Effects of Pulmonary Vein Ablation on Regional Atrial Vagal Innervation and Vulnerability to Atrial Fibrillation in Dogs

Utility of short-time electrocardiogram to assess risk for atrial arrhythmia recurrence: Impact of atrial premature beat occurrence 1 day after pulmonary vein isolation for atrial fibrillation

INTRODUCTION

Atrial premature beats (APBs) are the trigger for atrial fibrillation (AF). We sought to investigate the clinical significance of APB occurrence 1 day after pulmonary vein isolation (PVI) for AF using a short-time electrocardiogram.

METHODS

A total of 206 patients undergoing PVI for paroxysmal AF were included. Electrocardiogram recording for 100 consecutive beats was performed 1 day after PVI. The patients were divided into two groups: those with reproducible APBs (≥1 beat) during reassessment (APB group, n = 49) or those without (non-APB group, n = 157). Late recurrence was defined as atrial tachyarrhythmia recurrence 3-12 months after PVI. The impact of APB occurrence on outcomes was investigated.

RESULTS

Late recurrence occurred in 19 patients (9.2%). The presence of low-voltage areas, left atrial volume, and recurrence rate were higher in the APB group than in the non-APB group. In the APB group, the patients with recurrence had lower prematurity index (PI, coupling interval of APB/previous cycle length) compared to those without. Receiver-operating characteristic analysis revealed PI (<59.3) to be a predictive factor of recurrence (area under the curve: 0.733). The study subjects were then reclassified into three groups according to the absence of APB occurrence (n = 157), presence thereof with PI ≥ 59.3 (n = 33), and presence with PI < 59.3 (n = 16). The multivariate Cox models revealed that APB with PI < 59.3 was an independent predictor for recurrence (hazard ratio, 8.735; p < 0.001).

CONCLUSION

A short-time electrocardiogram enables risk assessment for arrhythmia recurrence, and APB with low PI 1 day after PVI is a powerful predictor.

Surgical versus catheter ablation in atrial fibrillation: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Atrial fibrillation (AF) is the most common cardiac arrhythmia with a high stroke and mortality rate. The video-assisted thoracoscopic radiofrequency pulmonary vein ablation is a treatment option for patients who fail catheter ablation. Randomized data comparing surgical versus catheter ablation are limited. We performed a meta-analysis of randomized control trials to explore the outcome efficacy between surgical and catheter radiofrequency pulmonary vein ablation in patients with AF.

METHODS

We comprehensively searched the databases of MEDLINE and EMBASE from inception to December 2020. Included studies were published randomized control trials that compared video-assisted thoracoscopic and catheter radiofrequency pulmonary vein ablation. Data from each study were combined using the fixed-effects, generic inverse variance method of DerSimonian and Laird to calculate odds ratios and 95% confidence intervals.

RESULTS

Six studies from November 2013 to 2020 were included in this meta-analysis involving 511 AF patients (79% paroxysmal) with 263 catheter ablation (mean age 56±3 years) and 248 surgical ablations (mean age 52 ±4 years). Catheter ablation was associated with increased atrial arrhythmias recurrence when compared to surgical ablation (pooled relative risk=1.85, 95 % confidence interval: 1.44-2.39, p<0.001, I² =0.0%) but associated with less total major adverse events (pooled relative risk=0.29, 95 % confidence interval: 0.16-0.53, p<0.001, I² =0.0%). In subgroup analysis, catheter ablation was associated with increased AF recurrence in refractory paroxysmal AF when compared to surgical ablation (pooled relative risk=2.47, 95 % confidence interval: 1.31-4.65, p=0.005, I² =0.0%) but not in persistent AF (relative risk=1.09, 95 % confidence interval: 0.60-2.0, p=0.773).

CONCLUSION

Catheter ablation was associated with higher atrial arrhythmia recurrence when compared with surgical ablation. However, our study suggests that the benefit of surgical ablation in patients with persistent AF is unclear. More studies and alternative ablation strategies investigation in persistent AF are warranted. This article is protected by copyright. All rights reserved.

Cardiac Autonomic Nervous System Remodeling May Play a Role in Atrial Fibrillation: A Study of the Autonomic Nervous System and Myocardial Receptors

BACKGROUND

The primary factors that originate and perpetuate atrial fibrillation (AF) are electrical and anatomical substrate alterations. However, the central mechanisms governing AF perpetuation have not been elucidated yet, which is reflected on the modest results of the treatment in patients with long persistent AF.

OBJECTIVE

To evaluate if human intrinsic cardiac autonomic nervous system (ICANS) remodeling, including nervous system fibers and muscarinic and β-adrenergic receptors, play a role in permanent AF.

METHODS

Heart necropsy samples from thirteen patients with heart disease and permanent AF and thirteen controls without AF were used. By using immunoperoxidase and histomorphometry quantification, we identified the following: the density of all fibers of the ICANS, sympathetic and parasympathetic fibers; and the percentage of myocardium positive for β-adrenergic receptors 1, 2 and 3; G protein-coupled receptor kinase-5 (GRK-5); and muscarinic receptors M1 to M5. The results were compared using ANOVA and nested ANOVA and were adjusted according to the left atrium volume for all variables, and β-blocker use to evaluate the expression of β-receptors and GRK-5.

RESULTS

There was an overall increase in the density of fibers of the ICANS (p=0.006), especially in atrial sympathetic nerve fibers (p=0.017). Only M1 muscarinic receptors were increased (5.87 vs 2.35, p=0.032). For adrenergic receptors, the results were positive for increased expression of β-3 (37.41 vs 34.18, p=0.039) and GRK-5 (51.16 vs 47.66; p<0.001). β-blocker use had no impact on β-receptor expression.

CONCLUSION

Increased ICANS innervation and remodeling receptor expression in regions prone to triggering AF may play a role in permanent AF.

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.

An anatomical approach to determine the location of the sinoatrial node during catheter ablation

INTRODUCTION

The sinoatrial node (SAN) should be identified before superior vena cava (SVC) isolation to avoid SAN injury. However, its location cannot be identified without restoring sinus rhythm. This study evaluated the usefulness of the anatomically defined SAN by comparing it with the electrically confirmed SAN (e-SAN) to predict the top-most position of e-SAN and thus establish a safe and more efficient anatomical reference for SVC isolation than the previously reported reference of the right superior pulmonary vein (RSPV) roof.

METHODS AND RESULTS

The e-SAN was identified as the earliest activation site in the electroanatomical map obtained during sinus rhythm. The anatomically defined SAN, the cranial edge of the crista terminalis (CT) visualized with intracardiac echocardiography (CT top), and the RSPV roof, which was obtained from the overlaid electroanatomical image of SVC and RSPV, were tagged on one map. The distance from the e-SAN to each reference was measured. Among 77 patients, the height of the e-SAN from the CT top was a median (interquartile range) of -2.0 (-8.0 to 4.0) mm. The e-SAN existed from 10 mm above the CT top or lower in 74 (96%) patients and from the RSPV roof or below in 73 (95%) patients. The reference of 10 mm above the CT top is more proximal to the right atrium than the RSPV roof and can provide longer isolatable SVC sleeves (30.0 [20.0-35.0] vs. 24.0 [18.0-30.0] mm, p < .001). The e-SAN tended to be found above the CT top when the heart rate during mapping was faster (adjusted odds ratio [95% confidence interval] per 10-bpm increase: 1.71 [1.20-2.43], p < .01).

CONCLUSION

The CT top is useful for predicting the upper limit of the e-SAN and can provide a better reference for SVC isolation than the RSPV roof.

Sinus rhythm heart rate increase after atrial fibrillation ablation is associated with lower risk of arrhythmia recurrence

BACKGROUND

Pulmonary vein isolation (PVI) with autonomic modulation may be more successful than PVI alone for atrial fibrillation (AF) ablation and may be signaled by changes in sinus rhythm heart rate (HR) post ablation. We sought to determine if a change in sinus rhythm HR predicted AF recurrence post PVI.

METHODS

Patients who underwent AF ablation from 2000 to 2011 were included if sinus rhythm was noted on ECG within 90 days pre and 7 days post ablation. Basic ECG interval and HR changes were analyzed and outcomes determined.

RESULTS

A total of 1152 patients were identified (74.3% male, mean age 57 ± 11 years). Mean AF duration was 5.2 ± 5.3 years. Paroxysmal AF was noted in 712 (61.8%) of the patients. Mean EF was 61% ± 6%. Sinus rhythm HR was 61 ± 11 pre-ablation and 76 ± 13 bpm post-ablation (27% ± 24% increase, p < .001). The ability of relative HR change post-ablation to predict AF recurrence was borderline (hazard ratio 0.65 [0.41-1.01], p = .067). With patients separated into quartiles based on the relative HR change, the upper quartile with the largest relative increase in HR had a significantly lower rate of AF recurrence compared to the lowest quartile following multi variable modeling (p = .038). There were significant changes in PR (171 ± 28 to 167 ± 30 ms) and QTc (424 ± 25 to 434 ± 29 ms) intervals (both p < .001) but these were not predictive of outcome.

CONCLUSION

Relative changes in HR post AF ablation correlates with AF recurrence. Further prospective studies are needed to confirm this relationship.

Early recurrence after pulmonary vein isolation is associated with inferior long-term outcomes: Insights from a retrospective cohort study

AIMS

The aim of this retrospective cohort study was to assess the influence of early recurrence (ER) after pulmonary vein isolation (PVI) for paroxysmal atrial fibrillation (AF) on long-term outcomes and to identify clinical variables associated with ER.

METHODS

We retrospectively collected clinical and procedural data from 1285 patients with paroxysmal AF who underwent PVI from 2011 to 2016. Kaplan-Meier, receiver operating characteristic (ROC) curve, logistic and Cox regression analyses were performed to analyze the influence of ER on long-term outcomes.

RESULTS

ER was observed in 13% of patients. Kaplan-Meier analyses showed significantly different outcomes in 1285 patients with and without ER (49% vs 74%, log rank P < .01) and in 286 patients in the subgroup that underwent reablation (44% vs 79%, log rank P < .01). The hazard ratio (HR) of ER was 1.7 within 48 hours (5% of patients), 2.7 within 1 month (5%), 3.0 within 2 months (2%), and 6.4 within 3 months (1%) for late recurrence (LR), P < .01. ROC analysis (area under the curve [AUC] = 0.79) resulted in 70.3% sensitivity and 74.2% specificity for a 14-day blanking period, and 53.1% sensitivity and 85.5% specificity for a 30-day blanking period. Female patients (odds ratio [OR] 1.69, P < .01) and those with diabetes (OR 1.95, P = .01) were at higher risk for ER.

CONCLUSIONS

ER is observed in a substantial number of patients with paroxysmal AF after PVI and has a continuous direct effect on LR according to the timing of ER. Randomized trials are required to assess the safety and effects of reablations in a shortened blanking period on long-term outcomes.

Left atrial structure and function predictors of recurrent fibrillation after catheter ablation: a systematic review and meta-analysis

BACKGROUND

Catheter ablation (CA) has become a conventional treatment for atrial fibrillation (AF), but remains with high recurrence rate. The aim of this meta-analysis was to determine left atrial (LA) structure and function indices that predict recurrence of AF.

METHODS

We systematically searched PubMed-Medline, EMBASE, Scopus, Google Scholar and the Cochrane Central Registry, up to September 2017 in order to select clinical trials and observational studies which reported echocardiographic predictors of AF recurrence after CA. Eighty-five articles with a total of 16 126 patients were finally included.

RESULTS

The pooled analysis showed that after a follow-up period of 21 ± 12 months, patients with AF recurrence had larger LA diameter with weighted mean difference (WMD: 2·99 ([95% CI 2·50-3·47], P<0·001), larger LA volume index (LAVI) maximal and LAVI minimal (P<0·0001 for both), larger LA area (P<0·0001), lower LA strain (P<0·0001) and lower LA total emptying fraction (LA EF) (P<0·0001) compared with those without AF recurrence. The most powerful LA predictors (in accuracy order) of AF recurrence were as follows: LA strain <19% (OR: 3·1[95% CI, -1.3-10·4], P<0·0001), followed by LA diameter ≥50 mm (OR: 2·75, [95% CI 1·66-4·56,] P<0·0001), and LAVmax >150 ml (OR: 2·25, [95% CI, 1.1-5·6], P = 0·0002).

CONCLUSIONS

Based on this meta-analysis results, a dilated left atrium with diameter more than 50 mm and volume above 150 ml or myocardial strain below 19% reflect an unstable LA that is unlikely to hold sinus rhythm after catheter ablation for atrial fibrillation.

Heart rate increase after pulmonary vein isolation predicts freedom from atrial fibrillation at 1 year

INTRODUCTION

Ablation of atrial vagal ganglia has been associated with improved pulmonary vein isolation (PVI) outcomes. Disruption of vagal reflexes results in heart rate (HR) increase. We investigated the association between HR change after PVI and freedom from atrial fibrillation (AF) at 1 year.

METHODS AND RESULTS

Patients who underwent PVI for paroxysmal AF were identified from the Johns Hopkins Hospital AF registry. Electrocardiograms taken pre-PVI and post-PVI were used to determine the change in HR. Patients followed-up at 3, 6, and 12 months. Of 257 patients (66% male, age 59+/-11 years), 134 (52%) remained free from AF at 1 year. The average HR increased from 60.6 ± 11.3 beats per minute (bpm) pre-PVI to 70.7 ± 12.0 bpm post-PVI. Patients with recurrence of AF had lower post-PVI HR than those who remained free from AF (67.8 ± 0.2 vs 73.3 ± 13.0 bpm; P <.001). The probability of AF recurrence at 1-year decreased as the change in HR increased (estimated odds ratio [OR], 0.83; 95% confidence interval [CI, 0.74-0.93]; P = .002). HR increase more than 15 bpm was associated with the lowest odds of AF recurrence (estimated OR, 0.39; 95% [0.17-0.85]; P = .018) compared to HR decrease.

CONCLUSIONS

Resting HR was found to increase after PVI. Increase in HR more than 15 bpm has a positive association with remaining free from atrial fibrillation at 1 year.

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.

Neurocardiology: Structure-Based Function

Cardiac control is mediated via a series of reflex control networks involving somata in the (i) intrinsic cardiac ganglia (heart), (ii) intrathoracic extracardiac ganglia (stellate, middle cervical), (iii) superior cervical ganglia, (iv) spinal cord, (v) brainstem, and (vi) higher centers. Each of these processing centers contains afferent, efferent, and local circuit neurons, which interact locally and in an interdependent fashion with the other levels to coordinate regional cardiac electrical and mechanical indices on a beat-to-beat basis. This control system is optimized to respond to normal physiological stressors (standing, exercise, and temperature); however, it can be catastrophically disrupted by pathological events such as myocardial ischemia. In fact, it is now recognized that autonomic dysregulation is central to the evolution of heart failure and arrhythmias. Autonomic regulation therapy is an emerging modality in the management of acute and chronic cardiac pathologies. Neuromodulation-based approaches that target select nexus points of this hierarchy for cardiac control offer unique opportunities to positively affect therapeutic outcomes via improved efficacy of cardiovascular reflex control. As such, understanding the anatomical and physiological basis for such control is necessary to implement effectively novel neuromodulation therapies. © 2016 American Physiological Society. Compr Physiol 6:1635-1653, 2016.

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.

Atrial fibrillation: mechanisms, therapeutics, and future directions

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia, affecting 1% to 2% of the general population. It is characterized by rapid and disorganized atrial activation leading to impaired atrial function, which can be diagnosed on an EKG by lack of a P-wave and irregular QRS complexes. AF is associated with increased morbidity and mortality and is a risk factor for embolic stroke and worsening heart failure. Current research on AF support and explore the hypothesis that initiation and maintenance of AF require pathophysiological remodeling of the atria, either specifically as in lone AF or secondary to other heart disease as in heart failure-associated AF. Remodeling in AF can be grouped into three categories that include: (i) electrical remodeling, which includes modulation of L-type Ca(2+) current, various K(+) currents and gap junction function; (ii) structural remodeling, which includes changes in tissues properties, size, and ultrastructure; and (iii) autonomic remodeling, including altered sympathovagal activity and hyperinnervation. Electrical, structural, and autonomic remodeling all contribute to creating an AF-prone substrate which is able to produce AF-associated electrical phenomena including a rapidly firing focus, complex multiple reentrant circuit or rotors. Although various remodeling events occur in AF, current AF therapies focus on ventricular rate and rhythm control strategies using pharmacotherapy and surgical interventions. Recent progress in the field has started to focus on the underlying substrate that drives and maintains AF (termed upstream therapies); however, much work is needed in this area. Here, we review current knowledge of AF mechanisms, therapies, and new areas of investigation.

Neuronally released vasoactive intestinal polypeptide alters atrial electrophysiological properties and may promote atrial fibrillation

BACKGROUND

Vagal hyperactivity promotes atrial fibrillation (AF), which has been almost exclusively attributed to acetylcholine. Vasoactive intestinal polypeptide (VIP) and acetylcholine are neurotransmitters co-released during vagal stimulation. Exogenous VIP has been shown to promote AF by shortening action potential duration (APD), increasing APD spatial heterogeneity, and causing intra-atrial conduction block.

OBJECTIVE

The purpose of this study was to investigate the effects of neuronally released VIP on atrial electrophysiologic properties during vagal stimulation.

METHODS

We used a specific VIP antagonist (H9935) to uncover the effects of endogenous VIP released during vagal stimulation in canine hearts.

RESULTS

H9935 significantly attenuated (1) the vagally induced shortening of atrial effective refractory period and widening of atrial vulnerability window during stimulation of cervical vagosympathetic trunks (VCNS) and (2) vagal effects on APD during stimulation through fat-pad ganglion plexus (VGPS). Atropine completely abolished these vagal effects during VCNS and VGPS. In contrast, VGPS-induced slowing of local conduction velocity was completely abolished by either VIP antagonist or atropine. In pacing-induced AF during VGPS, maximal dominant frequencies and their spatial gradients were reduced significantly by H9935 and, more pronouncedly, by atropine. Furthermore, VIP release in the atria during vagal stimulation was inhibited by atropine, which may account for the concealment of VIP effects with muscarinic blockade.

CONCLUSION

Neuronally released VIP contributes to vagal effects on atrial electrophysiologic properties and affects the pathophysiology of vagally induced AF. Neuronal release of VIP in the atria is inhibited by muscarinic blockade, a novel mechanism by which VIP effects are concealed by atropine during vagal stimulation.

Denervation as a common mechanism underlying different pulmonary vein isolation strategies for paroxysmal atrial fibrillation: evidenced by heart rate variability after ablation

BACKGROUNDS

Segmental and circumferential pulmonary vein isolations (SPVI and CPVI) have been demonstrated to be effective therapies for paroxysmal atrial fibrillation (PAF). PVI is well established as the endpoint of different ablation techniques, whereas it may not completely account for the long-term success.

METHODS

181 drug-refractory symptomatic PAF patients were referred for segmental or circumferential PVI (SPVI = 67; CPVI = 114). Heart rate variability (HRV) was assessed before and after the final ablation.

RESULTS

After following up for 62.23 ± 12.75 months, patients underwent 1.41 ± 0.68 procedures in average, and the success rates in SPVI and CPVI groups were comparable. 119 patients were free from AF recurrence (SPVI-S, n = 43; CPVI-S, n = 76). 56 patients had recurrent episodes (SPVI-R, n = 21; CPVI-R, n = 35). Either ablation technique decreased HRV significantly. Postablation SDNN and rMSSD were significantly lower in SPVI-S and CPVI-S subgroups than in SPVI-R and CPVI-R subgroups (SPVI-S versus SPVI-R: SDNN 91.8 ± 32.6 versus 111.5 ± 36.2 ms, rMSSD 47.4 ± 32.3 versus 55.2 ± 35.2 ms; CPVI-S versus CPVI-R: SDNN 83.0 ± 35.6 versus 101.0 ± 40.7 ms, rMSSD 41.1 ± 22.9 versus 59.2 ± 44.8 ms; all P < 0.05). Attenuation of SDNN and rMSSD remained for 12 months in SPVI-S and CPVI-S subgroups, whereas it recovered earlier in SPVI-R and CPVI-R subgroups. Multivariate logistic regression analysis identified SDNN as the only predictor of long-term success.

CONCLUSIONS

Beyond PVI, denervation may be a common mechanism underlying different ablation strategies for PAF.

Decreased postoperative atrial fibrillation following cardiac transplantation: the significance of autonomic denervation

BACKGROUND

Endocardial ablation approaches targeting the retroatrial cardiac ganglia to treat atrial fibrillation (AF) have been proposed. However, the potential value using this approach is unknown. Disruption of the autonomic inputs with orthotropic heart transplant (OHT) provides a unique opportunity to study the effects of autonomic innervation on AF genesis and maintenance. We hypothesized that due to denervation, the risk of postoperative AF would be lower following OHT compared to surgical maze even though both groups get isolation of the pulmonary veins.

METHODS AND RESULTS

We reviewed 155 OHTs (mean age 52 ± 11 years, 72% males) and used 1:1 age-, sex-, and date-of-surgery-matched two control groups from patients undergoing surgical maze or only coronary artery bypass grafting (CABG). Using conditional logistic regression we compared the odds of AF within 2 weeks following OHT versus controls. Postoperative AF occurred in 10/155 (6.5%) OHT patients. The conditional odds of postoperative AF were lower for OHT as compared to controls (vs maze: odds ratio [OR] 0.27 [95% confidence interval (CI) 0.13-0.57], vs CABG: OR 0.38 [0.17-0.81], P = 0.003; and on additional adjustment for left atrial enlargement, vs maze: OR 0.28 [0.13-0.60], vs CABG: OR 0.14 [0.04-0.47], P = 0.0009).

CONCLUSIONS

Risk of postoperative AF is significantly lower with OHT as in comparison to surgical maze. As both surgeries entail isolation of the pulmonary veins but only OHT causes disruption of autonomic innervation, this observation supports a mechanistic role of autonomic nervous system in AF. The benefit of targeting the cardiac autonomic system to treat AF needs further investigation.

Differential densities of cholinergic nerves in canine supraventricular regions of hearts

PURPOSE

Cholinergic nerve plays an important role in the induction and maintenance of atrial fibrillation (AF). Cholinergic innervation at supraventricular tissues is considered to be the histological basis and intervention-associated target site for the arrhythmia; however, the distribution of cholinergic nerve in supraventricular tissues has not been clearly studied. In this study, we investigated the cholinergic nerve innervation in canine supraventricular regions of hearts.

METHODS

We performed histological and immunohistochemical staining on canine tissues of left atrial appendage (LAA), right atrial appendage (RAA), left atrium (LA), right atrium (RA), atrial septum (AS), crista terminalis (CT), pulmonary vein (PV), and super vena cava (SVC) using hematoxylin and eosin (H&E) and antibodies to choline acetyltransferase.

RESULTS

Normal canine cardiovascular histological structures were shown from H&E staining. Cholinergic nerve densities at LAA and RAA were significantly higher than LA, which was higher than RA, but no significant difference was observed between LAA and RAA. Furthermore, RA was significantly higher than AS, CT, PV, and SVC and there were no significant differences among the latter four.

CONCLUSION

The heterogeneity of different densities of cholinergic nerve innervation of canine supraventricular regions establishes the histological basis of cholinergic nerve-mediated pathological conditions.

Vagal paroxysmal atrial fibrillation: prevalence and ablation outcome in patients without structural heart disease

INTRODUCTION

The prevalence of vagal and adrenergic atrial fibrillation (AF) and the success rate of pulmonary vein isolation (PVI) are not well defined. We investigated the prevalence of vagal and adrenergic AF and the ablation success rate of antral pulmonary vein isolation (APVI) in patients with these triggers compared with patients with random AF.

METHODS AND RESULTS

Two hundred and nine consecutive patients underwent APVI due to symptomatic drug refractory paroxysmal AF. Patients were diagnosed as vagal or adrenergic AF if >90% of AF episodes were related to vagal or adrenergic triggers; otherwise, a diagnosis of random AF was made. Clinical, electrocardiogram (ECG), and Holter follow-up was every 3 months in the first year and every 6 months afterward and for symptoms. Of 209 patients, 57 (27%) had vagal AF, 14 (7%) adrenergic AF, and 138 (66%) random AF. Vagal triggers were sleep (96.4%), postprandial (96.4%), late post-exercise (51%), cold stimulus (20%), coughing (7%), and swallowing (2%). At APVI, 94.3% of patients had isolation of all veins. Twenty-five (12%) patients had a second APVI. At a follow-up of 21 +/- 15 months, the percentage of patients free of AF was 75% in the vagal group, 86% in the adrenergic group, and 82% for random AF (P = 0.51).

CONCLUSION

In patients with PAF and no structural heart disease referred for APVI, vagal AF is present in approximately one quarter. APVI is equally effective in patients with vagal AF as in adrenergic and random AF.

An experimental study on the site dependency and mechanism of vagal denervation following radiofrequency catheter ablation for supraventricular arrhythmias including atrial fibrillation

Radiofrequency catheter ablation (RFCA) for supraventricular arrhythmias results in parasympathetic nervous damage. Recently, RFCA around the pulmonary veins (PVs) has become a standardized curative therapy for atrial fibrillation (AF). The aim of the present study was to elucidate the relationship between the degree of vagal denervation and RFCA sites, including the PV areas. In 21 dogs, RFCA was performed at the ostium of the right PV (n = 7), ostium of the left PV (n = 7), and posteroseptal site of the right atrium (n = 7). Electrical stimulation of the cervical vagal trunk (ESCV) was performed and the resultant increase in the P-P interval (PPI) observed on the ECG was measured. The PPI was compared between the different RFCA sites. In another 7 animals, the vagal ganglia located in the fat pads that innervate the sinoatrial (SA) node were also stimulated (ESFP), testing the degree of postganglionic damage. The PPI after RFCA was decreased with right PV RFCA whereas there was no change with left PV RFCA. The ESFP yielded a significantly greater decrease in the PPI than the ESCV. The PPI during ESFP was completely blocked by hexamethonium, injected into the fat pad. The ESCV after the hexa-methonium injection did not result in complete disappearance of the PPI. Thus, right PV RFCA markedly damaged the vagal innervation of the SA node, whereas left PV RFCA produced little damage. The major type of damage was partial postganglionic fiber damage. An alternate vagal pathway external to the fat pads is proposed.

Pulmonary vein region ablation in experimental vagal atrial fibrillation: role of pulmonary veins versus autonomic ganglia

BACKGROUND

Pulmonary vein (PV) -encircling radiofrequency ablation frequently is effective in vagal atrial fibrillation (AF), and there is evidence that PVs may be particularly prone to cholinergically induced arrhythmia mechanisms. However, PV ablation procedures also can affect intracardiac autonomic ganglia. The present study examined the relative role of PVs versus peri-PV autonomic ganglia in an experimental vagal AF model.

METHODS AND RESULTS

Cholinergic AF was studied under carbachol infusion in coronary perfused canine left atrial PV preparations in vitro and with cervical vagal stimulation in vivo. Carbachol caused dose-dependent AF promotion in vitro, which was not affected by excision of all PVs. Sustained AF could be induced easily in all dogs during vagal nerve stimulation in vivo both before and after isolation of all PVs with encircling lesions created by a bipolar radiofrequency ablation clamp device. PV elimination had no effect on atrial effective refractory period or its responses to cholinergic stimulation. Autonomic ganglia were identified by bradycardic and/or tachycardic responses to high-frequency subthreshold local stimulation. Ablation of the autonomic ganglia overlying all PV ostia suppressed the effective refractory period-abbreviating and AF-promoting effects of cervical vagal stimulation, whereas ablation of only left- or right-sided PV ostial ganglia failed to suppress AF. Dominant-frequency analysis suggested that the success of ablation in suppressing vagal AF depended on the elimination of high-frequency driver regions.

CONCLUSIONS

Intact PVs are not needed for maintenance of experimental cholinergic AF. Ablation of the autonomic ganglia at the base of the PVs suppresses vagal responses and may contribute to the effectiveness of PV-directed ablation procedures in vagal AF.

Atrial tachycardia induces remodelling of muscarinic receptors and their coupled potassium currents in canine left atrial and pulmonary vein cardiomyocytes

BACKGROUND AND PURPOSE

Both parasympathetic tone and atrial tachycardia (AT) remodelling of ion channels play important roles in atrial fibrillation (AF) pathophysiology. Different muscarinic cholinergic receptor (mAChR) subtypes (M2, M3, M4) in atrial cardiomyocytes are coupled to distinct K+-currents (called IKM2, IKM3, IKM4, respectively). Pulmonary veins (PVs) are important in AF and differential cholinergic current responses are a potential underlying mechanism. This study investigated AT-induced remodelling of mAChR subtypes and K+-currents in left-atrial (LA) and PV cardiomyocytes.

EXPERIMENTAL APPROACH

Receptor expression was assayed by western blot. IKM2, IKM3 and IKM4 were recorded with whole-cell patch-clamp in LA and PV cardiomyocytes of nonpaced control dogs and dogs after 7 days of AT-pacing (400 bpm).

KEY RESULTS

Current densities of IKM2, IKM3 and IKM4 were significantly reduced by AT-pacing in LA and PV cardiomyocytes. PV cardiomyocyte current-voltage relations were similar to LA for all three cholinergic currents, both in control and AT remodelling. Membrane-protein expression levels corresponding to M2, M3 and M4 subtypes were decreased significantly (by about 50%) after AT pacing. Agonist concentration-response relations for all three currents were unaffected by AT pacing.

CONCLUSIONS AND IMPLICATIONS

AT downregulated all three mAChR-coupled K+-current subtypes, along with corresponding mAChR protein expression. These changes in cholinergic receptor-coupled function may play a role in AF pathophysiology. Cholinergic receptor-coupled K+-currents in PV cardiomyocytes were similar to those in LA under control and AT-pacing conditions, suggesting that differential cholinergic current properties do not explain the role of PVs in AF.

Pulmonary vein encircling ablation alters the atrial electrophysiologic response to autonomic stimulation

OBJECTIVE

Pulmonary vein encircling ablation is often effective in the treatment of atrial fibrillation (AF). The success of the procedure does not depend upon creation of continuous lines of block. Thus mechanisms by which pulmonary vein encircling can cure AF remain unclear. Stimulation of cardiac autonomic ganglia alters atrial refractoriness and potentiates AF. We hypothesized that pulmonary vein encircling alters atrial autonomic function and that these alterations account in part for prevention of AF recurrences following ablation.

METHODS

Atrial effective refractory periods (ERP) and AF inducibility were quantified in ten dogs before and during central autonomic nerve stimulation. Pulmonary vein encircling ablation was then performed and electrophysiologic testing repeated. In two dogs subjected to sham procedures measurements were repeated without performance of ablation. Hearts were examined histologically.

RESULTS

Autonomic nerve stimulation led to decreased atrial refractoriness and increased AF inducibility and duration. Each of these effects were attenuated following pulmonary vein encircling (e.g., mean ERP decreased before (-23.7 +/- 1.8, p < 0.001) but not after ablation (-2.3 +/- 1.9, p = 0.25); AF inducibility increased by 26% before vs. 5% after ablation). No attenuation was seen in the sham operated animals. Histologic analysis following pulmonary vein encircling demonstrated destruction of some but not all autonomic ganglia.

CONCLUSION

Autonomic stimulation shortens atrial refractory periods and potentiates AF. Pulmonary vein encircling ablation partially destroys atrial autonomic inputs, attenuates the refractory period shortening effect of autonomic stimulation and decreases AF inducibility. Destruction of autonomic ganglia may contribute to the anti-fibrillatory effects of pulmonary vein encircling and warrants further investigation.

Slow Pathway Ablation Decreases Vulnerability to Pacing-Induced Atrial Fibrillation: Possible Role of Vagal Denervation

BACKGROUND

Studies indicate that success of radiofrequency (RF) ablation of atrial fibrillation (AF) may be in part due to vagal denervation. RFAof supraventricular tachycardia (SVT) has been associated with vagal denervation. The effects of slow pathway (SP) ablation on AF inducibility have not been studied.

OBJECTIVE

To test the hypothesis that SP ablation renders AF less inducible.

METHODS

Consecutive patients referred for SVT were studied. After atrioventricular nodal reentrant tachycardia (AVNRT) was confirmed they underwent induction of AF. After SP ablation AF induction was reattempted. Vulnerability to AF was reassessed.

RESULTS

Twenty-four patients were enrolled; eight were not inducible for AF in the preablative state. Mean CLof the AVNRT was 340 +/- 16 ms. The average RF ablation time was 131 +/- 42 seconds. Presence of junctional rhythm was required. Of the 16 with inducible AF two patients had AF induced during routine invasive electrophysiology study. None of these had inducible AF after SP ablation. Fourteen of 16 patients required specific AF induction. Ten of these were noninducible after SP ablation; two were inducible after SP ablation but with a more aggressive pacing protocol (P < 0.03 compared to preablation) and two had no change in AF vulnerability. Seven of the eight noninducible patients remained noninducible for AF post SP ablation. In the 12 patients who were inducible prior but noninducible after ablation the mean atrial effective refractory period (AERP) increased for both BCL at 400 and 600 ms (400/216 +/- 8 ms preablation vs 400/248 +/- 12 ms postablation, P < 0.03; 600/228 +/- 8 ms preablation vs 600/259 +/- 6 ms postablation, P < 0.04). There were no significant changes in AERP of patients who remained inducible or who were noninducible before ablation. The average ablation time for patients who became noninducible after ablation was significantly higher than those who had no change in inducibility or remained inducible but at a more aggressive pacing threshold (157 +/- 24 seconds vs 35 +/- 5 seconds; P < 0.005).

CONCLUSION

SP ablation acutely decreases vulnerability to pacing-induced AF in patients with AVNRT. This may reflect the effect of ablation on atrial vagal tone.

The Effects of Pulmonary Vein Isolation on the Dominant Frequency and Organization of Coronary Sinus Electrical Activity During Permanent Atrial Fibrillation

BACKGROUND

Pulmonary vein isolation (PVI) has been shown to suppress atrial fibrillation (AF). We examined the effects of PVI on disorganization and dominant frequencies (DF) in patients with permanent AF.

METHODS AND RESULTS

Twenty-eight patients with permanent AF (>6 months) who failed > or =1 antiarrhythmic drugs (AAD) and > or =2 cardioversions (CV) with AF reversion <30 minutes after CV were included. PVI and isolation of DFs in pulmonary veins (PVs) was performed during AF. Fast Fourier transformations of atrial electrograms were performed. Disorganization index (DI) was defined as the percentage of time spent in type III AF during 1-minute continuous recordings. The temporal stability and reproducibility of DIs from the same sites were verified over time prior to ablation. Highly disorganized AF activity concentrated in the posterior left atrium (PLA) including sites at the left atrial (PV-LA) junction (55.7% of sites in PLA, 32.9% in septum, and 11.4% in other sites). DF and DI from the coronary sinus (CS) before and after PVI were analyzed. PVI reduced the DI (14.3 +/- 25.0% before PVI vs 4.6 +/- 8.6% after PVI; P < 0.02). There was significant reduction of DI in 26 of 28 patients. The DF remained unchanged (5.6 +/- 1.3 Hz before PVI vs 5.9 +/- 0.9 Hz after PVI; P = 0.31). After a follow-up of 30 +/- 11 months, 15 (54%) of patients are free of symptomatic AF, 3 (10%) in sinus rhythm on AAD, 5 (18%) with paroxysmal AF, 4 (14%) in chronic AF, and 1 (4%) with atypical flutter.

CONCLUSIONS

In the vast majority of patients with chronic AF, PVI reduces AF disorganization without affecting the DF as measured in the CS.

Differential Densities of Muscarinic Acetylcholine Receptor and IK,ACh in Canine Supraventricular Tissues and the Effect of Amiodarone on Cholinergic Atrial Fibrillation and IK,ACh

BACKGROUND

Vagal nerve plays an important role in the induction and maintenance of atrial fibrillation (AF). This study investigated the differential densities of M2 receptor and acetylcholine-induced inward rectifier K+ current (I(K,ACh)) in atrial appendage, atrium, pulmonary vein (PV) and super vena cava (SVC) to discuss the role of atrial appendage and PV in cholinergic AF.

METHODS AND RESULTS

In 10 dogs, action potential duration was determined at 24 sites during bilateral cervical vagal stimulation and amiodarone administration. AF could be induced at first in right atrial appendage (RAA) and right atrium (RA) without left atrial appendage (LAA) and left atrium (LA). Amiodarone decreased the initiation of AF in vivo. Western blot and patch clamp were used to determine M2 receptor and I(K,ACh) in RAA, LAA, RA, LA, PV and SVC. The densities of M2 receptor and I(K,ACh) in LAA, RAA and LA were higher than that in RA, PV and SVC (21.34 +/- 0.92 vs. 8.24 +/- 0.45 pA/pF, p < 0.05). Furthermore, the densities of the M2 receptor and I(K,ACh) in LAA and RAA were higher than that in LA (21.34 +/- 0.92 vs. 14.17 +/- 0.65 pA/pF, p < 0.05). After amiodarone administration, densities of I(K,ACh) in LA and RA were not different, but densities of I(K,ACh )were also less in atrium than in atrial appendage.

CONCLUSIONS

Densities of the M2 receptor and I(K,ACh) are higher in atrial appendage than other sites. Atrial appendage perhaps plays an important role in initiation of cholinergic AF. However, PV and SVC less often play an important role in vagotonic paroxysmal AF. Reduced dispersion of I(K,ACh) is the mechanism for amiodarone to therapy AF.