Gross and microscopic anatomy of the human intrinsic cardiac nervous system

Augmentation of left ventricular contractility by cardiac sympathetic neural stimulation

BACKGROUND

Electric stimulation of mediastinal sympathetic cardiac nerves increases cardiac contractility but is not selective for the left ventricle because it elicits sinus tachycardia and enhanced atrioventricular conduction. The aim of this study was to identify sympathetic neural structures inside the heart that selectively control left ventricular inotropy and can be accessed by transvenous catheter stimulation.

METHODS AND RESULTS

In 20 sheep, high-frequency stimulation (200 Hz) during the myocardial refractory period with electrode catheters inside the coronary sinus evoked a systolic left ventricular pressure increase from 97+/-20 to 138+/-32 mm Hg (P<0.001) without changes in sinus rate or PR time. Likewise, the rate of systolic pressure development (1143+/-334 versus 1725+/-632 mm Hg/s; P=0.004) and rate of diastolic relaxation (531+/-128 versus 888+/-331 mm Hg/s; P=0.001) increased. The slope of the end-systolic pressure-volume relationship increased (2.3+/-0.8 versus 3.1+/-0.6 mm Hg/mL; P=0.04), as did cardiac output (3.5+/-0.8 versus 4.4+/-0.8 L/min; P<0.001). Systemic vascular resistance and right ventricular pressure remained unchanged. There was a sigmoid dose-response curve. Ultrasound analysis revealed an increase in circumferential and radial strain in all left ventricular segments that was significant for the posterior, lateral, and anterior segments. Pressure effects were maintained for at least 4 hours of continued high-frequency stimulation and abolished by beta1-receptor blockade. Histology showed distinct adrenergic nerve bundles at the high-frequency stimulation site.

CONCLUSIONS

Cardiac nerve fibers that innervate the left ventricle are amenable to transvenous electric catheter stimulation. This may permit direct interference with and modulation of the sympathetic tone of the left ventricle.

Anatomy of the Pericardial Space and Mediastinum: Relevance to Epicardial Mapping and Ablation

The pericardial space is a fairly new portal for interventional cardiac electrophysiologists to access the heart and requires an understanding of its anatomic peculiarities to maneuver safely around the epicardial surfaces of the heart and great veins. Subxiphoid puncture should allow the diaphragm and fibrous pericardium to be crossed without entering the right ventricle, which is the most anteriorly situated cardiac chamber. The phrenic nerves descend on the fibrous pericardium bilaterally. The right nerve is related to the superior caval vein and the superior right pulmonary vein, whereas the left nerve takes variable courses over the left atrial appendage and the left ventricle. Related to the fibrous pericardium overlying the posterior wall of the left atrium is the esophagus.

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.

Early detection of pulmonary vein reconnection after isolation in patients with paroxysmal atrial fibrillation: a comparison of ATP-induction and reassessment at 30 minutes postisolation

INTRODUCTION

Catheter ablation for paroxysmal AF (PAF) is limited by an unacceptable recurrence rate, mainly due to pulmonary vein (PV) reconnection. Strategies to minimize reconnection include adenosine infusion and also a waiting period of 30 minutes after PV isolation. The aim of the present study was to assess whether these two strategies revealed the same conduction gap.

METHODS AND RESULTS

In total, 88 consecutive patients (54 males, mean age of 60 years) with drug refractory PAF underwent circumferential PV isolation (CPVI). After isolation of ipsilateral PVs, with entry and exit block checked using a circular mapping catheter, 20 mg ATP was injected during isoproterenol infusion to reveal dormant conduction gap(s). Unless the reconnection revealed by ATP persisted, PVs were further remapped with the circular mapping catheter at 30 minutes postisolation. Totally, PV reconnection was observed in 56 (64%) patients. 24.3% veins (80/329) were found reconnected. Reassessment at 30 minutes postablation was more efficient as compared to ATP induction (19.8% vs 14.6% for ATP). The agreement between these 2 methods is moderate (kappa value = 0.50). In veins that transiently reconnected after ATP administration and later observed at 30 minutes postablation, 94% (17 of 19) of them were found being reconnected with the same gap.

CONCLUSION

Acute PV reconnection is common, occurring in 64% of patients, as detected by adenosine infusion and waiting time. Each shows a unique quality as compared to one another. The combined use of these 2 methods may reduce the AF recurrence rate after CPVI.

Ablation strategies for atrial fibrillation

Atrial fibrillation remains the most common arrhythmia in the USA and is associated with an increased risk for stroke, congestive heart failure and overall mortality. There has been a tremendous advance in the field of catheter ablation of atrial fibrillation that has resulted in better outcomes for patients. The approach for ablation of atrial fibrillation can be different depending on patients' presentation of paroxysmal or persistent atrial fibrillation. Pulmonary vein isolation remains the cornerstone of any ablation strategy for atrial fibrillation; however, further ablation, end points of the procedure, clinical end points for successful ablation and appropriate follow-up remain controversial. We aim to discuss these different approaches and the major controversies in catheter ablation of atrial fibrillation.

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.

Pathophysiologic basis of autonomic ganglionated plexus ablation in patients with atrial fibrillation

The intrinsic cardiac autonomic nervous system (ganglionated plexuses [GP]) plays a significant role in the initiation and maintenance of atrial fibrillation (AF) in both experimental models and AF patients. Left atrial GP, located in epicardial fat pads and the ligament of Marshall, contain afferent neurons from the atrial myocardium and the central autonomic nervous system, efferent neurons (cholinergic and adrenergic neurons), and interconnecting neurons, which allow communication between GP. Stimulation of the GP produces both parasympathetic stimulation (markedly shortens action potential duration) and sympathetic stimulation (increases calcium transient) in the pulmonary vein (PV) myocardium and atrial myocardium. In a canine model, GP stimulation resulted in early afterdepolarizations, and calcium transient triggered firing in the adjacent PV and initiated AF. Fractionated atrial potentials (FAP) were consistently located in the left atrium close to the stimulated GP. Ablation of the stimulated GP eliminated the FAP surrounding the GP. In patients with paroxysmal AF, epicardial and endocardial high-frequency stimulation produced a positive vagal response (transient AV block during AF and hypotension), allowing the identification and localization of five major left atrial GP (superior left GP, inferior left GP, Marshall tract GP, anterior right GP, inferior right GP). High-density electroanatomic maps of the left atrium and PVs obtained during AF showed the FAP are located in four main left atrial areas (left atrial appendage ridge FAP area, superior-left FAP area, inferoposterior FAP area, anterior-right FAP area). All five GP are located within one of the four FAP areas. In 63 patients with paroxysmal AF, GP ablation alone (before PV antrum isolation) significantly decreased the occurrence of PV firing (47/63 patients before ablation vs 9/63 patients after ablation, P <.01). GP ablation also decreased the inducibility of sustained AF (43/63 patients vs 23/63 patients, P <.01) and markedly reduced or eliminated the left atrial FAP areas.

Current status and outcomes of catheter ablation for atrial fibrillation

Catheter ablation has evolved as an effective treatment modality in patients with AF. In this review, the rationale and outcomes of ablation strategies targeting various mechanisms of AF based on our current understanding are discussed. Likely mechanisms responsible for the therapeutic effects of these approaches are reviewed.

Localization of multiple neurotransmitters in surgically derived specimens of human atrial ganglia

Dysfunction of the intrinsic cardiac nervous system is implicated in the genesis of atrial and ventricular arrhythmias. While this system has been studied extensively in animal models, far less is known about the intrinsic cardiac nervous system of humans. This study was initiated to anatomically identify neurotransmitters associated with the right atrial ganglionated plexus (RAGP) of the human heart. Biopsies of epicardial fat containing a portion of the RAGP were collected from eight patients during cardiothoracic surgery and processed for immunofluorescent detection of specific neuronal markers. Colocalization of markers was evaluated by confocal microscopy. Most intrinsic cardiac neuronal somata displayed immunoreactivity for the cholinergic marker choline acetyltransferase and the nitrergic marker neuronal nitric oxide synthase. A subpopulation of intrinsic cardiac neurons also stained for noradrenergic markers. While most intrinsic cardiac neurons received cholinergic innervation evident as punctate immunostaining for the high affinity choline transporter, some lacked cholinergic inputs. Moreover, peptidergic, nitrergic, and noradrenergic nerves provided substantial innervation of intrinsic cardiac ganglia. These findings demonstrate that the human RAGP has a complex neurochemical anatomy, which includes the presence of a dual cholinergic/nitrergic phenotype for most of its neurons, the presence of noradrenergic markers in a subpopulation of neurons, and innervation by a host of neurochemically distinct nerves. The putative role of multiple neurotransmitters in controlling intrinsic cardiac neurons and mediating efferent signaling to the heart indicates the possibility of novel therapeutic targets for arrhythmia prevention.

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

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

The role of pulmonary veins in atrial fibrillation: a complex yet simple story

Atrial fibrillation (AF) is the most common cardiac arrhythmia, with increased incidence among the elderly population. The concept that ectopic activity in pulmonary veins (PVs) could be responsible for triggering AF has been put forward, and the inter-relationship between PVs and left atrium has been the subject of many anatomical and physiological investigations. Variable configuration of action potentials among various PV cardiomyocytes has been reported. PV myocytes were shown to have a higher resting membrane potential and a lower action potential amplitude and duration than the left atrium. Much evidence has accumulated to indicate that spontaneous depolarization and/or re-entry from PVs could be the mode by which AF is initiated and/or sustained. Attempts have been made to link AF in certain pathophysiological states, notably, congestive heart failure, valvular disease and hyperthyroidism to PVs. There has been evidence to suggest that an increase in PV diameter may be the trigger for initiating AF. However, there is limited clinical knowledge available on the nature of the antiarrhythmic drugs that act upon PVs to alleviate AF. Most drugs currently employed are the standard agents generally utilized for the treatment of AF. Radiofrequency ablation (RFA) of the PVs and its isolation from the left atrium has become a major curative measure of AF. It is also possible that pharmacotherapy may be more effective or provide extra benefit to patients after a RFA procedure. The trend of the clinical evidence seems to suggest that a hybrid treatment may be beneficial in some population of patients.

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.

Minimally invasive pulmonary vein isolation and partial autonomic denervation for surgical treatment of atrial fibrillation

OBJECTIVE

It was our goal to determine the efficacy of a minimally invasive surgical approach to the treatment of atrial fibrillation that combines pulmonary vein antral isolation with targeted partial autonomic denervation.

METHODS

Eighty-three patients underwent video-assisted bilateral pulmonary vein antral electrical isolation with confirmation of block and partial autonomic denervation. Sixty-two (41 paroxysmal, 21 persistent/long-standing persistent) patients had a follow-up of 6 months or greater. Fifty-seven of these patients had a long-term rhythm monitor at 6 months (39 paroxysmal, 18 persistent/long-standing persistent).

RESULTS

Success was defined as no episodes of atrial fibrillation greater than 15 s duration on long-term monitoring. Treatment was successful in 32 of 39 (82.1%) patients with paroxysmal atrial fibrillation and 10 of 18 (55.6%) with persistent/long-standing persistent atrial fibrillation.

CONCLUSION

Early data suggest that pulmonary vein electrical isolation combined with targeted partial autonomic denervation is a safe and efficacious approach for the treatment of paroxysmal atrial fibrillation. Techniques are being developed for the minimally invasive surgical treatment of persistent and long-standing persistent atrial fibrillation from an epicardial approach.

New concepts in atrial fibrillation: neural mechanisms and calcium dynamics

Atrial fibrillation (AF) is a complex arrhythmia with multiple possible mechanisms. It requires a trigger for initiation and a favorable substrate for maintenance. Pulmonary vein myocardial sleeves have the potential to generate spontaneous activity, and this arrhythmogenic activity is surfaced by modulation of intracellular calcium dynamics. Direct autonomic nerve recordings in canine models show that simultaneous sympathovagal discharges are the most common triggers of paroxysmal atrial tachycardia and paroxysmal AF. Autonomic modulation as a potential therapeutic strategy has been targeted clinically and experimentally, but its effectiveness as an adjunctive therapeutic modality to catheter ablation of AF has been inconsistent. Further studies are warranted before application can be widely implied for therapies of clinical AF.

A randomized assessment of the incremental role of ablation of complex fractionated atrial electrograms after antral pulmonary vein isolation for long-lasting persistent atrial fibrillation

OBJECTIVES

This study sought to determine whether ablation of complex fractionated atrial electrograms (CFAEs) after antral pulmonary vein isolation (APVI) further improves the clinical outcome of APVI in patients with long-lasting persistent atrial fibrillation (AF).

BACKGROUND

Ablation of CFAEs has been reported to eliminate persistent AF. However, residual pulmonary vein arrhythmogenicity is a common mechanism of recurrence.

METHODS

In this randomized study, 119 consecutive patients (mean age 60 +/- 9 years) with long-lasting persistent AF underwent APVI with an irrigated-tip radiofrequency ablation catheter. Antral pulmonary vein isolation resulted in termination of AF in 19 of 119 patients (Group A, 16%). The remaining 100 patients who still were in AF were randomized to no further ablation and underwent cardioversion (Group B, n = 50) or to ablation of CFAEs in the left atrium or coronary sinus for up to 2 additional hours of procedure duration (Group C, n = 50).

RESULTS

Atrial fibrillation terminated during ablation of CFAEs in 9 of 50 patients (18%) in Group C. At 10 +/- 3 months after a single ablation procedure, 18 of 50 (36%) in Group B and 17 of 50 (34%) in Group C were in sinus rhythm without antiarrhythmic drugs (p = 0.84). In Group A, 15 of 19 patients (79%) were in sinus rhythm. A repeat ablation procedure was performed in 34 of 100 randomized patients (for AF in 30 and atrial flutter in 4). At 9 +/- 4 months after the final procedure, 34 of 50 (68%) in Group B and 30 of 50 (60%) in Group C were in sinus rhythm without antiarrhythmic drugs (p = 0.40).

CONCLUSIONS

Up to 2 h of additional ablation of CFAEs after APVI does not appear to improve clinical outcomes in patients with long-lasting persistent AF.

Autonomic innervation of the developing heart: origins and function

Maintenance of homeostatic circulation in mammals and birds is reliant upon autonomic innervation of the heart. Neural branches of mixed cellular origin and function innervate the heart at the arterial and venous poles as it matures, eventually coupling autonomic output to the cardiac components, including the conduction system. The development of neural identity is controlled by specific networks of genes and growth factors, whereas functional properties are governed by the use of different neurotransmitters. In this review, we summarize briefly the anatomic arrangement of the vertebrate autonomic nervous system and describe, in detail, the innervation of the heart. We discuss the timing of cardiac innervation in the chick and mouse, emphasizing the relationship of the cardiac neural networks to the anatomical structures within the heart. We also discuss the variable contribution of the neural crest to vagal cardiac nerves, and summarize the main neurotransmitters secreted by the developing sympathetic and parasympathetic autonomic divisions. We provide an overview of the main growth factor and gene families involved in neural development, discussing how these factors may impact upon the development of cardiac abnormalities in congenital syndromes associated with autonomic dysfunction.

Combined effect of pulmonary vein isolation and ablation of cardiac autonomic nerves for atrial fibrillation

This study was designed to determine whether endocardial high-frequency stimulation at the pulmonary vein (PV) antrums can localize cardiac autonomic ganglionated plexi (GP) and whether ablation at these sites can evoke a vagal response and provide a long-term benefit after PV isolation (PVI) for atrial fibrillation (AF). Radiofrequency ablation of each PV antrum was performed in 21 patients with paroxysmal AF (n = 17) or persistent (n = 4) AF. In 8 patients with paroxysmal AF, a ring electrode catheter was placed at each PV antrum. High-frequency stimulation prolonged the R-R interval in 6 of 8 patients at the left superior (LS) PV, in 3 of 8 patients at the left inferior (LI) PV, in 3 of 8 patients at the right superior (RS) PV, and in 3 of 8 patients at the right inferior (RI) PV. A decrease in sinus rate > 20% was observed in 4 of 21 patients during LS PVI, in 2 of 21 patients during RS PVI, and in 1 of 2 patients during RI PVI. Atrioventricular block or a > 5 second pause was observed in 5 of 21 patients during LS PVI. AF recurred during the follow-up period in 5 of the 16 patients (31%) who had no atrioventricular block or > 5 second pause during PVI but did not recur in 5 patients in whom atrioventricular block or a > 5 second pause developed during PVI. GP can be identified by endocardial stimulation. The AF recurrence rate is decreased when a vagal response is achieved by radiofrequency ablation.

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

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

Nerve supply of the human pulmonary veins: an anatomical study

BACKGROUND

Atrial ectopic discharges originating in the pulmonary veins (PVs) are known to initiate atrial fibrillation (AF), which may be terminated by catheter-based PV isolation. Because a functional relationship exists between cardiac autonomic effects and PVs in arrhythmogenesis, it has been suggested that discharges of the nerves that proceed to the PVs and interconnect with intrinsic ganglionated nerve plexuses are potential triggers of AF in man.

OBJECTIVE

This study sought to determine the characteristics and distribution of neural routes by which autonomic nerves supply the human PVs.

METHODS

We examined the intrinsic neural structures of 35 intact (nonsectioned) left atrial (LA)-PV complexes stained transmurally for acetylcholinesterase using a stereomicroscope.

RESULTS

The epicardial ganglionated nerves pass onto the extrapulmonary segments of the human PVs from the middle, left dorsal, and dorsal right atrial subplexuses. The left and right inferior PVs involved a lesser number of ganglia than the left and right superior PVs. Abundant extensions of epicardial nerves penetrate transmurally the PV walls and form a patchy neural network beneath the endothelium of PVs. The subendothelial neural meshwork with numerous free nerve endings, which appeared to be typical sensory compact nerve endings, was mostly situated at the roots of the 4 PVs. No ganglia were identified beneath the endothelium of the human PVs.

CONCLUSION

The richest areas containing epicardial ganglia, from which intrinsic nerves extend to the human PVs, are concentrated at the inferior surface of both the inferior and left superior PVs. Therefore, these locations might be considered as potential targets for focal pulmonary vein ablation in catheter-based therapy of AF.

Incidence, timing, and characteristics of acute changes in heart rate during ongoing circumferential pulmonary vein isolation

AIMS

Previous studies showed that catheter ablation of atrial fibrillation (AF) results in vagal denervation with an increase in average heart rate (HR) and a reduced overall HR variability (HRV) at follow-up. We analysed acute ablation-induced changes in HR and short-term HRV during percutaneous circumferential pulmonary vein isolation (CPVI). We also studied whether observed changes were predictors of successful outcome after first CPVI.

METHODS AND RESULTS

A total of 46 patients (35 men, 55 +/- 10 years) undergoing CARTO and computed tomography-guided CPVI for symptomatic AF were studied. Circumferential pulmonary vein isolation was performed under general anaesthesia by widely encircling the left and right pulmonary veins during sinus rhythm (SR). Radiofrequency (RF) current (35W, 48 degrees C) was applied with a 3.5 mm open irrigated tip catheter (Navistar Thermocool, Biosense Webster, Diamond Bar, CA, USA). Time- and frequency-domain analysis of short-term HRV was performed using 5 min electrocardiogram (ECG) recordings obtained at the beginning and the end of the CPVI procedure. Sinus rhythm cycle length was monitored continuously during CPVI. Circumferential pulmonary vein isolation was performed with 119 +/- 25 RF applications. Mean HR increased from 54 +/- 8 to 62 +/- 9 bpm (P < 0.001). Heart rate variability was significantly reduced (SDNN from 34 +/- 30 ms to 14 +/- 17 ms, P < 0.001, RMSSD from 27 +/- 22 ms to 13 +/- 14 ms, P < 0.001) with a marked change in sympathovagal balance towards less vagal activity (low frequency (LF)/high frequency (HF) ratio from 3.94 +/- 0.33 to 4.20 +/- 0.17, P < 0.001). Changes in RR interval, SDNN, and LF/HF ratio correlated significantly with RR interval (R = 0.56, P < 0.001), SDNN (R = 0.84, P < 0.001), and LF/HF ratio (R = -0.74, P < 0.001) at baseline. There were acute changes during ablation in HR and HRV, at the antero-superior junction between the left atrium (LA) and the right superior pulmonary vein (RSPV) in 36 patients (78%). Both HR and HRV at baseline and changes in HR/HRV were comparable between successful (n = 36) and failed (n = 10) patients.

CONCLUSION

(i) Percutaneous CPVI induces acute acceleration of HR and attenuation of short-term HRV (indicating vagal denervation during the procedure). (ii) Acute changes in HR and its variability invariably occur during RF energy delivery at the antero-superior junction between the LA and the RSPV. (iii) The degree of HR and short-term HRV changes depend on the vagal tone at the beginning of the procedure. (iv) In contrast to previously reported changes in overall HRV, acute changes in HR during the procedure are no predictors of long-term clinical outcome after CPVI.

Evaluation of catheter ablation of periatrial ganglionic plexi in patients with atrial fibrillation

Recent data suggests that the cardiac autonomic nervous system has an important role in the initiation and maintenance of atrial fibrillation (AF). This study investigated (1) the feasibility of identifying and targeting these autonomic ganglia using endocardial radiofrequency stimulation and ablation, respectively; (2) the efficacy of endocardial ablation to completely eliminate the vagal response elicited from epicardial stimulation; and (3) the effect of autonomic ablation on the acute inducibility of AF. The study included 18 patients referred for catheter ablation of suspected vagal-mediated AF. The endocardial left atrial surface was stimulated at high frequency (20 to 50 Hz) to elicit a vagal response. In selected patients (n = 5), pericardial access was obtained using a subxyphoid puncture to permit epicardial stimulation. Catheter ablation of the putative autonomic ganglionic sites was performed from the left atrial endocardium using irrigated radiofrequency energy. After ablation of all identifiable autonomic ganglia, high-frequency pacing was repeated to induce AF. In all patients, stimulation at certain endocardial sites elicited a vagal response. Endocardial ablation abrogated this vagal responsiveness. Furthermore, for sites accessible from the pericardium, the vagal response elicited using epicardial stimulation was also eliminated. Despite successful ablation of these ganglia, AF was still inducible in 17 of 18 patients. In conclusion, successful ablation of autonomic ganglia from an endocardial approach can be reliably achieved using an irrigated catheter. In addition, ablation of these structures in patients with vagal-mediated AF is insufficient to prevent its acute reinduction with high-frequency atrial stimulation.

Vagal reflex provoked by radiofrequency catheter ablation in the right aortic sinus cusp: a Bezold-Jarisch-like phenomenon

A 66-year-old woman with idiopathic premature ventricular contractions with a left bundle branch block QRS morphology and left inferior axis underwent electrophysiologic testing. Successful radiofrequency ablation was achieved in the right coronary cusp (RCC). However, radiofrequency ablation at sites adjacent to the successful ablation site provoked sinus bradycardia followed by atrioventricular conduction block. That phenomenon might be explained by a vagal reflex through stimulation of vagal pathways or receptors in the anterior epicardial fat pads neighboring to the RCC. A vagal reflex should be kept in mind as a complication during catheter ablation of ventricular arrhythmias originating from the RCC.

Neural mechanisms of paroxysmal atrial fibrillation and paroxysmal atrial tachycardia in ambulatory canines

BACKGROUND

The relationship between autonomic activation and the mechanisms of paroxysmal atrial fibrillation remains unclear.

METHODS AND RESULTS

We implanted a pacemaker and a radio transmitter in 7 dogs (group 1). After baseline recording, we paced the left atrium at 20 Hz for 1 week and then monitored left stellate ganglion nerve activity, left vagal nerve activity, and left atrial electrogram without pacing for 24 hours. This protocol repeated itself until sustained atrial fibrillation (>48 hours) was induced in 3+/-1 weeks. In another 6 dogs (group 2), we cryoablated left and right stellate ganglia and the cardiac branch of the left vagal nerve during the first surgery and then repeated the same pacing protocol until sustained atrial fibrillation was induced in 7+/-4 weeks (P=0.01). There were 4+/-2 episodes of paroxysmal atrial fibrillation per day and 10+/-3 episodes of paroxysmal atrial tachycardia per day in group 1. Simultaneous sympathovagal discharges were observed to immediately precede the onset of atrial arrhythmias in 73% of episodes. In comparison, group 2 dogs had no paroxysmal atrial fibrillation (P=0.046) or paroxysmal atrial tachycardia (P<0.001) episodes. Nerve sprouting, sympathetic hyperinnervation, and a massive elevation of transcardiac norepinephrine levels occurred in both groups.

CONCLUSIONS

Intermittent rapid left atrial pacing results in sympathetic hyperinnervation, paroxysmal atrial fibrillation, and paroxysmal atrial tachycardia. Simultaneous sympathovagal discharges are common triggers of these arrhythmias. Cryoablation of extrinsic sympathovagal nerves eliminated paroxysmal atrial fibrillation and paroxysmal atrial tachycardia, which suggests that simultaneous sympathovagal discharges and these arrhythmias are causally related. Because cryoablation only delayed but did not prevent sustained atrial fibrillation, autonomic nerve activity is not the only factor that determines atrial fibrillation maintenance.

Anatomic approach for ganglionic plexi ablation in patients with paroxysmal atrial fibrillation

There is evidence that parasympathetic denervation may prevent atrial fibrillation (AF) recurrences. This study aimed at applying an anatomic approach for ablation of atrial ganglionic plexi (GPs) in patients with paroxysmal AF. Nineteen patients with symptomatic, paroxysmal AF underwent anatomically guided radiofrequency ablation at the location of the 4 main left atrial GPs and were prospectively assessed for recurrence of AF or other atrial arrhythmia. This group was compared with 19 age- and gender-matched patients who previously underwent conventional circumferential pulmonary vein ablation. All ablation procedures were uneventful. Circumferential and GP ablations were accomplished with a radiofrequency delivery time of 28 +/- 5 versus 18 +/- 3 min (p <0.001) and a fluoroscopy time of 31 +/- 5 versus 18 +/- 5 min (p <0.001), respectively. Parasympathetic reflexes during radiofrequency ablation were elicited in 4 patients (21%). Arrhythmia recurred in 7 patients (37%) with circumferential ablation and 14 patients (74%) with GP ablation, during 1-year follow-up (p for log-rank test = 0.017). In 2 patients with GP ablation, left atrial flutters were documented in addition to AF during follow-up. Patients who underwent GP ablation had an almost 2.5 times higher risk of AF recurrence compared with those who underwent circumferential ablation (hazard ratio 2.6, 95% confidence interval 1.0 to 6.6, p = 0.038). In conclusion, anatomically guided GP ablation is feasible and safe in the electrophysiology laboratory, but this approach yields inferior clinical results compared with circumferential ablation.

Catheter Ablation of Left Atrial Ganglionated Plexi for Atrial Fibrillation

Radiofrequency ablation of pulmonary vein ostia does not provide complete and long-term elimination of atrial fibrillation. Combining this procedure with local radiofrequency application on sites with strong vagal reflexes results in partial parasympathetic denervation and increases the antiarrhythmic effect. A novel catheter-ablation technique to modify ganglionated plexi in the left atrium was assessed in 58 patients (mean age, 52.1 ± 1.9 years, 67% male) with drug-refractory atrial fibrillation, which was chronic in 21 (36%; mean duration, 14.3 ± 2.9 months; range, 5–39 months). The mean left atrial volume was 93.1 ± 6.1 mL. The patients underwent ablation of 4 areas of ganglionated plexi in the left atrium, with no circumferential ablation of the pulmonary veins; atrial fibrillation ceased immediately in 94.1% of them. Transient vagal bradycardia was seen in 93% of patients. For 7.2 ± 0.4 months after the procedure, 86.2% of them were free from arrhythmias, and no antiarrhythmic drugs were administered. Ganglionated plexi ablation is an efficient treatment for atrial fibrillation.

Mother rotor anchoring in branching tissue with heterogeneous membrane properties

Abstract Current understanding of atrial fibrillation is based on the co-existence of multiple re-entrant waves propagating randomly throughout the tissue. However, recent experimental results indicate that in many cases one or a small number of periodic, high-frequency re-entrant sources (mother rotors) can drive the arrhythmia. Owing to the high activation rate, mother rotors seem to be located in regions of shortened action potential duration. In this study a computer model of cardiac propagation was applied to investigate mechanisms leading to the formation and maintenance of such mother rotors. For this purpose, a region of short action potential duration was generated by varying the acetylcholine concentration across the tissue. A mother rotor initiated in the center of this region drifts away, and the activation terminates. If an additional heterogeneity such as a bundle is included into the model, a further drift mechanism directed to the bundle is observed and the rotor can be stabilized. Therefore, bundle insertions may play an important role in the maintenance of mother rotors. The influence of the driving rotor on the activation pattern was studied in a three-dimensional model of rectangular shape and a monolayer model of anatomically correct atrial geometry.

The role of autonomic denervation during catheter ablation of atrial fibrillation

PURPOSE OF REVIEW

To analyse recent experimental and clinical studies and show that all the pathological events occurring in the myocardium during atrial fibrillation are caused by changes in the autonomic nervous system. The current methods of radiofrequency ablation focus on damaging healthy myocardial tissue involved in the dysregulation caused by autonomic nervous system hyperactivity. Radiofrequency ablation should instead be targeted at compromised nerves and autonomic ganglia (ganglionated plexi).

RECENT FINDINGS

Experimental data show that electrical stimulation of the autonomic nervous system may facilitate the induction of atrial fibrillation. The active role of pulmonary veins in atrial fibrillation results from the high density of adrenergic and cholinergic nerves around pulmonary veins. The areas most suitable for autonomic nervous system modification procedures are located in the immediate vicinity of the pulmonary vein-left atrial junction. The first clinical results of radiofrequency ablation of ganglionated plexi resulting in autonomic denervation are encouraging, and show this as a promising approach. There remain many debatable points; the most important of which is the best approach for locating clusters of ganglionated plexi.

SUMMARY

Recent experimental and clinical findings have provided new insights into the causes of atrial fibrillation and allowed a re-evaluation of its treatment.