Relation between ligament of Marshall and adrenergic atrial tachyarrhythmia

Clinical neurocardiology: defining the value of neuroscience-based cardiovascular therapeutics - 2024 update

The intricate role of the autonomic nervous system (ANS) in regulating cardiac physiology has long been recognized. Aberrant function of the ANS is central to the pathophysiology of cardiovascular diseases. It stands to reason, therefore, that neuroscience-based cardiovascular therapeutics hold great promise in the treatment of cardiovascular diseases in humans. A decade after the inaugural edition, this White Paper reviews the current state of understanding of human cardiac neuroanatomy, neurophysiology and pathophysiology in specific disease conditions, autonomic testing, risk stratification, and neuromodulatory strategies to mitigate the progression of cardiovascular diseases.

Ethanol marshall bundle elimination, pulmonary vein isolation, and linear ablation for atrial fibrillation with or without heart failure

Background

In medical practice, atrial fibrillation (AF) is intricately associated with heart failure (HF). Currently, ethanol infusion of vein of Marshall (EIVOM) for AF ablation in HF patients remains significantly limited.

Method

This was a non-randomized, single-center, retrospective observational study. AF patients received 4-step ablation composed of EIVOM, pulmonary vein isolation (PVI) and linear ablation. The primary composite endpoint was defined as recurrence of atrial tachycardia over 30 s. Propensity score matching (PSM) was performed to reduce selection bias.

Results

From April 2020 to May 2022, 362 patients were included, comprising of 182 HF patients and 180 non-HF patients. EIVOM success rate was lower in HF patients than non-HF patients (86.8% vs. 93.9%). Cardiac effusion was more common in HF patients (44.0% vs. 37.2%), and 2 cases of atrial-esophageal fistula were observed in the HF group. During a median follow-up of 12 months, no significant difference in the primary endpoint was observed between HF and non-HF group. Different HF subgroups had similar AF recurrence. After PSM, AF recurrence rate remained statistically equivalent between the HF and non-HF groups.

Conclusion

EVIOM combining catheter ablation can be completed with comparable success rate in AF patients with or without HF. However, peri-procedural safety is a concern for HF patients undergoing EIVOM combing AF catheter ablation. During the follow-up, HF status before ablation is not related with increased AF recurrence.

Atrial Fibrillation and Underlying Structural and Electrophysiological Heterogeneity

As atrial fibrillation (AF) progresses from initial paroxysmal episodes to the persistent phase, maintaining sinus rhythm for an extended period through pharmacotherapy and catheter ablation becomes difficult. A major cause of the deteriorated treatment outcome is the atrial structural and electrophysiological heterogeneity, which AF itself can exacerbate. This heterogeneity exists or manifests in various dimensions, including anatomically segmental structural features, the distribution of histological fibrosis and the autonomic nervous system, sarcolemmal ion channels, and electrophysiological properties. All these types of heterogeneity are closely related to the development of AF. Recognizing the heterogeneity provides a valuable approach to comprehending the underlying mechanisms in the complex excitatory patterns of AF and the determining factors that govern the seemingly chaotic propagation. Furthermore, substrate modification based on heterogeneity is a potential therapeutic strategy. This review aims to consolidate the current knowledge on structural and electrophysiological atrial heterogeneity and its relation to the pathogenesis of AF, drawing insights from clinical studies, animal and cell experiments, molecular basis, and computer-based approaches, to advance our understanding of the pathophysiology and management of AF.

Combined ethanol and radiofrequency ablation for the elimination of focal atrial tachycardia originating from the Marshall bundle

Introduction and importance

Atrial tachycardias (AT) originating from the Marshall bundle (MB) are rare and present significant challenges in diagnosis and management. The authors present the case of a 29-year-old male with recurrent AT successfully treated with a combined ethanol and radiofrequency ablation approach. This case highlights the effectiveness of this dual ablation strategy in resolving AT originating from the MB, contributing valuable insights into managing complex AT cases.

Case presentation

A 29-year-old male with recurrent, symptomatic palpitations was initially suspected of orthodromic atrioventricular reentrant tachycardia, but an initial electrophysiological study (EPS) failed to induce arrhythmia. Subsequent spontaneous episodes led to a detailed EPS, revealing automatic AT originating presumably from an epicardial focus on the posterior wall of the left atrium (LA). Detailed mapping identified the earliest activation at the vein of Marshall (VoM) ostium within the coronary sinus (CS). Suspecting the involvement of MB structures, VoM ethanol ablation was performed. Complete arrhythmia elimination was achieved with radiofrequency ablation (RFA) at the VoM ostium within the CS, with no recurrence.

Discussion

Most cases in the literature are associated with atrial fibrillation (AF) or AT within AF, typically involving re-entry mechanisms. The given case is unique as it presents a highly probable VoM origin of automatic AT with no concomitant AF. The VoM's anatomical and electrophysiological properties make it a potential source of refractory AT. In this case, ethanol ablation supplemented by targeted, limited RFA emerged as an effective strategy, highlighting the importance of comprehensive mapping and tailored ablation approaches in managing complex atrial arrhythmias.

Conclusion

The potential implications for clinical practice include recognizing the VoM as a critical target in refractory AT cases and adopting a combined ablation strategy to improve patient outcomes in similarly challenging scenarios.

Impact of Ethanol Infusion to the Vein of Marshall in Atrial Fibrillation and Atrial Tachycardia

The ligament of Marshall is an epicardial structure characterized by its composition of fat, fibrous tissue, blood vessels, muscle bundles, nerve fibers, and ganglia. Its intricate network forms muscular connections with the coronary sinus and left atrium, alongside adjacent autonomic nerves and ganglion cells. This complexity plays a pivotal role in initiating focal electrical activities and sustaining micro- and macro-reentrant circuits, thereby contributing to the onset of atrial fibrillation and atrial tachycardia. However, endocardial ablation in this area may encounter challenges due to anatomical variations and insulation by fibrofatty tissue. Combining ethanol infusion into the vein of Marshall with radiofrequency ablation presents a promising strategy for effectively and safely eliminating this arrhythmogenic structure and terminating associated tachycardias.

Vein of Marshall Ethanol Infusion for AF Ablation; A Review

The outcomes of persistent atrial fibrillation (AF) ablation are modest with various adjunctive strategies beyond pulmonary vein isolation (PVI) yielding largely disappointing results in randomised controlled trials. Linear ablation is a commonly employed adjunct strategy but is limited by difficulty in achieving durable bidirectional block, particularly at the mitral isthmus. Epicardial connections play a role in AF initiation and perpetuation. The ligament of Marshall has been implicated as a source of AF triggers and is known to harbour sympathetic and parasympathetic nerve fibres that contribute to AF perpetuation. Ethanol infusion into the Vein of Marshall, a remnant of the superior vena cava and key component of the ligament of Marshall, may eliminate these AF triggers and can facilitate the ease of obtaining durable mitral isthmus block. While early trials have demonstrated the potential of Vein of Marshall 'ethanolisation' to reduce arrhythmia recurrence after persistent AF ablation, further randomised trials are needed to fully determine the potential long-term outcome benefits afforded by this technique.

Angiographic assessment of vein of Marshall in atrial fibrillation: Implications for identification and cannulation

Background

The vein of Marshall (VOM) ethanol infusion improves rhythm control in atrial fibrillation (AF). The identification and cannulation of the VOM can be technically challenging. This study aimed to assess the angiographic morphology of the VOM and investigate its value in the VOM ethanol infusion.

Methods

Patients with AF (n = 162) scheduled for combined catheter ablation and VOM ethanol infusion were enrolled. The VOM morphologic features in the right anterior oblique (RAO), the left anterior oblique (LAO), and the LAO cranial views were analyzed. The impact of morphology on the identification and cannulation of the VOM was investigated.

Results

The VOM was identified in 159 (98.1 %) and cannulated in 150 (92.6 %) patients. The VOM identification rate in the RAO and LAO/LAO cranial view was 97.3 % and 89.3 %, respectively. Of 134 patients with VOM identification in the LAO/LAO cranial view, 104 (77.6 %) had a VOM ostium clock location (VOMoClock) of ≤3 and 3-4 o'clock. The VOM cannulation success rate in the ≤3, 3-4, 4-5, and 5-6 o'clock groups was 100 %, 92.6 %, 88.5 %, and 77.8 %, respectively (p = 0.032). The median (interquartile range) cannulation time in the four groups was 10.5 (6.3), 12.0 (9.0), 13.0 (23.0), and 34.0 (30.0) minutes, respectively (p < 0.001). The diameter of the coronary sinus ostium in the RAO view and the VOMoClock were independent predictors for difficult cannulation.

Conclusions

The VOM morphologic features in different angiographic views provide valuable information which could facilitate the identification and cannulation of the VOM.

Double-wire technique to facilitate vein of Marshall cannulation and ethanol infusion in atrial fibrillation: a case series

BACKGROUND

The vein of Marshall (VOM) ethanol infusion is increasingly performed in combination with catheter ablation in atrial fibrillation (AF). The cannulation of the VOM can sometimes be challenging. This study aimed to evaluate the double-wire technique in cases of difficult cannulation of the VOM.

CASE PRESENTATION

Patients with AF scheduled for combined catheter ablation and VOM ethanol infusion were consecutively enrolled. The procedure was performed via the femoral vein. If the regular cannulation technique with one angioplasty wire failed or took more than 20 min, the double-wire technique using a stabilizing wire and a cannulation wire was performed. The unique technique was used mainly in two scenarios, when the Eustachian ridge was too prominent as a barrier for catheter manipulation or when the VOM ostium was close to the coronary sinus ostium. Of 162 patients scheduled for VOM ethanol infusion, the double-wire technique was applied in 6 (3.7%) patients and led to a 100% successful cannulation rate of the VOM. Of the six patients, two had a prominent Eustachian ridge, and four had a VOM ostium close to the coronary sinus ostium. The mean cannulation time was 33.3 ± 7.3 min. The ethanol infusion was successfully performed in 5 patients. One patient had a collateral circulation in the distal VOM, and ethanol infusion was not performed.

CONCLUSIONS

The double-wire technique can facilitate VOM cannulation and ethanol infusion in challenging cases.

WORD COUNT

231.

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.

Vein of Marshall Collateralization during Ethanol Infusion in Atrial Fibrillation: Solution for Effective Myocardium Staining

BACKGROUND

The vein of Marshall (VOM) ethanol infusion improves sinus rhythm maintenance in patients with atrial fibrillation (AF). Distal collateral circulation of VOM can be a challenge to effective ethanol infusion.

OBJECTIVE

This study aimed to evaluate the feasibility and efficacy of ethanol infusion in VOM with distal collateral circulation.

METHODS

Patients with AF scheduled for catheter ablation and VOM ethanol infusion were consecutively enrolled. During the procedure, non-occluded coronary sinus angiography was first performed for VOM identification. After VOM identification, an over-the-wire angioplasty balloon was used for cannulation and occluded angiography of the VOM. Those with distal VOM collateral circulation were included in this study. A method of slower ethanol injection (2 mL over 5 min) plus additional balloon occlusion time for 3 min after each injection was used.

RESULTS

Of 162 patients scheduled for VOM ethanol infusion, apparent distal VOM collateral circulation was revealed in seven (4.3%) patients. Five patients had collateral circulation to the left atrium, one to the right superior vena cava, and one to the great cardiac vein. Two patients did not undergo further ethanol infusion because of our inadequate experience during the early stage of the project. Five patients had successful VOM ethanol infusion with manifest localized myocardium staining.

CONCLUSIONS

Ethanol infusion in VOM with distal collateral circulation can be solved by slow injection of ethanol and enough balloon occlusion time between multiple injections.

Sex Differences in the Regional Analysis of Nonpulmonary Vein Foci and Epicardial Adipose Tissue in Patients With Atrial Fibrillation

BACKGROUND

The mechanism underlying the sex differences in atrial fibrillation (AF) recurrence following pulmonary vein (PV) isolation is not fully understood. We hypothesized that non-PV foci and epicardial adipose tissue (EAT) play a key role.

METHODS AND RESULTS

Data from 304 consecutive patients (75% males) who underwent contrast-enhanced computed tomography and catheter ablation of AF were reviewed. The EAT around the atrium was measured separately in 4 parts of the atrium. All patients underwent high-dose isoproterenol infusions to assess the non-PV foci. Significantly more non-PV foci and less EAT around the atrium were observed in female patients than in male patients. In males, those with non-PV foci on the left atrial (LA) anterior wall had significantly greater EAT for the same lesions than those without non-PV foci. During a median follow-up of 27 months, the predictors of AF recurrence after first catheter ablation were female sex, presence of non-PV foci, LA diameter, and septal EAT index. A sex-specific analysis revealed that LA diameter was a predictor only in males and that the presence of non-PV foci in the septal region was a strong predictor in males (hazard ratio [HR]: 2.24) and females (HR: 3.65).

CONCLUSIONS

Sex-specific differences were observed in non-PV foci sites and local EAT and in regard to the predictors of AF recurrence.

Optimization of intra-operative electrophysiological localization of the ligament of Marshall

Background

The ligament of Marshall (LOM) may play a role in the pathophysiology of several tachyarrhythmias and accurate electrophysiological localization of this structure is crucial for effective ablation therapy. This study therefore quantifies electrophysiological properties of the LOM, and identifies which electrogram (EGM) recording (uni- or bipolar) and processing technologies [local activation time (LAT) and/or voltage mapping] are most suitable for accurate localization of the LOM.

Methods

The LOM was electrophysiologically identified in 19 patients (mean age 66 ± 14 years; 12 male) undergoing elective cardiac surgery using intra-operative high-density epicardial mapping, to quantify and visualize EGM features during sinus rhythm.

Results

Only a third of LOM potentials that were visualized using unipolar EGMs, were still visible in bipolar activation maps. Unipolar LOM potentials had lower voltages (P50: LOM: 1.51 (0.42–4.29) mV vs. left atrium (LA): 8.34 (1.50–17.91) mV, p < 0.001), less steep slopes (P50: LOM: –0.48 (–1.96 to –0.17) V/s vs. LA: –1.24 (–2.59 to –0.21) V/s, p < 0.001), and prolonged activation duration (LOM: 20 (7.5–30.5) ms vs. LA: 16.5 (6–28) ms, p = 0.008) compared to LA potentials. Likewise, bipolar LOM voltages were also smaller (P50: LOM: 1.54 (0.48–3.28) mV vs. LA: 3.12 (0.50–7.19) mV, p < 0.001).

Conclusion

The LOM was most accurately localized in activation and voltage maps by using unipolar EGMs with annotation of primary deflections in case of single potentials and secondary deflections in case of double or fractionated potentials.

Ethanol Infusion of Vein of Marshall for the Treatment of Persistent Atrial Fibrillation: The Basics and Clinical Practice

Catheter ablation for persistent atrial fibrillation (PeAF) is particularly challenging, as the clinical outcomes are modest. Pulmonary vein isolation (PVI) plus linear ablation is one of the main strategies for PeAF ablation. Completely durable transmural lesions are difficult to achieve by catheter ablation during mitral isthmus ablation. The ligament of Marshall contains the vein of Marshall (VOM), myocardial tracts and innervation, and serves as arrhythmogenic foci that make it an attractive target in catheter ablation of atrial fibrillation. Additionally, it co-localizes with the mitral isthmus, and may serve as a part of the perimitral isthmus reentrant circuit. Ethanol infusion into the VOM results in rapid ablation of the neighboring myocardium and its innervation. Its incorporation into PVI significantly increases the success rate of mitral isthmus block and the clinical outcome of PeAF ablation.

Vein of Marshall ethanol infusion in the treatment of atrial fibrillation: From concept to clinical practice

The vein of Marshall (VOM) contains innervation, myocardial connections, and arrhythmogenic foci that make it an attractive target in catheter ablation of atrial fibrillation (AF). Additionally, it co-localizes with the mitral isthmus, which is critical to sustain perimitral flutter, and is a true atrial vein that communicates with underlying myocardium. Retrograde balloon cannulation of the VOM from the coronary sinus is feasible and allows for ethanol delivery, which results in rapid ablation of neighboring myocardium and its innervation. Here we review the body of work performed over a span of 13 years, from the inception of the technique, to its preclinical validation, to demonstration of its ablative and denervation effects, and finally to completion of a randomized clinical trial demonstrating favorable outcomes, improving rhythm control in catheter ablation of persistent AF.

Neuroscientific therapies for atrial fibrillation

The cardiac autonomic nervous system (ANS) plays an integral role in normal cardiac physiology as well as in disease states that cause cardiac arrhythmias. The cardiac ANS, comprised of a complex neural hierarchy in a nested series of interacting feedback loops, regulates atrial electrophysiology and is itself susceptible to remodelling by atrial rhythm. In light of the challenges of treating atrial fibrillation (AF) with conventional pharmacologic and myoablative techniques, increasingly interest has begun to focus on targeting the cardiac neuraxis for AF. Strong evidence from animal models and clinical patients demonstrates that parasympathetic and sympathetic activity within this neuraxis may trigger AF, and the ANS may either induce atrial remodelling or undergo remodelling itself to serve as a substrate for AF. Multiple nexus points within the cardiac neuraxis are therapeutic targets, and neuroablative and neuromodulatory therapies for AF include ganglionated plexus ablation, epicardial botulinum toxin injection, vagal nerve (tragus) stimulation, renal denervation, stellate ganglion block/resection, baroreceptor activation therapy, and spinal cord stimulation. Pre-clinical and clinical studies on these modalities have had promising results and are reviewed here.

Catheter Ablation of Paroxysmal Atrial Fibrillation Originating from Non-pulmonary Vein Areas

Pulmonary veins (PVs) are a major source of ectopic beats that initiate AF. PV isolation from the left atrium is an effective therapy for the majority of paroxysmal AF. However, investigators have reported that ectopy originating from non-PV areas can also initiate AF. Patients with recurrent AF after persistent PV isolation highlight the need to identify non-PV ectopy. Furthermore, adding non-PV ablation after multiple AF ablation procedures leads to lower AF recurrence and a higher AF cure rate. These findings suggest that non-PV ectopy is important in both the initiation and recurrence of AF. This article summarises current knowledge about the electrophysiological characteristics of non-PV AF, suitable mapping and ablation strategies, and the safety and efficacy of catheter ablation of AF initiated by ectopic foci originating from non-PV areas.

Clinical Utility of Intravenous Nifekalant Injection during Radiofrequency catheter Ablation for Persistent Atrial Fibrillation

Background

Radiofrequency catheter ablation (RFCA) for persistent atrial fibrillation (AF) is still challenging even in RFCA-era for AF. The aim of this study was to assess the clinical utility of nifekalant, a pure potassium channel blocker,during RFCA for persistent AF.

Methods and results

We retrospectively enrolled 157 consecutive persistentAF patientsundergoing first RFCA procedure withcomplex fractionated atrial electrogram (CFAE)ablation after pulmonary veins isolation and compared outcomes between patientswith (NFK group: N=79) and without (No-NFK group: N=78)additional CFAE ablation using intravenous nifekalant (0.3mg/kg). Primary endpoint was 24-month atrial arrhythmia-free survival post ablation.The prevalence of AF terminationwas significantly higher in NFK group than No-NFK group (64.6% versus 7.7%, P<0.001). Arrhythmia-free survival, however, was not significantly different between 2 groups (61.5% versus 54.1%, P=0.63).There was no significant difference between 2 groups in the prevalence of recurrent atrial tachycardia(25.0% versus 23.5%, P=0.89). Arrhythmia-free survivalin patients with AF termination during procedure was significantly higher thanthose without (73.0% versus 41.0%, P=0.002; adjusted hazard ratio 0.48, 95% confidence interval 0.17-0.84, P=0.02) amongNFK group,but not amongNo-NFK group (66.7% versus 53.2%, P=0.53).

Conclusions

Intravenous nifekalant injection during additional CFAE ablation did not improve sinus maintenancerate after RFCA procedure for AF, but AF termination by nifekalant injection could be a clinical predictor of better success rates after procedure.

Determinants of new wavefront locations in cholinergic atrial fibrillation

AIMS

Atrial fibrillation (AF) wavefront dynamics are complex and difficult to interpret, contributing to uncertainty about the mechanisms that maintain AF. We aimed to investigate the interplay between rotors, wavelets, and focal sources during fibrillation.

METHODS AND RESULTS

Arrhythmia wavefront dynamics were analysed for four optically mapped canine cholinergic AF preparations. A bilayer computer model was tuned to experimental preparations, and varied to have (i) fibrosis in both layers or the epicardium only, (ii) different spatial acetylcholine distributions, (iii) different intrinsic action potential duration between layers, and (iv) varied interlayer connectivity. Phase singularities (PSs) were identified and tracked over time to identify rotational drivers. New focal wavefronts were identified using phase contours. Phase singularity density and new wavefront locations were calculated during AF. There was a single dominant mechanism for sustaining AF in each of the preparations, either a rotational driver or repetitive new focal wavefronts. High-density PS sites existed preferentially around the pulmonary vein junctions. Three of the four preparations exhibited stable preferential sites of new wavefronts. Computational simulations predict that only a small number of connections are functionally important in sustaining AF, with new wavefront locations determined by the interplay between fibrosis distribution, acetylcholine concentration, and heterogeneity in repolarization within layers.

CONCLUSION

We were able to identify preferential sites of new wavefront initiation and rotational activity, in order to determine the mechanisms sustaining AF. Electrical measurements should be interpreted differently according to whether they are endocardial or epicardial recordings.

Selective ablation of the ligament of Marshall reduces ischemia and reperfusion-induced ventricular arrhythmias

Cardiac sympathetic tone overdrive is a key mechanism of arrhythmia. Cardiac sympathetic nerves denervation, such as LSG ablation or renal sympathetic denervation, suppressed both the prevalence of VAs and the incidence of SCD. Accumulating evidence demonstrates the ligament of Marshall (LOM) is a key component of the sympathetic conduit between the left stellate ganglion (LSG) and the ventricles. The present study aimed to investigate the roles of the distal segment of LOM (LOM_LSPV) denervation in ischemia and reperfusion (IR)-induced VAs, and compared that LSG denervation. Thirty-three canines were randomly divided into group 1 (IR group, n = 11), group 2 (LOM_LSPV Denervation + IR, n = 9), and group 3 (LSG Denervation + IR, n = 13). Hematoxylin-Eosin (HE) and Immunohistochemistry staining revealed that LOM_LSPV contained bundles of sympathetic but not parasympathetic nerves. IR increased the cardiac sympathetic tone [serum concentrations of noradrenaline (NE) and epinephrine (E)] and induced the prevalence of VAs [ventricular premature beat (VPB), salvo of VPB, ventricular tachycardia (VT), VT duration (VTD) and ventricular fibrillation (VF)]. Both LOM_LSPV denervation and LSG denervation could reduce the cardiac sympathetic tone in Baseline (BS) [heart rate variability (HRV)]. Compared with group 1, LOM_LSPV denervation and LSG denervation similarly reduced sympathetic tone [NE (1.39±0.068 ng/ml in group 2, 1.29±0.081 ng/ml in group 3 vs 2.32±0.17 ng/ml in group 1, P<0.05) and E (114.64±9.22 pg/ml in group 2, 112.60±9.69 pg/ml in group 3 vs 166.18±15.78 pg/ml in group 1, P<0.05),] and VAs [VT (0±3.00 in group 2, 0±1.75 in group 3 vs 8.00±11.00 in group 1, P<0.05) and VTD (0 ± 4 s in group 2, 0±0.88s in group 3 vs 10.0 ± 22.00s in group 1, P<0.05)] after 2h reperfusion. These findings indicated LOM_LSPV denervation reduced the prevalence of VT by suppressing SNS activity. These effects are comparable to those of LSG denervation. In myocardial IR, the anti-arrhythmic effects of LOM_LSPV Denervation may be related to the inhibition of the expression of NE and E.

Early Cardioversion in Atrial Fibrillation: Earlier Is Better, but Not Always and (Maybe) Not Immediately

Atrial fibrillation (AF) is the most common cardiac arrhythmia in humans. One of its important features is the tendency to become more persistent over time, even in the absence of underlying progressive heart disease. Conversion and maintenance of sinus rhythm by pharmacological or electrical methods become increasingly difficult the longer the arrhythmia persists. Electrical, mechanical, structural, and autonomic remodeling processes have been implicated in the mechanisms of AF initiation, perpetuation, and progression. Prevention or reversal of these remodeling processes can halt the progression of the disease. Cardioversion is a powerful tool and rhythm control is a widely used strategy in the management of AF. However, important questions remain unanswered regarding not only if, but also when to perform cardioversion. There are observations from past trials and clinical situations that support attempting to restore sinus rhythm, but further prospective randomized clinical trials are needed. Optimal timing of cardioversion remains somewhat uncertain, but it appears to be some time after the first few hours and before the first few months: the earlier, the better, but not always, and maybe not immediately, and it has to be tailored to the clinical situation and its many variables. This review is intended to summarize the evidence supporting early intervention for the prevention of remodeling in patients with AF.

Ganglionated plexi and ligament of Marshall ablation reduces atrial vulnerability and causes stellate ganglion remodeling in ambulatory dogs

BACKGROUND

Simultaneous activation of the stellate ganglion (SG), the ligament of Marshall (LOM), and the ganglionated plexi often precedes the onset of paroxysmal atrial tachyarrhythmia (PAT).

OBJECTIVE

The purpose of this study was to test the hypothesis that ablation of the LOM and the superior left ganglionated plexi (SLGP) reduces atrial vulnerability and results in remodeling of the SG.

METHODS

Nerve activity was correlated to PAT and ventricular rate (VR) at baseline, after ablation of the LOM and SLGP, and after atrial fibrillation. Neuronal cell death was assessed with tyrosine hydroxylase and terminal deoxynucleotidyl transferase dUTP nick end label (TUNEL) staining.

RESULTS

There were 4 ± 2 PAT episodes per day in controls. None were observed in the ablation group, even though SG nerve activity and VR increased from 2.2 µV (95% confidence interval [CI] 1.2-3.3 µV) and 80 bpm (95% CI 68-92 bpm) at baseline, to 3.0 µV (95% CI 2.6-3.4 µV, P = .046) and 90 bpm (95% CI 75-108 bpm, P = .026) after ablation, and to 3.1 µV (95% CI 1.7-4.5 µV, P = .116) and 95 bpm (95% CI 79-110 bpm, P = .075) after atrial fibrillation. There was an increase in tyrosine hydroxylase-negative cells in the ablation group and 19.7% (95% CI 8.6%-30.8%) TUNEL-positive staining in both the left and right SG. None were observed in the control group.

CONCLUSION

LOM and SLGP ablation caused left SG remodeling and cell death. There was reduced correlation of the VR response and PAT to SG nerve activity. These findings support the importance of SLGP and LOM in atrial arrhythmogenesis.

Cardiac Autonomic Denervation for Ablation of Atrial Fibrillation

The influence of the autonomic nervous system (ANS) on triggering and perpetuation of atrial fibrillation (AF) is well established. Ganglionated plexi (GP) ablation achieves autonomic denervation by affecting both the parasympathetic and sympathetic components of the ANS. GP ablation can be accomplished endocardially or epicardially, i.e. during the maze procedure or thoracoscopic approaches. Recent evidence indicates that anatomic GP ablation at relevant atrial sites appears to be safe and improves the results of pulmonary vein isolation in patients with paroxysmal and persistent AF.

Triggers and anatomical substrates in the genesis and perpetuation of atrial fibrillation

The definition of atrial fibrillation (AF) as a functional electrical disorder does not reflect the significant underlying structural abnormalities. Atrial and Pulmonary Vein (PV) muscle sleeve microstructural remodeling is present, and establishes a vulnerable substrate for AF maintenance. In spite of an incomplete understanding of the anatomo-functional basis for AF, current evidence demonstrates that this arrhythmia usually requires a trigger for initiation and a vulnerable electrophysiological and/or anatomical substrate for maintenance. It is still unclear whether the trigger mechanisms include focal enhanced automaticity, triggered activity and/or micro re-entry from myocardial tissue. Initiation of AF can be favored by both parasympathetic and sympathetic stimulation, which also seem to play a role in maintaining AF. Finally, evolving clinical evidence demonstrates that inflammation is associated with new-onset and recurrent AF through a mechanism that possibly involves cellular degeneration, apoptosis, and subsequent atrial fibrosis.

A review of mitral isthmus ablation

Mitral isthmus ablation forms part of the electrophysiologist’s armoury in the catheter ablation treatment of atrial fibrillation. It is well recognised however, that mitral isthmus ablation is technically challenging and incomplete ablation may be pro-arrhythmic, leading some to question its role. This article first reviews the evidence for the use of adjunctive mitral isthmus ablation and its association with the development of macroreentrant perimitral flutter. It then describes the practical techniques of mitral isthmus ablation, with particular emphasis on the assessment of bi-directional mitral isthmus block. The anatomy of the mitral isthmus is also discussed in order to understand the possible obstacles to successful ablation. Finally, novel techniques which may facilitate mitral isthmus ablation are reviewed.

Role of the vein of Marshall in atrial fibrillation recurrences after catheter ablation: therapeutic effect of ethanol infusion

Vein of Marshall Ethanol in Recurrent AF.

INTRODUCTION

Atrial fibrillation (AF) or flutter can recur after pulmonary vein (PV) antral isolation (PVAI). The vein of Marshall (VOM) has been linked to the genesis of AF. We hypothesized that the VOM may play a role in AF recurrences and that VOM ethanol infusion may have therapeutic value in this setting.

METHODS AND RESULTS

Sixty-one patients with recurrent AF or flutter after PVAI were studied. The VOM was successfully cannulated in 54; VOM and PV electrograms were recorded, and differential PV-VOM pacing was performed. VOM signals were present in all patients; however, VOM triggers of AF could not be demonstrated. VOM tachycardia was present in 1 patient. Left inferior (LIPV) and left superior (LSPV) reconnection was present in 32 and 30 patients, respectively. Differential pacing in VOM and LIPV showed VOM-mediated LIPV reconnection in 5/32 patients. In others, VOM and PV connected indirectly via left atrial tissues. Up to four 1 cc infusions of 98% ethanol were delivered in the VOM. Regardless of the reconnection pattern, ethanol infusion eliminated LIPV and LSPV reconnection in 23/32 and 13/30 patients, respectively. Ethanol terminated VOM and LIPV tachycardias in 2 patients. There were no acute procedural complications.

CONCLUSIONS

VOM signals are consistently present in recurrent AF. VOM may rarely play a role in PV reconnection. However, VOM ethanol infusion can be useful in patients with recurrent AF after PVAI, assisting in achieving redisconnection of reconnected left PVs.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Ligament of Marshall: why it is important for atrial fibrillation ablation

The ligament of Marshall (LOM) is located on the epicardium between the left atrial appendage and the left pulmonary veins. The corresponding endocardial structure is the left lateral ridge. LOM is a source of paroxysmal AF, and may activate at fast rates during persistent AF. Because of the importance of LOM in the mechanisms of AF, the techniques of LOM ablation are important to the practicing cardiac electrophysiologist. LOM contains muscle bundles (Marshall bundles) that directly connect to atrial myocardium and coronary sinus muscle sleeves. These muscle structures can serve as a source of triggers and drivers for AF, and may form the substrates of reentry. In some patients, these muscle bundles take part in accessory pathway conduction in patients with preexcitation syndrome. LOM can be mapped by either endocardial or epicardial approach. Elimination of the LOM potential during endocardial ablation confirms the successful creation of transmural lesion that includes the LOM. In patients who cannot be mapped or ablated via endocardial approach, epicardial approach is needed to map and ablate the LOM. In addition to the Marshall bundle, the LOM also has rich autonomic innervation. The ganglionated plexi are present in and around the LOM. These ganglionated plexi can be ablated during catheter ablation procedures or during open-heart surgery. In summary, LOM is important in the mechanisms of AF and may participate in accessory pathway conduction in patients with preexcitation syndrome. Mapping and catheter ablation of LOM is both feasible and clinically useful in controlling atrial arrhythmias.

Spontaneous atrial fibrillation initiated by tyramine in canine atria with increased sympathetic nerve sprouting

BACKGROUND

Chronic left ventricular myocardial infarction (LVMI) promotes atrial and pulmonary veins (PV) sympathetic nerve sprouting.

OBJECTIVES

To test the hypothesis that sympathetic stimulation with tyramine initiates atrial fibrillation (AF) by early after depolarization (EAD)-mediated triggered activity at the left atrial PV (LAPV) junction.

METHODS

LVMI was created in 6 dogs and 6 dogs served as controls. Six to 8 weeks later the activation pattern of the isolated LAPV was optically mapped using dual voltage and intracellular Ca(+2) (Ca(i) (2+) )-sensitive epifluorescent dyes before and after tyramine (5 μM) perfusion.

RESULTS

Tyramine initiated spontaneous AF in 5 of 6 atria but none in the control group (P < 0.01). The AF was initiated by late phase 3 EAD-mediated triggered activity that arose from the LAPV junction causing functional conduction block in LA, reentry, and AF. The AF was subsequently maintained by mixed reentrant and focal mechanisms. The EADs arose during the late phase 3, when the Ca(i) (2+) level was 64 ± 12% of the peak systolic Ca(i) (2+) transient amplitude, a property caused by tyramine's simultaneous shortening of the action potential duration and lengthening of the Ca(i) (2+) transient duration in the LVMI group but not in the control. Tyrosine hydroxylase and growth associated protein 43 positive nerve sprouts were significantly increased in the sinus node, LAA, and the LSPV in the LVMI group compared to control (P < 0.01).

CONCLUSIONS

Increased atrial sympathetic nerve sprouts after LVMI makes the LAPV junction susceptible to late phase 3 EAD-mediated triggered and AF during sympathetic stimulation with tyramine.

Novel insights into the cellular basis of atrial fibrillation

Atrial fibrillation is the most common clinical cardiac arrhythmia. It is often initiated by ectopic beats arising from the pulmonary veins and atria. While pulmonary vein myocytes most likely contribute to atrial ectopic beats initiating atrial fibrillation, emerging evidence suggests the existence of other cell populations that may also contribute to atrial arrhythmias. In addition to sinus node-like and intestinal Cajal-like cells, we recently characterized a novel, melanocyte-like cell population in murine and human hearts that may contribute to atrial arrhythmogenic triggers in mice. Murine cardiac melanocyte-like cells are electrically excitable, and express adrenergic and muscarinic receptors. Adult mice lacking the gene encoding dopachrome tautomerase (Dct) are susceptible to atrial arrhythmias, and Dct is expressed by both murine and human cardiac melanocytes. While Dct-expressing cells are present in human hearts in regions from which atrial arrhythmias often arise, the contribution of these cells to clinical atrial arrhythmias remains to be determined.

Intrinsic cardiac nerve activity and paroxysmal atrial tachyarrhythmia in ambulatory dogs

BACKGROUND

Little is known about the relationship between intrinsic cardiac nerve activity (ICNA) and spontaneous arrhythmias in ambulatory animals.

METHODS AND RESULTS

We implanted radiotransmitters to record extrinsic cardiac nerve activity (ECNA; including stellate ganglion nerve activity and vagal nerve activity) and ICNA (including superior left ganglionated plexi nerve activity and ligament of Marshall nerve activity) in 6 ambulatory dogs. Intermittent rapid left atrial pacing was performed to induce paroxysmal atrial fibrillation or atrial tachycardia. The vast majority (94%) of ligament of Marshall nerve activity were preceded by or coactivated with ECNA (stellate ganglion nerve activity or vagal nerve activity), whereas 6% of episodes were activated alone without concomitant stellate ganglion nerve activity or vagal nerve activity. Paroxysmal atrial fibrillation and atrial tachycardia were invariably (100%) preceded (<5 seconds) by ICNA. Most paroxysmal atrial tachycardia events (89%) were preceded by ICNA and sympathovagal coactivation, whereas 11% were preceded by ICNA and stellate ganglion nerve activity-only activation. Most paroxysmal atrial fibrillation events were preceded only by ICNA (72%); the remaining 28% were preceded by ECNA and ICNA together. Complex fractionated atrial electrograms were observed during ICNA discharges that preceded the onset of paroxysmal atrial tachycardia and atrial fibrillation. Immunostaining confirmed the presence of both adrenergic and cholinergic nerve at ICNA sites.

CONCLUSIONS

There is a significant temporal relationship between ECNA and ICNA. However, ICNA can also activate alone. All paroxysmal atrial tachycardia and atrial fibrillation episodes were invariably preceded by ICNA. These findings suggest that ICNA (either alone or in collaboration with ECNA) is an invariable trigger of paroxysmal atrial tachyarrhythmias. ICNA might contaminate local atrial electrograms, resulting in complex fractionated atrial electrogram-like activity.

Epicardial Catheter Ablation of Atrial Fibrillation

Atrial fibrillation (AF) can cause significant symptoms despite control of ventricular rate, and for some patients a rhythm-control strategy is more appropriate. Because antiarrhythmic drugs have limited efficacy for treating AF and can cause significant side effects, nonpharmacologic therapy has found a growing role in the treatment of this arrhythmia. While endocardial catheter ablation has shown superior results over drug therapy, long-term clinical outcomes are still disappointing, especially for persistent AF. This article discusses percutaneous epicardial catheter ablation, the rationale for using this approach to treat AF, anatomy relevant to the approach, challenges in performing such procedures, and finally, the potential future directions in this promising new field.

Electrophysiological characteristics of the Marshall bundle in humans

BACKGROUND

Marshall bundles (MBs) are the muscle bundles within the ligament of Marshall.

OBJECTIVE

This trial sought to the electrophysiological characteristics of the MB and the anatomical connections between MB and left atrium (LA) in patients with persistent atrial fibrillation (AF).

METHODS

We enrolled 72 patients (male:female 59:13, age 59.9 +/- 9.4 years) who underwent MB mapping and ablation for AF. MB mapping was done via an endocardial or epicardial approach during sinus rhythm and AF.

RESULTS

Recordings were successful in 64 of 72 patients (89%). A single connection was noted in 11 of 64 patients between the MB and the coronary sinus (CS) muscle sleeves. The MB recordings showed distinct MB potentials with a proximal-to-distal activation pattern during sinus rhythm. During AF, organized passive activations and dissociated slow MB ectopic activities were commonly observed in this type of connection. Double connections to both CS and LA around left pulmonary veins were noted in 23 of 64 patients (36%). After the ablation of the distal connection, MB recording showed typical double potentials as in single connection. Multiple connections were noted in 30 of 64 patients (47%). During sinus rhythm, the earliest activation was in the middle of the MB. The activation patterns were irregular and variable in each patient. During AF, rapid and fractionated complex activations were noted in all patients of this group.

CONCLUSION

We documented 3 different types of MB-LA connections. Rapid and fractionated activations were most commonly observed in the MB that had multiple LA connections.

Correlative anatomy for the electrophysiologist: ablation for atrial fibrillation. Part I: pulmonary vein ostia, superior vena cava, vein of Marshall

Ablation procedures for atrial fibrillation (AF) have become an established and increasingly used option for managing patients with symptomatic arrhythmia. The anatomic structures relevant to the pathogenesis of AF and ablation procedures are varied and include the pulmonary veins (PVs), other thoracic veins, the left atrial myocardium, and autonomic ganglia. Exact regional anatomic knowledge of these structures is essential to allow correlation with fluoroscopy and electrograms, and, importantly, to avoid complications from damage of adjacent structures within the chest. We have presented this information in a 2-part series. In the present article, we examine the general anatomic characteristics of the PVs, superior vena cava, and vein of Marshall. Features of particular relevance for the invasive electrophysiologist are pointed out. In a subsequent article, we discuss the regional anatomy of the left and right atria and anatomic considerations in preventing complications during AF ablation.

Transmural characteristics of atrial fibrillation in canine models of structural and electrical atrial remodeling assessed by simultaneous epicardial and endocardial mapping

BACKGROUND

Epicardial mapping has shown that atrial substrate may play a role in the characteristics of the resulting atrial fibrillation (AF). However, it is not known whether these differences also occur in 3 dimensions.

OBJECTIVE

This study sought to examine the 3-dimensional characteristics of AF by simultaneously analyzing AF on the epicardial and endocardial surfaces.

METHODS

Dogs were divided into 5 groups: congestive heart failure (CHF), rapid atrial pacing (RAP), mitral regurgitation (MR), control, and methylcholine. A noncontact mapping catheter (Ensite 3000 [Endocardial Solutions, Inc., St. Paul, Minnesota]) was placed in the left atrium (LA), and electrode plaques (240 unipoles) were placed over the epicardial surface. Several AF episodes of at least 30 s were recorded, and isopotential videos of activation and isochronal maps were constructed. In addition, each pair of matched electrograms were cross-correlated (XC) and analyzed with a fast Fourier transform (FFT).

RESULTS

The RAP model was the only one with an AF mechanism of multiple wavelets in every dog on both surfaces. In addition, when individual signals were compared, the RAP model had the least amount of similarities between the recording surfaces, whereas the CHF model had the most as it had a higher percentage of signals with XC coefficients >0.8 and a higher percentage of signals with similar dominant frequencies (30 +/- 35% vs. 12 +/- 13% and 66 +/- 30% vs. 26 +/- 10%, P < .05).

CONCLUSION

Although the RAP model had similar AF mechanisms in 3 dimensions, this did not correlate to transmural similarities. Focal mechanisms of AF may have a more uniform wavefront of activation, whereas models with mechanisms of multiple wavelets may have more 3-dimensional properties.

Retrograde ethanol infusion in the vein of Marshall: regional left atrial ablation, vagal denervation and feasibility in humans

BACKGROUND

The vein of Marshall (VOM) is an attractive target during ablation of atrial fibrillation due to its autonomic innervation, its location anterior to the left pulmonary veins and drainage in the coronary sinus.

METHODS AND RESULTS

We studied 17 dogs. A coronary sinus venogram showed a VOM in 13, which was successfully cannulated with an angioplasty wire and balloon. In 5 dogs, electroanatomical maps of the left atrium were performed at baseline and after ethanol infusion in the VOM, which demonstrated a new crescent-shaped scar, extending from the annular left atrium towards the posterior wall and left pulmonary veins. In 4 other dogs, effective refractory periods (ERP) were measured at 3 sites in the left atrium, before and after high-frequency bilateral vagal stimulation. The ERP decreased from 113.6+/-35.0 ms to 82.2+/-25.4 ms (p<0.05) after vagal stimulation. After VOM ethanol infusion, vagally-mediated ERP decrease was eliminated (from 108.6+/-24.1 ms to 96.4 +/-16.9ms, p=NS). The abolition of vagal effects was limited to sites near the VOM (ERP: 104+/-14 ms, vs 98.6+/-12.2 ms post vagal stimulation, p=ns), as opposed to sites remote to VOM (ERP: 107.2+/-14.9 ms, vs 78.6+/-14.7ms post vagal stimulation, p<0.05). To test feasibility in humans, 5 patients undergoing pulmonary vein antral isolation had successful VOM cannulation and ethanol infusion: left atrial voltage maps demonstrated new scar involving the infero-posterior left atrial wall extending towards the left pulmonary veins.

CONCLUSIONS

Ethanol infusion in then VOM achieves significant left atrial tissue ablation, abolishes local vagal responses and is feasible in humans.

Ethanol infusion in the vein of Marshall: Adjunctive effects during ablation of atrial fibrillation

BACKGROUND

The vein of Marshall (VOM) is a left atrial (LA) vein that contains autonomic innervation and triggers of AF. Its location coincides with areas usually ablated during pulmonary vein (PV) antral isolation (PVAI).

OBJECTIVE

This study sought to delineate the safety and ablative effects of ethanol infusion in the VOM during catheter ablation of atrial fibrillation (AF).

METHODS

Patients undergoing PVAI (n = 14) gave consent for adjunctive VOM ethanol infusion. In 10 of 14 patients, the VOM was cannulated with an angioplasty wire and balloon. Echocardiographic contrast was injected in the VOM under echocardiographic monitoring. Two infusions of 100% ethanol (1 ml each) were delivered via the angioplasty balloon in the VOM. LA bipolar voltage maps were created before and after ethanol infusion. Radiofrequency ablation times required to isolate each PV and other procedural data were compared with those of 10 age-, sex-, AF type- and LA size-matched control subjects undergoing conventional PVAI.

RESULTS

The VOM communicated with underlying myocardium, as shown by echocardiographic contrast passage into the LA. There were no acute complications related to VOM ethanol infusion, which led to the creation of a low-voltage area in the LA measuring 10.6 +/- 7.6 cm(2) and isolation of the left inferior PV in 4 of 10 patients. Radiofrequency ablation time required to achieve isolation of the left inferior PV was reduced (2.2 +/- 4 min vs. 11.4 +/- 10.3 min in control subjects, P <.05).

CONCLUSION

VOM ethanol infusion is safe in humans, decreases radiofrequency ablation time in the left inferior PV, and may have a role as an adjunct to PVAI.

Autonomic mechanism for initiation of rapid firing from atria and pulmonary veins: evidence by ablation of ganglionated plexi

AIMS

Previous studies showed that autonomic activation by high-frequency electrical stimulation (HFS) during myocardial refractoriness evokes rapid firing from pulmonary vein (PV) and atria, both in vitro and in vivo. This study sought to investigate the autonomic mechanism underlying the rapid firings at various sites by systematic ablation of multiple ganglionated plexi (GP).

METHODS AND RESULTS

In 43 mongrel dogs, rapid firing-mediated atrial fibrillation (AF) was induced by local HFS (200 Hz, impulse duration 0.1 ms, train duration 40 ms) to the PVs and atria during myocardial refractoriness. The main GP in the atrial fat pads or the ganglia along the ligament of Marshall (LOM) were then ablated. Ablation of the anterior right GP and inferior right GP significantly increased the AF threshold by HFS at the right atrium and PVs. The AF threshold at left atrium and PVs was significantly increased by ablation of the superior left GP and inferior left GP, and was further increased by ablation of the LOM. Ablation of left- or right-sided GP on the atria had a significant effect on contralateral PVs and atrium. Administration of esmolol (1 mg/kg) or atropine (1 mg) significantly increased AF threshold at all sites.

CONCLUSION

HFS applied to local atrial and PV sites initiated rapid firing via activation of the interactive autonomic network in the heart. GP in either left side or right side contributes to the rapid firings and AF originating from ipsolateral and contralateral PVs and atrium. Autonomic denervation suppresses or eliminates those rapid firings.

Autonomic elements within the ligament of Marshall and inferior left ganglionated plexus mediate functions of the atrial neural network

OBJECTIVES

We sought to systematically investigate the role of the ligament of Marshall (LOM) and inferior left ganglionated plexi (ILGP) in modulating electrophysiological functions.

METHODS

The following structures were exposed in 36 dogs: (1) LOM, (2) superior left GP (SLGP) near the junction of left superior pulmonary vein (LSPV) and left atrium, (3) ILGP near the left inferior pulmonary vein-atrial junction, (4) anterior right GP (ARGP) near the sino-atrial node, and (5) inferior right GP (IRGP) at the junction of inferior vena cava and atria. High frequency stimulation (HFS; 0.6-8.0 V, 20 Hz, 0.1 msec in duration) was applied to the LOM, SLGP, ILGP, ARGP, IRGP, or vagosympathetic trunk. Ventricular rate (VR) during atrial fibrillation (AF) was compared before and after ablation of GP in different sequences.

RESULTS

ARGP + ILGP ablation but not ARGP ablation alone eliminated the VR slowing response induced by LOM stimulation, suggesting that all the autonomic innervation from the LOM to AV node passes the ILGP. LOM ablation attenuated the VR slowing response caused by SLGP or left vagosympathetic stimulation, suggesting that LOM modulates the autonomic innervation between the AV node and the left vagosympathetic trunk or SLGP. ARGP attenuated while ARGP + ILGP ablation eliminated the VR slowing response induced by left vagosympathetic stimulation, suggesting that both ARGP and ILGP modulate the AV nodal innervation of the extrinsic and intrinsic cardiac autonomic nervous system (ANS).

CONCLUSION

The LOM and ILGP function as the "integration centers" that modulate the autonomic interactions between extrinsic and intrinsic cardiac ANS on AV nodal function.