction and maintenance of atrial fibrillation (AF). However, it is unclear how the distribution and concentration of local acetylcholine (ACh) promotes AF. In this study, we investigated the effect of the spatial distribution and concentration of ACh on fibrillation patterns in an in silico human atrial model. A human atrial action potential model with an ACh-dependent K⁺ current (I_KAch) was used to examine the effect of vagal activation. A simulation of cardiac wave dynamics was performed in a realistic 3D model of the atrium. A model of the ganglionated plexus (GP) and nerve was developed based on the "octopus hypothesis". The pattern of cardiac wave dynamics was examined by applying vagal activation to the GP areas or randomly. AF inducibility in the octopus hypothesis-based GP and nerve model was tested. The effect of the ACh concentration level was also examined. In the single cell simulation, an increase in the ACh concentration shortened APD₉₀ and increased the maximal slope of the restitution curve. In the 3D simulation, a random distribution of vagal activation promoted wavebreaks while ACh secretion limited to the GP areas did not induce a noticeable change in wave dynamics. The octopus hypothesis-based model of the GP and nerve exhibited AF inducibility at higher ACh concentrations. In conclusion, a 3D in silico model of the GP and parasympathetic nerve based on the octopus model exhibited higher AF inducibility with higher ACh concentrations.

Simplified Cardioneuroablation in the Treatment of Reflex Syncope, Functional AV Block, and Sinus Node Dysfunction

BACKGROUND

Cardio neuroablation (CNA) is a lesser-known technique for management of patients with excessive vagal activation on the basis of radiofrequency catheter ablation (RFCA) of the areas related to the three main autonomic ganglia around the heart. We investigated the effectiveness of selective and/or stepwise RFCA of these areas via right atrium (RA) and/or left atrium (LA) in the patients with recurrent syncope due to excessive vagal activity.

METHODS

Twenty-two patients presenting symptomatic functional bradyarrhythmias, neurally mediated reflex syncope (NMS), symptomatic atrioventricular (AV) block, and symptomatic sinus node dysfunction (SND; number = 8, 7, 7, respectively) were enrolled. The three main paracardiac ganglia were targeted via RA and LA in the patients with NMS and SND. The procedure was performed via RA in the patients with AV block, followed by RFCA of all ganglia via LA, if AV conduction disorder persists. The sites showing fragmented potentials were identified by electrical mapping and verified by high-frequency stimulation and ablated until atrial electrical potential was completely eliminated (<0.1 mV).

RESULTS

The patients with NMS and SND were free from new syncopal episode at a mean 12.3 ± 3.4 months and 9.5 ± 3.1 months follow-up, respectively. Ablation from RA was successful in six of seven patients with AV block. Despite the increased heart rate, the resolution of AV block after the RFCA could not be achieved in one patient who had partial resolution with atropine infusion on admission.

CONCLUSION

CNA may be an alternative and safe strategy to reduce NMS episodes, and to treat functional AV block and symptomatic SND, especially in young patients.

Surgical Treatment of Atrial Fibrillation

Atrial fibrillation (AF) is the most common chronic arrhythmia in the adult population. Ablation lines have largely replaced the historical and challenging cut and sew techniques. Surgical ablation of AF is commonly performed in cases with other indications for cardiac surgery and less commonly as a stand-alone therapy. Pulmonary vein isolation is the cornerstone of this procedure. Extended left atrial ablation lines may increase efficacy in cases with longstanding persistent or permanent AF. Additional efficacy by adding right atrial ablation is controversial but is often performed in cases undergoing right atrial or atrial septal surgery. Left atrial volume reduction is recommended in cases with large left atria and AF undergoing another cardiac surgery. Arrhythmia recurrence is not uncommon after surgical ablation of AF and varies among studies due to heterogeneity in patient population, lesion set and endpoints. Freedom from AF recurrence was 65-87% at 12 months and 58-70% at 2 years follow-up. Long-term monitoring is recommended due to an increased prevalence of asymptomatic recurrences. The strongest predictors of AF recurrence are longstanding or persistent AF and a large left atrium. The most common mechanisms of recurrence are pulmonary vein reconnection, nonpulmonary vein triggers, and gaps in the ablation lines. About 20% of atrial tachyarrhythmia recurrences are atrial flutter or atrial tachycardia. There are not enough data in the surgical literature to support withdrawal of anticoagulation after surgical AF ablation. Patients selected for stand-alone surgical ablation usually have low risk profiles and low postoperative mortality rates (0.2%).

Atrial fibrillation electrical remodelling via ablation of the epicardial neural networks and suprathreshold stimulation of vagosympathetic nerve

Background

Numerous studies have shown that the cardiac autonomic nervous system (CANS) is involved in the occurrence and persistence of atrial fibrillation (AF). The CANS is commonly considered to consist of the extrinsic and intrinsic autonomic nerves. The influence of exogenous and endogenous nerve stimulation plexus ablation on pulmonary vein sleeves and atrial myocardium provides important information in understanding the occurrence and persistence of AF. Vagosympathetic nerve stimulation and epicardial neural networks are important participants in atrial electrical remodelling (AER). Elucidation of the changes in the electrophysiological indicators of the atrial and pulmonary veins caused by epicardial neural network ablation and autonomic nerve stimulation may provide a theoretical basis for the clinical treatment of AF.

Material/Methods

A total of 13 beagle dogs were randomly divided into 2 groups: the control group (n=6), which was treated with a simple rapid atrial pacing (RAP) for 6 h, and the experimental group (n=7), which was treated with RAP+vagus nerve stimulation (VNS) for 6 h. Both groups were treated with epicardial ganglia plexus (GP) ablation after 6 h. We measured the monophasic action potential (MAP), various parts of the effective refractory period (ERP), and AF induction rate before and after pacing or ablation.

Results

With the extension of the pacing time, the atrial MAP and ERP of the 2 groups shortened and returned to normal after ablation plexus. After GP ablation, the atrial AF-induced rate did not decrease significantly compared with that of the pulmonary vein.

Conclusions

Vagus nerve threshold stimulation exacerbated the deterioration of electrical remodelling, whereas the epicardial neural network ablation blocked or reversed the AER.

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.