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

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.

Independent contribution of diabetes to increased prevalence and incidence of atrial fibrillation

OBJECTIVE

Diabetes has long been recognized as a risk factor for atrial fibrillation, but its independent contribution to atrial fibrillation has not been fully evaluated. We sought to compare the prevalence and incidence of atrial fibrillation in age- and sex-matched patients with and without type 2 diabetes.

RESEARCH DESIGN AND METHODS

Using an observational cohort design, we selected 10,213 members of an HMO diabetes registry as of 1 January 1999 plus 7,159 patients who entered the registry by 31 December 2004 and matched them to patients without diabetes on year of birth and sex. All patients were followed until they died, left the health plan, or until 31 December 2008. We compared the baseline prevalence of atrial fibrillation and then followed patients without atrial fibrillation to compare atrial fibrillation incidence while controlling for known risk factors.

RESULTS

Atrial fibrillation prevalence was significantly greater among patients with diabetes (3.6 vs. 2.5%, P < 0.0001). Over a mean follow-up of 7.2 +/- 2.8 years, diabetic patients without atrial fibrillation at baseline developed atrial fibrillation at an age- and sex-adjusted rate of 9.1 per 1,000 person-years (95% CI 8.6-9.7) compared with a rate of 6.6 (6.2-7.1) among nondiabetic patients. After full adjustment for other risk factors, diabetes was associated with a 26% increased risk of atrial fibrillation among women (hazard ratio 1.26 [95% CI 1.08-1.46]), but diabetes was not a statistically significant factor among men (1.09 [0.96-1.24]).

CONCLUSIONS

In this population, diabetes was an independent determinant of atrial fibrillation prevalence but predicted incidence only among women. These findings have potential public health implications and emphasize the need for further investigation of the mechanistic links between diabetes and atrial fibrillation.

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.

Differences in atrial fibrillation properties under vagal nerve stimulation versus atrial tachycardia remodeling

BACKGROUND

There are many similarities between atrial effects of atrial tachycardia remodeling (ATR) and vagal nerve stimulation (VS): both promote atrial fibrillation (AF), reduce atrial effective refractory period (AERP) and AERP rate accommodation, enhance AERP heterogeneity, and increase inward-rectifier K+ current.

OBJECTIVE

This study sought to compare the consequences of ATR and VS at similar levels of AERP abbreviation in dogs.

METHODS

ATR dogs (n = 6) were subjected to 7-day atrial tachypacing at 400 beats/min, with radiofrequency-induced atrioventricular block and ventricular demand pacing (80 beats/min) to control ventricular response. VS was applied in 6 matched dogs with stimulation parameters selected to produce similar mean AERP values to ATR dogs.

RESULTS

ATR and VS produced similarly short AERPs (79 +/- 12 and 80 +/- 12 ms, respectively), AERP rate-adaptation loss, and AERP heterogeneity increases. Although both ATR and VS increased AF duration, VS was significantly more effective in AF promotion, with mean AF duration of 992 +/- 134 seconds, versus 440 +/- 240 seconds (P <.05) under ATR. The greater AF-promoting effect of VS was associated with greater mean dominant frequency values during AF (11.7 +/- 1.8 versus 10.0 +/- 1.3 Hz ATR, P <.05). VS greatly enhanced the spatial dominant frequency variability, increasing the coefficient of variation to 15.2 +/- 1.9 Hz, versus 8.9 +/- 1.5 Hz for ATR (P <.05), primarily by increasing the per-dog maximum dominant frequency (15.4 +/- 0.6 Hz versus 12.5 +/- 0.6 for ATR, P <.01).

CONCLUSION

For matched AERP values, VS promotes AF more strongly than ATR. Despite similar AERP changes, VS produces considerably greater increases in dominant frequencies, particularly maximum values, consistent with previous suggestions that inward-rectifier K+ current enhancement is particularly effective at accelerating and stabilizing spiral wave rotors that maintain AF.

Dorsal spinal cord stimulation obtunds the capacity of intrathoracic extracardiac neurons to transduce myocardial ischemia

Populations of intrathoracic extracardiac neurons transduce myocardial ischemia, thereby contributing to sympathetic control of regional cardiac indices during such pathology. Our objective was to determine whether electrical neuromodulation using spinal cord stimulation (SCS) modulates such local reflex control. In 10 anesthetized canines, middle cervical ganglion neurons were identified that transduce the ventricular milieu. Their capacity to transduce a global (rapid ventricular pacing) vs. regional (transient regional ischemia) ventricular stress was tested before and during SCS (50 Hz, 0.2 ms duration at 90% MT) applied to the dorsal aspect of the T1 to T4 spinal cord. Rapid ventricular pacing and transient myocardial ischemia both activated cardiac-related middle cervical ganglion neurons. SCS obtunded their capacity to reflexly respond to the regional ventricular ischemia, but not rapid ventricular pacing. In conclusion, spinal cord inputs to the intrathoracic extracardiac nervous system obtund the latter's capacity to transduce regional ventricular ischemia, but not global cardiac stress. Given the substantial body of literature indicating the adverse consequences of excessive adrenergic neuronal excitation on cardiac function, these data delineate the intrathoracic extracardiac nervous system as a potential target for neuromodulation therapy in minimizing such effects.

Targeted G-protein inhibition as a novel approach to decrease vagal atrial fibrillation by selective parasympathetic attenuation

AIMS

The parasympathetic nervous system is thought to play a key role in atrial fibrillation (AF). Since parasympathetic signalling is primarily mediated by the heterotrimeric G-protein, Galpha(i)betagamma, we hypothesized that targeted inhibition of Galpha(i) interactions in the posterior left atrium (PLA) would modify the substrate for vagal AF.

METHODS AND RESULTS

Cell-penetrating(cp)-Galpha(i)1/2 and cp-Galpha(i)3 C-terminal peptides were assessed for their ability to attenuate cholinergic-parasympathetic signalling in isolated feline atrial myocytes and in canine left atrium (LA). Confocal fluorescence microscopy indicated that cp-Galpha(i)1/2 and/or cp-Galpha(i)3 peptides moderated carbachol attenuation of cellular Ca(2+) transients in isolated atrial myocytes. High-density epicardial mapping of dog PLA, left atrial pulmonary veins (PVs), and left atrial appendage (LAA) indicated that the delivery of cp-Galpha(i)1/2 peptide or cp-Galpha(i)3 peptide into the PLA prolonged effective refractory periods at baseline and during vagal stimulation in the PLA and to varying extents also in the LAA and PV regions. After delivery of cp-Galpha(i) peptides into the PLA, AF inducibility during vagal stimulation was significantly diminished.

CONCLUSION

These results demonstrate the feasibility of using specific G(i)-protein inhibition to achieve selective parasympathetic denervation in the PLA, with a resulting change in vagal responsiveness across the entire LA.

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.

Prevention of atrial fibrillation: report from a national heart, lung, and blood institute workshop

The National Heart, Lung, and Blood Institute convened an expert panel April 28 to 29, 2008, to identify gaps and recommend research strategies to prevent atrial fibrillation (AF). The panel reviewed the existing basic scientific, epidemiological, and clinical literature about AF and identified opportunities to advance AF prevention research. After discussion, the panel proposed the following recommendations: (1) enhance understanding of the epidemiology of AF in the population by systematically and longitudinally investigating symptomatic and asymptomatic AF in cohort studies; (2) improve detection of AF by evaluating the ability of existing and emerging methods and technologies to detect AF; (3) improve noninvasive modalities for identifying key components of cardiovascular remodeling that promote AF, including genetic, fibrotic, autonomic, structural, and electrical remodeling markers; (4) develop additional animal models reflective of the pathophysiology of human AF; (5) conduct secondary analyses of already-completed clinical trials to enhance knowledge of potentially effective methods to prevent AF and routinely include AF as an outcome in ongoing and future cardiovascular studies; and (6) conduct clinical studies focused on secondary prevention of AF recurrence, which would inform future primary prevention investigations.

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.

Relationship between right cervical vagus nerve stimulation and atrial fibrillation inducibility: therapeutic intensities do not increase arrhythmogenesis

BACKGROUND

Strong vagus nerve stimulation (VNS) is routinely used to induce and maintain atrial fibrillation (AF) in acute animal studies. Taken as a surrogate of increased vagal tone, such observations suggest an arrhythmogenic role of VNS in AF. In contrast, VNS has been demonstrated to have profound therapeutic effects in heart failure and other ailments.

OBJECTIVE

The purpose of this study was to examine the relationship between right cervical VNS and AF, especially the potential arrhythmogenic effects of therapeutic VNS.

METHODS

The relationship between VNS intensities and AF inducibility was studied in eight acute dogs at baseline and four different levels of VNS, which were set to prolong spontaneous sinus cycle length (SCL) by 20%, 40%, 60%, or 100%. The effect of mild VNS treatment on AF induction was further investigated in six chronically instrumented conscious dogs. These dogs were implanted with right cervical VNS stimulators and specialized atrial pacemakers. VNS intensity was titrated to slow the sinus rate by 10%.

RESULTS

In acute studies, it was found that mild to moderate VNS (i.e., producing < or =40% SCL prolongation) did not increase AF inducibility, while strong VNS (i.e., producing > or =60% SCL prolongation) did. In chronic studies, compared with controls, AF induction did not change during the 4-week VNS treatment.

CONCLUSIONS

AF inducibility by right cervical VNS is intensity dependent: strong VNS (producing > or =60% SCL prolongation) facilitates AF, while moderate VNS (producing < or =40% SCL prolongation) appears not to affect AF. The nonarrhythmogenic effect of therapeutic chronic VNS was further verified in conscious animals. We conclude that VNS with moderate intensities can be used to deliver therapeutic benefits without arrhythmogenic risk.

[Atrial fibrillation and the autonomous nervous system]

The autonomic nervous system has a crucial role in the genesis, maintenance and abruption of atrial fibrillation. The substrate and trigger mechanism of atrial fibrillation can be influenced by the changing autonomic tone. The authors summarize the current knowledge on the relationship between autonomic nervous system and atrial fibrillation. The special neuroanatomical status and the role of autonomic reflexes and baroreflex in the initiation, maintenance, and termination of arrhythmia are reviewed. Furthermore, the mechanism and consequences of autonomic effect of the curative radiofrequency catheter ablation of pulmonary vein with atrial vagal neuroablation are discussed. At the end we also summarize the pharmacologic therapy of atrial fibrillation. Classification of atrial fibrillation, as either vagal or adrenergic, has only limited impact on current management.

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.

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 atrial fibrillation: for whom and how?

Catheter ablation is the treatment of choice for certain patients with drug-refractory paroxysmal or even persistent atrial fibrillation. Several techniques are used with a similar success rate of approximately 70% over 6 to 12 months of follow-up. Pulmonary vein isolation by conventional antral or electroanatomic circumferential ablation is mainly used in patients with paroxysmal atrial fibrillation. Electrogram-guided and combined approaches are also used, particularly in patients with persistent atrial fibrillation, whereas new methods such as autonomic denervation are under investigation.